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SIMIT 7

FLOWNET Library

Reference manual

Siemens Automation

https://industrialautomation.co/product-category/siemens/page/5339/

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Edition

January 2013

Siemens offers simulation software to plan, simulate and optimize plants and machines. The simulation- and optimization-results are only non-binding suggestions for the user. The quality of the simulation and optimizing results depend on the correctness and the completeness of the input data. Therefore, the input data and the results have to be validated by the user.

Trademarks

SIMIT® is a registered trademark of Siemens AG in Germany and in other countries.

Other names used in this document can be trademarks, the use of which by third-parties for their own purposes could violate the rights of the owners.

Copyright Siemens AG 2013 All rights reserved

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages.All rights, including rights created by patent grant or registration or a utility model or design, are reserved. Siemens AG Industry Sector Industry Automation Division Process Automation SIMIT-HB-V7FLOWNET-2013-01-en

Exclusion of liability

We have checked that the contents of this document correspond to the hardware and software described. However, deviations cannot be entirely excluded, and we do not guarantee complete conformance. The information contained in this document is, however, reviewed regularly and any necessary changes will be included in the next edition. We welcome suggestions for improvement.

Siemens AG 2013

Subject to change without prior notice.

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Copyright Siemens AG, 2013 SIMIT 7 – FLOWNET

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Contents

1 PREFACE 1

1.1 Target group 1

1.2 Contents 1

1.3 Symbols 1

2 INTRODUCTION 3

3 FLOWNETS 4

3.1 Flownet basics 4

3.2 Variables used in the flownets 7

3.3 Modelling flownet branches 8

3.4 Modelling flownet nodes 9

3.4.1 Mass balance for the nodes 9 3.4.2 Enthalpy balance for the nodes 10 3.4.3 Determining the density of the medium in the nodes 10

3.4.3.1 Water/steam medium 10 3.4.3.2 Liquid medium 10 3.4.3.3 Ideal gas medium 10

3.4.4 Determining the temperature of the medium in the nodes 11

3.5 Heat exchange with the environment 11

3.6 Parameterisation of flownets 11

3.6.1 Flownet media 12 3.6.2 Parameters for branches 12 3.6.3 Parameters for nodes 12 3.6.4 Parameters for liquid medium 13 3.6.5 Parameters for ideal gas medium 13 3.6.6 Initialisation of variables 13 3.6.7 Parameter overview 14

4 FLOWNET COMPONENT LIBRARY 15

4.1 The topology connector 15

4.2 General components 16

4.2.1 Valve – control valve 17 4.2.2 StopValve – non-return valve 20 4.2.3 Pump – pump 21 4.2.4 Pnode – pressure setting 25 4.2.5 Mnode – mass flow setting 26 Siemens Automation


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4.2.6 NetParam – network parameterisation 27 4.2.7 BranchParam – branch parameterisation 29 4.2.8 Joint – joint 29 4.2.9 JointParam – parameterisable joint 30

4.3 Measuring components 32

4.3.1 PipeMeasure – pipe measuring point 32 4.3.2 Measurements – measuring indicator 34 4.3.3 FlowIndicator – flow indicator 35 4.3.4 LevelIndicator – level indicator 35 4.3.5 PressureIndicator – pressure indicator 36 4.3.6 TemperatureIndicator – temperature indicator 37 4.3.7 WeightIndicator – weight indicator 37

4.4 Component types for water/steam medium 38

4.4.1 NetWS – water/steam network parameterisation 39 4.4.2 PnodeWS – water/steam pressure settings 40 4.4.3 MnodeWS – water/steam mass flow settings 41 4.4.4 JointWS – water/steam joint 42 4.4.5 JointParamWS – water/steam parameterisable joint 43 4.4.6 StorageTankWS – water storage tank 45 4.4.7 DrumWS – steam drum 49 4.4.8 ElectricalHeaterWS – electric heat exchanger for water/steam 54 4.4.9 HeatExchangerWS – heat exchanger water/steam to water/steam 56

4.5 Component types for liquid medium 59

4.5.1 NetLiquid – liquid network parameterisation 60 4.5.2 PnodeLiquid – liquid pressure settings 61 4.5.3 MnodeLiquid – liquid mass flow settings 62 4.5.4 JointLiquid – liquid joint 63 4.5.5 JointParamLiquid – liquid parameterisable joint 64 4.5.6 StorageTankLiquid – liquid storage tank 66 4.5.7 ElectricalHeaterLiquid – electric heat exchanger for liquid 69 4.5.8 HeatExchangerLiquid – heat exchanger liquid to liquid 72

4.6 Component types for gas medium 75

4.6.1 NetGas – gas network parameterisation 76 4.6.2 PnodeGas – gas pressure settings 77 4.6.3 MnodeGas – gas mass flow setting 78 4.6.4 JointGas – gas joint 79 4.6.5 JointParamGas – gas parameterisable joint 80 4.6.6 StorageTankGas – gas storage tank 82 4.6.7 ElectricalHeaterGas – electric heat exchanger for gas 85 4.6.8 HeatExchangerGas – heat exchanger gas to gas 88

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5 CREATING YOUR OWN COMPONENT TYPES FOR FLOWNETS 92

5.1 Topological properties 92

5.1.1 Type FLN1 connections 93 5.1.2 Topology of internal nodes 94 5.1.3 Topology of external nodes 94 5.1.4 Topology of a branch object 95

5.2 Connection to the flownet solver 95

5.2.1 Connection type FLN2 for branch objects 96 5.2.2 Connection type FLN3 for external nodes 97

5.2.2.1 Connector of type FLN3 with direction OUT 98 5.2.2.2 Connection of type FLN3 with direction IN 99

5.2.3 Connection type FLN4 for internal nodes 100 5.2.4 Connection type FLN5 for parameters of a flownet 100 5.2.5 Connection type FLN6 for parameterisation of a branch 102 5.2.6 Connection type FLN7 for parameterisation of an internal node 102

5.3 Constants and functions 103

5.3.1 Constants 103 5.3.2 Functions 103 5.3.3 Own Functions 105

5.4 Initialising flownet simulations 107

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Table of figures Figure 3-1: Example flownet 4Figure 3-2: Flownet graph 5Figure 3-3: Flownet graph for example shown in Figure 3-1 5Figure 3-4a,b: Minimal flownet graph and minimal flownet 6Figure 3-5: Incomplete flownet branch 6Figure 3-6: Error message for incomplete flownet branch 6Figure 3-7: Error message for an isolated flownet component 7Figure 3-8: Error message for components with different cycles 7Figure 3-9: Branch with branch objects 8Figure 4-1: Connector component types in the basic library 15Figure 4-2: Topology flownet connector 15Figure 4-3: Flownet connector on a branch 16Figure 4-4: Flownet connector as joint 16Figure 4-5: GENERAL library directory 17Figure 4-6: Valve with drive 18Figure 4-7: Application of the Characteristic component on valve 18Figure 4-8: Parameters for the Valve component type 19Figure 4-9: Additional parameters for the Valve component type 19Figure 4-10: Symbolic representation of the valve position 19Figure 4-11: Representation of the valve position and flow direction in symbol 20Figure 4-12: Operating window for the valve component type 20Figure 4-13: Parameters for the StopValve component type 21Figure 4-14: Pump with drive 22Figure 4-15: Pump characteristic 22Figure 4-16: Extended characteristic 23Figure 4-17: Parameters for the Pump component type 24Figure 4-18: Additional parameters for the Pump component type 24Figure 4-19: Representation of the pump operating status in symbol 24Figure 4-20: Operating window for the Pump component type 24Figure 4-21: Operating window for the component type Pnode 25Figure 4-22: Extended operating window for the component type Pnode 25Figure 4-23: Operating window for the Mnode component type 26Figure 4-24: Extended operating window for the Mnode component type 27Figure 4-25: Parameters for the NetParam component type 28Figure 4-26: Additional parameters for the NetParam component type 29Figure 4-27: Parameters for the BranchParam component type 29Figure 4-28: Operating window for the Joint component type 30Figure 4-29: Parameters for the JointParam component type 31Figure 4-30: Additional parameters for the JointParam component type 31Figure 4-31: Operating window for the JointParam component type 31Figure 4-32: Library directory MEASURE 32Figure 4-33: Indication of medium flow for the PipeMeasure component type 33

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Figure 4-34: Operating window for the PipeMeasure component type 33Figure 4-35: Extended operating window for the PipeMeasure component type 34Figure 4-36: Components of the Measurements type at a pipe measuring point 34Figure 4-37: Operating window for the Measurements component type 35Figure 4-38: Operating window for the FlowIndicator component type 35Figure 4-39: Operating window for the LevelIndicator component type 36Figure 4-40: Operating window for the PressureIndicator component type 36Figure 4-41: Operating window for the TemperatureIndicator component type 37Figure 4-42: Operating window for the WeightIndicator component type 38Figure 4-43: Library directory WATER.STEAM 38Figure 4-44: Parameters for the NetWS component type 39Figure 4-45: Additional parameters for the NetWS component type 40Figure 4-46: Operating window for the component type PnodeWS 41Figure 4-47: Extended operating window for the component type PnodeWS 41Figure 4-48: Operating window for the MnodeWS component type 42Figure 4-49: Extended operating window for the MnodeWS component type 42Figure 4-50: Operating window for the JointWS component type 43Figure 4-51: Parameters for the JointParamWS component type 44Figure 4-52: Additional parameters for the JointParamWS component type 44Figure 4-53: Operating window for the JointParamWS component type 44Figure 4-54: Empty tank indicator on the symbol 46Figure 4-55: Full tank indication on the symbol 47Figure 4-56: Parameters for the StorageTankWS component type 47Figure 4-57: Additional parameters for the StorageTankWS component type 48Figure 4-58: Operating window for the StorageTankWS component type 48Figure 4-59: Empty drum indicator on the symbol 51Figure 4-60: Full drum indication on the symbol 51Figure 4-61: Parameters for the DrumWS component type 52Figure 4-62: Additional parameters for the DrumWS component type 53Figure 4-63: Operating window for the DrumWS component type 53Figure 4-64: Extended operating window for the DrumWS component type 53Figure 4-65: Diagram of the segments for the electrical heat exchanger

ElectricalHeaterWS 54Figure 4-66: Parameters for the ElectricalHeaterWS component type 55Figure 4-67: Operating window for the ElectricalHeaterWS component type 56Figure 4-68: One tube model of the heat exchanger 57Figure 4-69: Heat balance for the heat exchanger HeatExchangerWS 57Figure 4-70: Parameters for the HeatExchangerWS component type 59Figure 4-71: Operating window for the HeatExchangerWS component type 59Figure 4-72: Library directory LIQUID 60Figure 4-73: Parameters for the NetLiquid component type 61Figure 4-74: Additional parameters for the NetLiquid component type 61Figure 4-75: Operating window for the PnodeLiquid component type 62Figure 4-76: Extended operating window for the PnodeLiquid component type 62Figure 4-77: Operating window for the MnodeLiquid component type 63Siemens Automation


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Figure 4-78: Extended operating window for the MnodeLiquid component type 63Figure 4-79: Operating window for the JointLiquid component type 64Figure 4-80: Parameters for the JointParamLiquid component type 65Figure 4-81: Operating window for the JointParamLiquid component type 65Figure 4-82: Operating window for the JointParamLiquid component type 65Figure 4-83: Empty tank indicator on the symbol 67Figure 4-84: Full tank indicator on the symbol 67Figure 4-85: Parameters for the StorageTankLiquid component type 68Figure 4-86: Additional parameters for the StorageTankLiquid component type 69Figure 4-87: Operating window for the StorageTankLiquid component type 69Figure 4-88: Diagram of the segmentation for the heat exchanger 70Figure 4-89: Parameters for the ElectricalHeaterLiquid component type 71Figure 4-90: Additional parameters for the ElectricalHeaterLiquid component

type 71Figure 4-91: Operating window for the ElectricalHeaterLiquid component type 72Figure 4-92: One tube model for the heat exchanger 73Figure 4-93: Diagram of the heat balancing for the heat exchanger 73Figure 4-94: Parameters for the HeatExchangerLiquid component type 75Figure 4-95: Operating window for the HeatExchangerLiquid component type 75Figure 4-96: Library directory GAS 76Figure 4-97: Parameters for the NetGas component type 77Figure 4-98: Additional parameters for the NetGas component type 77Figure 4-99: Operating window for the PnodeGas component type 78Figure 4-100: Extended operating window for the component type PnodeGas 78Figure 4-101: Operating window for the MnodeGas component type 79Figure 4-102: Extended operating window for the component type MnodeGas 79Figure 4-103: Operating window for the JointGas component type 80Figure 4-104: Parameters for the JointParamGas component type 81Figure 4-105: Additional parameters for the JointParamGas component type 81Figure 4-106: Operating window for the JointParamGas component type 81Figure 4-107: Empty tank indicator on the symbol 83Figure 4-108: Full tank indicator on the symbol 84Figure 4-109: Parameters for the StorageTankGas component type 84Figure 4-110: Additional parameters for the StorageTankGas component type 85Figure 4-111: Operating window for the StorageTankGas component type 85Figure 4-112: Diagram of the heat transfer in a segmented heat exchanger 86Figure 4-113: Parameters for the ElectricalHeaterGas component type 87Figure 4-114: Additional parameters for the ElectricalHeaterGas component type 87Figure 4-115: Operating window for the ElectricalHeaterGas component type 88Figure 4-116: One tube model for the heat exchanger 89Figure 4-117: Diagram of the heat balancing for the heat exchanger 89Figure 4-118: Parameters for the HeatExchangerGas component type 91Figure 4-119: Operating window for the HeatExchangerGas component type 91Figure 5-1: Topology in the component type navigation menu 93Figure 5-2: Connectors of type FLN1 93

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Figure 5-3: Linking connectors of type FLN1 with a connecting line 93Figure 5-4: Linking connectors of type FLN1 through superposition 94Figure 5-5: Topology of an internal node 94Figure 5-6: Topology of an external node 95Figure 5-7: Topology of a branch object 95Figure 5-8: Data exchange between flownet components and flownet solver 96Figure 5-9: Visibility in the properties window of a connection of type FLN2 to

FLN7. 96Figure 5-10: Definition of a connection of type FLN2 96Figure 5-11: Signals of a connection of type FLN2 97Figure 5-12: Assigning variables to a branch object 97Figure 5-13: Signals of a connection of type FLN3 with direction OUT 98Figure 5-14: Variables of a pressure node 99Figure 5-15: Signals of a connection of type FLN3 with direction IN 99Figure 5-16: Variables of a mass flow node 99Figure 5-17: Definition of a connector of type FLN4 100Figure 5-18: Signals of a connection of type FLN4 100Figure 5-19: Definition of a connection of type FLN6 102Figure 5-20: Definition of a connection of type FLN7 102Figure 5-21: Cross-section of a partially full cylinder 105Figure 5-22: Initialisation of flownet simulations 108

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List of tables Table 3-1: Flownet variables 8Table 3-2: List of flownet parameters 14Table 4-1: Signals of the Measure connection type 32Table 5-1: FLN3 connection type signals 98Table 5-2: Signals of connection type FLN5 101Table 5-3: Signals of connection type FLN7 103Table 5-4: Constants for flownet components 103Table 5-5: State variables for water/steam 104Table 5-6: State functions for water/steam 104

s Preface


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1 PREFACE

1.1 Target group This manual is intended for anyone who uses the SIMIT simulation system. It describes the process for simulating pipe networks using the FLOWNET library, i.e. the component types provided by the library and the simulation processes that are used by these types of component. An understanding of the process and component types is essential for creating simulations. This manual provides the necessary information.

