Workbench - Mechanical Introduction 12.0
Chapter 6
Thermal Analysis
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Thermal Analysis
Chapter Overview
Training Manual
• In this chapter, performing steady-state thermal analyses in Simulation will
be covered:
A. Geometry
B. Assemblies – Solid Body Contact
C. Heat Loads
D. Solution Options
E. Results and Postprocessing
F. Workshop 6.1
• The capabilities described in this section are generally applicable to ANSYS
DesignSpace Entra licenses and above, except for an ANSYS Structural
license.
• Note: advanced topics including thermal transient analyses are covered in
the ANSYS Thermal Analysis training course.
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Thermal Analysis
Basics of Steady-State Heat Transfer
Training Manual
• For a steady-state (static) thermal analysis in Simulation, the
temperatures {T} are solved for in the matrix below:
K T T   QT 
• Assumptions:
– No transient effects are considered in a steady-state analysis
– [K] can be constant or a function of temperature
– {Q} can be constant or a function of temperature
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Thermal Analysis
Basics of Steady-State Heat Transfer
Training Manual
• Fourier’s Law provides the basis of the previous equation:
• Heat flow within a solid (Fourier’s Law) is the basis of [K]
• Heat flux, heat flow rate, and convection are treated as boundary conditions on
the system {Q}
• Convection is treated as a boundary condition although temperaturedependent film coefficients are possible
• It is important to remember these assumptions related to performing
thermal analyses in Simulation.
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Thermal Analysis
A. Geometry
Training Manual
• In thermal analyses all body types are supported:
– Solid, surface, and line bodies.
• Line bodies cross-section and orientation is defined within DesignModeler.
• The “Point Mass” feature is not available in thermal analyses.
• Shell and line body assumptions:
– Shells: no through-thickness temperature gradients.
– Line bodies: no through thickness variation. Assumes a constant
temperature across the cross-section.
• Temperature variation will still be considered along the line body
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Thermal Analysis
… Material Properties
Training Manual
• The only required material property is thermal conductivity
• Thermal Conductivity is
input in the Engineering
Data application
• Temperature-dependent
thermal conductivity is
input as a table
If any temperature-dependent material properties exist, this will
result in a nonlinear solution.
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Thermal Analysis
B. Assemblies – Solid Body Contact
Training Manual
• As with structural analyses, contact regions are automatically created to
enable heat transfer between parts of assemblies.
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Thermal Analysis
… Assemblies – Contact Region
Training Manual
– If parts are initially in contact heat transfer can occur between them.
– If parts are initially out of contact no heat transfer takes place (see pinball
explanation below).
– Summary:
Contact Type
Bonded
No Separation
Rough
Frictionless
Frictional
Heat Transfer Between Parts in Contact Region?
Initially Touching
Inside Pinball Region Outside Pinball Region
Yes
Yes
No
Yes
Yes
No
Yes
No
No
Yes
No
No
Yes
No
No
– The pinball region determines when contact occurs and is automatically
defined and set to a relatively small value to accommodate small gaps in
the model
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Thermal Analysis
… Assemblies – Contact Region
Training Manual
• If the contact is bonded or no separation,
then heat transfer will occur (solid green
lines) when the surfaces are within the
pinball radius.
Pinball Radius
In this figure on the right, the
gap between the two parts is
bigger than the pinball region,
so no heat transfer will occur
between the parts
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Thermal Analysis
… Assemblies – Thermal Conductance
Training Manual
• By default, perfect thermal contact conductance between parts is
assumed, meaning no temperature drop occurs at the interface.
• Numerous conditions can contribute to less than perfect contact
conductance:
–
–
–
–
–
–
–
–
surface flatness
surface finish
oxides
entrapped fluids
contact pressure
surface temperature
use of conductive grease
....
DT
T
x
• Continued . . .
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Thermal Analysis
… Assemblies – Thermal Conductance
Training Manual
– The amount of heat flow across a contact interface is defined by the
contact heat flux q:
q  TCC  Ttarget  Tcontact 
– where Tcontact is the temperature of a contact “node” and Ttarget is the
temperature of the corresponding target “node”.
– By default, TCC is set to a relatively ‘high’ value based on the largest
material conductivity defined in the model KXX and the diagonal of the
overall geometry bounding box ASMDIAG.
TCC  KXX 10,000 / ASMDIAG
– This essentially provides ‘perfect’ conductance between parts.
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Thermal Analysis
… Assemblies – Thermal Conductance
Training Manual
• In ANSYS Professional licenses and above, the user may define a
finite thermal contact conductance (TCC) for Pure Penalty or
Augmented Lagrange Formulations.
– TCC is input for each contact region in the Details view.
– If thermal contact resistance is known, invert this value and divide by the
contacting area to obtain TCC value.
