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Refrigeration and Cryogenics Maciej Chorowski. Faculty of Mechanical and Power Engineering. Pressure-enthalpy diagram. Temperature entropy diagram. Refrigeration – processes.
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Refrigeration and CryogenicsMaciej Chorowski Faculty of Mechanical and Power Engineering
Refrigeration – processes • A refrigeration process indicates the change of thermodynamic properties of the refrigerant and the energy transfer between the refrigerant and the surroundings.
COEFFICIENT OF PERFORMANCEOF REFRIGERATION CYCLE • The coefficient of performance is an index of performance of a thermodynamic cycle or a thermal system. Because the COP can be greater than 1, COP is used instead of thermal efficiency. The coefficient of performance can be used for the analysis of the following: • A refrigerator that is used to produce a refrigeration effect only, that is, COPref • A heat pump in which the heating effect is produced by rejected heat COPhp • A heat recovery system in which both the refrigeration effect and the heating effect are used at thesame time, COPhr
Refrigeration processes of a vapor compression refrigerating system • Evaporation. In this process, the refrigerant evaporates at a lower temperature than that of its surroundings, absorbing its latent heat of vaporization. • Superheating. Saturated refrigerant vapor is usually superheated to ensure that liquid refrigerant does not flow into the compressor. • Compression. Refrigerant is compressed to a higher pressure and temperature for condensation. • Condensation. Gaseous refrigerant is condensed to liquid form by being desuperheated, then condensed, and finally subcooled, transferring its latent heat of condensation to a coolant. • Throttling and expansion. The higher-pressure liquid refrigerant is throttled to the lower evaporating pressure and is ready for evaporation.