[ssa]

Hello, I am using the Eulerian multiphase model to model a 2-phase flow, and my model requires a custom fluid-fluid exchange coefficient, Kpq, which I have detailed in the udf below.
My udf compiles and loads correctly, however, the Fluent user interface still requires a definition of interfacial area in the Phase Interactions dialogue box, which I don't need because I defined my own Kpq from my understanding... How does Fluent incorporate this definition of interfacial area concentration if a custom Kpq is already defined?
I have tried "removing" it by defining it in a udf as a constant (e.g. IA=1), I have also tried defining it as ia-symmetric, and cancelling out these terms in my Kpq udf (since ia is incorporated in Kpq)... but I'm unsure if either of these methods is correct mathematically. Here's my Kpq udf:

#include "udf.h"
#include "math.h"
#define a 0.000008
#define mu_p 0.00096
#define rhop 1027

DEFINE_EXCHANGE_PROPERTY(drag, c, mixture_thread ,P_col,RBC_col)
{
Thread *pt, *st;/* thread pointers for primary and secondary phases*/
real phi , k_p_q;
pt = THREAD_SUB_THREAD(mixture_thread, RBC_col);
st = THREAD_SUB_THREAD(mixture_thread, P_col);
phi=C_VOF(c,pt); /* RBC volume fraction*/

k_p_q= (exp(2.68*phi)+pow(phi,0.43))*9*mu_p/(2*pow(a,2));
return k_p_q;
}

Thanks for the help!