This is from Fundamentals of Engineering Thermodynamics, 6th edition. Chapter 7,

Question

This is from Fundamentals of Engineering Thermodynamics, 6th edition. Chapter 7, problem 22. Exergy analysis of a closed system.

Here is the full problem:
Refrigerant 134a vapor initially at 1 bar and 20oC fills a rigid vessel. The vapor is cooled until the temperature becomes -32oC. There is no work during the process. For the refrigerant, determine the heat transfer per unit mass and the change in specific exergy, each in kJ/kg. Let T0=20oC, p0=0.1MPa and ignore the effects of motion and gravity. Here is my problem: The solution is given on this site. I'm stuck on Step 3, when it gives values for specific volume/internal energy/ and entropy. It says that they get the values from R134a tables, and I see the "f" values on table A-10, but I don't know what the "fg" values are or where they got them from. I know that in later steps those are used for determining the quality of the mixture at T=-32C, but where did that value come from to begin with (and what is it?) Thank you.
Refrigerant 134a vapor initially at 1 bar and 20oC fills a rigid vessel. The vapor is cooled until the temperature becomes -32oC. There is no work during the process. For the refrigerant, determine the heat transfer per unit mass and the change in specific exergy, each in kJ/kg. Let T0=20oC, p0=0.1MPa and ignore the effects of motion and gravity. Here is my problem: The solution is given on this site. I'm stuck on Step 3, when it gives values for specific volume/internal energy/ and entropy. It says that they get the values from R134a tables, and I see the "f" values on table A-10, but I don't know what the "fg" values are or where they got them from. I know that in later steps those are used for determining the quality of the mixture at T=-32C, but where did that value come from to begin with (and what is it?) Thank you.

Explanation / Answer

It is the property change when state changes from saturated liquid to saturated vapor and is represented by fg for example if we take hfg it is the enthalpy difference between saturated vapor and saturated liquid hg-hf . hence hfgis the amount of enthalpy gain when R134-a changes its state from saturated vapor to liquid

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