# Define variable cooling power by temperature

**URL:** <https://prepomax.discourse.group/t/define-variable-cooling-power-by-temperature/2752>\
**Category:** General Questions\
**Created:** [June 3, 2025, 8:59am UTC](https://prepomax.discourse.group/t/define-variable-cooling-power-by-temperature/2752 "2025-06-03T08:59:51Z")\
**Posts on this page:** 3\
**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:** [June 3, 2025, 8:59am UTC](https://prepomax.discourse.group/t/define-variable-cooling-power-by-temperature/2752/1 "2025-06-03T08:59:51Z")

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Hey, i want to define a variable heat flux to a surface or Volume that is temperature dependent. I asked about this a while ago already and was given the info that i would have to write a subroutine. Since then i’ve managed to recompile the basic calculix and Prepomax and have found the calculix documentation and the dflux.f subroutine which i think is the one i need?  
But i don’t really understand what my subroutine would need to look like?  
ideally i would like to be able to define a temperature/heat flux table and assign the flux to one volume in my model.  
are there any tutorials where i can see how to write a custom subroutine? i could only find a few where a keyword is used but none regarding the actual subroutine.  
Or did somebody maybe even do something similar and could send me his subroutine so i have a refrence for what i need.

thanks a lot 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:** [June 3, 2025, 9:35am UTC](https://prepomax.discourse.group/t/define-variable-cooling-power-by-temperature/2752/2 "2025-06-03T09:35:53Z")

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It would be better to ask on the CalculiX forum ([https://calculix.discourse.group/](https://calculix.discourse.group/)) since it’s strictly solver-related and there should be no need to modify anything in PrePoMax if you recompile CalculiX with a custom subroutine. Then you just modify the heat flux label to user the subroutine.

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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:** [June 3, 2025, 9:42am UTC](https://prepomax.discourse.group/t/define-variable-cooling-power-by-temperature/2752/3 "2025-06-03T09:42:07Z")

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makes sense, i’ll ask there thanks 🙂