CFD Online Logo CFD Online URL
Home > Forums > Fluent UDF and Scheme Programming

temperature dependent heat flux

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

LinkBack Thread Tools Display Modes
Old   December 11, 2012, 09:45
Default temperature dependent heat flux
New Member
Rohini Bala Chandran
Join Date: Apr 2012
Posts: 8
Rep Power: 5
rohinibc is on a distinguished road

So I am trying to set up a model in Fluent where in I specify a modified flux boundary condition on the wall in my domain. In this case, the wall is adjacent to a solid zone. I intend to model the wall as a thin opaque surface, which when subjected to a certain flux value, absorbs and re-emits radiation. in this case, the difference between what is absorbed and emitted (to the external surroundings) is essentially the amount of heat that is conducted through the solid adjacent to the wall.

So, my boundary condition at the wall becomes:

wall_abs*(Q_wall) = wall_eps*sigma_sbc*(T_wall^4) - k_solid*grad(T)


wall_abs = absorptivity of the wall; wall_eps = emissivity of the wall; sigma_sbc = stefan-boltzmann constant; k_solid = thermal conductivity of the solid adjacent to the wall; grad(T) = temperature gradient at the wall; T_wall = wall temperature.

When I implement my BC at the wall to be temperature dependent by using DEFINE_PROFILE, it doesn't seem to work out very well and returns unphysical results. I basically had my profile written out as:

DEFINE_PROFILE(flux_profile, t,i)
face_t f;
real eps_wall=0.2; /*emissivity of the wall*/
real abs_wall=0.2; /*absoprtivity of the wall*/
real H = 1000; /*Incident irradiation*/
F_PROFILE(f,t,i) = (abs_wall*H) - (eps_wall*SIGMA_SBC*pow(F_T(f,t),4)); /*Net flux that is conducted from the wall into the solid cells adjacent to the wall*/

Does anybody have any suggestions on how to go about this?
rohinibc is offline   Reply With Quote


define_flux, define_profile, udfs

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
temperature and pressure dependent specific heat? xechvol FLUENT 4 December 18, 2012 10:46
Heat Flux Profile at Fluid-Porous Interface Hitch8 CFX 4 December 15, 2012 10:57
Enforce bounds error with heat loss boundary condition at solid walls Chander CFX 2 May 1, 2012 20:11
Heat Flux Wall Boundary Confusion. Joee FLUENT 1 August 21, 2010 12:20
temperature increased does not match the heat flux GUOQIANGWOO FLUENT 2 April 6, 2010 01:29

All times are GMT -4. The time now is 08:58.