It assumes knowledge of the basic SIMIT system and a a well-founded knowledge of the use of PCs and their Windows user interface in addition to fundamental knowledge of the physical and mathematical relations on which the component types are based. These constitute essential basic knowledge in the thermodynamics of flow.

1.2 Contents This manual describes the component types contained in the FLOWNET library and the modelling approach on which the library is based. Section 2 is an introduction explaining the basic features of the FLOWNET library.

Section 3 describes how piping networks can be simulated using flownets. The modelling approach for flownets is described in detail.

The components contained in the FLOWNET library are described in section 4 and the subsequent sections are useful for understanding their function in a flownet.

Section 5 explains how to create your own component types for flownets. The topological aspects and the data exchange between the components and the flownet solver are explained in detail. The information on flownets provided in section 3 is required in order to understand this section.

1.3 Symbols Particularly important information is highlighted in the text as follows:

NOTE Notes contain important supplementary information about the documentation contents. They also highlight those properties of the system or operator input to which we want to draw particular attention.

CAUTION This means that the system will not respond as described if the specified precautionary measures are not applied.

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STOP

WARNING This means that the system may suffer irreparable damage or that data may be lost if the relevant precautionary measures are not applied.

s Introduction



2 INTRODUCTION The FLOWNET library is an extension of SIMIT, which provides component types for creating simulations of piping networks. By connecting components in this library, a model of a piping network, a flownet, is created, which simulates the thermodynamic processes in piping networks. In conjunction with the FLOWNET library, a special solution method can be applied in SIMIT that calculates the flow, pressure and specific enthalpy in the piping network simulation.

Although the SIMIT flownets are based on a modelling approach that employs physical balance equations, the aim is not to use the dynamic process simulations to facilitate the design of system components or systems, but instead to provide a physically plausible simulation of the thermodynamic variables in piping networks for virtual commissioning. This simulation should be easy to create using components on a graphical interface and be stable even in extreme situations. During the implementation of the component types in the FLOWNET library, the focus was on simple parameterisation of the components and stable behaviour in the flownet, rather than a detailed simulation of the physics.

The component types in the FLOWNET library can be used to create flownets for a variety of media:

• water/steam,

• liquids or

• ideal gases.

The Component Type Editor (CTE) of SIMIT can be used to create your own flownet components and thus extend your flownet library. The flownet solution method can also be used by the components via FLOWNET specific connection types.

NOTE When the simulation starts, it will check whether your SIMIT installation has a licence for the FLOWNET library. If there are flownet components in the simulation project, i.e. components that use the solution method for flownets, then the simulation can only be run if you have a FLOWNET licence.

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3 FLOWNETS A flownet in SIMIT is a connection of flownet components used for simulating thermodynamic processes in pipe networks. The simulation of flownets is based on a special solution method, which is parameterised and configured via the flownet components. The modelling approach described later restricts the flownet to homogenous media, but can be used for liquids, ideal gases or water in physical condition that is either liquid or steam.

The FLOWNET library provides component types that can be used to configure flownets, i.e. to model flownets. As usual in SIMIT, the diagram editor is used to model flownets. The symbol used for the flownet component types, such as valves or pumps, is the same as that is normally used in piping diagrams. This allows a flownet model, as shown in Figure 3-1, to be easily constructed in the form of a piping diagram using the component type symbols.

Figure 3-1: Example flownet

The flownet topology for configuring the flownet solver is derived from the interconnection of flownet components. While the simulation is running, the flownet solver and components exchange data: calculated values or flownet parameters.

3.1 Flownet basics The process for simulating piping networks is based on mapping the connection of SIMIT components to flownets as a graph of nodes and branches. The branches model the flow paths and the nodes model the connections, i.e. the intersections or joints of the flow paths. The determining variables at the nodes are pressure and the specific enthalpy and for the branches the flow (mass flow).

All physical variables with a vector nature, such as the flow of fluids, are represented in the flownet as one-dimensional variables with direction information, i.e. as vector quantities (lines of flow). The direction is indicated by the sign. The variables are numbered arbitrarily for reference.

Flownets can be depicted by graphs, whose branches (edges) form the pipes with their fittings (valves, pumps, etc.) and their nodes form the pipe joints. The graph is directional, i.e. the direction of a branch indicates the direction of flow. The graph is also interconnected,

s Flownets



like the flownet. The graph represents the topology of the flownet on the level of pipelines and joints. The graph in Figure 3-2 depicts seven nodes Ki and nine branches Zi

.

Figure 3-2: Flownet graph

The example in Figure 3-1 results in a graph like the one in Figure 3-3 with three branches and four nodes.

Figure 3-3: Flownet graph for example shown in Figure 3-1

The boundary conditions for the flownet are set via the nodes K1, K3 and K4. For example, the pressure on the connections of both tanks is defined at these external nodes. In contrast, K2

The solution method for flownets is based on the flow in the branches being dependant on the pressure using the momentum balance and the balancing of the flow of matter and enthalpy at the nodes. The state variables for such a system are the flow of mass in the branches and the pressure and specific enthalpy at the nodes. Other variables, such as density and temperature in the flownet can be derived according to the medium in question.

is an internal node, for which the relevant variables, such as pressure, are calculated using the flownet solution method.

If the flownet components in a branch change neither the rate nor the enthalpy of flow in that branch, the branch is removed from the flownet, i.e. both nodes are merged to form one node.

The solution method for flownets is, as usual for SIMIT, a cyclical solution method with equidistant cycles, which extends the standard solution method. Flownet component types can also be used in addition to other component types, such as those in the basic library. Specific connections are used for data exchange between flownet components and the flownet solver. Through these connections, the components receive values calculated by the flownet solver; these are then used to calculate variables that are sent back to the flownet solver. Siemens Automation


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NOTE Dependend on the structure of the flowner and on the parameters of the flownet’s components the calculation of the flownet variables could become instable and so the values of state variables can become infinite. The stability of a flownet is not proven in SIMIT.

In this case setting a smaller value for the cycle time of the flownet and/or a changing the parameters of the flownet balances might establish stability for the calculation of the flownet.

It is clear that a flownet must consist of a minimum of one branch with two nodes. Figure 3-4a shows the minimal graph and corresponding minimal flownet. The nodes can be external (as in Figure 3-4b) or internal.

Figure 3-4a,b: Minimal flownet graph and minimal flownet

If, as shown in Figure 3-5, a branch is not closed by two nodes, the error message "Isolated branch component(s)“ shown in Figure 3-6, stating the components in the branch, appears on start up of the simulation and the simulation will not run.

Figure 3-5: Incomplete flownet branch

Figure 3-6: Error message for incomplete flownet branch

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A similar error message (Figure 3-7) appears if the flownet only contains an isolated component. The corresponding graph then consists of only one branch or node and does not meet the minimum requirements for a flownet.

Figure 3-7: Error message for an isolated flownet component

The flownet components and the flownet solver are also processed cyclically in SIMIT. The flownet components must be assigned to a cycle. All components of a flownet must be parameterised with the same cycle. Otherwise the simulation start up will be interrupted with a message such as that shown in Figure 3-8.

Figure 3-8: Error message for components with different cycles

3.2 Variables used in the flownets The mass flow, pressure and specific enthalpy as well as the derived density and temperature are regarded as basic physical variables in the flownets. These variables are listed in Table 3-1 along with the symbols and units used in this manual.

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Variable Symbol Unit

Mass flow m kg/s

Pressure p bar (absolute)

Specific enthalpy h kJ/kg

Density ρ kg/m³

Temperature T °C

Table 3-1: Flownet variables

3.3 Modelling flownet branches It is assumed that branches do not store any mass. The mass flow rate and density are therefore consistent in the same branch.

This condition is always met made for incompressible media. For compressible media no mass is stored in the branch if the branches have "no" volume. The density decreases for compressible media in the direction of falling pressure, i.e. in the direction of flow, the density change is negligible for slight throttling, so it is acceptable to regard the density as constant.

Thus only the pressure on the connection points needs to be considered for branch objects. The relationships between the pressures on either side of a branch object and the mass flow in a branch, such as 2m~p ∆ρ , are purely of an algebraic nature.

Momentum balance is applied to each branch k using pressure forces. Friction forces, acceleration forces and gravity are ignored. With a uniform cross-section kA on a branch of length Lk

the following applies

∑κ

κ∆−∆= ,kkkkk

k pApAdtmd

L

,

where B,kA,kk ppp −=∆ is the pressure difference along the entire branch k and

B,kA,k,k ppp κκκ −=∆ are the pressure differences of the individual branch elements (see Figure 3-9). If pressure is applied in bars, then the rate of change of the mass flow km is given by

25

smkg

barbar10

∆−

∆= ∑

κ

κ,kk

k

kk ppLA

dtmd

.

Figure 3-9: Branch with branch objects

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The length and cross-section of a branch are generally unknown so a reasonable estimate must be made. Taking a cross-section of 0.05 m2

for example and a length of 10 m, results in a factor

k

kk L

A510=Α

of 500 m. This factor is herein after reffered to as momentum factor.

3.4 Modelling flownet nodes The dynamic inflow and outflow of the medium is balanced at each node. Each node is assigned a material balance envelope, i.e. a volume. The mass in and outflow are balanced as well as the enthalpy in and outflow as a measure of the energy conversion.

3.4.1 Mass balance for the nodes The pressure in a node i is determined through the mass balance, the balancing of the inflow and outflow from the node connected branches:

∑κ

κ=ρ

mdt

dV i

i .

iV is the volume of the material balance envelope assigned to the node, iρ is the density of the medium within the material balance envelope and κm are the inflows and outflows. Inflows are positive ( 0>κm ), outflows are negative ( 0<κm ).

Using the equation of state ( )h,pρ=ρ and assuming an isenthalpic change of state for the pressure in the node, the following applies:

∑κ

κ

−

=

ρ= m

dpd

Vdt

dp

hi

ii

i

1

const

.

The term

i

ii dp

dV ρ

is a measure of the compressibility of the medium. Using the compression modulus Ki

1−

ρ=

i

iiii dp

dVMK

the following applies for the mass balance:

∑∑κ

κκ

κ == mcmMK

dtdp

ii

ii .

The default setting for the specific compression modulus iii M/Kc = in the flownet solution method is the same for all nodes in the flownet. However, various factors result in increased compressibility ci

3.6 of gases and steam in contrast to liquids, and this is taken into

consideration for media with higher and lower densities (see section ).

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3.4.2 Enthalpy balance for the nodes The specific enthalpy is also considered as another state variable of a node. In principle, the convective inflow of enthalpy and the existing enthalpy in the node form a mixed enthalpy, which is added to the outflow. The balancing for a node i is given by

( ) ∑

κκκ= mh

dtMhd ii ,

where iM is the mass and ih is the specific enthalpy of the medium within the material balance envelope.

From

( )∑∈κ

κκ −=iZ

ii

i hhmMdt

dh

1 ,

it follows that by using the difference in enthalpy only the inflows to the nodes i ( iZ∈κ ) need to be summed.

Just like the mass balance factors ci ii M/m 1=, the default thermal factors in the flownet solution method are equal for all nodes, but have different values for media with higher and lower densities.

3.4.3 Determining the density of the medium in the nodes The values for the density in the nodes are calculated from the pressure and specific enthalpy values. The relations used depend on the medium in the flownet.

3.4.3.1 Water/steam medium

In the case of water/steam the density in the nodes is calculated using the equation of state for water/steam with pressure p and specific enthalpy h:

( )h,pρ=ρ .

3.4.3.2 Liquid medium

In the case of liquids, calculation is based on constant density throughout the entire flownet. The default is a density of 997.337 kg/m³.

3.4.3.3 Ideal gas medium

The gas equation TRmVp S= is used for ideal gas. Using the specific heat capacity cp

the density is given by

+

−

⋅==ρ

00

2

barPa10

Tc

hhR

p

Vm

pS

with pressure p in bar, the specific heat capacity cp in kJ/kgK and the specific gas constant RS in kJ/kgK. If the triple point of water is used for the zero point (T0, h0) then T0 = 273,15 K and h0 = 0. The density is then calculated using the following relation

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+

⋅=ρ

K15273

barPa102

,chR

p

pS

.

In the flownet solution method, the specific gas constant has a value of 0.287 kJ/kgK (specific gas constant for dry air).

3.4.4 Determining the temperature of the medium in the nodes The temperatures used in the FLOWNET library components are calculated from the values for pressure p and specific enthalpy h. The equation of state for water/steam medium

( )h,pTT =

is used. In the case of ideal gases and liquids, the temperature is determined from the specific heat capacity cp

and the specific enthalpy according to

pchT = .

3.5 Heat exchange with the environment Heat exchange with the environment is accounted for with a corresponding term in the enthalpy balance equation for the node:

( ) ( )

−−−= ∑

∈κκκ

iZEnviii

i

i TTchhmMdt

dh

1 .

where TEnv is the ambient temperature, Ti

is the temperature of the node and

iii Ac α=

is the determining heat transfer factor, which is the product of the heat transfer coefficient α i and the heat transfer surface Ai

3.6 Parameterisation of flownets

.

