CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

a question about define heat flux

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   October 7, 2009, 03:01
Default a question about define heat flux
  #1
New Member
 
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 8
hunter is on a distinguished road
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 is offline   Reply With Quote

Old   October 7, 2009, 03:44
Default
  #2
New Member
 
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 8
hunter is on a distinguished road
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 is offline   Reply With Quote

Old   October 7, 2009, 04:01
Default
  #3
New Member
 
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 8
hunter is on a distinguished road
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.
hunter is offline   Reply With Quote

Old   November 7, 2012, 23:36
Default DEFINE_HEAT_FLUX usage
  #4
New Member
 
Bruce
Join Date: Mar 2012
Posts: 8
Rep Power: 5
XJTH is on a distinguished road
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 View Post
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
XJTH is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Heat Flux Wall Boundary Confusion. Joee FLUENT 1 August 21, 2010 12:20
Wall Heat Flux not a listed variable mike CFX 8 February 5, 2009 14:32
Wall Heat Flux Boundaries conditions Abigail FLUENT 2 July 24, 2007 09:34
Natural convection with heat flux Anton FLUENT 5 April 2, 2007 04:03
How to define heat flux Coriolius CD-adapco 11 October 13, 2004 01:36


All times are GMT -4. The time now is 17:11.