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L7-1ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0November 2010
Introduction to ANSYSMechanical
Customer Training Material
Lecture 7
Thermal Analysis
Introduction to ANSYS Mechanical
L7-2ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialChapter Overview• In this chapter, performing steady-state thermal analyses in Mechanical will
be covered:A.GeometryB.Assemblies – Solid Body ContactC.Heat LoadsD.Solution OptionsE. Results and PostprocessingF. Workshop 7.1
• The capabilities described in this section are generally applicable to ANSYS DesignSpace 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.
Introduction to ANSYS Mechanical
L7-3ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialBasics of Steady-State Heat Transfer• For a steady-state (static) thermal analysis in Mechanical, the
temperatures {T} are solved for in the matrix below:
• 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
TQTTK
Introduction to ANSYS Mechanical
L7-4ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialBasics of Steady-State Heat Transfer• 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 temperature-dependent
film coefficients are possible• It is important to remember these assumptions related to performing
thermal analyses in Mechanical.
Introduction to ANSYS Mechanical
L7-5ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialA. Geometry• 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
Introduction to ANSYS Mechanical
L7-6ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Material Properties
• 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.
• The only required material property for steady state is thermal conductivity.
Introduction to ANSYS Mechanical
L7-7ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialB. Assemblies – Solid Body Contact• As with structural analyses, contact regions are automatically created to
enable heat transfer between parts of assemblies.
Introduction to ANSYS Mechanical
L7-8ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Assemblies – Contact Region
– 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:
– 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
Initially Touching Inside Pinball Region Outside Pinball RegionBonded Yes Yes NoNo Separation Yes Yes NoRough Yes No NoFrictionless Yes No NoFrictional Yes No No
Contact Type Heat Transfer Between Parts in Contact Region?
Introduction to ANSYS Mechanical
L7-9ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Assemblies – Contact Region
• 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
Introduction to ANSYS Mechanical
L7-10ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Assemblies – Thermal Conductance
• 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– . . . .
• Continued . . .
DT
T
x
Introduction to ANSYS Mechanical
L7-11ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Assemblies – Thermal Conductance
– The amount of heat flow across a contact interface is defined by the contact heat flux q:
– 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.
– This essentially provides ‘perfect’ conductance between parts.
contacttarget TTTCCq
ASMDIAGKXXTCC /000,10
Introduction to ANSYS Mechanical
L7-12ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Assemblies – Thermal Conductance• 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.
Introduction to ANSYS Mechanical
L7-13ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Assemblies – Spot Weld• Spot welds provide discreet heat transfer points:– Spotweld definition is done in the CAD software (currently only
DesignModeler and Unigraphics).
T1
T2
Introduction to ANSYS Mechanical
L7-14ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialC. Heat Loads
• 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.
Introduction to ANSYS Mechanical
L7-15ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Thermal Boundary Conditions
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
Introduction to ANSYS Mechanical
L7-16ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Thermal Boundary Conditions• 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
– “h” and “Tambient” are user input values.– The film coefficient h can be constant or temperature dependent
ambientsurface TThAq
Introduction to ANSYS Mechanical
L7-17ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Thermal Boundary Conditions• Temperature-Dependent Convection:
– Select “Tabular (Temperature)” for the coefficient type.
– Enter coefficient vs temperature tabular data.
– In the details, specify how temperature is to be handled for h(T).
Introduction to ANSYS Mechanical
L7-18ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Thermal Boundary Conditions• Several common convection correlations can be imported from a
sample library. New correlations can be stored in libraries.
Introduction to ANSYS Mechanical
L7-19ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material. . . Thermal Boundary Conditions• Radiation:– Applied to surfaces (edges in 2D analyses)
– Where:• σ = Stefan-Boltzman constant• ε = Emissivity• A = Area of radiating surface• F = Form factor
– Correlations:– To ambient (form factor assumed to be 1) OR – Surface to surface (view factors calculated).
– Stefan Boltzman constant is set automatically based on the active working unit system
44ambientsurfaceR TTFAQ
Introduction to ANSYS Mechanical
L7-20ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialD. Solution Options• 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.
Introduction to ANSYS Mechanical
L7-21ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Solving the Model• 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.
Introduction to ANSYS Mechanical
L7-22ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialE. Results and Postprocessing• Various results are available for postprocessing:– Temperature– Heat Flux– “Reaction” Heat Flow Rate– User defined results
• In Mechanical, 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.
Introduction to ANSYS Mechanical
L7-23ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Temperature• Temperature:– Temperature is a scalar quantity and has no
direction associated with it.
Introduction to ANSYS Mechanical
L7-24ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Heat Flux• Heat flux contour or vector plots are available:
– Heat flux q is defined as
– “Total Heat Flux” and “Directional Heat Flux” can be requested
• The magnitude & direction can be plotted as vectors by activating vector mode
TKXXq
Introduction to ANSYS Mechanical
L7-25ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training Material… Reaction Heat Flow Rate• 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.
OR
Select from Probe menu
Drag and drop boundary condition
Introduction to ANSYS Mechanical
L7-26ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved.
Release 13.0 November 2010
Customer Training MaterialF. Workshop 7 – Steady State Thermal Analysis
• Workshop 7.1 – Steady State Thermal Analysis• Goal:– Analyze the pump housing shown below for its heat transfer
characteristics.