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hunter October 7, 2009 03:01

a question about define heat flux
 
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:
Area-Weighted Average
Surface Heat Transfer Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 743.67706

Area-Weighted Average
Surface Heat Transfer Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled-shadow -738.45538

Area-Weighted Average
Wall Func. Heat Tran. Coef. (w/m2-k)
-------------------------------- --------------------
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.;
}

hunter October 7, 2009 03:44

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.;
}

Area-Weighted Average
Surface Heat Transfer Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 744.04559

Area-Weighted Average
Wall Func. Heat Tran. Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 6000.0054


if i did not hooked it, then the results is as below:
Area-Weighted Average
Wall Func. Heat Tran. Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 6000.0054

Area-Weighted Average
Surface Heat Transfer Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 902.71478

hunter October 7, 2009 04:01

I found that Surface Heat Transfer Coef. is defined by h=q/(T_wall-T_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.

XJTH November 7, 2012 23:36

DEFINE_HEAT_FLUX usage
 
hello,could please to introduce how to use the DEFINE_HEAT_FLUX Macro ?
ie. how to identify the special wall face ?

Quote:

Originally Posted by hunter (Post 231711)
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.;
}

Area-Weighted Average
Surface Heat Transfer Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 744.04559

Area-Weighted Average
Wall Func. Heat Tran. Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 6000.0054


if i did not hooked it, then the results is as below:
Area-Weighted Average
Wall Func. Heat Tran. Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 6000.0054

Area-Weighted Average
Surface Heat Transfer Coef. (w/m2-k)
-------------------------------- --------------------
wall_coupled 902.71478



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