Refrigeration principle: when the system is working, the compressor will suck the low pressure and low temperature refrigerant steam generated by the evaporator into the cylinder, and when the pressure rises (temperature also rises) to slightly higher than the pressure in the condenser after compression, the high pressure refrigerant steam will be discharged into the condenser. Therefore, the compressor plays the role of compressing and delivering refrigerant steam. In the condenser, refrigerant steam with higher temperature and pressure condenses into liquid through heat exchange with air with lower temperature (or constant temperature water). At this time, the liquid refrigerant enters the evaporator after being depressurized (cooled) by the expansion valve, and vaporizes after absorbing the heat of compressed air in the evaporator. In this way, the cooled object will be cooled, and the refrigerant steam will be sucked away by the compressor to start the next cycle. In this way, the refrigerant in the system has completed a cycle through four processes of compression, condensation, expansion (throttling) and evaporation, which is carried out repeatedly. The purpose of refrigeration is achieved through continuous refrigeration cycle.

Heat exchange principle:

1. Sensible heat: Most of the heat transfer depends on the temperature difference to conduct heat.

2. Latent heat: the heat transferred by the phase change of substances at constant temperature.

In the refrigeration system, most of the heat conduction is carried out in the way of latent heat conduction, and a small part is carried out in the way of sensible heat conduction.