intro1 m12 thermal
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Chapter 12
Thermal Analysis
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Chapter 12 Thermal Analysis
Overview INTR
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INTR In this chapter, we will describe the specifics of a thermal analysis.
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e purpose s wo- o :
To reiterate the general analysis procedure.
To introduce you to thermal loads and boundary conditions
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Chapter 12 A. Preprocessing
Geometry INTR
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INTRGeometry
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an e er e crea e w n or mpor e .
Include details to improve results:
Goal is to sufficientl model the thermal mass of the structure. NT
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Convection loads requires areas be correctly modeled.
Heat generation loads requires the volumes be correctly modeled.
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Chapter 12 A. Preprocessing
Meshing INTR
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Element type
The table below shows commonly used thermal element types.DUCTI
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The nodal DOF is: TEMP.
Commonly used thermal element types
2-D Solid 3-D Solid 3-D Shell Line Elements2-D Solid 3-D Solid 3-D Shell Line Elements NT
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Linear PLANE55 SOLID70 SHELL57 LINK31, 32, 33, 34
SHELL131
Quadratic PLANE77 SOLID90 SHELL132PLANE35 SOLID87
Linear PLANE55 SOLID70 SHELL57 LINK31, 32, 33, 34
SHELL131
Quadratic PLANE77 SOLID90 SHELL132PLANE35 SOLID87SYS
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Material properties
Minimum requirement is Kx, thermal conductivity for steady state
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Setting preferences to thermal limits the Material Model GUI to
display only Thermal properties.
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ea cons an s ec on proper es
Primarily needed for shell and line elements.
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Chapter 12 B. Solution
Overview INTR
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Thermal loading conditions can be:
Temperatures Regions of the model where temperatures are known.
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Heat flow Points where the heat flow rate is known.
Heat flux Surfaces where the heat flow rate per unit area is known.NTOA
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Convections Surfaces where heat is transferred to (or from)
surroundings by means of convection. Input consists of
film coefficient h and bulk temperature of the surrounding
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Heat generation Regions where the volumetric heat generation rate is
known.
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Adiabatic surfaces Perfectly insulated surfaces where no heat transfer takes
place.
*
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.
Input consists of emissivity, Stefan-Boltzmann constant,
and optionally, temperature at a space node.
*Not covered in this course
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Chapter 12 B. Solution
Nodal Coordinate System INTR
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INTR Unlike the structural analysis displacement and force boundary
conditions, the analogous thermal analysis temperature and heatDUCTI
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ow oun ary con ons are no epen en on e no a
coordinate system.
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Chapter 12 B. Solution
Temperature Constraints INTR
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INTRTemperature Constraints
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.
To apply displacement constraints :
Main Menu > Solution > Define Loads > Apply > NTOA
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Thermal > Temperature
Choose where you want to apply the
constraint.
Pick the desired entities in the graphicsSYS
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window.
Then enter the temperature value. Value
defaults to zero.
Or use the D family of commands: DK, DL,art1
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DA, D.
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Chapter 12 B. Solution
Concentrated Heat Flow INTR
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node or keypoint number (which you can identify by picking)DUCTI
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heat flow magnitude (which should be consistent with the system of
units you are using)
Use: NTOA
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Main Menu > Solution > Define Loads > Apply > Thermal > Heat Flow
Or the commands FK orF
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Chapter 12 B. Solution
Heat Flux INTR
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INTRHeat Flux:
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o app y ea ux:
Main Menu > Solution > DefineLoads > Apply > Thermal > Heat flux
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apply the heat flux-- usually on
lines for 2-D models, on areas
for 3-D models.SYS
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graphics window.
Then enter the heat flux
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Or use the SF family ofcommands: SFL, SFA, SFE,
SF.
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Chapter 12 B. Solution
Convections INTR
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INTRConvective Loads
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o app y a convec on:
Main Menu > Solution > Define Loads > Apply> Thermal > Convection
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convection -- usually on lines for 2-D
models, on areas for 3-D models.
Pick the desired entities in the graphicsSYS
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.
Then enter the film coefficient and bulk
temperature values.
Or use the SF command famil :art1
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SFL, SFA, SFE, SF.
