[edypw1]

I am simulating the nucleation of n-butanol using multiphase eulerian in laminar flow. As for the population balance model, I have activated the nucleation feature and input my UDF (kindly refer to my UDF below).

The experiment is a 2D counter-flow setup where there are two jet inlets, hot and cold. The hot inlet consists of hot saturated n-butanol+helium vapour whereas the cold inlet consists of cold helium vapour. The fluids from both inlets will collide at the stagnation plane (at the centre) and nucleation will occur (saturation ratio>1).

However, from my results in Fluent, I simulated that nucleation occurs at the walls of the hot inlet jet and not at the stagnation plane. This is not ideal, and I have no idea why this phenomenon happens. Please help.

An IMG of my setup in details and the contours of the nucleation in the form of number density in one of the "bin" size is attached below. *Kindly refer*


#include "udf.h"
#include "sg_pb.h"
#include "sg_mphase.h"

# define PI 3.14159265
# define K 1.38064852e-23 /* Boltzmann constant */
# define butane_mol_wt 0.07412 /* n-butanol molecular weight */
# define helium_mol_wt 0.004003 /* helium molecular weight */
# define ro_gas 0.179 /* helium gas density */

DEFINE_PB_NUCLEATION_RATE(nuc_rate, cell, thread)
{
real J; /* nucleation */
real T, butane_mol_frac, butane_mass_frac, helium_mass_frac, sigma, ro_liquid, vap_press, sat, d, v, m, r, ar, v_c, m_c, delta_G, scc, jbd;

Thread *tc = THREAD_SUPER_THREAD(thread); /* obtain mixture thread */
Thread **pt = THREAD_SUB_THREADS(tc); /* pointer to sub_threads */
Thread *tp = pt[S_PHASE]; /* secondary phase thread */

T = C_T(cell,tp); /* Temperature of second phase in Kelvin */

butane_mol_frac = C_VOF(cell,tp); /* mole fraction of n-butanol vapor in primary phase (helium) */

butane_mass_frac = (butane_mol_frac*butane_mol_wt)/((butane_mol_frac*butane_mol_wt)+((1-butane_mol_frac)/helium_mol_wt));
helium_mass_frac = 1.0 - butane_mass_frac;

sigma = (4.833e-2)-((8.181e-5)*T); /*surface tension */
ro_liquid = 990.9563548-(0.524148*T)-(0.00032*pow(T,2.0)); /* density of n-butanol liquid */
vap_press = exp(98.494-(9412.6064/T)-(10.54*(double)log((double)T))); /* equilibrium vapor pressure */
sat = (butane_mol_frac/vap_press)*101325.0; /* supersaturation */
d = (sigma*m)/(ro_liquid*K*T*((double)log((double)sat))); /* diameter of critical cluster */
v = (4.0/3.0)*PI*(pow(d/2,3.0)); /* volume of a single particle with size 1 nm */
m = (ro_liquid)*v; /* mass of one n-butanol molecule*/
r = d/2.0; /*radius of critical cluster */
ar = 4.0*PI*(pow(r,2.0)); /* surface area */
v_c = (4.0/3.0)*PI*(pow(r,3.0)); /* volume of critical cluster */
m_c = (ro_liquid)*(v_c); /* mass of critical cluster */
delta_G = ((4.0*PI)/3.0)*(pow(r,2.0))*sigma; /* free energy formation of critical cluster */
scc = (1.0/sat)*(exp((ar*sigma)/(K*T)));
jbd = ((pow((ro_gas*butane_mass_frac),2.0))/(ro_liquid*butane_mol_wt))*(pow(((2.0*sigma)/(PI*butane_mol_wt)),0.5))*(exp(-delta_G/(K*T)))*(pow((m_c/butane_mol_wt),(2.0/3.0)));

if (sat<=1.0)
{
J = 0.;
}
else
{
J = scc*jbd;
}
return J;
}

Attached IMG: https://ibb.co/F4ZTQvk