The variables for the branches and nodes of a flownet are calculated using the various parameters described above. Default values for these parameters are set in the flownet solution method, but these can be changed using special component types from the FLOWNET library.

You can use the following component types to parameterise networks:

• NetParam for general parameterisation of flownets (see section 4.2.6),

• NetWS for parameterisation of networks with water/steam medium (see section 4.4.1),

• NetLiquid for parameterisation of networks with liquid medium (see section 4.5.1) and

• NetGas for parameterisation of networks with ideal gas medium (see section 4.6.1).

You can use the following component types for specific parameterisation of individual nodes:

• JointParam for general parameterisation of a node (see section 4.2.9), Siemens Automation


s Flownets



• JointParamWS for parameterisation of a node in a network with water/steam medium (see section 4.4.5),

• JointParamLiquid for parameterisation of a node in a network with liquid medium (see section 4.5.5),

• JointParamGas for parameterisation of a node in a network with ideal gas medium (see section 4.6.5).

The component type

• BranchParam (see section 4.2.7)

can be used to parameterise individual branches.

The connection types that you can use for your self-created flownet component parameters are described in sections 5.2.4, 5.2.5 and 5.2.6.

3.6.1 Flownet media The following media can be specified for a flownet:

• water/steam,

• ideal gas or

• liquid Water/steam is the default medium.

3.6.2 Parameters for branches The momentum factor Α can be set for flownet branches. The same factor m450=Α is used as default for all branches in the flownet solution method. If there are several momentum factors in a branch, then the effective factor Α in the branch is given by

∑κΑ

=Α k

11

using the k factors κΑ .

3.6.3 Parameters for nodes The following variables can be parameterised for nodes in a flownet:

• Specific compression modulus M/Kc = • Thermal factor M/m 1=

Both variables can be individually specified for water and steam as well as liquid and gas.

Transitions between the parameters cL and mL and the parameters cG and mG

<ρ≥ρ

=m³/kg500fürm³/kg500für

G

L

cc

c

for media water/steam are calculated by the flownet solution method based on the density according to the following scheme:

and

s Flownets



<ρ≥ρ

=m³/kg500fürm³/kg500für

G

L

mm

m

The transition between both parameter values can also be set with a linear transfer function:

( ) ( )( )

ρ−ρρρ−ρρ

−+

ρ<ρρ>ρ

=

else

fürfür

GL

LGLGL

GG

LL

ccc

cc

c

and

( )

−−−

+

ρ<ρρ>ρ

=

else

fürfür

LLG

LGL

GG

LL

vvvvmm

m

mm

m

using both key values kg/m³ 5 =ρG and kg/m³ 1000 =ρG .

For liquid medium the corresponding variables cL and mL are always applicable, and for ideal gas the variables cG and mG

For heat exchange with the environment, the ambient temperature T

are applicable.

env

M/Ac α= and the heat transfer

factor can be parameterised. The default temperature is set at C 20 °=envT with factor 0=c , i.e. there is no heat exchange with the default settings.

3.6.4 Parameters for liquid medium If liquid medium is set for the flownet, calculations are based on constant density. The density value to be used can be entered as a parameter.

The specific heat capacity cp

3.6.5 Parameters for ideal gas medium

of the medium can be entered as an additional variable for the flownet as well as specifically for each individual node. The default value is 4.18 kJ/kgK.

For ideal gas medium, the gas constant RS and the specific heat capacity cp

kJ/kgK 0,287 =SR can be entered

for the flownet. The default values are and kJ/kgK 1 =pc .

3.6.6 Initialisation of variables Each time the simulation is started, the flownet state variables are initialised as follows.

All branch mass flow rates are initialised with a value of zero ( 0 =m ). This initialisation cannot be changed. The default values for the pressures in the nodes are bar 1 =p , but they can be changed to other values via a parameter. The initial value h for the specific enthalpy depends on the medium in the flownet as follows:

• kJ/kg 100 =h for water/steam,

• kJ/kg 83,6 =h for liquid and

Siemens Automation


s Flownets



• kJ/kg 20 =h for ideal gas.

These initial values can be changed via a parameter.

3.6.7 Parameter overview Table 3-2 provides an overview of the available flownet parameters. The signal column lists the names of the input or output signals for the component, the designation column gives the names of the parameters as given in the component properties dialog. The default values and units are shown in the last column. If explicit parameters are not set, then the defaults for the flownet as described above apply.

Signal Designation Description Default

Value Unit

MEDIUM Medium Medium in flownet: - water/steam: 0 - liquid: 2 - ideal gas: 1

0 -

CG sCompressionGas Specific compression modulus M/Kc = for ideal gas or steam

10 bar/kg

CL sCompressionLiquid Specific compression modulus M/Kc = for liquids

100 bar/kg

MG FactorThermalGas Thermal factor M/m 1= for ideal gas or steam

100 kg

ML

-1

FactorThermalLiquid Thermal factor M/m 1= for liquids 0.1 kg

P_INIT

-1

PressureInit Initial pressure value 1 bar

H_INIT sEnthalpyInit Initial value for specific enthalpy 20 / 83.6 / 100

kJ/kg

DENSITY Density(Liquid) Density (only applies to liquid) 997.337 kg/m³

T_ENV TemperatureEnvironment Ambient temperature T 20 env °C

C_ENV FactorHeatExchangeEnv Heat transfer factor Ac α= 0 kW/K

L_CR sHeatCapLiquid Specific heat capacity cp 4.18 for liquids kJ/kgK

IG_R GasConstant Gas constant R 0.287 S kJ/kgK

IG_CR sHeatCapGas Specific heat capacity cp 1.0 for gas kJ/kgK

ST SmoothTransition Switches to linear transition of the compression modulus and thermal factor for water/steam

False

AL FactorMomentum Momentum factor Α 450 m

Table 3-2: List of flownet parameters

s FLOWNET component library



4 FLOWNET COMPONENT LIBRARY The component types in the FLOWNET library are divided into

• component types for simulating pipe measuring points (directory MEASURE),

• component types for networks with any media (directory GENERAL),

• component types for networks with water/steam medium (directory MEDIUM\WATER.STEAM),

• component types for networks with liquid medium (directory MEDIUM\LIQUID),

• component types for networks with gas medium (directory MEDIUM\GAS).

4.1 The topology connector In the CONNECTORS directory of the SIMIT basic library is a connector that can be used to create topological connections for flownet components that transcend diagram limits:

• the Topology connector

(see Figure 4-1).

Figure 4-1: Connector component types in the basic library

The Topology symbol is shown in Figure 4-2.

Figure 4-2: Topology flownet connector

The Topology connector can be used to create a topological flownet connection between two or more branch components. Figure 4-3a shows two components connected by the CON_A connector. The connection is functionally identical to the direct connection of both components via a connecting line, as shown in Figure 4-3b. Figure 4-4a shows three components connected by the NODE_A connector. This configuration is functionally identical to the connection using a node shown in Figure 4-4b. Siemens Automation





Figure 4-3: Flownet connector on a branch

Figure 4-4: Flownet connector as joint

4.2 General components In the GENERAL (Figure 4-5) directory of the FLOWNET library there are component types that can be used in the flownet with any medium.




Figure 4-5: GENERAL library directory

4.2.1 Valve – control valve

Symbol

Function

The Valve component type is used for simulating a control valve. Depending on the valve position, the pressure drop across the valve is calculated by

2

32

2

hsec12960

mkgbar

ρ

−=

∆

Vc

mp

Where

AB ppp −=∆ is the pressure drop across the valve in bar,

m is the mass flow rate in kg/s,

ρ is the density of the medium in kg/m³ and

Vk is the flow coefficient of the valve in m³/h.

The reference direction is defined for the mass flow m from connection A to connection B, i.e. it is 0>m for mass flow in the reference direction. The pressure drop is therefore a negative value: 0<∆p .

Siemens Automation





At the Position connection, the H position of the valve drive is given as a percentage value, to which the drive component types of the SIMIT basic library can be set (Figure 4-6), for example.

Figure 4-6: Valve with drive

The valve position value is limited to %H 1000 ≤≤ .The valve position is mapped onto flow coefficient Vc using the valve characteristic. The following applies

%H

SScc

VVV

V

100111

100

−+= for a linear characteristic,

2

100 100111

−+=

%H

SScc

VVV

V for a quadratic characteristic,

1100

100

−= %

H

VV

V Scc

for an equal percentage characteristic.

The position ratio

0

100

V

VV c

cS =

is applied here as a quotient consisting of the flow coefficient cV100%H 100=

for a completely open valve ( ) and the flow coefficient cV0 0=H for a completely closed valve ( ).

Any valve characteristic can be created with the Characteristic component type from the SIMIT standard library. The characteristic component is simply placed upstream of the valve's Position input (Figure 4-7).

Figure 4-7: Application of the Characteristic component on valve




The linear characteristic is then set on the valve, so that the characteristic specified by the characteristic component is only scaled by the factor ( ) 00100 VVV c/cc − and displaced by

0Vc .

Parameter

The valve characteristic and flow coefficient can be adjusted via parameters.

• Characteristic Set valve characteristics: linear, quadratic, equal-percentage; adjustable online

• Cvs Flow coefficient cV100 /hm10 6

0100 ³cc VV−+≥ with ; adjustable online

• Cv0 Flow coefficient cV0 m³/h10 6

0−≥Vc with

The parameters, their units and default values are shown in Figure 4-8.

Figure 4-8: Parameters for the Valve component type

Additional parameters

Additional parameters can be used to visualise the operating states of the components in symbols (Figure 4-9).

Figure 4-9: Additional parameters for the Valve component type

When ShowFlow is set to True the valve position is shown as in Figure 4-10.

Figure 4-10: Symbolic representation of the valve position

If ShowFlowDirection is also set to true, then the valve position and the direction of flow is shown as in Figure 4-11.

Siemens Automation





Figure 4-11: Representation of the valve position and flow direction in symbol

Both additional parameters can be adjusted online.

Operating window

The pressure drop p∆ and the flow rate m are shown in the operating window (Figure 4-12).

Figure 4-12: Operating window for the valve component type

4.2.2 StopValve – non-return valve

Symbol

Function

The StopValve component type is used for simulating a non-return valve. Depending on the direction of flow, the pressure drop across the non-return valve is given by

<

ρ

−

>

ρ

−

=∆

0for h

sec12960

mkg

0for h

sec12960

mkg

bar 2

32

0

2

2

32

100

2

mc

m

mc

m

p

V

V

Where

AB ppp −=∆ is the pressure drop across the non-return valve in bar,




m is the mass flow rate in kg/s,

ρ is the density of the medium in kg/m³ and

Vc is the flow coefficient of the valve in m³/h.

The reference direction is defined for the mass flow m from connection A to connection B, i.e. it is 0>m for mass flow in the reference direction.

Parameter

Both flow coefficients for the valve can be set via parameters:

• Cvs Flow coefficient cV100 /hm10 6

0100 ³cc VV−+≥ with

• Cv0 Flow coefficient cV0 m³/h10 6

0−≥Vc with


Figure 4-13: Parameters for the StopValve component type

In order to implement the non-return function, the flow coefficient cV0

4.2.3 Pump – pump

must be sufficiently small.

Symbol

Function

The component type Pump calculates the pressure boost, which depends on the flow and speed, according to

( )( )

0für2

2

002 >∆−∆+∆=∆ m

m

mpppnp*

*

.

Where

AB ppp −=∆ is the pressure boost in bar,

m is the mass flow rate in kg/s, Siemens Automation





0p∆ is the zero flow head in bar,

*p∆ is the nominal pressure boost in bar,

*m is the nominal flow in kg/s and

n is the dimensionless speed value.

The reference direction is defined for the flow m from connection A to connection B, i.e. we have 0>m for flow in the reference direction.

The speed N is preset as a percentage value at the Speed input and is limited to %N 1000 ≤≤ . It follows that %/Nn 100= and therefore 10 ≤≤ n . For example, drives from

the SIMIT basic library can be used here, as shown in Figure 4-14.

Figure 4-14: Pump with drive

The quadratic relation between pressure boost and flow defined above is illustrated in Figure 4-15 for the operation of the pump in normal range, i.e. for 0>m 0>∆p .

Figure 4-15: Pump characteristic

The pump characteristic is increased steadily, according to

( )( )

0for2

2

002 <∆−∆+∆=∆ m

mk

mpppnp*

*




when the flow is reversed ( 0<m ). The throttling effect can be influenced by the flow coefficient k. Figure 4-16 shows an extended characteristic for various values of k.

-3

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

1,5

-2 -1,5 -1 -0,5 0 0,5 1 1,5 2

Flow

Pres

sure

boo

st k = 1

k = 2

k = 3

K = 0,5

Figure 4-16: Extended characteristic

It is clear that the throttling effect is greater at smaller values of the flow coefficient k.

To stabilise a simulation that contains a component of this type, flow reversal ( 0<∆p ) is also calculated using the above equations. For switched off pumps, i.e. with zero speed, this results in pure throttling for both the flow in and against the pump direction:

( )

( )( )

( )

>∆−∆

<∆−∆

=∆0f

0f

2

2

0

2

2

0

morm

mpp

mormk

mppp

*

*

*

*

Parameter

The determining variables for the pump characteristic are set with parameters:

• ZeroFlowHead Zero flow head 0p∆ , *pp ∆>∆ 0 ; adjustable online

• NominalPressure Nominal pressure boost *p∆ , 0>∆ *p ; adjustable online

• NominalMassflow Nominal mass flow *m , 0>*m ; adjustable online

The parameters, their units and default values are shown in Figure 4-24. Siemens Automation





Figure 4-17: Parameters for the Pump component type


The additional parameter Throttling sets a positive flow coefficient k ( 0>k ) (Figure 4-18).

Figure 4-18: Additional parameters for the Pump component type

If the additional parameter Showflow is set to true, then the operating status will be shown in the pump symbol (Figure 4-19).

Figure 4-19: Representation of the pump operating status in symbol

Operating window

The pressure boost p∆ and the flow rate m are shown in the operating window (Figure 4-20).

