# Simulation of thermal contact conductance

**URL:** <https://prepomax.discourse.group/t/simulation-of-thermal-contact-conductance/2631>\
**Category:** General Questions\
**Created:** [April 16, 2025, 6:45am UTC](https://prepomax.discourse.group/t/simulation-of-thermal-contact-conductance/2631 "2025-04-16T06:45:43Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![maloama](https://avatars.discourse-cdn.com/v4/letter/m/e95f7d/32.png) [@maloama](https://prepomax.discourse.group/u/maloama)\
**Post date:** [April 16, 2025, 6:45am UTC](https://prepomax.discourse.group/t/simulation-of-thermal-contact-conductance/2631/1 "2025-04-16T06:45:43Z")

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Hello,  
i want to simulate the thermal conductance of two pieces of metal that are pressed together with screws. Since i want to simulate a relatively large temperature range the force/displacement pressing the pieces together would not be constant since the screws and materials elongate differently, is that possible in prepomax?  
I found the option for boundarie conditions to set a fixed displacement and know how to simulate a hertz contact, but i am not too confident that those will help me because i haven’t found a way so define stuff like surface roughness that i would need for accurate results.  
Thanks for the help 🙂

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**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\
**Post date:** [April 16, 2025, 7:33am UTC](https://prepomax.discourse.group/t/simulation-of-thermal-contact-conductance/2631/2 "2025-04-16T07:33:18Z")

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You can account for thermal expansion even in a purely mechanical analysis. Temperature can be applied as defined field in a static step. Then each material will contract/expand based on its thermal expansion property.

There are two main types of thermal interfaces - tie constraint (perfect mechanical bonding and perfect heat transfer) and contact (possible sliding/separation and heat transfer based on the specified gap conductance).

Gap conductance in contact is defined as conductance vs contact pressure. It may also vary with temperature.

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**Author:** ![maloama](https://avatars.discourse-cdn.com/v4/letter/m/e95f7d/32.png) [@maloama](https://prepomax.discourse.group/u/maloama)\
**Post date:** [April 28, 2025, 9:41am UTC](https://prepomax.discourse.group/t/simulation-of-thermal-contact-conductance/2631/3 "2025-04-28T09:41:29Z")

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Thank you, helped me a lot. I tried simulating quite a few things since my last post  
Ultimately i want to simulate a coldhead in contact with a heat shield. i managed to simulate the heatshield in two variations: with the contact area to the coldhead set to a fixed temperature and a variable temperature flux. this both worked.  
but in order to get accurate results i would need to have two bodies (shield and coldhead) and the coldhead would need a variable cooling power thats variable by Temperature. I found and used the amplitude function, but that is only time variable (afaik), is there a possibility to define cooling power by temperature of an object/node in prepomax?

thanks for the help 🙂

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<div class="post-metadata">

**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\
**Post date:** [April 28, 2025, 10:11am UTC](https://prepomax.discourse.group/t/simulation-of-thermal-contact-conductance/2631/4 "2025-04-28T10:11:49Z")

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> [@maloama](#):
>
> is there a possibility to define cooling power by temperature of an object/node in prepomax?

Not with built-in CalculiX features. This would likely require the use of a Fortran subroutine.