Modern ships generally use mechanical refrigeration, mainly: evaporative refrigeration, the most common application, using the principle of absorbing latent heat of vaporization during liquid vaporization; refrigeration; vapor compression refrigeration; absorption refrigeration; steam injection refrigeration; gas expansion refrigeration Mainly used in low-temperature liquefaction of aircraft air conditioners and gases; semiconductor refrigeration, mostly used in submarines, medical equipment and small air conditioners.

1. Vapor compression refrigeration selects a liquid with a very low boiling point (Freon 22) as a refrigerant.

The liquid refrigerant is throttled into the evaporation coil in the cold storage through the expansion valve 5, the refrigerant absorbs heat at a lower pressure, and the heat is taken from the cold storage, and the storage temperature is lowered. The refrigerant is used to discharge the refrigerant from the evaporator. Extracted in order to maintain a stable low pressure in the evaporator, while compressing the gaseous refrigerant to a high temperature and high pressure to the condenser, so that the gaseous refrigerant is exothermic and condensed into a liquid condition. In the condenser, the refrigerant gas is carried out by using the outboard seawater. Cooling, re-liquefying, and then re-vaporizing the heat in the evaporating coil through the expansion valve to achieve continuous cooling of the evaporator, compressor, condenser and expansion valve. The four devices are vapor compression refrigeration devices. Basic components.

2. Absorption refrigeration

Low-pressure steam becomes high-pressure steam. Without a compressor, the refrigerant vapor generated in the evaporator is absorbed into a solution by a liquid (absorbent) that strongly absorbs the refrigerant, and then pumped to the generator (high pressure) by a liquid pump. Heating to release the high-pressure refrigerant vapor, the absorbent solution is re-extracted to absorb the refrigerant after throttling and decompression. The working fluid consisting of refrigerant and absorbent must be used for working absorption refrigerant: ammonia-water solution (ammonia) - Refrigerant, water - absorbent) - cryogenic system; lithium bromide - aqueous solution (water - refrigerant, lithium bromide - absorbent) - air conditioning system.
The main advantages of the absorption refrigerating device: when using waste heat or low-parameter heat source refrigeration and water as the refrigerant, there is no need to use the compressor, there is no noise and vibration during operation, no poison and pollution at all, and there is no danger of explosion.
The main disadvantages are: the thermal coefficient is lower than the compression type; the cooling water consumption is large; the lithium bromide-water solution has higher requirements on the sealing of the equipment, and the low temperature below 0 °C cannot be obtained. The lithium bromide-aqueous solution has a strong corrosive effect on the steel in the atmosphere. Life is lower than vapor compression.
3. Steam-jet cooling water vaporizes and absorbs heat under vacuum, and can obtain low temperature above 0 °C, and uses steam ejector as a vacuuming device - so it is called.

Main advantages: simple equipment structure, less floor space, easy to manufacture and manage. Water is used as a refrigerant, which is harmless to the human body. The latent heat of gasification is large.

Disadvantages: Working under high vacuum, only when the low temperature is above 0 °C, the steam consumption is large and the economy is poor.