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October 7, 2009, 03:01 
a question about define heat flux

#1 
New Member
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
I would like to set the heat transfer coef. between the flow and the solid h=3500. the udf is listed below. but why the udf didn't work? the result is the same with or without hooking the udf in the functions hooks. who has some ideas about that? thank you very much!
btw：the calculated h is listed belwo: AreaWeighted Average Surface Heat Transfer Coef. (w/m2k)   wall_coupled 743.67706 AreaWeighted Average Surface Heat Transfer Coef. (w/m2k)   wall_coupledshadow 738.45538 AreaWeighted Average Wall Func. Heat Tran. Coef. (w/m2k)   wall_coupled 6000.0054 #include "udf.h" DEFINE_HEAT_FLUX(heat_flux, f, t, c0, t0, cid, cir) { cid[0] = 0.; cid[1] = 3500; cid[2] = 3500; cid[3] = 0.; } 

October 7, 2009, 03:44 

#2 
New Member
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
I modified the udf as below. and the results is listed below also. but the heat trasfer coef. is still not equal to h=3500, who know why? thank you very much
#include "udf.h" real h = 0.; /* heat transfer coefficient (W/m^2 C) */ DEFINE_ADJUST(htc_adjust, domain) { /* Define the heat transfer coefficient. */ h = 3500; } DEFINE_HEAT_FLUX(heat_flux, f, t, c0, t0, cid, cir) { cid[0] = 0.; cid[1] = h; cid[2] = h; cid[3] = 0.; } AreaWeighted Average Surface Heat Transfer Coef. (w/m2k)   wall_coupled 744.04559 AreaWeighted Average Wall Func. Heat Tran. Coef. (w/m2k)   wall_coupled 6000.0054 if i did not hooked it, then the results is as below: AreaWeighted Average Wall Func. Heat Tran. Coef. (w/m2k)   wall_coupled 6000.0054 AreaWeighted Average Surface Heat Transfer Coef. (w/m2k)   wall_coupled 902.71478 

October 7, 2009, 04:01 

#3 
New Member
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
I found that Surface Heat Transfer Coef. is defined by h=q/(T_wallT_ref), where q is the heat flux, T_wall is the wall temperature and T_ref is the reference temperature which means the average temperature of the fluid.
The default value of the T_ref is 288.16K. But I think maybe in different conditions the T_ref is different, so I would change it to the average temperature of the fluid. Actually I should set this T_ref to the fluid temperature close to the wall, where I want to know the htc. 

November 7, 2012, 23:36 
DEFINE_HEAT_FLUX usage

#4  
New Member
Bruce
Join Date: Mar 2012
Posts: 8
Rep Power: 6 
hello,could please to introduce how to use the DEFINE_HEAT_FLUX Macro ?
ie. how to identify the special wall face ？ Quote:


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