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Hello Experts,

Kindly help me with this UDF, compiled to study CO2 mass transfer (or dissolution) from Gas_Mixture (CO2+O2+N2) to Liquid_Mixture (CO2+H2O). Note-CO2 is the first species in both mixture.

Towards this, I have already calculated Mass transfer coefficient (Kl), area density (Av) and unit less Henry's constant (He).

UDF-1

DEFINE_MASS_TRANSFER(gas_liquid_source, cell, thread, from_index, from_species_index, to_index, to_species_index)
{
#if !RP_HOST

Thread *gas = THREAD_SUB_THREAD(thread, from_index);
Thread *liq = THREAD_SUB_THREAD(thread, to_index);

m_gl=Kl*Av*(He*C_R(cell,gas)*C_YI(cell,gas,0)-C_R(cell,liq)*C_YI(cell,liq,0));

return m_gl;

#endif
}

UDF-2

DEFINE_MASS_TRANSFER(gas_liquid_source, cell, thread, from_index, from_species_index, to_index, to_species_index)
{
#if !RP_HOST

Thread *gas = THREAD_SUB_THREAD(thread, from_index);
Thread *liq = THREAD_SUB_THREAD(thread, to_index);

m_gl=Kl*Av*(He*C_R(cell,gas)*C_YI(cell,gas,0)*C_VOF(cell,gas)-C_R(cell,liq)*C_YI(cell,liq,0)*C_VOF(cell,liq));

return m_gl;

#endif
}

Only difference in these two UDFs is the C_VOF(cell,gas) and C_VOF(cell,liq) appearing in the second one, while these have been ignored in the first one.

Can anyone tell me which one is correct? Is multiplication of volume fraction of phase necessary or it can be ignored while computing the driving force?