mech-ht 13.0 l05 steadystate
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Customer Training Material
ec ure
Stead -State
Heat Transfer
Heat Transfer
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ANSYS Mechanical Heat Transfer
Customer Training MaterialChapter Contents
Steady State Heat Transfer:
A. Steady State Theory
B. Model Setu
C. Steady State ExampleD. Multiple Step Solutions
. ,
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ANSYS Mechanical Heat Transfer
Customer Training MaterialA. Steady State Theory
When the flow of heat does not vary with time, heat transfer is
referred to as steady-state.
Since the flow of heat does not var with time the tem erature of
the system and the thermal loads on the system also do not varywith time.
From the First Law of Thermod namics the stead -state heat
balance can be expressed simply as:
- =
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Theory
For steady-state heat transfer, the differential equation expressing thermal
equilibrium is:
0...
=+
+
+
qT
kT
kT
k zzyyxx
The corresponding finite element equation expressing equilibrium is:
=
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ANSYS Mechanical Heat Transfer
Customer Training MaterialB. Model Setup
General Notes on Thermal Loads and Boundary Conditions:
In Mechanical, model boundaries that have no applied loads are
Symmetry boundary conditions are imposed by letting theboundaries be adiabatic (exception is symmetry models using
, .
Reaction heat flow rates are available at fixed temperature DOFs,
convective boundaries and radiation regions.
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Model Setup
Analysis Settings:
Step Controls: control multiple steps
as wells as auto time stepping.
Nonlinear Controls: specifyconvergence criteria and control line
search solver option.
Output Control: controls content and
frequency with which results are
saved.
Analysis Data Management: general
options controlling file management
and solver units.
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ANSYS Mechanical Heat Transfer
Customer Training MaterialC. Steady State Example
This example presents a walk through
for a steady state analysis.
The model represents and electrical coil
composed of an iron core surrounded by
a copper coil separated by a plastic
insulator. The assembly rests on a steel
mounting plate.
We assume the coil is in operation for
sufficient time to reach a steady state.
Boundary Conditions:
The iron core generates heat at 0.001
W/mm^3.
The copper coil is experiencing forcedconvective heat loss at a rate of 0.1
W/mm^2 in a 30 C ambient environment.
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and assumed to be at a fixed 25 C.
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Example
After specifying a Steady State Thermal analysis type, selecting the
desired geometry and adding or creating the necessary materials in
Workbench, we begin the model setup in Mechanical.
The materials are assigned in the details of each part as shown here:
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Example
After evaluating the default mesh, several mesh controls are added to
modify element size and shape:
Note, the DesignModeler geometry was assembled as a multi-body part,
thus the mesh is continuous across parts which means no contact is
necessary.
Multi-body Part MeshDetail Showing Shared
Nodes
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RMB and Generate Mesh to
Evaluate Any Changes
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Example
The boundary conditions detailed earlier are applied to the
appropriate regions of the model:
Highlighting the Steady-State Thermal (A5) branch allows all BCs to be
displayed on a common plot.
Since the model is steady state and linear we will leave the Analysis
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ett ngs n t e r e au t con gurat on an so ve t e mo e .
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Example
When the solution is finished its good practice to
check the validity of the solution before proceeding:
By inspecting the core details we can see that the
cores volume is 44698 mm^3.
Since the heat generation load is 0.001 W/mm^3, we
can calculate the heat generation as 44.698 W.
e s ea y s a e assump on means a e
temperature and convection boundary conditions must
equal the heat input.
and dropping both boundary conditions onto the
Solution branch.
An RMB to Evaluate All Results will update the
reaction probes.
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Example
By summing the probe results we find good
agreement:
Hgen - Rtemp - Rconv = 0
44.698 10.532 34.165 = 0.001
Having verified an energy balance we can
proceed to postprocess other results.
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Customer Training Material. . . Steady State Example
Results Can BeScoped to Individual
Parts to Refine the
Solution Display for
Each
Directional Results, Heat
Temperature Plot for
All Bodies Gives a
Good Overview of the
Distribution
Flux Here, Can Be Displayed
as Vectors to Enhance the
Interpretation of Heat Flow
Throughout theAssembly
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Steady State Example
In addition to the default results, user defined results can be
requested. These results may be combined in expressions as well.
Worksheet View for
Solution Branch
Shows User Results
Available
User Defined Result Definitions:
TEMP = temperature. ENERGY (kinetic) = N/A .
TF = thermal flux.
ENERGY (Potential) = thermal heat dissipation
energy.
TERR = thermal error energy.
HEAT = heat flow.
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VOLUME = displays the volume of all elements
attached to scoped region.
N command).
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ANSYS Mechanical Heat Transfer
Customer Training MaterialD. Multiple Step Solutions
Multiple steady state solutions can be setup and solved sequentially
from the Analysis Settings:
The graph and table display solution points.
By changing the Current Step Number each step is configured
independently.
Note this is not a transient analysis.
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Customer Training Material. . . Multiple Step Solutions
Loads can be varied for each solution bychoosing the Current Step Number.
Example, temperature load:
ga n e grap an a e sp ay e npu
variation. Loads will ramp from the previous step:
Note: for linear anal ses sin le solution there is nodifference between ramped or step applied loads.
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ANSYS Mechanical Heat Transfer
Customer Training Material. . . Multiple Step Solutions
The Analysis Settings
can be set up for multiple
steps rather than one at a
time.
Worksheet view allows
review of all settings in a
sin le a e.
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Customer Training Material
or s op
Solenoid
Heat Transfer
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