1. Chapter 11
Thermal Contact

2. Thermal Contact Contact Resistance DT
Two surfaces (at different temperatures) in contact experience a temperature drop across the interface. The drop is due to imperfect contact between the two surfaces. The imperfect contact, and hence the contact resistance, can be influenced by many factors such as:
surface flatness
surface finish
oxides
entrapped fluids
contact pressure
surface temperature
use of conductive grease DT T x
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3. Thermal Contact
ANSYS can simulate this behavior and other complex thermal problems using …
Coupled-field structural-thermal Contact
Supports general thermal contact analysis capability.
Typical applications:
Metal forming
Assembly contact
Gas turbine
Thermal Assembly
Frictional Heating
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4. Thermal Contact
Coupled-field solids (PLANE13, SOLID5) and surface-to-surface contact elements with KEYOPT(1) = 1
Can also be used with pure thermal elements
Fix all structural DOFs on contact elements
Key features:
Heat conduction between contacting surfaces
Heat generation due to frictional dissipated energy
Heat convection and/or radiation
Between surfaces with small gap
From free surface to environment
Heat flux input at open gap
NOTE: This course will focus on conduction between contacting surfaces. See the ANSYS documentation for more information regarding additional thermal contact capabilities.
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5. Thermal Contact Heat conduction: q = TCC * (TT - TC)
TCC is thermal contact conductance coefficient (real constant)
Can be a table parameter (function of pressure and temperature)
TT and TC are target and contact surface temperatures
Heat flows when contact status is closed
Model temperature discontinuity across contact interface
No DT (continuous material)
DT (contact interface)
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6. Thermal Contact Frictional heat generation: q = FHTG * t * v
FHTG is fraction of energy converted to heat (real constant)
t is the equivalent frictional stress
v is the sliding rate
Heat can be distributed unequally between contact and target:
qc = FWGT * FHTG * t * v
qt = (1-FWGT) * FHTG * t * v
Frictional energy is typically dissipated in three forms:
Acoustic (noise)
Mechanical (abrasion)
Thermal (heat)
FHTG is the fraction of frictional energy dissipated as heat. By default, FHTG=1.0
By default, the frictional heat energy is evenly distributed between the contact and target surfaces (FWGT=0.5)
Brake Pad on Wheel
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7. Thermal Contact Convection: q = CONV * (TE - TC)
CONV is convection coefficient (SFE table parameter load)
TE is target temperature, or bulk temp for free surface (SFE)
TC is contact temperature
Heat flows between contact and target when 0 < gap < pinball
Heat flows from contact to environment for free surface
Free surface is recognized for any of these conditions:
Open far-field contact (gap > pinball)
Contact elements only (omit target elements)
If target elements are present, Keyopt(3)=1 for target elements
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8. Thermal Contact Radiation:
q = RDVF * EMIS * SBCT * [(TE + TOFFST)4 - (TC + TOFFST)4]
RDVF is radiation view factor (real constant)
RDVF can be table parameter (function of time, temp, gap distance)
EMIS is surface emissivity (material property)
SBCT is Stefan-Boltzmann constant (real constant)
TOFFST is temperature offset from absolute zero (TOFFST command)
Heat flows between contact and target when 0 < gap < pinball
Heat flows from contact to environment for free surface
Free surface recognized as for convection
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9. Thermal Contact External heat flux input
SFE applied to contact surface only (not target surface)
Heat flux acts only if contact status is open
For near-field contact, the flux acts on both contact and target
For free surface flux acts only on contact element
Free surface recognized as for convection
Cannot be applied simultaneously with convection on a given element
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10. Thermal Contact Thermal contact tips Conductance TCC
Has units of heat / (time*degree*area)
Typically less than the equivalent conductance of contacting solids
For frictional heating, TIME must have true chronological units
However, if structural inertia and damping are unimportant, turn them off with TIMINT,STRUC,OFF for faster solution
Unsymmetric solver option may benefit frictional sliding
NROPT,UNSYM
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11. Thermal Contact … Example Problem
Thermal Contact – Conductance Problem
Two bodies of dissimilar materials are in contact.
The extreme ends of the bodies are held at different, constant temperatures.
A force on the top surface causes contact pressure between the two components.
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12. Thermal Contact … Example Problem
This example will be solved as a plane strain, symmetric model.
The top surface will be deflected 0.01 inches toward the bottom component.
Contact elements will include constant thermal conductance.
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13. Thermal Contact … Example Problem
Read in the model using the input file “th_contact.inp”.
Create the contact pair using the Contact Wizard.
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14. Thermal Contact … Example Problem
Select the top line of the bottom component for the Target Surface.
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15. Thermal Contact … Example Problem
Select the bottom two lines of the top component for the Contact Surface.
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16. Thermal Contact … Example Problem
Complete the creation of the contact pair with default options.
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17. Thermal Contact … Example Problem
Modify the Contact Element options to include the TEMP degree of freedom.
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18. Thermal Contact … Example Problem
Modify the Contact Element REAL constant to include the thermal contact conductance coefficient (TCC).
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19. Thermal Contact … Example Problem
For this example, use a constant TCC = .001.
Thermal Contact Options
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20. Thermal Contact … Example Problem
Apply the structural boundary conditions.
Symmetry
Fixed in X & Y
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21. Thermal Contact … Example Problem
Apply the enforced displacement.
Displaced in Y-dir
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22. Thermal Contact … Example Problem
Apply the thermal boundary conditions.
Temp = 200 F
Temp = 70 F
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23. Thermal Contact … Example Problem
Run the solution.
Plot deflection in the Y-Direction to verify structural solution.
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24. Thermal Contact … Example Problem
Plot nodal TEMP.
Note the mismatch in the temperature at the contact surface.
Remember: TCC = .001.
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25. Thermal Contact … Example Problem
Now re-run the problem after modifying TCC = 1.
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26. Thermal Contact … Example Problem
Plot nodal TEMP.
Note the consistent temperature at the contact surface.
Remember: TCC = 1.
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