Thermal contact conductance can
be input which is the same as
including thermal contact
resistance at a contact interface.
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Thermal Analysis
… Assemblies – Spot Weld
Training Manual
• Spot welds provide discreet heat transfer points:
– Spotweld definition is done in the CAD software (currently only
DesignModeler and Unigraphics).
T2
T1
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Thermal Analysis
C. Heat Loads
Training Manual
• Heat Flow:
– A heat flow rate can be applied to a vertex, edge, or surface. The load is
distributed for multiple selections.
– Heat flow has units of energy/time.
• Perfectly insulated (heat flow = 0):
– Available to remove surfaces from previously applied boundary conditions.
• Heat Flux:
– Heat flux can be applied to surfaces only (edges in 2D).
– Heat flux has units of energy/time/area.
• Internal Heat Generation:
– An internal heat generation rate can be applied to bodies only.
– Heat generation has units of energy/time/volume.
A positive value for heat load will add energy to the system.
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Thermal Analysis
… Thermal Boundary Conditions
Training Manual
Temperature, Convection and Radiation:
• At least one type of thermal boundary condition must be present to prevent the
thermal equivalent of rigid body motion.
• Given Temperature or Convection load should not be applied on surfaces that
already have another heat load or thermal boundary condition applied to it.
• Perfect insulation will override thermal boundary conditions.
• Given Temperature:
– Imposes a temperature on vertices, edges, surfaces or bodies
– Temperature is the degree of freedom solved for
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Thermal Analysis
… Thermal Boundary Conditions
Training Manual
• Convection:
– Applied to surfaces only (edges in 2D analyses).
– Convection q is defined by a film coefficient h, the surface area A, and the
difference in the surface temperature Tsurface & ambient temperature
Tambient
q  hATsurface  Tambient 
– “h” and “Tambient” are user input values.
– The film coefficient h can be constant or temperature dependent
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Thermal Analysis
… Thermal Boundary Conditions
Training Manual
• Temperature-Dependent Convection:
– Select “Tabular (Temperature)” for the
coefficient type.
– Enter coefficient vs temperature
tablular data.
– In the details, specify how temperature
is to be handled for h(T).
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Thermal Analysis
… Thermal Boundary Conditions
Training Manual
• Several common convection correlations can be imported from a
sample library. New correlations can be stored in libraries.
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Thermal Analysis
… Thermal Boundary Conditions
Training Manual
• Radiation:
– Applied to surfaces (edges in 2D analyses)
4
4

QR  FATsurface
 Tambient
– Where:
• σ = Stefan-Boltzman constant
• ε = Emmisivity
• A = Area of radiating surface
• F = Form factor (1)
– Provides for radiation to ambient only, not between surfaces (form factor
assumed to be 1).
– Stefan Boltzman constant is set automatically based on the active
working unit system.
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Thermal Analysis
D. Solution Options
Training Manual
• Inserting the “Steady-State Thermal” from the
Workbench toolbox will set up a SS Thermal
system in the project schematic.
• In Mechanical the “Analysis Settings” can be used
to set solution options for the thermal analysis.
– Note, the same Analysis Data Management
options discussed in chapter 4 regarding static
analyses are available here.
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Thermal Analysis
… Solving the Model
Training Manual
• To perform a thermal-stress solution link a structural analysis to
the thermal model at the Solution level.
• An “imported load” branch is inserted in the Static Structural
branch along with any applied structural loads and supports.
– Solve the Structural branch.
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Thermal Analysis
E. Results and Postprocessing
Training Manual
• Various results are available for postprocessing:
–
–
–
–
Temperature
Heat Flux
“Reaction” Heat Flow Rate
User defined results
• In Simulation, results are usually requested before solving, but they
can be requested afterwards, too.
– A new solution is not required for retrieving output of a solved model.
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Thermal Analysis
… Temperature
Training Manual
• Temperature:
– Temperature is a scalar quantity and has no
direction associated with it.
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Thermal Analysis
… Heat Flux
Training Manual
• Heat flux contour or vector plots are available:
– Heat flux q is defined as
q   KXX  T
– “Total Heat Flux” and “Directional Heat Flux” can be
requested
• The magnitude & direction can be plotted as vectors by activating
vector mode
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Thermal Analysis
… Reaction Heat Flow Rate
Training Manual
• Reaction heat flow rates are available for Given Temperature,
convection or radiation boundary conditions:
– Reaction heat flow rate is requested by inserting a probe - OR
– Alternately users can drag and drop a boundary condition onto the
Solution branch to retrieve the reaction.
Select from
Probe menu
OR
Drag and drop
boundary condition
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Thermal Analysis
F. Workshop 6 – Steady State Thermal Analysis
Training Manual
• Workshop 6 – Steady State Thermal Analysis
• Goal:
– Analyze the pump housing shown below for its heat transfer
characteristics.
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