UDF for Temperature Dependent Energy Source
 

Hello All,

I am solving a problem wherein there is an energy source term with two parts:
1) Part dependent on Temperature [i.e. T*(Cp_g - Cp_s) ]
2) Part independent of Temperature

Can anybody suggest how to include temperature dependent source term in the UDF as we know Energy equation solves for Temperature.

Thanks a lot
Mukesh

Hi Mukesh,

did you get any response or help in this please? i'm also having the same problem.

i was thinking using DEFINE_SOURCE and C_T macro, but not yet sure how to relate them.

problem on UDF returned parameters
 

Dear all,

i've the following UDF code that attempts to apply a temperature-dependent source term to a solid cell.

#include "udf.h"
#include "mem.h"

DEFINE_SOURCE(cell_x_source,cell,thread,dS,eqn)
{
real source;
int Ro=12e-3; /*12mOhm at 20C*/
int To=20; /*temperature 20C*/
int Iphase=20; /*Arms*/

source=Iphase*Iphase*Ro*((C_T(cell,thread)-273)/To)/C_VOLUME(cell,thread);
Message("C_T output: %g\n",C_T(cell,thread));
Message("source output: %g\n",source);
Message("C_VOLUME output: %g\n",C_VOLUME(cell,thread));

return source;
}


While running 100 iterations, i observe in the Message output that the C_VOLUME of the solid cell is changing rather than keeping at a constant value as expected. why is this happening please?

The final outcome of the run was:
Error: Divergence detected in AMG solver: temperature
Error Object: #f

Hope to receive any comments/ideas you may have.

Hello,

Though I'm not sure if we could use the MACRO C_T(c,t) for SOURCE term in Energy equation, still I suggest you remove that C_VOLUME(c,t) as we must define source term as per unit volume to correctly solve the Energy eqn in FLUENT.

Hope that works.

All The Best,
Mukesh

Dear Mukesh,
thank you for your response.

The C_VOLUME in my equation is to obtain the volume of the solid cell, and use it to divide my energy/power in order to express the source in per volume. Note that in the source equation, i've divided by C_VOLUME.

My only query is: Why the C_VOLUME value is changing from one iteration to the next?

Could you please send in your energy equation so as to check the units. FLUENT solves equations with source in Unit/volume terms only. So please check the units.

Best of Luck......Mukesh

Dear Mukesh,

In my application, my source term:

source=Iphase*Iphase*Ro*((C_T(cell,thread)-273)/To)/C_VOLUME(cell,thread);

where,
Iphase*Iphase*Ro*((C_T(cell,thread)-273)/To) is in units of Watts

C_VOLUME(cell,thread) is in units of cubic meters;

Dear machtech001,
I want to write a UDF in which there is a constant term and also a negative term which is related to temperature.
I am new to UDF how can I accomplish that?
I want to use Average Temp of the solid zone and
source term should be used just in solid zone.

#include "udf.h"

DEFINE_SOURCE(source_term,cell,thread,dS,eqn)
{
real source;
real temp=C_T(cell,thread);
int a=0.5546;
int b=1.84*10
^-4;
int I=700;
int SCR=1000;
int A=373.83;
source=261682243-(a*(1-b)*temp)*I*SCR*A
return source
}

I have the same problem as you do,,did you get any response or solution to your case?

I am looking your support to write a udf for ansys fluent dry iron thermal analysis.

In the first cycle of dry iron the energy source will be ON till the mid-point of iron reach at 170 °C then after energy source will OFF till the midpoint of iron cool down to 135 °C . When the mid point of iron will less than 135 °C then energy source will ON again till the mid-point of iron reach at 170 °C. This cycle will...