An R717 based vapour compression refrigerating machine works between 38°C and –20°C temperatures. The ammonia leaves the compressor dry and saturated. Liquid ammonia is under cooled to 30°C temperature inside the condenser, before throttling. Find the theoretical COP of the machine. The cP of saturated ammonia liquid is 4.91 kJ/kg-K. if net refrigeration required is 25.0 TR, find the mass flow rate of ammonia in kg/h, assuming relative COP 0.75. The saturation properties of R717 are given in the following table:
|
|
Liquid
|
Vapour
|
|
t, °C
|
h, kJ/kg
|
s, kJ/kg-K
|
h, kJ/kg
|
|
38
|
380.78
|
1.6134
|
1489.36
|
|
–20
|
108.55
|
0.6538
|
1437.68
|