Figure 4-20: Operating window for the Pump component type




4.2.4 Pnode – pressure setting

Symbol

Function

The Pnode component type defines values for the pressure p and specific enthalpy h at its connection A. This type of component forms a boundary for the flownet. When the flownet is represented as a graph, this corresponds to an (external) node, for which the pressure and specific enthalpy are predefined.

Operating window

The values for pressure p and specific enthalpy h can be input digitally in the operating window (Figure 4-21).

Figure 4-21: Operating window for the component type Pnode

These variables have the following default values:

• Pressure arp b1= (Pressure input)

• specific enthalpy kJ/kg100=h (sEnthalpy input)

The corresponding values for the medium flowing into or out of the external node are shown in the extended operating window: mass flow rate m , density r, temperature T and specific enthalpy h (Figure 4-22).

Figure 4-22: Extended operating window for the component type Pnode Siemens Automation





For outflow we have 0>m , for inflow we have 0<m .

4.2.5 Mnode – mass flow setting

Symbol

Function

The Mnode component type defined values for the mass flow rate m and specific enthalpy h at its connection A. This type of component forms a boundary for the flownet. When the flownet is represented as a graph, this corresponds to an in or outflow through an (internal) node or branch. An internal node with defined inflow or outflow is added to the flownet for each component of this type.

Operating window

The values for mass flow rate m and specific enthalpy h can be input digitally in the operating window (Figure 4-23).

Figure 4-23: Operating window for the Mnode component type


• mass flow rate 0=m (Massflow input)


The variables of the assigned internal node are shown in the extended operating window (Figure 4-24): pressure p, density r, temperature T and specific enthalpy h.




Figure 4-24: Extended operating window for the Mnode component type

4.2.6 NetParam – network parameterisation

Symbol

Function

The NetParam component type is used for parameterisation of the flownet. The component can be added to any point on any branch of the flownet.

Parameter

The variables for the flownet can be specified as parameters for the components:

• Medium The following can be selected as medium for the flownet "Water/Steam", "Liquid", or "Ideal Gas"

• FactorMomentum Momentum factor for the flow through a branch of the flownet

• sCompressionGas Specific compression modulus for the "Water/Steam" medium with density

kg/m³500<ρ or the "Ideal Gas" medium

• sCompressionLiquid Specific compression modulus for the "Water/Steam" medium with density

kg/m³500>ρ or the "Liquid" medium

• FactorThermalGas Factor for the enthalpy balancing with "Water/Steam" medium with density

kg/m³500<ρ or the "Ideal Gas" medium

• FactorThermalLiquid Factor for the enthalpy balancing with "Water/Steam" medium with density

kg/m³500>ρ or the "Liquid" medium

• DensityLiquid Medium density; only applies to the "Liquid" medium Siemens Automation





• sHeatCapGas Specific heat capacity for gas‚ only applies to the "Ideal Gas" medium

• sHeatCapLiquid Specific heat capacity for liquids; only applies to the "Liquid" medium

• GasConstant Specific gas constant‚ only applies to the "Ideal Gas" medium


Figure 4-25: Parameters for the NetParam component type


Initial values and specific characteristics for internal nodes of the flownet can be set via additional parameters:

• PressureInit Initialisation value for the pressure in the internal node of the flownet

• sEnthalpyInit Initialisation value for the specific enthalpy in the internal node of the flownet

• SmoothTransition When this additional parameter is set to true, the variables sCompression and FactorThermal are set with a density dependant linear transfer function

• TemperatureEnvironment Ambient temperature

• FactorHeatExchangeEnv Proportionality factor for heat exchange between the medium in the internal nodes and the environment; at zero value no heat exchange occurs

The additional parameters, their units and default values are shown in Figure 4-26.




Figure 4-26: Additional parameters for the NetParam component type

4.2.7 BranchParam – branch parameterisation

Symbol

Function

The BranchParam component type is used for parameterisation of the branches in a flownet. The components are placed anywhere along the branch to be parameterised.

Parameter

The momentum balance factor can be defined in the branch that is to be parameterised.


The default values for the parameter are shown in Figure 4-27.

Figure 4-27: Parameters for the BranchParam component type

4.2.8 Joint – joint

Symbol

Function

The component type Joint can be used to join three branches connected at A, B and C in one node. The Joint component adds an internal node to the flownet. Siemens Automation





Operating window

The pressure p, specific enthalpy h, density r and the temperature T of the node are shown in the operating window (Figure 4-28).

Figure 4-28: Operating window for the Joint component type

4.2.9 JointParam – parameterisable joint

Symbol

Function

The component type JointParam can be used to join three branches connected at A, B and C in one node. The JointParam component adds an internal node to the flownet.

Parameter

The following variables of the node associated with JointParam can be parameterised:

• sCompressionGas Specific compression modulus for low density media (gas/steam, kg/m³500<ρ )

• sCompressionLiquid Specific compression modulus for high density media (liquids, kg/m³500>ρ )

• FactorThermalGas Factor for the enthalpy balancing for low density media (gas/steam, kg/m³500<ρ )

• FactorThermalLiquid Factor for the enthalpy balancing for high density media (liquids, kg/m³500>ρ )





Figure 4-29: Parameters for the JointParam component type


Initial values and specific characteristics for the node can be set via additional parameters:

• PressureInit Initialisation value for the pressure in the node

• sEnthalpyInit Initialisation value for the specific enthalpy in the node




Figure 4-30: Additional parameters for the JointParam component type

Operating window


Figure 4-31: Operating window for the JointParam component type Siemens Automation





4.3 Measuring components Components for simulating measurements in the pipe network can be found in the MEASURE (Figure 4-32) directory.

Figure 4-32: Library directory MEASURE

Connections from the Measure connection type are applied to the measuring components. Descriptions of the individual signals for this type are given in Table 4-1.

Signal Description Unit

Temperature Temperature measurement °C

Pressure Pressure measurement bar

Level Measured level m

Weight Measured weight kg

Flow Measured flow kg/s

Table 4-1: Signals of the Measure connection type

4.3.1 PipeMeasure – pipe measuring point

Symbol




Function

The PipeMeasure component type creates a measuring point in the pipe. It is inserted with its connections A and B at the required measuring point in the flownet. The measuring process for the various variables is not simulated with suitable models, only the variables calculated by the flownet solver are output.

The measurement variables are output at the Measure connection:

• absolute flow rate value m ,

• pressure Ap at connection A and

• temperature T.

No other signals are sent from the Measure connection.

When the simulation is running, the direction of the medium flow is shown by an arrow on the symbol (Figure 4-33).

Figure 4-33: Indication of medium flow for the PipeMeasure component type

Operating window

The variables output via the Measure connection are also displayed in the operating window (Figure 4-34).

Figure 4-34: Operating window for the PipeMeasure component type

Values for the specific enthalpy and the density of the medium at the measuring point are displayed in the extended operating window (Figure 4-35).

Siemens Automation





Figure 4-35: Extended operating window for the PipeMeasure component type

4.3.2 Measurements – measuring indicator

Symbol

Function

The MeasureAll component type provides the bundled values measured via the Measure input as individual signals at its outputs: pressure, temperature, flow, level and weight.

This type of component can be connected to the pipe measuring point, for example and thereby output measuring variables as individual signals (Figure 4-36).

Figure 4-36: Components of the Measurements type at a pipe measuring point

Operating window

The output measuring variables are also displayed in the operating window for the component type (Figure 4-37).




Figure 4-37: Operating window for the Measurements component type

4.3.3 FlowIndicator – flow indicator

Symbol

Function

The FlowIndicator component type displays the defined flow at its Measure input.

Operating window

The flow rate value obtained via the Measure input is displayed in the operating window (Figure 4-38).

Figure 4-38: Operating window for the FlowIndicator component type

4.3.4 LevelIndicator – level indicator

Symbol

Siemens Automation





Function

The LevelIndicator component type displays the defined level at its Measure input.

Operating window

The level value obtained via the Measure input is displayed in the operating window (Figure 4-39).

Figure 4-39: Operating window for the LevelIndicator component type

4.3.5 PressureIndicator – pressure indicator

Symbol

Function

The PressureIndicator component type displays the defined pressure at its Measure input.

Operating window

The pressure value obtained via the Measure input is displayed in the operating window (Figure 4-40).

Figure 4-40: Operating window for the PressureIndicator component type




4.3.6 TemperatureIndicator – temperature indicator

Symbol

Function

The TemperatureIndicator component type displays the defined temperature at its Measure input.

Operating window

The temperature value obtained via the Measure input is displayed in the operating window (Figure 4-41).

Figure 4-41: Operating window for the TemperatureIndicator component type

4.3.7 WeightIndicator – weight indicator

Symbol

Function

The WeightIndicator component type displays the defined weight at its Measure input.

Operating window

The weight value obtained via the Measure input is displayed in the operating window (Figure 4-42).

Siemens Automation





Figure 4-42: Operating window for the WeightIndicator component type

4.4 Component types for water/steam medium Component types that can be used in the flownet with the water/steam medium are located in the folder MEDIUM\WATER.STEAM (Figure 4-43) in the FLOWNET library. The medium parameter for a flownet that contains these components must be set to the value "Water/Steam".

Figure 4-43: Library directory WATER.STEAM




4.4.1 NetWS – water/steam network parameterisation

Symbol

Function

The NetWS component type is used to parameterise a network for the water/steam medium. The components can be added to any point on any branch of the flownet.

Parameter



• sCompressionSteam Specific compression module for density kg/m³500<ρ (steam)

• sCompressionWater Specific compression module for density kg/m³500>ρ (water)

• FactorThermalSteam Factor for enthalpy balancing for density kg/m³500<ρ (steam)

• FactorThermalWater Factor for enthalpy balancing for density kg/m³500>ρ (water)


Figure 4-44: Parameters for the NetWS component type



• PressureInit Initialisation value for the pressure in the internal node of the flownet

• sEnthalpyInit Initialisation value for the specific enthalpy in the internal node of the flownet Siemens Automation





• SmoothTransition When this additional parameter is set to true, the variables sCompression and FactorThermal are set with a density dependant linear transfer function




Figure 4-45: Additional parameters for the NetWS component type

4.4.2 PnodeWS – water/steam pressure settings

Symbol

Function

The PnodeWS component type defines values for the pressure p and specific enthalpy h at its connection A. This type of component forms a boundary for the flownet. When the flownet is represented as a graph, this corresponds to an (external) node, for which the pressure and specific enthalpy are predefined.

Operating window

The values for pressure p and specific enthalpy h can be input digitally in the operating window (Figure 4-46).




Figure 4-46: Operating window for the component type PnodeWS




The corresponding values for the medium flowing into or out of the external node are shown in the extended operating window: mass flow rate m , density r, temperature T and specific enthalpy h (Figure 4-47).

Figure 4-47: Extended operating window for the component type PnodeWS


4.4.3 MnodeWS – water/steam mass flow settings Symbol

Function The MnodeWS component type defines values for the mass flow rate m and specific enthalpy h at its connection A. This type of component forms a boundary for the flownet. When the flownet is represented as a graph, this corresponds to an in or outflow through an (internal) node or branch. An internal node with defined inflow or outflow is added to the flownet for each component of this type.

Siemens Automation





Operating window

The values for mass flow rate m and specific enthalpy h can be input digitally in the operating window (Figure 4-48).

Figure 4-48: Operating window for the MnodeWS component type




The variables of the assigned internal node are shown in the extended operating window (Figure 4-49): pressure p, density r, temperature T and specific enthalpy h.

Figure 4-49: Extended operating window for the MnodeWS component type

4.4.4 JointWS – water/steam joint

Symbol

Function

The component type JointWS can be used to join three branches connected at A, B and C in one node. The JointWS component adds an internal node to the flownet.




Operating window


Figure 4-50: Operating window for the JointWS component type

4.4.5 JointParamWS – water/steam parameterisable joint

Symbol

Function

The component type JointParamWS can be used to join three branches connected at A, B and C in one node. The JointParamWS component adds an internal node to the flownet.

Parameter

The node associated with JointParamWS can be parameterised:

• sCompressionSteam Specific compression module for density kg/m³500<ρ (steam)

• sCompressionWater Specific compression module for density kg/m³500>ρ (water)

• FactorThermalSteam Factor for enthalpy balancing for density kg/m³500<ρ (steam)

• FactorThermalWater Factor for enthalpy balancing for density kg/m³500>ρ (water)


Siemens Automation





Figure 4-51: Parameters for the JointParamWS component type



• PressureInit Initial value for the pressure in the node

• sEnthalpyInit Initial value for the specific enthalpy in the node




Figure 4-52: Additional parameters for the JointParamWS component type

Operating window


Figure 4-53: Operating window for the JointParamWS component type




4.4.6 StorageTankWS – water storage tank

Symbol

Function

The StorageTankWS component type provides the simulation with an open water tank, i.e. a tank that is not sealed from the environment.

The medium flows in and out of the tank via STUBx. For each of the N connections, the throttling effect is defined by

2

32

2

hsec12960

mkgbar

ρ

−=

∆

Vc

mp .

The tank can have a minimum of one and a maximum of 16 connections. The connections can be moved to any position on the outline of the component symbol by using the mouse while simultaneously pressing ALT.

It is assumed that the water in the tank is immediately completely mixed i.e. it is an homogenous medium with an overall consistent density and enthalpy.

The inflow and outflow of water is balanced across the N connections of the tank. The balanced mass M of the N flow rates im of the medium in the tank, is defined by

∑=

=N

iim

dtdM

1

.

The water volume balancing via the volume flow results in the rate of change of density ρ given by

ρρ−

ρ=

ρ ∑∑∈=∈=

N

Zi,ii

i

N

Zi,ii mm

Mdtd

11

1 ,

where only the inflows ( Zi∈ ) need to be summed.

The specific enthalpy of the water is defined by the enthalpy balance equation

−= ∑∑

∈=∈=

N

Zi,ii

N

Zi,iii mhmh

Mdtdh

11

1

Again, only the inflows ( Zi∈ ) need to be summed.

The dynamic behaviour of the water in the tank is described by these balances for mass M, density ρ and specific enthalpy h.

Siemens Automation





The calculated variables for the level l of water in the tank, its mass M and temperature T as well as pressure p0

on the tank base are output at the Measure connection. The temperature T is calculated from the density and specific enthalpy of the water using the equation of state

( )h,TT ρ= .

