Arefrigerator uses refrigerant-134a as the working fluid and operates on an ideal vapor-compression refrigeration cycle between 0.14 and 0.8 mpa. if the mass flow rate of the refrigerant is 0.05 kg/s, determine (a) the rate of heat removal from the refrigerated space and the power input to the compressor, (b) the rate of heat rejection to the environment, and (c) the cop of the refrigerator.

(a) The rate of heat removal from the refrigerated space is 10.06KJ/s and the power input to the compressor is 7.57KJ/s

(b) The rate of heat rejection to the environment is 2.49KJ/s

(c) The COP of the refrigerator is 1.33

Explanation:

Mass flow rate of refrigerant = 0.05kg/s

From the steam table, enthalpies of the saturated liquid and vapor refrigerant at 0.14MPa and 0.8MPa are

0.14MPa: hf = 59.3KJ/kg, hg = 1410.4KJ/kg

0.8MPa: hf = 260.4KJ/kg, hg = 1460.2KJ/kg

(a) Rate of heat removal from the refrigerated space = 0.05(260.4 - 59.3) = 10.06KJ/s

Power input to the compressor = 10.06 - 2.49 = 7.57KJ/s

(b) Rate of rejection of heat to the environment = 0.05(1460.2 - 1410.4) = 2.49KJ/s

(c) COP of the refrigerator = 10.06 ÷ 7.57 = 1.33

d. platinum would have the greatest temperature increase because it has the lowest specific heat.