the pressure of the Merkle model in interPhaseChangeFoam
 

Here,I want to simulate the evaporation of a droplet of gasoline in the atmosphere, I've followed the instructions in the tutorial http://www.tfd.chalmers.se/~hani/kur...ChangeFoam.pdf
but I have a doubt about the pressure in Merkle model.When p<pSat, the liquid evaporates.I think the p should be the partial pressure of vapor in the atmosphere pressure.But how should I edit the pEqn.H to calculate the partial pressure of vapor ? or maybe the p is just the total pressure ( the atmosphere pressure 1.1MPa)?
I'm really looking forward to your answer. Thanks very much.