[vjo]

Dear experts,
Please bear with me.


As per my understanding VOF model cannot generate mass during phase change in boiling or condensation. Therefore Ansys provides an in-built 'Evaporation and condensation model or LEE model' with it. Now if we dont want to use this model, we can provide 'mass source terms' using a UDF into the Ansys and these will be added to governing equations and will act as mass generation.
Therefore i DID NOT SELECT 'evaporation and condensation' model in FLuent and used following UDF in ansys for source terms. BUT no mass is being generated (no bubble formation)..!! My simulation is for flow boiling of water in a channel with constant heat flux. Please help me.!!


DEFINE_SOURCE(liq_src, cell, pri_th, dS, eqn)
{
Thread *mix_th, *sec_th;
real l_mass;
mix_th = THREAD_SUPER_THREAD(pri_th);
sec_th = THREAD_SUB_THREAD(mix_th, 1);
l_mass = 0;

if (T_sat != 0.0) {
// Perform the calculation involving T_sat
if (C_T(cell, mix_th) >= T_sat) {
l_mass = -0.1 * C_VOF(cell, pri_th) * C_R(cell, pri_th)
* fabs((C_T(cell, pri_th) - T_sat) / T_sat);
dS[eqn] = -0.1 * C_R(cell, pri_th)
* fabs((C_T(cell, pri_th) - T_sat) / T_sat);
}
else {
l_mass = 0.1 * C_VOF(cell, sec_th) * C_R(cell, sec_th)
* fabs((T_sat - C_T(cell, mix_th)) / T_sat);
dS[eqn] = 0.1 * C_VOF(cell, sec_th)
* fabs((T_sat - C_T(cell, mix_th)) / T_sat);
}
}

return l_mass;
}

DEFINE_SOURCE(vap_src, cell, sec_th, dS, eqn)
{
Thread *mix_th, *pri_th;
real v_mass;
mix_th = THREAD_SUPER_THREAD(sec_th);
pri_th = THREAD_SUB_THREAD(mix_th, 0);
v_mass = 0;

if (T_sat != 0.0) {
if (C_T(cell, mix_th) >= T_sat) {
v_mass = 0.1 * C_VOF(cell, pri_th) * C_R(cell, pri_th)
* fabs((C_T(cell, mix_th) - T_sat) / T_sat);
dS[eqn] = 0.1 * C_VOF(cell, pri_th)
* fabs((C_T(cell, mix_th) - T_sat) / T_sat);
}
else {
v_mass = -0.1 * C_VOF(cell, sec_th) * C_R(cell, sec_th)
* fabs((T_sat - C_T(cell, mix_th)) / T_sat);
dS[eqn] = -0.1 * C_R(cell, sec_th)
* fabs((T_sat - C_T(cell, mix_th)) / T_sat);
}
}

return v_mass;
}

DEFINE_SOURCE(enrg_src, cell, mix_th, dS, eqn)
{
Thread *pri_th, *sec_th;
real m_dot, delta_T;

pri_th = THREAD_SUB_THREAD(mix_th, 0);
sec_th = THREAD_SUB_THREAD(mix_th, 1);

delta_T = fabs(C_T(cell, mix_th) - T_sat);

if (C_T(cell, mix_th) >= T_sat) {
m_dot = -0.1 * C_VOF(cell, pri_th) * C_R(cell, pri_th) * delta_T / T_sat;
dS[eqn] = -0.1* C_VOF(cell, pri_th) * C_R(cell, pri_th) / T_sat;
}
else {
m_dot = 0.1 * C_VOF(cell, sec_th) * C_R(cell, sec_th) * delta_T / T_sat;
dS[eqn] = 0.1 * C_VOF(cell, sec_th) * C_R(cell, sec_th) / T_sat;
}
return (H_LV * m_dot);
}