Refrigerant
Release time:
2024-06-03
Refrigerants are classified according to their components, including pure refrigerant and mixed refrigerant.
According to the chemical composition, there are mainly inorganic, freon and hydrocarbons.
| Category | Examples | |||
| Pure refrigerant | inorganic compound | R702（H2）、R704(He),R717(NH3),R744(CO2) | ||
| HC | hydrocarbon refrigerant | R600a,R290,R1270(Propylene) | ||
| Freons and alkanes | CFC | There are only chlorine, fluorine, carbon atoms, which are called chlorofluorocarbons. | R11,R12,R113Wait | ODPHigh value |
| HCFC | In addition to chlorine, fluorine, carbon atoms in the molecule, there are hydrogen atoms, called hydrochlorofluorocarbons | R22,R123,R124Wait | ||
| HFC | There are no chlorine atoms in the molecule, but hydrogen atoms, fluorine atoms and carbon atoms, called hydrofluorocarbons. | R134a,R32,R125,R152a,R143aWait | PartGWPhigher value, need to be replaced gradually | |
| HFO | Hydrocarbon fluorine composition of olefins. | R1234yf,R1234ze | Because it is an olefin, the general life is shorter and the harm is smaller. | |
| mixed refrigerant | ||||
| Azeotropic mixed refrigerant | The temperature does not change when the phase change occurs. | R5XX | ||
| non-azeotropic refrigerant mixtures | The temperature changes continuously when the phase change occurs | R4XX | With temperature slip | |
Considerations when selecting refrigerants
1. Environmental acceptability. ODP and GWP values comply with relevant laws and regulations.
2. The thermal properties meet the specified usage requirements. Including pressure-pressure ratio moderate; unit volume & unit mass refrigeration capacity; exhaust temperature is not high, isentropic compression specific work small; high COP.
3. Good heat transfer and fluidity.
4. It is non-toxic, has no pungent odor, does not ignite or explode, and is safe to use.
5. The price is cheap and the source is wide.
Refrigerants that meet the above conditions in all aspects are difficult to find, and the corresponding refrigerant should be selected according to the use scenario, system characteristics, and compressor characteristics. The ODP and GWP values are the constraints of laws and regulations, and meeting the environmental impact index is the premise for all refrigerants to be put into use.
Standard boiling point and critical temperature
Requirements: low standard boiling point, high critical temperature. Can adapt to a wider range of applications, that is, lower evaporation temperature, higher condensation temperature.
For any working fluid, the closer the condensation temperature is to the critical temperature, the lower the latent heat of liquefaction, the greater the dryness after throttling, the greater the throttling loss (entropy loss), and the smaller the latent heat of evaporation. Therefore, the vapor compression refrigeration cycle should be far from the critical point.
The saturated vapor pressure of a pure working fluid is a single-value function of the saturation temperature. The above figure shows the saturation temperature-saturation pressure curve of the main refrigerant. (Mixed refrigerant refers to the saturated gas pressure, Vapor Pressure) For the common working temperature, it can be seen from the figure that the refrigerant belongs to low-pressure, medium-pressure, high-pressure refrigerant.
The evaporation temperature of a refrigerant at standard atmospheric pressure (101.3kPaA) is called the normal boiling point, Tn.
The critical temperature is the temperature at which the substance is in the critical point state, Tc. It is the maximum temperature at which the refrigerant can be pressurized and liquefied. Above the critical temperature, the liquid cannot be liquefied by compression.
For most substances, the critical temperature has the following relationship with the standard evaporation temperature:
This indicates that it is not possible to have a refrigerant with both a high critical temperature and a very low standard boiling point. Therefore, for each type of working fluid, the operating temperature range is limited.
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