Equilibrium liquid-gas ratio in a binary mixture

[KarenRei]

Hi all. I'm in need of a formula to calculate (roughly) the percentage of an ammonia-water mixture (arbitrary ratio of ammonia to water) that will boil off under different pressure/temperature conditions, in the ballpark range of 0.2-1.3 bar and 220K-350K. I don't necessarily need to know the resultant ratio of NH3/H2O in the vapor phase, as their molecular weights are so similar and I only need rough figures... though it certainly wouldn't hurt. But the key issue is calculating the percentage of the mass that ends up in the vapour phase at equilibrium.

I've been searching and I've run into a number of papers arguing over what exactly should be the coefficients to what formulae for determining the bubble point in ammonia-water mixtures (often with 1-2 dozen different coefficients :Þ ), but it's not bubble points that I need.

I considered setting the situation up in CEA2 - I think that would work - but all that would do for me is give specific datapoints. So I could interpolate between them, but obviously that's not ideal...

 

[KarenRei]

Nope, CEA2 didn't do the trick :( For some reason, while they have a thermo.inp entry for NH3(L), it puts all of the NH3 in gas phase regardless of the temperature (it handles water fine, but as if the NH3 wasn't there). So I'm back to having no ideas for how to deal with this issue.