Question of udf DEFINE_HEAT_FLUX

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  • Last Post 05 June 2020
ASDzxc posted this 02 June 2020

Hi there,

can DEFINE_HEAT_FLUX be used for CHT problems? is there any test cases for this UDF (not radiations cases)

for example, in fluid-wall coupling convective heat transfer problem, can it be used to modify the fluid-wall heat transfer coefficient?

      In the figure that I uploaded, is h(T_f-T_interface)=-k_wall*(T_interface-T_wall)/d2 correct?, where h is the coefficient assigned using udf, k_wall is the wall conductivity.

DEFINE_HEAT_FLUX(heat_flux, f, t, c0, t0, cid, cir)

{

       real h=2000.;

       cid[1] = h;

       cid[2] = h;

       cid[0] = 0.;

       cid[3] = 0.;

 

}

thanks,

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rwoolhou posted this 03 June 2020

No, it's for external walls. You want to read the  7.4.15.3.6. Augmented Heat Transfer section of the Fluent User's Guide. 

 

 

ASDzxc posted this 03 June 2020

Thanks for your reply, sir.

I've checked the section that you mentioned. It seems that I may adjust the convective heat transfer (at fluid-solid interface) by modifing the "Convective Augmentation Factor" (or "caf_fac" in udf), if I have "perturbed flow and/or disturbed boundary layers". Am I correct?

P.S. I checked the section "Augmented Heat Transfer", but I didn't find any sentence that restrict the use of "Convective Augmentation Factor" to external walls.

rwoolhou posted this 03 June 2020

The augmentation is fine for all "wet" walls and I've used it to help account for small pins on a nominally flat surface before. 

The Define Heat Flux macro is used for external walls as it forces a set heat load onto that surface: on internal walls Fluent works that out based on local flow & temperature. 

ASDzxc posted this 05 June 2020

Thanks, sir. 

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