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-   -   UDF for heat source in Soldification and melting model (https://www.cfd-online.com/Forums/fluent/137777-udf-heat-source-soldification-melting-model.html)

 karthik82 June 23, 2014 02:14

UDF for heat source in Soldification and melting model

Hi all,

I am using solidification and melting model for simulating melting process for a phase change material in a spherical capsule. Only energy equation is solved. The default model assumes linear temperature enthalpy relationship. But I need to use a heat source in energy equation (enthalpy varies with temp) to incorporate polynomial enthalpy temperature relationship.

My source term is:
Se = density/deltaT*f[T] , (unit will be W/meter cube, since f(T) is J/kg).

I wrote my UDF which is shown below.

#include "udf.h"
#define C1 1757.9
#define C2 3.0e6
#define C3 2e9
#define C4 1e12
#define C5 2e14
#define C6 3e16
#define C7 1e18
{
real source,time,rho,temp,pretime;
rho = C_R(c,t);
temp = C_T(c,t);
time = CURRENT_TIME;
pretime= PREVIOUS_TIME;
source = -(rho/(time-pretime))*(C1*pow(temp,6)-C2*pow(temp,5)+C3*pow(temp,4)-C4*pow(temp,3)+C5*pow(temp,2)-C6*temp+C7);
return source;
}

Negative sign in source indicates the process is melting ( heat sink).
Please kindly advise me whether this is right format and once I interpret the simulation says

and

This deltaT is time difference between real flow time ( whether we have to take time-step difference or real flow time difference ?)
During execution the cell temperature is too low. And I get temperature limited to 1.0 K in the output.