The pressure p on the tank base is calculated as the sum of the weight pressure lgρ of the water and the atmospheric pressure pU

according to

.lgpp U ρ+=

Limiting case "empty tank"

When the tank is empty, the outflow is strongly throttled. The flow coefficient is thereby set to the value kv0

The tank is considered empty when the tank filling V is lower than a specified minimum filling V

for maximum throttling of all connections through which water flows out.

min

:

minVV < .

When the tank is empty, balancing of the states is stopped, i.e. changes to the three state variables mass, density and specific enthalpy are rejected. The empty state is terminated when there is a sufficient increase in the tank filling. In each cycle the validity of

.%

HVM min

min

+ρ≥

1001

is checked. The required increase can be set via the hysteresis HminFigure 4-54

. A corresponding indicator for an empty tank is shown on the component symbol ( ).

Figure 4-54: Empty tank indicator on the symbol

Limiting case "full tank"

For a full tank, only the balanced contents are limited in the calculation of the state variables according to .VM ρ=

A corresponding indicator is shown on the symbol (Figure 4-55).




Figure 4-55: Full tank indication on the symbol

CAUTION It is not checked whether the state variables (pressure, enthalpy) for the inflow and tank contents always possess values for the state water.

In the simulation, corresponding specified inflows may result in a situation where the state values for the tank contents describe a water-steam mixture or pure steam, which has no physical meaning.

Parameter

All relevant geometric variables of the tank are set via parameters:

• Volume Volume V of the tank; adjustable online

• Height Height of the tank; adjustable online

• NbrOfStubs Number N of connections

The parameters, their units and default values are shown in Figure 4-56 .

Figure 4-56: Parameters for the StorageTankWS component type


The atmospheric pressure PressureOutside and initial value for the tank fill level (LevelInit), the specific enthalpy (EnthalpyInit) and density (DensityInit) of the water are set via additional parameters:

• PressureOutside Atmospheric pressure pU

• LevelInit Initial value for the level

; adjustable online

Siemens Automation





• EnthalpyInit Initial value for the specific enthalpy in the contents

• DensityInit Initial value for the density of the contents

• Cvs A uniform flow coefficient cV

• Cv0 A uniform flow coefficient c

for all connections

V0

• MinVolume Minimal tank volume V

for strong throttling at the tank connections

min

• MinVolumeHys Hysteresis H

; adjustable online

min

The additional parameters, their units and default values are shown in

; adjustable online

Figure 4-57.

Figure 4-57: Additional parameters for the StorageTankWS component type

Operating window

The level l, the pressure p, the temperature T and the mass M of the water in the tank is displayed in the operating window (Figure 4-58).

Figure 4-58: Operating window for the StorageTankWS component type




4.4.7 DrumWS – steam drum

Symbol

Function

The DrumWS component type provides the simulation with a drum, i.e. a closed container that is water/steam tight.

The drum is assumed to be a cylindrical, horizontal or vertically standing container, where media flow in and out via the STUBWx and/or STUBSx connections. For each of the connections, the throttling effect is defined by

2

32

2

hsec12960

mkgbar

ρ

−=

∆

Vc

mp

At the NW connections STUBWx medium with the state variables of the saturated water can be drawn out, likewise medium with the state variables of the saturated steam can be drawn out at the NS

It can be assumed that the medium in the drum immediately separates into two homogenous saturated phases: the saturated liquid phase and the saturated steam phase.

connections STUBSx. The drum can have a minimum of one and a maximum of eight connections of each type. The connections can be moved to any position on the outline of the component symbol by using the mouse while simultaneously pressing ALT.

The inflow and outflow of water/steam are balanced via the SW NNN += drum connections. This results in a mass of water and steam in the drum, balanced via the flow rate, given by

∑=

=N

iim

dtdM

1

Given that VM ρ=

the rate of change in the mean density results in

∑=

=ρ N

iim

dtdV

1

.

In addition, the energy is balanced as per

( ) ∑=

=N

iii mh

dthMd

1

where h is the specific enthalpy (mean enthalpy) of water/steam in the drum and hi is the specific enthalpy of the inflow and outflow at the i-th connection. The specific enthalpy of the Siemens Automation





medium in the drum must be applied for outflows, i.e. h′ for outflow of saturated water and h ′′ for outflow of saturated steam. The balancing results from

( ) ( ) ( ) ∑∑∑′′

−′′+′

−′+−=∈=∈=∈=

N

i,ii

N

i,ii

N

i,iii

Amhh

Amhh

Zmhh

dtdhM

111

where the inflows Z , outflows of saturated water A′ and/or outflows of saturated steam A ′′ are summed.

In order to model a heat exchange with an ideal insulated drum, the enthalpy balance equation is extended as follows

( ) ( ) ( ) ( )ST

N

i,ii

N

i,ii

N

i,iii TTA

Amhh

Amhh

Zmhh

dtdhM −α+

′′−′′+

′−′+−= ∑∑∑

∈=∈=∈= 111

.

TT is the temperature of the drum wall, ST is the saturation temperature of water/steam.

The heat stored in the drum wall is defined by the heat balance

( )TSTT

T TTAcMdt

dT−α=

1

The level of water l, the saturation temperature TS, saturation pressure pS

The STUBWx connections are taken to be at the bottom of the drum. The pressure at these connections is the sum

and the mass M of water/steam is output at the Measure connection.

Splgp +ρ′=

of the saturated steam and the hydrostatic pressure of the water.

Limiting case "empty drum"

When the drum is empty, the outflow is strongly throttled. The flow coefficient is thereby set to the value cv0

The drum is considered empty when the fill level M

for maximum throttling of all connections through which water or steam flows out.

W /ρ is lower than a specified minimum fill level Vmin

:

ρ< minW VM .

When the drum is empty, balancing of the states is stopped, i.e. changes to the density and specific enthalpy are rejected. The empty state is terminated when there is a sufficient increase in the amount of water. In each cycle the validity of

.%

HVM min

minW

+ρ≥

1001


. A corresponding indicator for an empty drum is shown on the component symbol ( ).




Figure 4-59: Empty drum indicator on the symbol

Limiting case "full drum"

The drum is regarded as full when the amount of water reaches the maximum possible value.

( )ρ−> mimW VVM .

When the drum is full, balancing of the states is stopped, i.e. changes to the density and specific enthalpy are rejected. The full state is terminated when there is a sufficient decrease in the amount of water. In each cycle the validity of

+ρ−ρ≤

%H

VVM minminW 100

1

is checked. The required decrease can be set via the hysteresis HminFigure 4-60

. A corresponding indicator for a full drum is shown on the component symbol ( ).

Figure 4-60: Full drum indication on the symbol

Parameter

All relevant geometric variables of the drum are set via parameters:

• NbrOfStubsW Number NW

• NbrOfStubsS Number N

of connections STUBWx

S

• Position Position of the drum: Vertically or Horizontally

of connections STUBSx

• VolumeDrum Volume V of the drum; adjustable online

• HeightOrLength Height or length of the drum; adjustable online

• MassDrum Mass MT of the drum; adjustable online

Siemens Automation





• SurfaceDrum Inner surface A of the drum; adjustable online

• sHeatCapDrum Specific heat capacity cT

• HeatTransCoe Heat transfer coefficient α of the drum for water/steam ; adjustable online

of the drum; adjustable online


Figure 4-61: Parameters for the DrumWS component type


Initial values and other variables can be set via additional parameters:

• VolumeInit Initial value for the water volume

• TemperatureInit Initial value for the temperature of water/steam (saturation temperature)

• Cvs Uniform flow coefficient cV

• Cv0 Uniform flow coefficient c

for all connections

V0

• MinVolume Minimal drum volume V

for strong throttling at the drum connections

min


; adjustable online

min


; adjustable online

Figure 4-62.




Figure 4-62: Additional parameters for the DrumWS component type

Operating window

The saturation pressure pS and the pressure pWFigure 4-63

at the STUBWx connections are displayed in the operating window ( ). The saturation pressure TS, the drum temperature TT

, the mass M of water/steam and the water level l are also displayed.

Figure 4-63: Operating window for the DrumWS component type

The values for density r and specific enthalpy h of water/steam are shown in the extended operating window (Figure 4-64). Mix indicates the mean variables, Water the variables for saturated water and Steam the variables for saturated steam.

Figure 4-64: Extended operating window for the DrumWS component type

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4.4.8 ElectricalHeaterWS – electric heat exchanger for water/steam

Symbol

Function

The ElectricalHeaterWS component type is used to simulate an electric heat exchanger. The electric heating power Pel

Water/steam is directed via the connections TS_IN and TS_OUT as a heated medium. The flow

in kW is set via the connection ElectricalPower.

m is throttled according to the relation

2

32

2

hsec12900

mkgbar

ρ

−=

∆

TSVc

mp .

with the flow coefficient cV

For the heat exchange, a simple one tube model divided into segments is applied (

. The reference direction for the flow is chosen as from TS_IN to TS_OUT.

Figure 4-65). The number N of segments can be set to a value between 4 and 16.

Figure 4-65: Diagram of the segments for the electrical heat exchanger ElectricalHeaterWS

It is assumed that the supplied electrical energy is completely converted into heat. The heat balance for a segment i of the tube with extremely simplified heat transfer is given by




( )i,Ti,TSTelTi,T TTbPa

dtdT

−+=

where

.cM

Ab,

cMa

TT

TSTST

TTT

α==

1

In addition, the water/steam-sided enthalpy balancing for a segment i is

( ) ( )i,TSi,TTSi,TSi,TSTSi,TS TTbhha

dtdh

−+−= −1

where

.V

Ab,

VmN

aTSTS

TSTSTS

TSTSTS ρ

α=

ρ=

TT,i and TTS,i are the temperatures of the tube segments and the medium in the segments, hT,i and hTS,i

Parameter

are the corresponding specific enthalpies.

The segmentation and coefficients for the balance equations are defined by parameters:

• NbrOfSegments Number N of segments: 164 ≤≤ N

• Cvs Flow coefficient c

• Volume Volume V

V

TS

• Surface Surface A

of the medium (tube inside volume)

TS

• HeatTransCoef Heat transfer coefficient α

of the tube on the water/steam side

TS

• sHeatCapTube Specific heat capacity c

from tube to water/steam

T

• MassTube Mass M

of the tube

T

The parameters, their units and default values are shown in

of the tube

Figure 4-66.

Figure 4-66: Parameters for the ElectricalHeaterWS component type Siemens Automation





Operating window

The flow rate m , pressure drop ∆p and enthalpy difference ∆h of the heated medium as well as the electrical heating power Pel Figure 4-67 are displayed in the operating window ( ). The temperatures of the tube (Tube), and the heated medium (Tube side) for the first and last segment (T1 and TN

) are also displayed.

Figure 4-67: Operating window for the ElectricalHeaterWS component type

4.4.9 HeatExchangerWS – heat exchanger water/steam to water/steam

Symbol

Function

The HeatExchangerWS component type is used to simulate a heat exchanger for the media water/steam on the tube side and shell side. The simulation is implemented for three types

• parallel-flow heat exchanger

• counter-flow heat exchanger and

• cross-flow heat exchanger.

Both media are routed on the tube side via the connections TS_IN and TS_OUT, and on the shell side via the connections SS_IN and SS_OUT.

The flow m is throttled on both the tube and shell side according to the relation




2

32

2

hsec12900

mkgbar

ρ

−=

∆

Vc

mp

with the relevant flow coefficient cv


. The chosen reference direction for the flow is from connection _IN to _OUT on both the tube and shell side.


Figure 4-68: One tube model of the heat exchanger

The water/steam heat on the tube and shell side and the heat in the tube itself (Figure 4-69) are balanced.

Figure 4-69: Heat balance for the heat exchanger HeatExchangerWS

Both heat transfers from the shell side medium to the tube and from the tube to the tube side medium are applied, in a very simplified form, as

( )TSSSSSSTSSSSTSS TTAqAQ −α== −− ,

( )TSTTSTSTSTTSTST TTAqAQ −α== −−

For each segment i the following heat balances

( ) ( )i,TSi,TTSi,TSi,TSTSi,TS TTbhha

dtdh

−+−= −1 , Siemens Automation





( ) ( )i,Ti,TSTi,Ti,SSTi,T TTbTTa

dtdT

−+−= ,

( ) ( )i,SSi,TSSi,SSi,SSSSi,SS TTbhha

dtdh

−+−= −1

apply with the following coefficients, which are valid for all segments:

.cM

Ab,

cMA

a,V

Ab,

VmN

a,V

Ab,

VmN

aTT

TSTST

TT

SSSST

SSSS

SSSSSS

SSSS

SSSS

TSTS

TSTSTS

TSTS

TSTS

α=

α=

ρα

=ρ

=ρ

α=

ρ=

The values set for the media in the shell and tube side of the flownet apply to the density ρTS, ρSS and the specific heat capacity cTS, cSS

For initialisation, the temperatures of the tube segments are set to the temperature of the tube side medium, calculated from the pressure (input FNTS.PRESSURE) and the specific enthalpy (output FNTS.HSPEC).

.

Parameter


• Type Type of heat exchanger: ParallelFlow (parallel flow), CounterFlow (counter flow), CrossFlow (cross flow)


• CvsSS Shell side flow coefficient c

• CvsTS Tube side flow coefficient c

V

• VolumeSS Shell side volume V

V

• VolumeTS Tube side volume V

SS

TS

• SurfaceSS Shell side surface A

SS

• SurfaceTS Tube side surface A

of the tube (exterior surface of the tube)

TS

• HeatTransCoefSS Heat transfer coefficient α

of the tube (interior surface of the tube)

SS

• HeatTransCoefTS Heat transfer coefficient α

on the tube exterior

TS

• sHeatCapTube Specific heat capacity c

on the tube interior

T

• MassTube Mass M

of the tube

T


of the tube

Figure 4-70.




Figure 4-70: Parameters for the HeatExchangerWS component type

Operating window

The flow rate m , pressure drop ∆p and enthalpy difference ∆h of the shell side and tube side media are displayed in the operating window. The temperatures of the tube (Tube), and the medium (Shell side and Tube side) for the first and last segment (T1 and TN


Figure 4-71: Operating window for the HeatExchangerWS component type

4.5 Component types for liquid medium Component types that can be used in the flownet with the liquid medium are located in the directory MEDIUM\LIQUID (Figure 4-72) in the FLOWNET library. The medium parameter for a flownet that contains these components should be set to the value "Liquid", if applicable.

