Refrigeration and Cryogenics Maciej Chorowski Faculty of Mechanical and Power Engineering

Pressure-enthalpy diagram

Temperature entropy diagram

Refrigeration – processes A refrigeration process indicates the change of thermodynamic properties of the refrigerant and the energy transfer between the refrigerant and the surroundings.

CARNOT CYCLE

COEFFICIENT OF PERFORMANCE OF 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, COP ref A heat pump in which the heating effect is produced by rejected heat COP hp A heat recovery system in which both the refrigeration effect and the heating effect are used at thesame time, COP hr

CARNOT vapor cycle

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.

Single stage vapour compression cycle

Superheating

Subcooling