Principle of heat pump-The refrigerant-Freon

② Freon-12 (code: R12)

     R12 is a halogenated substance of an alkane, the scientific name is difluoromethylene chloride, and the molecular formula is CF2Cl2.It is a medium-pressure medium temperature refrigerant widely used in small and medium-sized refrigeration equipment in China.The standard evaporating temperature of R12 is -29.8 ° C, thecondensing pressure is generally 0.78 to 0.98 MPa, the solidification temperature is -155 ° C, and the standard cooling capacity per unit volume is about 288 kcal / m 3 .

      R12 is a colorless, transparent, odorless, almost non-toxic, non-flammable, non-explosive, safe refrigerant.When the air volume concentration exceeds 80%, it will cause suffocation and death.When exposed to an open flame or at temperatures above 400 °C, R12 releases gases harmful to humans.

     R12 is miscible with any proportion of lubricating oil and can dissolve various organic substances, but its water absorption is extremely weak.Therefore, there is no oil separator in the small freon refrigeration unit, and a dryer is installed.At the same time, it is stipulated that the water content in R12 should not exceed 0.0025%. Generally, natural rubber should not be used as sealing gasket in the system, but artificial rubber such as nitrile rubber or chlorohydrin should be used.Otherwise, the gasket may expand and cause refrigerant leakage.

③ Freon-22 (code: R22)

    R22 is also a halogenated substance of an alkane, the scientific name is difluorochloromethane, and the molecular formula is CHClF2.The standard evaporating temperature is about -41 ° C, the solidification temperature is about -160 ° C, the condensing pressure is similar to that of ammonia, and the standard cooling capacity per unit volume is about 454 kcal/m 3 .

    Many properties of R22 are similar to those of R12, but the chemical stability is not as good as R12, and the toxicity is slightly larger than R12.However, R22's unit volume cooling capacity is much larger than R12, close to ammonia.When the temperature requirement is -40 to -70 °C, R22 is more suitable than R12, so R22 is widely used in the two-stage compression or air conditioning refrigeration system of -40 to -60 °C.