Considering the average temperature in a UDF

[eng_m_m.abd89]

Hello, this is my UDF for heat source; it worked well, but now I want to consider the average temperature instead of the cell temperature. My domain is three bodies [the battery, battery wall, and fluid around them]. I want to consider only the average temperature of the battery. Any help with performing this?

/*my_battery_heat_source_trial.c*/
#include "udf.h"
#include "stdio.h"
#include "math.h"
#include "mem.h"
#include "time.h"

// Inputs
#define V_bat 0.0000165 // Battery volume (m^3)
#define H_chem 11740 // Total heat release of chemical reaction (J)
#define H_sc 17560 // Total heat release of short circuit (J)
#define rho 2600 // Density of battery (kg/m^3)
#define Cp 1720 // Specific heat capacity (J/kg.K)
#define A 0.92 // Pre-exponential factor (unitless)
#define b 28.5 // Reaction rate constant (unitless)
#define T_ref 533.15 // Normalized temperature coefficient (K)
#define T_chem 413.15 // Start temperature of chemical reactions (K)
#define T_tr 533.15 // Triggering temperature of thermal runaway (K)
#define C_chem_max 12
#define C_elec_max 12


// UDF to define heat generation source term
DEFINE_SOURCE(my_battery_heat_source_trial,c,t,ds, eqn)
{
// Declaring Local variable for chemical and electrical energy concentration
real C_chem = 1.0;
real C_chem_old = 1.0;
real C_elec = 1.0;
real C_elec_old = 1.0;
real dC_chem_dt = 0.0;
real dC_elec_dt = 0.0;
real q_chem;
real q_elec;
real qv;
real T = C_T(c,t); // Get the temperature from the cell
real dt = CURRENT_TIMESTEP; // Get the simulation time step
// Function to compute the rate of change of C_chem (dC_chem/dt)
if (T>T_chem && T<=T_tr && C_chem>=0 && C_chem<=1)
dC_chem_dt =(Cp / H_chem) * A * rho * V_bat * pow((T / T_ref), b);
else if (T>T_tr && C_chem>=0 && C_chem<=1)
dC_chem_dt = C_chem_max;
else
dC_chem_dt = 0.0;
// Update the chemical energy concentration
C_chem = C_chem_old - (dC_chem_dt * dt);
// Function to compute volumetric chemical heat generation rate (q_chem)
q_chem = (1.0/V_bat) * H_chem * dC_chem_dt;
// Function to compute short-circuit reaction rate (dC_elec/dt)
if (T>T_tr && C_chem>=0 && C_chem<=1)
dC_elec_dt = C_elec_max;
else
dC_elec_dt = 0.0;
// Update the electrical energy concentration
C_elec = C_elec_old - (dC_elec_dt * dt);
// Function to compute volumetric electric heat generation rate (q_elec)
q_elec = (1.0/V_bat) * H_sc * dC_elec_dt;
// Compute heat generation rates
qv = q_chem + q_elec; // Total heat generation rate (W/m³)
ds[eqn]=0;
return qv; // Return total heat source term for Fluent
}

[Rob]

You'll need to loop over the cell zone cells and remember to account for NODE/HOST issues. 

[eng_m_m.abd89]

Any advice on where/how to start writing it, as I am new to the UDF and don't know how to make the loop over the battery cells? 

[Rob]

Look for examples using begin_c_loop and end_c_loop for some ideas. 

[eng_m_m.abd89]

Hi, Thanks for your support, I don`t know how to thank you!

I have updated the UDF and it worked with no error, but just because I am new to the Ansys and UDFs, I want to make sure that I am not making any mistake. the below is my UDF, what do you think of it? will it compute the heat source using the avergaed temperature of the battery cell?

