Question

In your refrigerator the working substance evaporates from liquid to vapor at -20 °C inside a pipe around the cold section. Outside (on the back or below) is a black grille inside which the working substance condenses from vapor to liquid at +40 °C. For each location find the pressure and the change in specific volume (v) if 

(a) the substance is R-12 

(b) the substance is ammonia 

Answer 1

The properties come from the saturated tables where each phase change takes place at constant pressure and constant temperature.

Substance	T	Psat , kPa	∆v = vfg
R-12	40°C	961	0.017
R-12	-20°C	151	0.108
Ammonia	40 °C	1555	0.0814
Ammonia	-20°C	190	0.622