How Does Internal Energy and Temperature Determine the Phase of R134A?

[Ry122]

if you're given just the temperature and internal energy of R134A how do you determine the phase of the substance? If I was given the pressure instead of internal energy then i would just look in my tables to see if the pressure is above or below the saturated pressure and i would then know whether it's subcooled or superheated. i don't know where the substance is with respect to the saturated liquid curve if all I have is the enthalpy. is enthalpy represented in any way on a pv or pt graph?

Also, when substances are subcooled they would always have to be a mixture of vapour and liquid wouldn't they since when you move below the saturated r134a or water curve you move slightly closer to the vapour side of the parabola and vice versa.

 

[Valkarie]

The phase of a substance cannot be determined from just the temperature and internal energy. Enthalpy is not represented on a PV or PT graph, but it can be determined from the temperature and pressure values. Generally, enthalpy is used to determine whether a given state is in a superheated, saturated, or subcooled state. Subcooled substances do not necessarily have to be a mixture of vapor and liquid. If the temperature of the substance is below the saturation temperature, the substance will be entirely liquid.