Siemens Automation





Figure 4-72: Library directory LIQUID

4.5.1 NetLiquid – liquid network parameterisation

Symbol

Function

The NetLiquid component type is used for parameterisation of a flownet for liquids. The components can be added to any point on any branch of the flownet.

Parameter


• Density Density of the liquid

• sHeatCapacity Specific heat capacity of the liquid


• sCompression Specific compression modulus of the liquid




• FactorThermal Factor for enthalpy balancing


Figure 4-73: Parameters for the NetLiquid component type



• PressureInit Initialisation value for the pressure in the internal nodes of the flownet

• TemperatureInit Initialisation value for the temperature in the internal nodes of the flownet




Figure 4-74: Additional parameters for the NetLiquid component type

4.5.2 PnodeLiquid – liquid pressure settings

Symbol

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Function

The PnodeLiquid component type outputs values for pressure and temperature at its connection. It creates a boundary for the connected flownet. When the flownet is represented as a graph, PnodeLiquid corresponds to an (external) node, for which the pressure and temperature are predefined.

Operating window

The values for pressure and temperature can be input digitally in the operating window (Figure 4-75).

Figure 4-75: Operating window for the PnodeLiquid component type



• Temperature C20 °=T (Temperature input)

The corresponding values for the medium flowing into or out of the node are shown in the extended operating window (Figure 4-76): mass flow rate m , density r and temperature T.

Figure 4-76: Extended operating window for the PnodeLiquid component type


4.5.3 MnodeLiquid – liquid mass flow settings

Symbol




Function The MnodeLiquid component type outputs values for mass flow rate and temperature at its connection. It creates a boundary for the connected flownet. When the flownet is represented as a graph, MnodeLiquid corresponds to an in or outflow through an (internal) node or branch. Thus an internal node with a defined in or outflow is added to the flownet.

Operating window

The values for mass flow rate and temperature can be input digitally in the operating window (Figure 4-77).

Figure 4-77: Operating window for the MnodeLiquid component type




The variables of the assigned internal node are shown in the extended operating window (Figure 4-78): pressure p, density r and temperature T.

Figure 4-78: Extended operating window for the MnodeLiquid component type

For inflow we have 0>m , for outflow we have 0<m .

4.5.4 JointLiquid – liquid joint

Symbol

Siemens Automation





Function

The JointLiquid component type can be used to join three connected branches in one node. All connections are equal. The JointLiquid component adds an internal node to the flownet.

Operating window

The pressure p and temperature T of the node is displayed in the operating window (Figure 4-79).

Figure 4-79: Operating window for the JointLiquid component type

4.5.5 JointParamLiquid – liquid parameterisable joint

Symbol

Function

The JointParamLiquid component type can be used to join three connected branches in one node. All connections are equal. The JointParamLiquid component adds an internal node to the flownet. This node can be parameterised.

Parameter

The node associated with JointParamLiquid can be parameterised:

• sHeatCapacity Specific heat capacity of the liquid

• sCompression Specific compression module of the liquid






Figure 4-80: Parameters for the JointParamLiquid component type



• PressureInit Initial value for the pressure in the node

• TemperatureInit Initial value for the temperature in the node


• FactorHeatExchangeEnv Proportionality factor for heat exchange between the liquid in the internal nodes and the environment; at zero value no heat exchange occurs


Figure 4-81: Operating window for the JointParamLiquid component type

Operating window

The pressure p and temperature T of the node is displayed in the operating window (Figure 4-82).

Figure 4-82: Operating window for the JointParamLiquid component type

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4.5.6 StorageTankLiquid – liquid storage tank Symbol

Function The StorageTankLiquid component type provides the simulation with an open tank for liquid, i.e. a tank that is not sealed from the environment.

The medium flows in and out of the tank via STUBx connections. For each of the N connections, a throttling effect defined by

2

32

2

hsec12960

mkgbar

ρ

−=

∆

Vc

mp

is assumed. The tank can have a minimum of one and a maximum of 16 connections. The connections can be moved to any position on the outline of the component symbol by using the mouse while simultaneously pressing ALT.

It is assumed that the liquid in the tank is immediately completely mixed i.e. it is an homogenous medium with an overall consistent density and temperature.

The inflow and outflow is balanced across the N connections of the tank. The balanced mass M of the N flow rates im of the liquid in the tank, is defined by

∑=

=N

iim

dtdM

1

.

The temperature of the liquid is balanced as the mixing temperature from the inflows ( Zi∈ ) according to

−= ∑∑

∈=∈=

N

Zi,ii

N

Zi,iii

LmTmh

cMdtdT

11

11 .

The dynamic behaviour of the liquid in the tank is described by these balances for mass M, and temperature T.

The calculated variables for the level l of liquid in the tank, its mass M and temperature T as well as pressure p0

lgρ on the tank base are output at the Measure connection. The pressure p

on the tank base is the sum of the weight pressure of the liquid and the atmospheric pressure pU

:

.lgpp U ρ+=





When the tank is empty, the outflow is strongly throttled. The flow coefficient is thereby set to the value cv0

The tank is considered empty when the tank filling V is lower than a specified minimum tank filing V

for maximum throttling of all connections through which the medium flows out.

min

:

minVV < .

When the tank is empty, balancing of the states is stopped, i.e. changes to the mass and temperature of the liquid are rejected. The empty state is terminated when there is a sufficient increase in the fill level. In each interval the validity of

.%

HVM min

min

+ρ≥

1001





For a full tank, only the balanced contents are limited in the calculation: .VM ρ=

A corresponding indicator is shown on the symbol (Figure 4-84).

Figure 4-84: Full tank indicator on the symbol

Parameter

The following are set as geometric variables of the tank via parameters:

Siemens Automation






• Height of the tank; adjustable online



Figure 4-85: Parameters for the StorageTankLiquid component type


The initialisation values for the atmospheric pressure PressureOutside, the fill level (LevelInit) of the tank and the temperature (TemperatureInit) of the liquid are set via additional parameters:

• PressureOutside Atmospheric pressure pU

• LevelInit Initial value for the level

; adjustable online

• TemperatureInit Initial value for the temperature of the contents

• Cvs Uniform flow coefficient kV

• Cv0 Uniform flow coefficient k

for all connections

V0

• Density Density ρ of the liquid in the tank

for maximum throttling at the tank connections

• sHeatCapacity Specific heat capacity cG

• MinVolume Minimal tank volume V

of the liquid in the tank

min


; adjustable online

min


; adjustable online

Figure 4-86.




Figure 4-86: Additional parameters for the StorageTankLiquid component type

Operating window

The level l, the pressure p, the temperature T and the mass M of the liquid in the tank is displayed in the operating window (Figure 4-87).

Figure 4-87: Operating window for the StorageTankLiquid component type

4.5.7 ElectricalHeaterLiquid – electric heat exchanger for liquid Symbol

Function The ElectricalHeaterLiquid component type is used to simulate an electric heat exchanger. The electric heating power Pel

The liquid is directed via the connections TS_IN and TS_OUT as a heated medium. The flow



Siemens Automation





2

32

2

hsec12900

mkgbar

ρ

−=

∆

Vc

mp .

with flow coefficient cV




Figure 4-88: Diagram of the segmentation for the heat exchanger


( )i,Ti,LTelTi,T TTbPa

dtdT

−+=

where

.cM

Ab,

cMa

TTT

TTT

α==

1

In addition, the heat balance of the liquid in a segment i is given by

( ) ( )i,Li,Ti,Li,Li,L TTbTTa

dtdT

−+−= −1

where

.Vc

Ab,

VmN

aLρα

=ρ

=

TT,i and TL,i are the temperatures of the tube segments and the liquids in the segment i. The flownet values apply for the density ρ and the specific heat capacity cG

Parameter

of the liquid.







• Volume Volume V of the liquid (tube inside volume)

V

• Surface Surface A of the tube interior

• HeatTransCoef Heat transfer coefficient α from tube to liquid

• sHeatCapTube Specific heat capacity cT

• MassTube Mass M

of the tube

T


of the tube

Figure 4-89.

Figure 4-89: Parameters for the ElectricalHeaterLiquid component type


For initialisation of the heat exchanger, the temperatures of the liquid and the tube can be set to the same value (Figure 4-90) via the additional parameter TemperatureInit.

Figure 4-90: Additional parameters for the ElectricalHeaterLiquid component type

Operating window

The flow rate m , pressure drop ∆p and temperature difference ∆T of the liquid as well as the electrical heating power Pel Figure 4-91 are displayed in the operating window ( ). The temperatures of the tube (Tube), and the liquid (Tube side) for the first and last segment (T1 and TN) are also displayed.

Siemens Automation





Figure 4-91: Operating window for the ElectricalHeaterLiquid component type

4.5.8 HeatExchangerLiquid – heat exchanger liquid to liquid

Symbol

Function

The HeatExchangerLiquid component type is used to simulate a heat exchanger for liquids on the tube side and shell side. The simulation is implemented for three types






2

32

2

hsec12900

mkgbar

ρ

−=

∆

Vc

mp .








Figure 4-92: One tube model for the heat exchanger

The liquid heat on the tube and shell side and the heat in the tube itself (Figure 4-93) are balanced.

Figure 4-93: Diagram of the heat balancing for the heat exchanger

Both heat transfers from the shell side liquid to the tube and from the tube to the tube side liquid are applied, in a very simplified form, as


( )TSTTSTSTSTTSTST TTAqAQ −α== −−

For each segment i the following heat balances apply

( ) ( )i,TSi,TTSi,TSi,TSTSi,TS TTbTTa

dtdT

−+−= −1 ,


dtdT

−+−= ,

( ) ( )i,SSi,TSSi,SSi,SSSSi,SS TTbTTa

dtdT

−+−= −1

with the following coefficients, which are valid for all segments

.cM

Ab,

cMA

a,Vc

Ab,

VmN

a,Vc

Ab,

VmN

aTT

TSTST

TT

SSSST

SSSSSS

SSSSSS

SSSS

SSSS

TSTSTS

TSTSTS

TSTS

TSTS

α=

α=

ρα

=ρ

=ρα

=ρ

=

Siemens Automation





The values set for the liquid in the shell and tube side of the flownet apply to the density ρTS, ρSS and the specific heat capacity cTS, cSS

For initialisation, the temperatures of the tube segments are set to the temperature of the tube side liquid, calculated from the specific enthalpy ( FNTS.HSPEC input).

.

Parameter






V


V


SS

TS


SS



TS



SS



TS

• sHeatCapTube Specific heat capacity of the tube c


T

• MassTube Mass M

T


of the tube

Figure 4-94:




Figure 4-94: Parameters for the HeatExchangerLiquid component type

Operating window

The flow rate m , pressure drop ∆p and enthalpy difference ∆h of the shell side and tube side liquid are displayed in the operating window (Figure 4-95). The temperatures of the tube (Tube), and the liquid (Shell side and Tube side) for the first and last segment (T1 and TN


Figure 4-95: Operating window for the HeatExchangerLiquid component type

4.6 Component types for gas medium Component types that can be used in the flownet with the ideal gas medium are located in the directory MEDIUM\GAS (Figure 4-96) in the FLOWNET library. The medium parameter for a flownet that contains these components should be set to the value "Ideal Gas", if applicable.

Siemens Automation





Figure 4-96: Library directory GAS

4.6.1 NetGas – gas network parameterisation Symbol

Function

The NetGas component type is used for parameterisation of a flownet for gases. The components can be added to any point on any branch of the flownet.

Parameter


• GasConstant Specific gas constant

• sHeatCapacity Specific heat capacity of the gas


• sCompression Specific compression modulus of the gas

• FactorTherma Factor for enthalpy balancing





Figure 4-97: Parameters for the NetGas component type



• PressureInit Initialisation value for the pressure in the internal nodes of the flownet

• TemperatureInit Initialisation value for the temperature in the internal nodes of the flownet


• FactorHeatExchangeEnv Proportionality factor for heat exchange between the gases in the internal nodes and the environment; at zero value no heat exchange occurs


Figure 4-98: Additional parameters for the NetGas component type

4.6.2 PnodeGas – gas pressure settings

Symbol

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Function

The PnodeGas component type outputs values for pressure and temperature at its connection. It creates a boundary for the connected flownet. When the flownet is represented as a graph, PnodeGas corresponds to an (external) node, for which the pressure and temperature are predefined.

Operating window

The values for pressure and temperature can be input digitally in the operating window (Figure 4-99).

Figure 4-99: Operating window for the PnodeGas component type




The corresponding values for mass flow m , density r and temperature T for medium flowing into or out of the node is displayed in the extended operating window (Figure 4-100) .

Figure 4-100: Extended operating window for the component type PnodeGas


4.6.3 MnodeGas – gas mass flow setting

Symbol




Function

The MnodeGas component type outputs values for mass flow rate and temperature at its connection. It creates a boundary for the connected flownet. When the flownet is represented as a graph, Mnode corresponds to an in or outflow through an (internal) node or branch. Thus an internal node with a defined in or outflow is added to the flownet.

Operating window

The values for mass flow rate and temperature can be input digitally in the operating window (Figure 4-101).

Figure 4-101: Operating window for the MnodeGas component type




The variables of the assigned internal node are shown in the extended operating window (Figure 4-102): pressure p, density r and temperature T.

Figure 4-102: Extended operating window for the component type MnodeGas

For inflow we have 0>m , for outflow we have 0<m .

4.6.4 JointGas – gas joint

Symbol

Siemens Automation





Function

The JointGas component type can be used to join three connected branches in one node. All connections are equal. The JointGas component adds an internal node to the flownet.

Operating window

The pressure p, temperature T and density r of the node are displayed in the operating window (Figure 4-103).

Figure 4-103: Operating window for the JointGas component type

4.6.5 JointParamGas – gas parameterisable joint

Symbol

Function

The JointParamGas component type can be used to join three connected branches in one node. All connections are equal. The JointParamGas component adds an internal node to the flownet. This node can be parameterised.

