The refrigeration cycle is basically the Rankine cycle run in reverse, with one major difference. If the Rankine cycle was reversed the turbine would be processing the working fluid in the liquid state which would result in damage to the blades of the rotor. Instead, an expansion valve is used, meaning that the cycle efficiency drops because a valve produces no work whereas a turbine does. It is assumed when performing calculations for the ideal refrigeration cycle that the expansion valve is isentropic (the same as a turbine) but actually an expansion valve is isenthalpic.
In order to remove heat from an enclosed space and transfer it to the surroundings a refrigeration cycle must have a temperature at the condenser which is above the temperature of the surroundings, and a temperature at the evaporator which is below that of the surroundings. This is required so that heat can be transferred from the condenser to the surroundings, and to the evaporator from the surroundings because according to the zeroth law of thermodynamics heat can only be transferred from a hotter body to a cooler body.
Links:
Vapour Compression
Refrigeration Cycle A more detailed discussion
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