ANSWER: flash gas fraction
Explanation: Flash gas fraction is the quality of refrigerant at the inlet to the evaporator. This is the mass fraction of vapor in liquid-vapor mixture of refrigerant.
Explanation: Condensation process in vapor compression cycle is a constant pressure process. Refrigerant is first superheated and then condensed.
ANSWER: to expand the refrigerant
Explanation: High pressure condensed refrigerant is expanded in capillary tube or throttling value.