Parameter

The node associated with JointParamGas can be parameterised:

• GasConstant Specific gas constant

• sHeatCapacity Specific heat capacity of the gas

• sCompression Specific compression modulus of the gas






Figure 4-104: Parameters for the JointParamGas component type



• PressureInit Initialisation value for the pressure in the node

• TemperatureInit Initialisation value for the temperature in the node


• FactorHeatExchangeEnv Proportionality factor for heat exchange between the gas in the internal nodes and the environment; at zero value no heat exchange occurs


Figure 4-105: Additional parameters for the JointParamGas component type

Operating window

The pressure p, temperature T and density r of the node are displayed in the operating window (Figure 4-106).

Figure 4-106: Operating window for the JointParamGas component type

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4.6.6 StorageTankGas – gas storage tank

Symbol

Function

The StorageTankGas component type provides the simulation with a gas tank.

The medium flows in and out of the tank via STUBx connections. For each of the N connections, a throttling effect defined by

2

32

2

hsec12960

mkgbar

ρ

−=

∆

Vc

mp

is assumed. The tank can have a minimum of one and a maximum of 16 connections. The connections can be moved to any position on the outline of the component symbol by using the mouse while simultaneously pressing ALT.

It is assumed that the gas in the tank is immediately completely mixed i.e. it is an homogenous medium with an overall consistent density and temperature.

The inflow and outflow is balanced across the N connections of the tank. The balanced mass M of the N flow rates im of the gas in the tank, is defined by

∑=

=N

iim

dtdM

1

.

The specific enthalpy h of the gas is balanced as mixed enthalpy from the inflows ( Zi∈ ) as per

−= ∑∑

∈=∈=

N

Zi,ii

N

Zi,iii mhmh

Mdtdh

11

1

The dynamic behaviour of the gas in the tank is described by these balances for mass M and specific enthalpy h.

At the connection Measure, the variables for pressure p, temperature

GchT =

and mass M of the gas are output. The pressure is calculated from the equation for ideal gas:

( )

barPa10

K152735⋅

+=

V

M,TRp S .





When the tank is empty, the outflow is strongly throttled. The flow coefficient is thereby set to the value cv0

The tank is considered empty when the tank filling M is lower than a specified minimum tank filling M

for maximum throttling of all connections through which gas flows.

min

:

minMM < .

When the tank is empty, balancing of the states is stopped, i.e. changes to the mass and specific enthalpy of the gas are rejected. The empty state is terminated when there is a sufficient increase in the fill level. In each interval the validity of

.%

HMM min

min

+≥

1001





In order to limit the pressure in the tank to meaningful values while the simulation is running, the tank is considered full when its pressure p reaches a specified maximum pressure pmax

:

maxpp < .

When the tank is full, the inflow is strongly throttled. The flow coefficient is thereby set to the value cv0

When the tank is full, balancing of the states is stopped, i.e. changes to the mass and specific enthalpy of the gas are rejected. The full state is terminated when there is a sufficient decrease

for maximum throttling of all connections through which gas flows in.

M∆ in the content. In each cycle the validity of

+≥∆

%H

MM minmin 100

1

is checked. The required decrease can be set via the hysteresis HminFigure 4-108

. A corresponding indicator for an full tank is shown on the component symbol ( ).

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Figure 4-108: Full tank indicator on the symbol

Parameter

The following are set as geometric variables of the tank via parameters:



The parameters, their units and default values are shown in Figure 4-109 .

Figure 4-109: Parameters for the StorageTankGas component type


Initial values and other variables can be predetermined via additional parameters:

• PressureInit Initialisation value for the pressure; adjustable online

• TemperatureInit Initialisation value for the temperature of the gases

• PressureMax Maximum tank pressure pmax

• Cvs Uniform flow coefficient c

; adjustable online

V

• Cv0 Uniform flow coefficient c

for all connections

V0

• GasConstant Specific gas constant R

for maximum throttling at the tank connections

S

• sHeatCapacity Specific heat capacity c

for the gas in the tank

G

• MinMass Minimum tank filling M

of the gas in the tank

min of the tank; adjustable online




• MinVolumeHys Hysteresis Hmin


; adjustable online

Figure 4-110.

Figure 4-110: Additional parameters for the StorageTankGas component type

Operating window

The pressure p, temperature T and mass M of the gases in the tank are displayed in the operating window (Figure 4-111).

Figure 4-111: Operating window for the StorageTankGas component type

4.6.7 ElectricalHeaterGas – electric heat exchanger for gas

Symbol

Siemens Automation





Function

The ElectricalHeaterGas component type is used to simulate an electric heat exchanger for gas. The electric heating power Pel

The gas is directed via the connections TS_IN and TS_OUT as a heated medium. The flow



2

32

2

hsec12900

mkgbar

ρ

−=

∆

Vc

mp

with flow coefficient cV




Figure 4-112: Diagram of the heat transfer in a segmented heat exchanger


( )i,GTi,GTelTi,T TTbPa

dtdT

−+=

where

.cM

Ab,

cMa

TTT

TTT

α==

1

In addition, the heat balance of the gas in a segment i is given by

( ) ( )i,Gi,Ti,Gi,Li,L TTbTTa

dtdT

−+−= −1

where

.Vc

Ab,

VmN

aGρα

=ρ

=




TT,i and TG,i are the temperatures of the tube segments and the gases in the segment i. The flownet values apply for the density ρ and the specific heat capacity cG

Parameter

of the gases.




• Volume Volume V of the gases (tube inside volume)

V

• Surface Surface A of the tube interior

• HeatTransCoef Heat transfer coefficient α from tube to gas

• sHeatCapTube Specific heat capacity cT

• MassTube Mass M

of the tube

T


of the tube

Figure 4-113.

Figure 4-113: Parameters for the ElectricalHeaterGas component type


For initialisation of the heat exchanger, the temperatures of the gas and the tube can be set to the same value (Figure 4-114) via the additional parameter TemperatureInit.

Figure 4-114: Additional parameters for the ElectricalHeaterGas component type

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Operating window

The flow rate m , pressure drop ∆p and temperature difference ∆T of the gas as well as the electrical heating power Pel Figure 4-115 are displayed in the operating window ( ). The temperatures of the tube (tube), and the gas (tube side) for the first and last segment (T1 and TN


Figure 4-115: Operating window for the ElectricalHeaterGas component type

4.6.8 HeatExchangerGas – heat exchanger gas to gas

Symbol

Function

The HeatExchangerGas component type is used to simulate a heat exchanger for the gases on the tube side and shell side. The simulation is implemented for three types









2

32

2

hsec12900

mkgbar

ρ

−=

∆

Vc

mp





Figure 4-116: One tube model for the heat exchanger

The gas heat on the tube and shell side and the heat in the tube itself (Figure 4-117) are balanced.

Figure 4-117: Diagram of the heat balancing for the heat exchanger

Both heat transfers from the shell side gas to the tube and from the tube to the tube side gas are applied, in a very simplified form, as


( )TSTTSTSTSTTSTST TTAqAQ −α== −− .

For each segment i the heat balances

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( ) ( )i,TSi,TTSi,TSi,TSTSi,TS TTbTTa

dtdT

−+−= −1 ,


dtdT

−+−= ,

( ) ( )i,SSi,TSSi,SSi,SSSSi,SS TTbTTa

dtdT

−+−= −1

apply with the following coefficients, which are valid for all segments:

.cM

Ab,

cMA

a,Vc

Ab,

VmN

a,Vc

Ab,

VmN

aTT

TSTST

TT

SSSST

SSSSSS

SSSSSS

SSSS

SSSS

TSTSTS

TSTSTS

TSTS

TSTS

α=

α=

ρα

=ρ

=ρα

=ρ

=

The values set for the gas in the shell and tube side of the flownet apply to the density ρTS, ρSS and the specific heat capacity cTS, cSS

For initialisation, the temperatures of the tube segments are set to the temperature of the tube side gas, calculated from the specific enthalpy ( FNTS.HSPEC input).

.

Parameter






V


V


SS

TS


SS



TS



SS



TS

• sHeatCapTube Specific heat capacity of the tube c


T

• MassTube Mass M

T of the tube





Figure 4-118: Parameters for the HeatExchangerGas component type

Operating window

The flow rate m , pressure drop ∆p and enthalpy difference ∆h of the shell side and tube side gas are displayed in the operating window (Figure 4-119). The temperatures of the tube (Tube), and the gas (Shell side and Tube side) for the first and last segment (T1 and TN


Figure 4-119: Operating window for the HeatExchangerGas component type

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s Creating your own component types for flownets



5 CREATING YOUR OWN COMPONENT TYPES FOR FLOWNETS

The CTE component type editor enables you to create your own component types, which utilise the mechanisms of the FLOWNET process. You can expand the functions of the components supplied with the FLOWNET library, e.g. add physical effects that are not covered by the supplied library components and thus enhance your flownet simulations. You can also extend the FLOWNET library by creating your own component types from scratch.

Two aspects must be considered when creating components:

• the topological aspect and

• the connection to the solution method.

The topological aspect is covered by appropriate extensions to the component type definition. Special connection types are provided for the connection to the solution method.

In addition, the general descriptions of component properties in the CTE manual form the basis for creating flownet components. The general properties also apply in full to flownet components.

5.1 Topological properties The topology of a flownet is automatically determined when compiling a simulation project from interconnected flownet components. Each flownet component must thus provide relevant topological information about itself, i.e. information about how it is to be treated topologically in the flownet. From a topological point of view it is necessary to know how the reference direction for variables in a flownet is defined for a component and how the data exchange between the components and the solution method for the flownet is set up.

The flownet elements with topological information are

• internal nodes,

• external nodes and

• branch objects.

Relationships with the topological connections of the flownet components must be defined for each of these elements. To do this, open the topology editor by double clicking on the Topology entry in the component type navigation menu (Figure 5-1).




Figure 5-1: Topology in the component type navigation menu

5.1.1 Type FLN1 connections The FLN1 connection type indicates the connections that are used to connect flownet components with one another. The topology of a flownet is derived from interconnected connectors of this type and the topological information on the individual flownet components. FLN1 is purely a topological connection type, which means it does not carry any signals. Connectors of this type will be simply referred to as topological connectors in the following text. Topological connectors are represented by circles (Figure 5-2).

Figure 5-2: Connectors of type FLN1

If a connecting line is used to join topological connectors to each other in the diagram editor, then the connectors are hidden and only visible as faint shadows (Figure 5-3).

Figure 5-3: Linking connectors of type FLN1 with a connecting line

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They can also be joined by superimposing the connectors. Once linked, both connectors are hidden (Figure 5-4).

Figure 5-4: Linking connectors of type FLN1 through superposition

5.1.2 Topology of internal nodes An internal flownet node in a component type is defined as follows in the topology description: INTERNAL_NODE i;

Topological component connectors must also be assigned to this internal node. Three connectors can be assigned in the topological description as per the following example: FROM i TO a; FROM i TO b; FROM i TO c;

The three connectors a, b and c must be defined as type FLN1 connectors in the component type. Figure 5-5 shows a diagram of the resulting topological structure of this component type.

Figure 5-5: Topology of an internal node

5.1.3 Topology of external nodes External nodes represent the boundaries of the flownet. External nodes can be used to predefine pressure and enthalpy in nodes and inflows and outflows for the flownet.

In the topological description of a component type an external node e is defined as follows: EXTERNAL_NODE e;

This external node must be assigned at least one topological connector of a component. The topological description should be completed as follows, for example: FROM e TO a;

The topological connector a must be defined in the component type as a connection of type FLN1. Figure 5-6 shows a diagram of the resulting topological structure of the component type.




Figure 5-6: Topology of an external node

5.1.4 Topology of a branch object Branch objects are part of a flownet branch, such as throttling of pressure.

The reference direction for the variables of a branch object is defined in the topological description of the flownet component. For example, the definition FROM a TO b;

defines the branch object with a reference direction from connector a to connector b of the component. Both of the topological connectors a and b must be defined in the component type as connectors of type FLN1.

Flow variables are positive in the reference direction. For a branch object (see Figure 5-7), these are the mass flow m and the flow of enthalpy hmH = .

Figure 5-7: Topology of a branch object

Pressure boosts are applied in the reference direction, i.e. the pressure variation is defined here as

ab ppp −=∆

For pressure drops in the reference direction (throttling), p∆ is therefore negative and for pressure boosts in the reference direction p∆ is positive.

5.2 Connection to the flownet solver The flownet objects of a component and the flownet solver exchange data via special flownet connections. There are six different connection types FLN2 to FLN7 available for this purpose (Figure 5-8). Their use with flownet components is explained in the following sections 5.2.1 to 5.2.6.

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Figure 5-8: Data exchange between flownet components and flownet solver

Connection types FNL2 to FNL7 only provide connection to the flownet solver and thus must be set as invisible on the component symbol. In the connection properties, the usage "Property view only" (see Figure 5-9) or "CTE view only" must be set.

Figure 5-9: Visibility in the properties window of a connection of type FLN2 to FLN7.

5.2.1 Connection type FLN2 for branch objects A branch object can exchange variables with the flownet solver via a connection of type FLN2. The topological description of a branch object is completed as follows for a connector with the name FN FROM a TO b : FN;

The connector must always be defined in the OUT direction (Figure 5-10). It connects the component to the flownet solver in order to exchange variables that are relevant to the branch object between the flownet solver and the component. It maps the branch-influencing effect on the flownet i.e. the effect that the branch object has on the branch.

Figure 5-10: Definition of a connection of type FLN2

Figure 5-11 shows the input and output signals with the direction of data flow between the components and the flownet solver.




Figure 5-11: Signals of a connection of type FLN2

The components receive four variables via the input signals for calculating the effect of the branch object:

1. specific enthalpy h (FN.HSPEC), 2. mass flow m (FN.MFL), 3. pressure pa

4. densityρ (FN.DENSITY). (FN.PRESSURE),

The pressure pa

Figure 5-12

relates to the "from" connector (FROM) of the topological description, which is the connector a in our example. Density ρ and enthalpy h are variables of the supplied medium ( ).

Figure 5-12: Assigning variables to a branch object

The output signals for the branch object are calculated in the component and sent to the flownet solver:

1. change in specific enthalpy ∆h (FN.DELTAH), 2. pressure variation ∆p = pb – pa

3. derivative of pressure variation with respect to the mass flow d∆p/d (FN.DELTAP),

M (FN.DPDMFL).

