CFD Online Discussion Forums - electrostatic forces between a large numbers of droplets

Hi every body
I want to calculate the electrostatic forces between a large numbers of water droplets dispersed in oil continuum under the electrostatic field. I have used lagrangian frame work in DPM model in fluent 6.3.26. and for electrostatic body forces acting on droplets I have written a UDF code according to Dipole-Dipole interaction model. My UDF searches all particles in the all cells all over the domain to calculate electrostatic forces. But this is very time consuming and for large number of droplets it is not so efficient. Some have suggested using parcel concept in this case but I don’t know how I can use parcels concept in my UDF to reduce run time. If anybody has suggestion in this case or any suggestion that help me I will be very thankful.

This is my UDF code:
/* UDF for computing the electric force on particles in all cells of a domain */

#include "udf.h"
#include "mem.h"
#include "dpm.h"
#include "surf.h"
#include "stdio.h"
#define epsoil 2.2 /* epsilon for oil */
#define E0 25 /* electric background field,v/m */
#define beta 0.9934
#define M_PI 3.14159265358979323846

DEFINE_DPM_BODY_FORCE(particle_body_force,p,i)
{
double bforce,Fr,Ft,d2,d1,s,tet,k1,k2,m;

/* get the cell and Thread that the particle is currently in */
cell_t c;
Thread *t;
Domain *d;
/* Particle index for looping over all particles in the cell */
Particle *pi;
/* loop over all particles in all cells of domain to find their position and diameter */
int ii;
double p1[2],p2[2];
Fr=0;
Ft=0;
bforce=0;

d = Get_Domain(1); /* mixture domain if multiphase */
for(ii=0;ii<2;ii++)
{p1[ii]= p->state.pos[ii];
}
d1 = P_DIAM(p);
m=P_MASS(p);

thread_loop_c(t,d) /*loops over all cell threads in domain*/
{

begin_c_loop(c,t) /* loops over cells in a cell thread */
{

begin_particle_cell_loop(pi,c,t)
{

for(ii=0;ii<2;ii++)
{
p2[ii]=pi->state.pos[ii];
}
d2=pi->state.diam;
s=sqrt(pow(p1[0]-p2[0],2)+pow(p1[1]-p2[1],2));
if (s > (d1/2+d2/2))
{
tet=atan((p2[1]-p1[1])/(p2[0]-p1[0]));
Fr=12*M_PI*pow(beta,2)*epsoil*pow(E0,2)*pow(d1/2,3)*pow(d2/2,3)*(3*k1*pow(cos(tet),2)-1)/pow(s,4);
Ft=(1)*12*M_PI*pow(beta,2)*epsoil*pow(E0,2)*pow(d1/2,3)*pow(d2/2,3)*k2*sin(2*tet)/pow(s,4);
if(i==0) bforce+=((1)*Fr*cos(tet)+(1)*Ft*cos(M_PI/2+tet));
else if(i==1) bforce+=((-1)*Fr*sin(tet)+(-1)*Ft*sin(M_PI/2+tet));

}

}
end_particle_cell_loop(pi,c,t)

}
end_c_loop(c,t)

}/*end of thread_loop_c(t,d)*/

return (bforce/m);

}