81
The TXV meters the flow of liquid refrigerant entering the
evaporator at a rate that matches the amount of refrigerant
being boiled off in the evaporator (gas). The valve maintains
the proper “superheat” of approximately 10°F (T3b - T3a).
Superheat is the temperature of a gas above the boiling point
for that liquid. If a refrigerant liquid boils at a temperature of
40°F in a cooling coil, and then the refrigerant gas increases in
temperature, superheat has been added. If this refrigerant
changed from a liquid to a gas or vapor at 40°F and then the
refrigerant vapor increased in temperature to 50°F, it has
been superheated by 10°F.
Superheat