Liquid vaporization refrigeration is realized by using the heat absorption effect of liquid vaporization and the heat release effect of condensation. The liquid vaporizes to form steam. When the liquid (refrigerant) is in a closed container, there is no other gas in the container except the liquid and the vapor generated by the liquid itself. The liquid and vapor will reach equilibrium at a certain pressure. At this time, the gas is called saturated steam, the pressure is called saturation pressure, and the temperature is called saturation temperature. In equilibrium, the liquid is no longer vaporized. At this time, if part of the steam is removed from the container, the liquid must continue to vaporize to produce part of the steam to maintain this equilibrium. When liquid vaporizes, it needs to absorb heat, which is called latent heat of vaporization. The latent heat of vaporization comes from the object to be cooled. In order to make this process continuous, it is necessary to continuously extract the steam from the container, condense it into liquid and then return to the container. If the steam extracted from the container is directly condensed into liquid, the temperature of the cooling medium required is lower than the evaporation temperature of the liquid. We hope that the condensation of steam is carried out at room temperature, so we need to increase the pressure of steam to the saturation pressure at room temperature. The refrigerant will evaporate at low temperature and low pressure to produce cooling effect; It condenses at room temperature and high pressure to release heat to the surrounding environment or cooling medium. When the steam condenses at room temperature and high pressure, it becomes a high-pressure liquid, and its pressure needs to be reduced to the evaporation pressure before it can enter the vessel. Liquid vaporization refrigeration cycle is composed of four processes: working medium vaporization, steam pressurization, high-pressure steam condensation and high-pressure liquid depressurization.