Thermal Analysis

1
Thermal Analysis

• Chapter Six

2
Chapter Overview

• In this chapter, performing steady-state and
  transient thermal analyses in Simulation will be
  covered
• Geometry
• Assemblies Solid Body Contact
• Heat Loads
• Solution Options
• Results and Postprocessing
• Workshop 6.1
• Thermal Transient Setup
• Transient Settings
• Transient Loads
• Transient Results
• Workshop 6.2
• The capabilities described in this section are
  generally applicable to ANSYS DesignSpace Entra
  licenses and above, except for an ANSYS
  Structural license.

3
Basics of Steady-State Heat Transfer

• For a steady-state (static) thermal analysis in
  Simulation, the temperatures T are solved for
  in the matrix belowAssumptions
• 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

4
Basics of Steady-State Heat Transfer

• Fouriers Law provides the basis of the previous
  equation
• Heat flow within a solid (Fouriers 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
  Simulation.

5
Physics Filters

• If a thermal-only solution is to be performed the
  Physics Filter can be used to filter the GUI
• Under View menu gt Physics Filter, unselect the
  Structural and Electromagnetic options
• This applies to options in the Environment and
  Solutionlevels only
• If a thermal-stress simulation is to be
  performed, do not turn off the structural physics
  filter

6
A. Geometry

• In thermal analyses, all types of bodies
  supported by Simulation may be used.
• Solid, surface, and line bodies are supported
• For surface bodies, thickness must be input in
  the Details view of the Geometry branch
• Line bodie cross-section and orientation is
  defined within DesignModeler
• Cross-section and orientation information results
  in an effective thermal cross-section
• Only temperature results are available for line
  bodies
• The Point Mass feature is not available in
  thermal analyses

7
Geometry

• Shell and line body assumptions
• For shell bodies through-thickness temperature
  gradients are not available. Shells assume
  temperatures on top and bottom of surface are the
  same
• For line bodies through thickness variation in
  the temperature is not available. Line bodies
  assume the temperature is constant across the
  cross-section
• Temperature variation will still be considered
  along the line body

8
Material Properties

• 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.
9
B. Assemblies Solid Body Contact

• When importing assemblies of solid parts, contact
  regions are automatically created between the
  solid bodies enabling heat transfer between parts
  in an assembly

Model shown is from a sample Inventor assembly.
10
Assemblies Contact Region

• No heat spreading is considered in the
  contact/target interface
• Heat flow within the contact region is in the
  contact normal direction only
• Heat flows only if a target element is present in
  the normal direction of a contact element

11
Assemblies Contact Region

• If the parts are initially in contact heat
  transfer will occur between the parts.
• If the parts are initially out of contact no heat
  transfer takes place
• 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

12
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

13
Assemblies Thermal Conductance

• The amount of heat flow between two parts 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.

14
Assemblies Thermal Conductance

• Perfect thermal contact conductance between parts
  means that no temperature drop is assumed at the
  interface
• One may want to include finite thermal
  conductance instead
• The contact conductance can be influenced by many
  factors
• surface flatness
• surface finish
• oxides
• entrapped fluids
• contact pressure
• surface temperature
• use of conductive grease

15
Assemblies Thermal Conductance

• In ANSYS Professional licenses and above, the
  user may define a finite thermal contact
  conductance (TCC) if the Pure Penalty or
  Augmented Lagrange Formulation is used
• The thermal contact conductance per unit area 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

If Thermal Conductance is left at Program
Chosen, near-perfect thermal contact conductance
will be defined. thermal contact conductance can
be input which is the same as including thermal
contact resistance at a contact interface.
16
Assemblies Thermal Conductance

• Thermal Contact Notes
• For symmetric contact the user does not need to
  account for a double thermal contact resistance
• MPC bonded contact allows for perfect thermal
  contact conductance

17
Assemblies Surface Body Contact

• Edge contact is a subset of general contact
• For contact including shell faces or solid edges
  only bonded or no separation behavior is allowed
• For contact involving shell edges only bonded
  behavior using MPC formulation is allowed
• The user can set the search direction as
  eitherthe target normal or pinball region.
• If a gap exists the pinball region can beused
  for the search direction to detect contact
  beyond a gap

