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CHAPTER (14)

TURBOMACHINARY

Dr. MUNZER EBAID

SUMMARY

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Types of Fluid Machines

1. Positive Displacement Machines.

2. Turbo-Machines.

They operates by forcing fluid into or out of a chamber. Ex. ( Automotive Engines, Gear Pumps(

They involve the flow of fluid through rotating blades or rotors that Added Energy to the fluid, ( Ex. Pumps (Liquids), Fan, blowers and compressors (Gases).

OR Remove Energy from the fluid. ( Ex. Wind turbines, Gas turbines and Hydraulic turbines)

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Hub

Blade

PROPELLER

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Thrust (T) of a propeller is a function of:

Reynolds Number Advance Ratio Thrust Coefficient

n=revolution per seconds

42)( DnCTThrust T

nD

VfCT

0

53DnCPPower P Power (P) of a propeller

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Fig. (14.2)

Coefficient of Thrust Coefficient of Power

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Blade Specifications

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EFFICIENCY

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Axial flow pumps are best suited for Low Heads and High Flow Rates

AXIAL FLOW PUMPS

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AXIAL FLOW PUMPS

Head and Discharge Coefficient for Pumps

Thrust Coefficient of a Pump =

Head Coefficient of a Pump = gnD

HCC TH 22

4

Discharge Coefficient of a Pump =

Power Coefficient of a Pump =

22

2

24242424 44

)(

nD

HgD

nD

Hg

nD

HA

nD

Ap

nD

FC TT

QH

QP

CfC

CfC

09/10/2019 Dr. Munzer Ebaid 10 Dimensionless performance curves for a typical Axial-Flow Pump

QH

QP

CfC

CfC

Fig.

(14.6) Efficiency Curve

0.72

1.55

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Performance curves for a typical axial-flow pump

Fig.

(14.7)

cm

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Radial - FLOW MACHINES

Centrifugal Pumps

Axial

Radial

Casing with varying area

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Performance curves for a typical centrifugal pump; D = 37.1 cm

Fig.

(14.9)

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Dimensionless performance curves for a typical centrifugal pump from data given in Fig. 14.9

Fig.

(14.10)

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SPECIFIC SPEED

The specific speed is a parameter used to pick a type of a pump or a turbine that is best used for a given application and is obtained as shown below

1. Axial Pump or Turbine used for Low Head, High Discharge

2. Radial Pump or Turbine used for High Head, Low Discharge

Specific speed is obtained by combining both both

To eliminate the diameter (D) QC HC

3

22

nD

QC

gDn

HC

Q

H

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Used in USA

Fig.

(14.14)

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Suction Limitation of Pumps

The pressure at the suction side of the pump is most significant to avoid Cavitation

Cavitation usually occurs when the pressure of a flowing liquid equal the vapour

pressure of the liquid at a given temperature.

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4343

21

NPSHg

NQN SS

)(),(),( feetNPSHgpmQrpmNWhere

Critical value for Cavitation to occur

)8500( SSN

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Centrifugal pump performance curve

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Centrifugal Compressors

For an Ideal gas and Isentropic Compression process (Adiabatic and reversible)

)()( 21 ptopfromgasthecompresstorequiredpowerThe

theoP is called the Theoretical Adiabatic Power with no cooling

Efficiency of a compressor with no water cooling=

SHAFTactual

theo

CompP

P

)(

Is called the Theoretical Isothermal Power with cooling theoP

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Turbines

A turbine is defined as a machine that extracts energy from a flowing

fluid.

(a) Types of Turbines

1. Impulse Turbines.

2. Reaction Turbines.

3. Wind Turbines.

(b) Types of Turbines in relation to the direction of flow

1. Axial Kaplan Turbine. ( Flow is axial).

2. Axial Pelton Turbine. (Flow is axial).

3. Radial Francis Turbine. (Flow is radial).

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TTurbine QhP

g

Vh

j

T2

2

0LosshIf

g

VQP J

Turbine2

2

Apply energy equation between (1) & (2), we have:

Pelton Wheel

Loss

partMech

T

partMech

P hg

Vz

g

ph

g

Vz

g

ph

.

2

222

2

.

2

111

1

22

JVV 1

1 2

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Torque applied on the turbine shaft

Applying momentum Eqn. to a control volume

It is assumed that the exiting velocity has a negligible momentum, then

+Ve

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The mass flow rate across the control volume is , so the torque is Q

For Max. Power, JWheel VV )( 21

Then: Max. Power of the Turbine 2

2

JVQP

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Reaction Turbine

1. The vanes of the reaction turbine are under pressure unlike the Impulse

turbine where the pressure is atmospheric.

2. The flow fills the chamber in which the impeller is located.

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The Torque and the power produced at the shaft is given below

Eqn. (14.25)

Eqn. (14.25) is a function of the flow velocities directions 21 ,

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Wind Turbines: Extracts energy from the wind to produce Power

The max. theoretical power produced by a wind turbine

U: Wind speed

A: Area captured by the wind turbine

Wind Turbines

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END OF CHAPTER (14)