Questions 25 to 30 refer to the following

A vapour compression refrigeration cycle uses refrigerant 134A and operates with an evaporator

pressure of 60 kPa and a condenser pressure of 1,200 kPa. The mass flow rate of the refrigerant is

3 kg/s. The refrigerant is saturated liquid at the condenser outlet, and saturated vapour at the

evaporator outlet. The compression is isentropic and is achieved by a two-stage piston compressor

with equal compression ratios across each stage. The expansion occurs across a thermostatic

expansion valve.

QUESTION 25

Calculate the specific enthalpy of the refrigerant at the compressor inlet and at the condenser

outlet.

QUESTION 26

Calculate the dryness fraction and the specific enthalpy of the refrigerant at the evaporator inlet.

QUESTION 27

Calculate the amount of heat absorbed by the evaporator (the amount of refrigeration).

QUESTION 28

Calculate the temperature of the refrigerant gas at the compressor outlet, and the shaft work input

required by the compressor.

QUESTION 29

Calculate the COP of the refrigeration system and the maximum surrounding ambient temperature

at which the system can operate as described.

QUESTION 30

Calculate the minimum theoretical temperature that this system can generate and explain why this

minimum temperature would not be achieved in the refrigerated space surrounding the evaporator.