As a representative of the fourth generation refrigerant

water has numerous advantages

such as non-pollution (ODP=0

GWP<1)

accessible

low-cost

secure

stable and large latent heat of vaporization

which can completely satisfy the requirements of the environment as a refrigerant. However

low molecular weight

large specific volume and high adiabatic index of water vapor determine that the water vapor systems have the characteristics of small differential pressure

large compression ratio

small unit volume capacity

large volume flow and high discharge temperature. It also puts forward higher requirements for water vapor compressors

which seriously limit the use and promotion of water as a refrigerant. Currently

the water vapor compressors mainly are centrifugal

screw and roots compressor. Centrifugal water vapor compressor has the advantage of large volume flow rate

but it has small single stage compression ratio

high discharge temperature and droplet sensitivity. At the same time

the blade and shell material of the centrifugal water vapor compressor are severe and expensive. Therefore the centrifugal water vapor compressor is suitable for the largest volume flow rate and smallest compression ratio system. Screw water vapor compressor has the advantages of good stability

large compression ratio and wet compression; however the volume flow rate is smaller. It is more suitable for the refrigeration system with small volume flow rate and large compression ratio. Roots water vapor compressor has the advantages of less vibration components and simple structure

however it also has small compression ratio

so it is usually used in the medium heating capacity and large temperature rise systems. In order to promote water refrigerant to be wildly used in production and livelihood field

researching and developing practicable compressors for different usage occasions and steam requirements is an interesting and significant research project in future.