5.2.2 Connection type FLN3 for external nodes Variables are exchanged between external nodes and the flownet solver via connections of type FLN3. A connector of type FLN3 is assigned to the external node in the topology description, for a connector with name FN, as follows: EXTERNAL_NODE e : FN;

The connection type FLN3 provides signals in the forward and reverse direction as listed in Table 5-1. Siemens Automation





Forward signals Backward signals

Name Variable Name Variable

HFW Specific enthalpy HBW Specific enthalpy

PRESSURE Pressure MFL Mass flow rate

Table 5-1: FLN3 connection type signals

The following applies: if the FN connector is defined with the direction OUT, then the pressure and specific enthalpy are specified via this connector for the external node of the flownet. If the connector is defined with the direction IN then the mass flow and the specific enthalpy are specified for the external node.

5.2.2.1 Connector of type FLN3 with direction OUT

If the connector is defined with direction OUT then the pressure calculated in the component is set for the flownet solver via this connector. The external node is thus a pressure node. The following variables can be set at its outputs:

1. pressure pe

2. specific enthalpy h (FN.PRESSURE),

e

At its inputs, the mass flow supplied to or discharged from the flownet via the external node, calculated by the flownet solver is returned to the components. In the case of discharge from the flownet, the specific enthalpy of the flow is also returned to the components:

(FN.HFW).

3. mass flow m (FN.MFL), 4. specific enthalpy ha

Figure 5-13

(FN.HBW).

illustrates the signal direction for data exchange between the components and the flownet solver.

Figure 5-13: Signals of a connection of type FLN3 with direction OUT

The mass flow m is positive flow into the flownet ( 0>m ) and for outflow it is negative ( 0>m ). This does not depend on the direction choosen in the topology description.




Figure 5-14: Variables of a pressure node

5.2.2.2 Connection of type FLN3 with direction IN

If the connector FN is defined with direction IN then the mass flow set in the component is defined for the flownet via this connector. The external node active in the flownet is thus a node with mass inflow, or a mass flow node. The following variables can be set at its outputs:

1. mass flow m (FN.MFL) 2. specific enthalpy h (FN.HBW)

At its inputs, the pressure calculated by the flownet solver for the external node is returned to the components. If discharge from the flownet is set with negative mass flow, then the specific enthalpy of the medium is returned to the components:

1. pressure pe

2. specific enthalpy h (FN.PRESSURE)

e

Figure 5-15

(FN.HFW)

illustrates the signal direction for data exchange between the components and the flownet solver.

Figure 5-15: Signals of a connection of type FLN3 with direction IN

Mass flow nodes operate in the flownet like internal nodes with mass inflow or outflow. These nodes are therefore treated as internal nodes in the flownet, i.e. for an external node, an internal node with additional inflow or outflow is created in the flownet. The pressure returned to the components pe thus corresponds to the pressure in this internal node and likewise for the specific enthalpy he Figure 5-16 ( ):

Figure 5-16: Variables of a mass flow node

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5.2.3 Connection type FLN4 for internal nodes The pressure, specific enthalpy and density variables calculated by the flownet solution method for an internal node can be used in a component via a connector of type FLN4. The topological description of a component type is completed as follows for a connector with the name FN INTERNAL_NODE i : FN;

The connector must always be defined in the IN direction (Figure 5-17). It connects the components to the flownet in order to map the variables relevant for the internal node i, calculated by the flownet solver, to the components.

Figure 5-17: Definition of a connector of type FLN4

The variables calculated in the node i are provided via the connector inputs (see Figure 5-18):

1. pressure pi

2. specific enthalpy h (FN.PRESSURE)

i

3. density (FN.HSPEC)

iρ (FN.DENSITY)

Figure 5-18: Signals of a connection of type FLN4

5.2.4 Connection type FLN5 for parameters of a flownet Parameters of a flownet can be exchanged between components and the flownet solver via a connector of type FLN5. This connector can be assigned to any flow net object: a branch object or an internal or external node. The topological definition of the object should be completed, for a connector with name FN as per

• FROM a TO b : FN; or

• INTERNAL_NODE i : FN; or

• EXTERNAL_NODE e : FN;

The signals of connection type FLN5 are listed in Table 5-2. Their meaning in the mathematical model of the flownet is explained in section 3.6.




NOTE The relations used for calculating the flownet variables, such as temperature, for the relevant medium are defined via the MEDIUM parameter. This can only be done during initialisation of the simulation. Changes made to the parameters while the simulation is running have no effect.

Signal Description

MEDIUM Flownet medium: MEDIUM := 0 for water/steam, MEDIUM := 1 for ideal gas, MEDIUM := 2 for liquid; cannot be changed while the simulation is running

CG Specific compression modulus M/K for water/steam medium

with density m³/kg500<ρ and for ideal gas medium

CL Specific compression modulus M/K for water/steam medium

with density m³/kg500≥ρ and for liquid medium

MG Thermal factor M/1 for water/steam medium with density m³/kg500<ρ and for ideal gas medium

ML Thermal factor M/1 for water/steam medium with density m³/kg500≥ρ and for liquid medium

P_INIT Initial value for the pressure in the internal node of the flownet

H_INIT Initial value for the specific enthalpy in the internal node of the flownet

DENSITY Density of the medium in the flownet when liquid is set as the medium

T_ENV Ambient temperature

C_ENV Heat transfer factor Ac α= for heat exchange in the internal nodes of the flownet with the environment

L_CR Specific heat capacity cp

IG_R

for liquid medium

Specific gas constant RS

IG_CR

for ideal gas medium

Specific heat capacity cp

ST

for ideal gas as medium

binary signal; if ST := 'True’, then a linear transfer is applied for parameters CL, CG and ML, MG for the water/steam medium

AL Momentum factor Α for branches in the flownet

Table 5-2: Signals of connection type FLN5

Depending on the direction of the connector FN its signals are inputs or outputs. Depending on the direction, flownet parameters can be set or used in components. If the connector is defined by direction OUT, then the variables set in the components are provided to the flownet as parameters. These parameters are available in the components for evaluation, if the connector is defined with direction IN.

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5.2.5 Connection type FLN6 for parameterisation of a branch The dynamic of the flow rate can be parameterised individually for each branch. To do this, a connector FN, via which the momentum factor Α is transferred to the flownet solver, must be added to the topological definition of the branch object as follows: FROM a TO b: FN;

If a connector of type FLN6 is defined with direction OUT (Figure 5-19), then the momentum factor Α for the branch containing the object is transferred to the flownet solver via this connection.


If the connector is defined with direction IN, then the momentum factor Α for the branch is transferred to the branch object from the flownet solver.

5.2.6 Connection type FLN7 for parameterisation of an internal node

Each internal node can be parameterised individually. A connector, via which the parameter will be transmitted to the flownet solver, must be added to the topological definition of an internal node. For a connector FN the definition is completed as follows: Internal_Node i: FN;

FN is always created as an output of type FLN7 (Figure 5-20).


The variables listed in Table 5-3 are transmitted to the flownet solver for the internal node. Their meaning in the mathematical model of the flownet is explained in section 3.6.




Signal Description

CG Specific compression module ii M/K for water/steam medium with density m³/kg500<ρ and for ideal gas medium

CL Specific compression module ii M/K for water/steam medium with density m³/kg500≥ρ and for liquid medium

MG Thermal factor iM/1 for water/steam medium with density m³/kg500<ρ and for ideal gas medium

ML Thermal factor iM/1 for water/steam medium with density m³/kg500≥ρ and for liquid medium

P_INIT Initial pressure value

H_INIT Initial value for specific enthalpy

T_ENV Ambient temperature

C_ENV Heat transfer factor Aci α= for heat exchange with the environment

L_CR Specific heat capacity cp

IG_R

for liquid medium

Specific gas constant RS

IG_CR

for ideal gas medium

Specific heat capacity cp

Table 5-3: Signals of connection type FLN7

for ideal gas as medium

5.3 Constants and functions You can use various constants and functions when creating your own flownet components.

5.3.1 Constants The available constants are listed in Table 5-4.

Name Data type

Value Description

_GRAVITY analog 9,81 Gravitational constant (gravitational acceleration)

_T0 analog 273,15 Absolute zero temperature

Table 5-4: Constants for flownet components

5.3.2 Functions Functions for calculating state variables are available for flownet components with water/steam medium. The available state variables and units are summarised in Table 5-5.

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Variable Unit

p Pressure bar

p Saturated pressure S bar

T Temperature °C

T Saturated temperature S °C

h Specific enthalpy kJ/kg

h’ Specific enthalpy of saturated water kJ/kg

h’’ Specific enthalpy of saturated steam kJ/kg

ρ Density kg/m³

ρ’ Density of saturated water kg/m³

ρ’’ Density of saturated steam kg/m³

Table 5-5: State variables for water/steam

All state functions FNAME return a state variable ZVAL as an analog value. This is called up by

ZVAL = _WaterSteam.FNAME(PARAM1 (, PARAM2)).

The available state functions are described in Table 5-6.

ZVAL FNAME PARAM1 PARAM2 State function

ρ rph p h ( )h,pρ=ρ

T trh ρ h ( )h,TT ρ=

T tvp S p - S ( )SS pTT =

p pvt S T - S ( )SS Tpp =

ρ’ rsvt T - S ( )ST'ρ=ρ′

ρ’’ rssvt T - S ( )STρ ′′=ρ ′′

ρ’ rsvp p - S ( )Sp'ρ=ρ′

ρ’’ rssvp p - S ( )Spρ ′′=ρ ′′

h’ hsvt T - S ( )ST'h'h =

h’’ hssvt T - S ( )SThh ′′=′′

h’ hsvp p - S ( )Sp'h'h =

h’’ hssvp p - S ( )Sphh ′′=′′

Table 5-6: State functions for water/steam

The saturated pressure pS and saturated temperature TS are limited for the saturation function as follows:




C943730 °≤≤ ,TS and bar64220bar00650 ,p, S ≤≤ .

The relevant limit values are set for values outside this range.

The values for pressure p and specific enthalpy h are limited to the following ranges for the state equation ( )h,pρ=ρ :

bar490bar0070 ≤≤ p, and kJ/kg3998kJ/kg20 ≤≤ h .

The specific enthalpy is limited to the following range for the state function ( )h,TT ρ=

kJ/kg4158kJ/kg9 ≤≤ h

The limits for the density ρ depend on the enthalpy value: The smallest permissible density value is 0.0012344 kg/m³ (when kJ/kg4160=h ), the maximum permissible density value is 1045.239 kg/m³ (when kJ/kg96=h ).

The auxiliary function Cylniv can be used to calculate fill levels in horizontal cylinders. For a cylinder of length L and radius r with specified volume V it calculates a fill level of H (Figure 5-21). This can be called up with:

H = _Utilities.Cylniv(V, L, r).

Figure 5-21: Cross-section of a partially full cylinder

5.3.3 Own Functions The FLOWNET library provides you with three different media: water/steam, idela gas and liquid. The signal MEDIUM of the connection type FLN5 is assigned a respective key number (0, 1 or 2) for each medium. According to this key number the corresponding state equations for calculating the density and temperature are choosen by the flownet solver.

With the FLOWNET library you also have the alternative to simulate flownets with other than the three media given. You simply have to provide specific state equations for the calculation of the density and temperature in the nodes of the flownet by a “global function”.

Such a global function must consist of a .NET assemby that is named Userdefined.dll and which has its “Assembly Name” specified as “Userdefined” in the project settings. It must have the namespace Userdefined and a public class named FlownetFunctions. This class has to comprise two public static functions for calculation of the states:

• public static double trh(long m, double r, double h),

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• public static double rph(long m, double p, double h).

The function trh has to calculate the temperature from density r and specific enthalpy h, the function rph has to calculate the density from pressure p and specific enthalpy h. The units are to be taken as follows:

• temperature in °C,

• density in kg/m³,

• pressure in bar, and

• specific enthalpy in kJ/kg.

The medium has to be defined by a freely choosen negative number. This neagtive key number is the first parameter m of both functions. In your own functions you only need to consider self-defined negative media key numbers, if the value given is ≥ 0 computation will be performed by SIMIT, your functions will not be evaluated in this case.

This way you can implement any media in both functions and use them in a simulation project. Please note that you need to take attention only for negative key numbers in self defined functions. For non-negative key numbers SIMIT uses the functions that are included in it. Your self defined functions are not called by SIMIT in that case.

A framework for your self defined functions might be set-up as follows: namespace Userdefined { public class FlownetFunctions { public static double trh(long m, double r, double h) { switch (m) { case -1: // Calculations for media key number -1 … return 0.0; case -2: // Calculations for media key number -2 … return 0.0; default: // Should not occur! return 0.0; } } public static double rph(long m, double p, double h) { switch (m) { case -1: // Calculations for media key number -1 … return 0.0; case -2: // Calculations for media key number -2 … return 0.0; default: // Should not occur! return 0.0; } }




} }

To assign a specific own defined media to a flownet simply set the appropriate negative media key number for the signal MEDIUM of the connection type FLN5.

CAUTION If you set a negative key number for the medium without providing the necessary functions for the calculation of the density and temperature, the flownet solver assignes a zero value to all densities and temeratures in the flownet!

You can call both functions too by

_ FlownetFunctions.trh(m, r, p)

respective

_ FlownetFunctions.rph(m, p, h)

in own component types. Moreover you can implement further functions in the class FlownetFunctions and use them by a similar function call in your component types.

You have to locate the assembly Userdefined.dll in SIMIT’s workspace in the subfolder GlobalFunctions. The assembly will then automatically be copied to each new simulation project and therefore be archived with your simulation project.

NOTE Modifications of the assembly are not affecting already existing simulation projects. A modified assembly is only copied to new projects.

If you want to use the modified assembly in your already existing projects too, simply copy this asembly to the folder globalFunctions of these projects.

5.4 Initialising flownet simulations The initialisation of flownet simulations involves two steps: when the simulation is started up, the components are initialised, i.e. the simulation model created from the connected components is initialised. Then the flownet solver is initialised. The flownet solver uses the values that are sent to it via connections of type FLN2 to FLN7 and initialised in the components (Figure 5-22).

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Figure 5-22: Initialisation of flownet simulations

As there are no variables available of the flownet solver during initialisation of the components, it is advisable to pre-assign the inputs of the component types with suitable values. Values that are consistent with the default values of the flownet solver are recommended.

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