As a natural working medium, CO2 is an important research direction of CFCs working medium substitution. This paper mainly introduces the relevant contents of CO2 refrigeration compressor, and mainly compares the CO2 refrigeration compressor with other compressors, analyzes the advantages of CO2 refrigerant and its comparison with other refrigerants.
At present, CO2 refrigeration compressor has become the research and development object of more and more enterprises. Global compressor manufacturers have successively launched CO2 compressor and provided CO2 solutions for the commercial sector.
CO2 refrigeration compressor are performance characteristics
(1). High efficiency.
Compressor suction, compression, exhaust process continuous one-way, so the harmful overheating of the inhalation gas is small, the pressure difference between the adjacent two Chambers is small, the leakage of gas is small. There is no clearance volume, so there is no expansion process that causes the gas transmission coefficient to drop, and the volume efficiency is high, usually reaching more than 95%.
(2). Less vibration, less noise.
As the suction, compression, exhaust process is continuous at the same time, the pressure rise is slow, so the torque change amplitude is small, small vibration, small noise. The torque is only 1/10 of that of the rolling rotor type and reciprocating.
(3). Simple structure, small size, light weight, high reliability.
The ratio of the number of parts in the compressor chamber to the number of rolling and reciprocating parts is 1:3:7, so the volume is 40% smaller than reciprocating, and the weight is 15% lighter. Because there is no suction, exhaust valve, less vulnerable parts, and there is a flexible mechanism with adjustable axial and radial clearance, can avoid the loss and damage caused by liquid strike, so the operation reliability of the compressor is high. As a result, the refrigeration compressor can maintain high efficiency and high reliability even under high speed operation, and its maximum reporting can reach 13000r/min.
(4). Due to the use of gas support mechanism, it is allowed to take liquid compression, once the pressure in the compression chamber is too high, can make the moving disk and static disk end face off, the pressure can be released immediately.
(5). The inner chamber of the shell is the exhaust chamber, which reduces the suction preheating and increases the gas transmission coefficient of the compressor.
(6). Shape line machining precision is very high, must use special precision machining equipment, and high seal requirements, seal structure complex.
(7). Compressor cooling capacity range is 0.75 ~ 15KW (excluding special models), and most of them are between 3 ~ 5KW, most of which are used in small household air-conditioning, commercial air-conditioning systems. This type of compressor is not used for refrigeration at minus 5 ℃.
CO2 refrigerants properties
CO2 refrigerant (R744) CO2 belongs to the natural working medium, is a colorless, odorless gas at room temperature. The critical temperature and pressure were 31.1 ℃ and 7.37 MPa respectively. As a refrigerating medium, CO2 has many advantages compared with other working medium, which are shown in the following:
First of all, from the perspective of environmental protection, the ODP of C02 is 0 and the GWP is 1, which is far less than that of CFCs and HFCs. Moreover, most of the CO2 used in practice is chemical by-products. Using CO2 as refrigerant is equivalent to delaying the emission of these exhaust gases, which is beneficial to the environment. Therefore, C02 is an environmentally friendly working medium.
Secondly, from the perspective of the thermophysical properties of the working medium, CO2 is suitable for the refrigeration cycle and equipment. This is mainly manifested in:
The latent heat of CO2 evaporation is large, and the refrigerating capacity per unit volume is high (up to 22.6 MJ/m3 at 0℃), which is about 5 ~ 8 times that of traditional refrigerants.
The motion viscosity of CO2 is small, and at low temperature is also very small.
The thermal conductivity is high, the ratio of liquid density to vapor density is small, the refrigerant can be distributed evenly between the circuits after throttling. These excellent flow and heat transfer properties of CO2 can significantly reduce the size of the compressor and system, making the whole system very compact.
In addition, CO2 is stable in chemical properties, non-toxic, harmless and non-flammable, and will not decompose toxic gases at high temperature. Moreover, CO2 is cheap, easy to obtain and has excellent economy.
The main disadvantages of CO2 as a refrigerant are its low critical temperature (31.1 ℃) and high critical pressure (7.37 MPa). In particular, if the latter is adopted, the working pressure of CO2 refrigeration system can reach up to 10 MPa, which brings many new requirements to the design of system and components.