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Chapter 12 B. Solution
Heat Generation INTR
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INTRHeat Generation
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o app y ea genera on:
Maine Menu > Solution > Define Loads >Apply > Thermal > Heat Generation
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the heat generation-- usually on
areas for 2-D models, on volumes
for 3-D models.SYS
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graphics window.
Then enter the heat generation
values.art1
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Or use the BF family ofcommands: BFL, BFA, BFE, BF.
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Chapter 12 B. Solution
Adiabatic Surfaces INTR
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INTR Adiabatic Surfaces
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.
This is the default condition, i.e, any surface with no boundaryconditions specified is automatically treated as an adiabatic surface
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Chapter 12 B. Solution
Modifying and Deleting Loads INTR
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o mo y a oa va ue, s mp y reapp y e oa
with the new value.
To delete loads: NTOA
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Main Menu > Solution > Define Loads > Delete
When you delete solid model loads, ANSYS also
automatically deletes all corresponding finite elementSYS
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Chapter 12 B. Solution
Solutions Options INTR
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INTRSteady State vs. Transient Analysis
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s ea y s a e ana ys s assumes a e oa ng con ons ave
settled down to a steady level, with little or no time dependency.
A transientanal sis conditions that are chan in with time. NTOA
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NTOA For example, consider the analysis of a clothes iron which takes 1
minute to reach a constant temperatureSYS
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The analysis of the clothes iron for the first 1 minute of operation would be
transient.
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state.
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Chapter 12 C. Postprocessing
Review Results INTR
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thermal gradient distribution thermal flux distribution
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Chapter 12 C. Postprocessing
Review Results INTR
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Temperature Distribution:
To plot temperature contours D
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General Postproc > Plot Results > Contour Plot > Nodal Solution > Temperature
Or use the PLNSOL command.
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Chapter 12 C. Postprocessing
Review Results INTR
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Thermal Gradients:
To plot thermal gradient contours: D
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General Postproc > Plot Results > Contour Plot > Nodal Solu orPLNSOL command
General Postproc > Plot Results > Contour Plot > Element Solu orPLESOL command
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Chapter 12 C. Postprocessing
Review Results INTR
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Thermal Flux:
To lot thermal radient contours: D
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General Postproc > Plot Results > Contour Plot > Nodal Solu orPLNSOL command
General Postproc > Plot Results > Contour Plot > Element Solu orPLESOL command
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Chapter 12 C. Postprocessing
Review Results INTR
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INTRReaction Forces
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e sum o e reac on ea ows mus a ance e sum o e
applied heat flows
Best viewed as a listin : NTOA
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General Postprocessor > List Results > Reaction Solution orPRRSOL
command
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Chapter 12 C. Postprocessing
Verify Results INTR
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INTRIt is always a good idea to do a sanity check and make sure that
the solution is acceptable. What you need to check depends onD
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e ype o pro em you are so v ng, u ere are some yp ca
questions to ask:
Do FEA results a ree hand calculations or ex erimental data? NTOA
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Is the temperature solution correct? Check the FEA temperature
solution first since FEA heat fluxes are second order results.SYS
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Do the reaction heat flows balance the applied heat flows?
Where is the maximum heat flux located?art1
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If it is at a singularity, such as a point load or a re-entrant corner, thevalue is generally meaningless.
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Chapter 12 C. Postprocessing
Verify Results INTR
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This is always debatable, but you can gain confidence in the mesh byD
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us ng error es ma on.
Other ways to check mesh adequacy: Plot the element solution (unaveraged stresses) and look for
elements with hi h heat flux radients. These re ions are NTOA
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candidates for mesh refinement.
If there is a significant difference between the nodal (averaged)
and element (unaveraged) heat flux contours, the mesh may be tooSYS
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.
Similarly, if there is a significant difference between
PowerGraphics and full graphics heat flux, the mesh may be too
coarse.
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Re-mesh with twice as many elements, re-solve, and compare theresults. (But this may not always be practical.)
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Chapter 12 D. Workshop
Workshop INTR
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INTR Refer to yourWorkshop Supplementfor instructions on:
W12. Axisymmetric Pipe with FinsD
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