Learning Forum

[ASDzxc]

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,

[Rob]

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]

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.

[Rob]

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]

Thanks, sir.