 

/*my_battery_heat_source_trial.c*/

#include "udf.h"

#include "stdio.h"

#include "math.h"

#include "mem.h"

#include "time.h"

 

// Inputs

#define V_bat 0.0000165  // Battery volume (m^3)

#define H_chem 11740     // Total heat release of chemical reaction (J)

#define H_sc 17560       // Total heat release of short circuit (J)

#define rho 2600         // Density of battery (kg/m^3)

#define Cp 1720          // Specific heat capacity (J/kg.K)

#define A 0.92           // Pre-exponential factor (unitless)

#define b 28.5           // Reaction rate constant (unitless)

#define T_ref 533.15     // Normalized temperature coefficient (K)

#define T_chem 413.15    // Start temperature of chemical reactions (K)

#define T_tr 533.15      // Triggering temperature of thermal runaway (K)

#define C_chem_max 12    

#define C_elec_max 12    

 

// Global variable to store the computed average temperature

real avg_temp = 300.0;  // Initial assumption (K)

 

// Function to Compute Average Temperature in Battery Zone (2D)

real compute_avg_temperature(Domain *domain, int battery_zone_id)

{

   real T_avg = 0.0, area = 0.0, area_tot = 0.0;

   real T;

   Thread *t;

   cell_t c;

   /* Get thread corresponding to battery zone */

   t = Lookup_Thread(domain, battery_zone_id);

 

   begin_c_loop(c, t)

   {

      area = C_VOLUME(c, t);

      T = C_T(c,t);   // Get the temperature from the cell

 

      area_tot += area;

      T_avg += T * area;

   }

   end_c_loop(c, t)

   T_avg /= area_tot; // Compute area-weighted avg temp

}

 

// Update Average Temperature Before Each Iteration

DEFINE_ADJUST(update_avg_temp, d)

{

   int battery_zone_id = 6;  // Set the battery zone ID

   avg_temp = compute_avg_temperature(d, battery_zone_id);

   printf("Updated Battery Avg Temperature: %g K\n", avg_temp);

}

 

 

// UDF to define heat generation source term

DEFINE_SOURCE(my_battery_heat_source_trial_avg,c,t,ds,eqn) 

{

// Declaring Local variable for chemical and electrical energy concentration

real C_chem = 1.0; 

real C_chem_old = 1.0;

real C_elec = 1.0; 

real C_elec_old = 1.0; 

real dC_chem_dt = 0.0;

real dC_elec_dt = 0.0;

real q_chem;

real q_elec;

real qv;

real dt = CURRENT_TIMESTEP;  // Get the simulation time step

 

// Function to compute the rate of change of C_chem (dC_chem/dt)

if (avg_temp>T_chem && avg_temp<=T_tr && C_chem>=0 && C_chem<=1)

dC_chem_dt =(Cp / H_chem) * A * rho * V_bat * pow((avg_temp / T_ref), b);

else if (avg_temp>T_tr && C_chem>=0 && C_chem<=1)

dC_chem_dt = C_chem_max; 

else

dC_chem_dt = 0.0;

// Update the chemical energy concentration

C_chem = C_chem_old - (dC_chem_dt * dt);

// Function to compute volumetric chemical heat generation rate (q_chem)

q_chem = (1.0/V_bat) * H_chem * dC_chem_dt;

// Function to compute short-circuit reaction rate (dC_elec/dt)

if (avg_temp>T_tr && C_chem>=0 && C_chem<=1)

dC_elec_dt = C_elec_max;

else

dC_elec_dt = 0.0;

// Update the electrical energy concentration

C_elec = C_elec_old - (dC_elec_dt * dt);

// Function to compute volumetric electric heat generation rate (q_elec)

q_elec = (1.0/V_bat) * H_sc * dC_elec_dt;

// Compute heat generation rates

qv = q_chem + q_elec; // Total heat generation rate (W/m³)

ds[eqn]=0;

return qv; // Return total heat source term for Fluent

}

[Rob]

You're welcome. 

I can't see anything from a quick look but you may want to print the result of  T_avg /= area_tot to the screen?  I would use some caution using "area" labels for volume, I know why you've done it, but a comment may be useful for when you revisit the code in 3d. I have UDFs from about 2003 that are still valid, and most UDFs are written using something else (tutorials in my case - I code as little as possible) as a starting point.