[asaleem89]

I'm trying to model air-vapor mixture using the species transport model. The flow is incompressible, but the density variation due to temperature or humidity is taken into consideration using the expression given below:
rho=p/(RT(m/M))
where, m is the mass fraction of species and M is the molecular weight of the species
I have written a UDF but on interpretation, it's giving a "structure implementation error". Here is the UDF:

#include "udf.h"

DEFINE_PROPERTY(cell_density, c, t)
{
real sum=0; int i;
Material *sp;

real rho;

real m=18.01534;
real R= UNIVERSAL_GAS_CONSTANT/m;

Property *prop;
mixture_species_loop(THREAD_MATERIAL(t),sp,i)
{
prop= (MATERIAL_PROPERTY(sp));
rho= generic_property(c,t,prop,PROP_rho,C_T(c,t),C_P(c, t));

sum += C_P(c,t)/(R*C_T(c,t)*(C_YI(c,t,i)/m));
}

return sum;
}