I am using OpenFOAM - a finite volume based CFD package to model two phase flow with phase change.

Assuming I have a cell that is 1 litre in volume and this cell is entirely saturated with water. According to the temperature and pressure (based on Liquid-Vapour equilibrium), lets say that the water entirely vaporises to steam. According to Ideal gas law this means, 1 litre of water forms (considering pressure as 1 atm and Temperature as 373K):

pv = nRT,

(1 atm)*V(m3) = (55 mol)*(8.21e-5 m3.atm/K.mol)*(373K)

V(gas) = 1.684 m3 = 1684 litres.

Though this is physical in real world (heating water in a vessel with no lid), how can this phenomena of degassing be explained from a finite volume perspective (this large volume accomodated in a small cell, I can assume of this like blowing air into a balloon and at some stage the balloon explodes)?

I have been looking at flash calculations (Rachford-Rice) but I am not sure if the total volumes (V_feed = V_vapour + V_liquid) are balanced. We can determine the saturations of fluids, but the vapour volume can exceed the feed volume I think.

Does anyone have an idea on how to model this phase change physics in a finite volume framework? In specific, I am looking at phase change in a long column something like in a geothermal well and not at the pore-scale. Any redirection to suitable papers and suggestions are highly appreciated.

Thanks!