Carnot Vapour compression Refrigeration cycle
(a) Schematic representation (b) T-s diagram
(a) Schematic representation (b) T-s diagram
Processes: -
1-2: Isentropic compression from state 1 (wet vapour) to state 2 (saturated vapour)
2-3: Heat rejection (QH) in the condenser
3-4: Isentropic expansion from state 3 (saturated liquid)
4-1: Heat absorption ( QL) in the evaporator
The COP of the refrigerator,
1-2: Isentropic compression from state 1 (wet vapour) to state 2 (saturated vapour)
2-3: Heat rejection (QH) in the condenser
3-4: Isentropic expansion from state 3 (saturated liquid)
4-1: Heat absorption ( QL) in the evaporator
The COP of the refrigerator,
Practical Vapour compression refrigeration cycle
(Ws)compressor=h2-h1
QH=h2-h3
h3=h4
and QL=h1-h4
The COP of the refrigerator is given by,
In the ideal refrigeration cycle, the refrigerant leaves the evaporator as wet vapour.
In some cases the refrigerant leaves the evaporator as either saturated vapour or superheated vapour.
T-s diagram for a vapour compression refrigeration cycle when the refrigerant leaves the evaporator as (a) saturated vapour (b) superheated vapour
Gas refrigeration cycle
(a) Schematic diagram (b) T-s diagram
The simplest gas refrigeration cycle is the reversed Brayton cycle
Processes: -
1-2: isentropic compression for state 1 (atmospheric air) to state 2
2-3: energy exchange with the surrounding, air is cooled
3-4: isentropic expansion to state 4
Work obtained during the expansion process can be used to run the compressor
Work done on the compressor,
Processes: -
1-2: isentropic compression for state 1 (atmospheric air) to state 2
2-3: energy exchange with the surrounding, air is cooled
3-4: isentropic expansion to state 4
Work obtained during the expansion process can be used to run the compressor
Work done on the compressor,
The net work required= CP (T2-T1-T3+T4)
The COP of this refrigeration system is given by,
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