# CFLUX boundary conditions

**URL:** <https://calculix.discourse.group/t/cflux-boundary-conditions/2724>\
**Category:** Uncategorized\
**Created:** [April 28, 2025, 7:10am UTC](https://calculix.discourse.group/t/cflux-boundary-conditions/2724 "2025-04-28T07:10:52Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![FranSordoni](https://avatars.discourse-cdn.com/v4/letter/f/71e660/32.png) [@FranSordoni](https://calculix.discourse.group/u/FranSordoni)\
**Post date:** [April 28, 2025, 7:10am UTC](https://calculix.discourse.group/t/cflux-boundary-conditions/2724/1 "2025-04-28T07:10:52Z")

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Hello, I am trying to apply concentrated heat flux as a boundary condition but when I check the results, the nodes to which I impose a heat flux, have a different one.  
I have only applied boundary conditions of that nature, I haven’t imposed any temperature as a boundary condition but I have initialized the temperatures.  
What should I change to make sure that the heat flux in the nodes that I selected is the one that I imposed?

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**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [April 28, 2025, 7:41am UTC](https://calculix.discourse.group/t/cflux-boundary-conditions/2724/2 "2025-04-28T07:41:05Z")

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Are you checking RFL ? Do you remember what I warned you about ?

> [@CFLUX Submodeling](https://calculix.discourse.group/t/cflux-submodeling/2659/2):
>
> HFL is integration point variable (heat flux per unit area vector components) extrapolated and averaged at nodes in the .frd file (you can get the integration point values with \*EL PRINT). RFL stands for total flux (external concentrated heat sources) at a node. Just like with RF (reaction force in mechanical analyses), this includes both applied and reaction fluxes.

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**Author:** ![FranSordoni](https://avatars.discourse-cdn.com/v4/letter/f/71e660/32.png) [@FranSordoni](https://calculix.discourse.group/u/FranSordoni)\
**Post date:** [April 28, 2025, 7:46am UTC](https://calculix.discourse.group/t/cflux-boundary-conditions/2724/3 "2025-04-28T07:46:39Z")

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Yes, what i am doing is reading the RFL results from the previous simulation and applying it to the nodes. Should I instead check for the HFL in the results of the last simulation?

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**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [April 28, 2025, 7:58am UTC](https://calculix.discourse.group/t/cflux-boundary-conditions/2724/4 "2025-04-28T07:58:03Z")

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Just like reaction forces, RFL will give you a sum of applied and reaction flux if you check it for nodes with \*CFLUX applied. From the manual (just replace forces with fluxes and \*CLOAD/\*DLOAD with \*CFLUX/\*DFLUX):

> Summarizing, selecting RF gives you the sum of the reaction forces and the loading forces. This is equal to the reaction forces only if the elements belonging to the selected nodes are not loaded by a \*DLOAD card, and the nodes themselves are not loaded by a \*CLOAD card.

I explained what HFL is in a reply to your previous thread. It’s heat flux per unit area, just extrapolated and averaged at nodes. So it may not be what you are looking for.

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**Author:** ![vicmw](https://avatars.discourse-cdn.com/v4/letter/v/6de8d8/32.png) [@vicmw](https://calculix.discourse.group/u/vicmw)\
**Post date:** [April 29, 2025, 7:04am UTC](https://calculix.discourse.group/t/cflux-boundary-conditions/2724/5 "2025-04-29T07:04:08Z")

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Rather HFL is heat flux (heat flow rate per unit area) and \*CFLUX and RFL, despite their names, are heat flow rates, not heat fluxes.