18
Assemblies Spot Weld

• Spot welds provide discreet heat transfer points
• Spotweld definition is done in the CAD software
  (currently only DesignModeler and Unigraphics)
• Spotwelds can be created in Simulation manually
  at vertices

19
C. Heat Loads

• Heat Flow
• A heat flow rate can be applied to a vertex,
  edge, or surface. The load gets distributed for
  multiple selections
• Heat flow has units of energy/time
• Heat Flux
• A heat flux can be applied to surfaces only
• 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.

20
Adiabatic Conditions

• Perfectly Insulated
• Perfectly insulated condition is applied to
  surfaces
• This is the default condition in thermal analyses
  when no load is applied
• This load type is used as a way to remove loading
  on specified surfaces
• For example, it may be easier for a user to apply
  heat flux or convection on an entire part, then
  use the perfectly insulated condition to
  selectively remove the loading on some surfaces

21
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

22
Thermal Boundary Conditions

• Convection
• Applied to surfaces only (edges in 2D analyses)
• Convection q is related to a film coefficient h,
  the surface area A, and the difference in the
  surface temperature Tsurface ambient
  temperature Tbulk
• h and Tbulk are user-input values
• The film coefficient h can be constant or
  temperature dependent

23
Thermal Boundary Conditions

• Temperature-Dependent Convection
• Select New Convection for the Correlation
• The Engineering Data tab will open and the
  Coefficient Type can then be defined for the
  convection load
• Determine what temperature is used for h(T)
• Average film temperatureT(TsurfaceTbulk)/2
• Surface temperatureT Tsurface
• Bulk temperatureT Tbulk
• Difference of surface and bulk
  temperaturesT(Tsurface-Tbulk)

24
Thermal Boundary Conditions

• Temperature-Dependent Convection (continued)
• The user inputs the film coefficients and
  temperatures in a table. The values are plotted
  on a graph, as shown below

Temperature-dependent convection will result in a
nonlinear solution. The only exception is if the
film coefficient h is based on a function of the
bulk temperature only.
Right mouse click on the table to add or delete
values.
25
Thermal Boundary Conditions

• Temperature-Dependent Convection (continued)
• The convection data can also be imported from a
  file

26
Thermal Boundary Conditions

• Radiation
• Applied to surfaces (edges in 2D analyses)
• Where
• s Stefan-Boltzman constant
• e 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 determined and set
  automatically based on the active working unit
  system

27
D. Solution Options

• Solution options are set under the Solutions
  branch
• The ANSYS database can be saved
• Two solvers are available in Simulation
• Default Program Chosen
• Iterative PCG solver
• Direct sparse solver
• The Weak Springs and Large Deflectionoptions
  are meant for structural analyses only,so they
  can be ignored for a thermal analysis

28
Solution Options

• Informative settings show the user the status of
  the analysis
• Analysis Type
• Nonlinear solution
• Solver working directory
• Any solver messages which appear after solution
  can be checked afterwards underSolver Messages

29
Solving the Model

• To solve the model, request results and Solve
• If a Solution Information branch is requested,
  the details of the solution output can be
  examined

30
Solving the Model

• To perform a thermal-stress solution add
  structural supports and/or loads and request
  structural results, then solve the model
• The following will be performed automatically
• A steady-state thermal analysis will be performed
• The temperature field will be mapped back onto
  the structural model
• A structural analysis will be performed
• Simulation automates this type of coupled-field
  solution

31
E. Results and Postprocessing

• Various results are available for postprocessing
• Temperature
• Heat Flux
• Reaction Heat Flow Rate
• 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.

32
Temperature

• Temperature
• Temperature is a scalar quantity and has no
  direction associated with it.

33
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

34
Reaction Heat Flow Rate

• Reaction heat flow rates is available for Given
  Temperature or Convection boundary conditions
• Reaction heat flow rate is printed in the Details
  view after a solution.

