[fard734]

Dear friends,
The following code is a part of a UDF, which is used for calculation of interfacial area density of a single droplet. interfacial area density will be used for prediction of evaporation rate from a single droplet using VOF model. The UDF dosnt work, anybody know what is the problem?
what is the correlation of "length of interface in a cell"

/**** Compute the interfacial area density ****/
NV_V(G,=,C_VOF_G(c,w_liq)); /* vof gradient vector assignment*/

theta = atan(G[0]/G[1]); /* compute angle of VOF gradient vector, n1/n2 because of how geometry is set up in Fluent */
cotan = cos(theta) / sin(theta); /* compute cotangent of angle*/

A = C_VOLUME(c,mixture_thread)/(2*pi); /* in 2D- axis area computed from volume */

len = sqrt((2*C_VOF(c,w_liq)*A/cotan) + (2*C_VOF(c,w_liq)*A*cotan)); /* compute length of interface in a cell */

ad = len/A; /* calculate interfacial area density*/
/***** Computed the area density ad = length of interface / area of cell ***/

if (C_VOF(c, w_liq) != 0.0 && C_VOF(c, w_liq) != 1.0)
{
Message("AD = %f, theta = %f\n",ad, theta);

/* Compute m_lg only if P_sat > (Pcell*XW) */
if (P_sat - (P_cell*X_W) > 0.0)
{
m_lg = cur_ts * ad *(2*a_c/(2-a_c)) * sqrt(MW_W/(2*pi*R)) * ((P_sat - (P_cell*X_W)) / sqrt(T_cell));
}
else
{ m_lg = 0.0;}
}
else
{ m_lg = 0.0;}

return (m_lg); /* return value of mass transfer rate */

}