Calculating percentage of liquid in a coil?

[MechEng92]

I'm currently designing a unit that's performance is very sensitive to the charge of refrigerant. I have a spread sheet that calculates the charge of refrigerant needed based on operating conditions, however the one part that remains a dark art is the percentage of liquid in the evaporator and condenser coils. This seems to have a major effect on the total charge of the unit.

Does anyone know a method of calculating the percentage of liquid refrigerant in the coils?

 

[Drazen]

I was studying such subjects not less than six months within five semester courses related to thermodynamics, but never in practice. As far as I know, research institutes and firms related to them deal with such issues.

 

[ME27272727]

I've never had to do such a calculation in practice. In theory, this sounds like it would be a thermodynamics problem, where if you have two intensive properties (Temp and pressure will do), you can find the quality of the mixture. You would have to pick multiple points on the evaporator, use the quality at each point to add up the total liquid volume. I deal more with the systems outside of each piece of equipment. Perhaps someone who designs in inside "guts" of this equipment can chime in with software that will calculate all of this on the fly?