Question

A Compound refrigeration system using R12 as refrigerant

consists of three evaporators of capacities 18TR, 27TR and
9TR at saturation temperatures of -5°C, 0°C and 5°C
respectively. The system is provided with individual expansion
valves and flash intercoolers. The condenser temperature is
40°C and the liquid refrigerant leaving the condenser is
subcooled to 30°C. Assume isentropic compression at each
stage of compression. Draw (i) A labelled complete circuit
diagram of this multipressure VCRS (ii) P-h and T-s diagram
of this circuit.

Note- Use of Psychrometric chart and Refrigerant
properties/diagrams is allowed.

Answer 1

The system diagram would involve the following components:

Compressor: The refrigerant R12 enters the compressor at low pressure and is compressed to a higher pressure and temperature.

Condenser: The high-pressure, high-temperature refrigerant then flows to the condenser. The condenser temperature is 40°C. Here, heat is transferred from the refrigerant to the surroundings, and the refrigerant condenses into a high-pressure liquid.

Subcooler: The liquid refrigerant leaving the condenser is subcooled to 30°C. This process involves removing additional heat from the liquid refrigerant to lower its temperature below the condensing temperature.