35
Reaction Heat Flow Rate

• The Worksheet tab for the Environment branch
  has a tabular summary of reaction heat flow rates
• Note if a thermal support shares a vertex, edge,
  or surface with another thermal support or load
  the reported reaction heat flow rate may be
  incorrect. The solution will still be valid, but
  the reported values may not be accurate

36
F. Workshop 6.1 Steady State Thermal Analysis

• Workshop 6.1 Steady State Thermal Analysis
• Goal
• Analyze the pump housing shown below for its heat
  transfer characteristics.

37
Transient Thermal Analysis

• The previous discussion related to steady state
  analyses only. The following section introduces
  the ability to apply time dependent boundary
  conditions on thermal models
• The previous sections are equally applicable in
  steady state or transient analyses
• Three additional areas will be addressed
  concerning transient analysis
• Input time dependent boundary conditions
• Set up transient solution options
• Access results over time

38
G Thermal Transient Setup

• A thermal transient analysis is specified from
  the Environment branch
• An End Time must then be entered to indicate
  the duration of the analysis
• Supported transient loads
• Temperature
• Heat flux
• Heat generation rate
• Heat flow
• Convection film coefficient
• Ambient temperature for radiation or convection

39
. . . Thermal Transient Setup

• When a transient analysis is requested the GUI
  will update with new information sections
• Environment will contain an Initial Condition
  branch
• Solution will contain a Transient Settings
  branch
• A timeline and table will be inserted below the
  graphics screen

40
. . . Initial Conditions

• Initial conditions can be handled in 2 ways
• Uniform specified temperature
• Non uniform temperature distribution based on a
  previously solved Environment
• Choose the steady state result to be used as an
  initial condition then, RMB gt Generate Transient
  Environment with Initial Condition

41
H. Transient Settings

• Transient settings and details

The next several pages contain descriptions of
individual areas
42
. . . Transient Settings

• Transient Details
• Time stepping controls
• Visibility of transient information

43
. . . Transient Settings

• Automatic Step Resets
• Automatic time step reset places resets at
  extreme inflection points in the load history
• The slider controls the reset frequency
• Manual resets can be added by RMB in the
  transient settings graph and at the desired time
  point
• Manual reset points can be moved by dragging with
  the cursor

Move reset point
44
. . . Transient Settings

• Time reset points are indicated by the triangular
  markers at the top of the chart
• Automatic resets solid
• Manual resets wire frame

45
. . . Transient Settings

• The visible column in the time line legend
  controls specific information to be plotted
• Notice here the heat flux is applied as a step
  function with solution resets at each inflection
  point

46
I. Transient Loads

• Transient loads are applied using the same
  techniques discussed earlier. The only
  difference will be the setup in the details for
  the load
• Instead of choosing Constant (default), choose
  Load History
• The history data can be imported from a
  previously saved file or created using the
  Engineering Data application

47
. . . Transient Loads

• After choosing New Load History, time and load
  data is entered in the Engineering Data
  application
• The plot builds as the data is entered

• Project load histories are managed the same way
  as materials and convections

48
J. Transient Results

• Transient results are plotted like steady state,
  by highlighting the branch, however additional
  information and controls are available

The details view and graphics legend include the
display time
Timeline and tabular data are available for each
result time solved for
Check boxes control timeline display
49
. . . Transient Results

• To view results from different time points
• Click on the time point of interest in the
  timeline
• The details will indicate a red background until
  the results are retrieved for the selected time
  point
• To complete the operation, in the timeline RMB gt
  Retrieve Results

Results not updated
New time point selected
50
. . . Transient Results

• Transient animations are controlled using the
  same controller as steady state animations
• To animate a specific range use the mouse to drag
  over the desired times
• The resulting animation will span the highlighted
  region

51
K. Workshop 6.2 Transient Thermal Analysis

• Workshop 6.2 Transient Thermal Analysis
• Goal
• Analyze the heating base on a steam iron like the
  ones shown here for steady state and cyclic
  loading conditions

52
(No Transcript)