China currently mainly produces and consumes 7 controlled substances including Freon-12, Freon-11, Freon-113, Halon-1211, Halon-1301, carbon tetrachloride, 1,1,1-trichloroethane, etc.:

1、Freon is a transparent, odorless, non-toxic, non flammable, explosive and chemically stable refrigerant. Freon refrigerants with different chemical composition and structure have different thermodynamic properties, which can be applied to high temperature, medium and low temperature  refrigerating machine to meet the requirements of different refrigeration temperatures.

2、Freon has low solubility in water, and acidic substances will be generated when moisture enters the refrigeration device, and it is easy to cause "ice blockage" in the low-temperature system and block the throttle valve or pipeline. In addition, to avoid the effect of Freon and natural rubber, the device should use nitrile rubber as gasket or sealing ring.

3、Commonly used Freon refrigerants are R12, R22, R502 and R134a, because other types of refrigerants are now deactivated or banned. No explanation here.

4、Freon 12 (CF2CL2, R12): Freon refrigerant is one of the most widely used refrigerants. It is widely used in refrigeration devices such as medium and small food storage, household refrigerators, and water and road refrigeration transportation. R12 has good thermodynamic properties, low refrigeration pressure, air-cooled or natural condensation pressure is about 0.8-1.2KPa. The standard evaporating temperature of R12 is -29°C, which is a medium-temperature refrigerant. It can be used in medium and small piston compressors to obtain a low temperature of -70°C. For large centrifugal compressors, a low temperature of -80℃ can be obtained. In recent years, the alternative refrigerant for refrigerators is R134a.

5、Freon 22 (CHF2CL, R22): It is one of the most widely used Freon refrigerants, mainly used in household air conditioners and low-temperature refrigerators. The thermodynamic properties of R22 are similar to ammonia. The standard vaporization temperature is -40.8°C, and the condensation pressure usually does not exceed 1.6MPa. R22 is non-flammable, non-explosive, safer and more reliable than ammonia in use. The unit volume of R22 is about 60% higher than that of R12, and its cooling capacity and saturation pressure per unit volume at low temperatures are higher than those of R12 and ammonia. In recent years, most of the refrigerants of large air-conditioning chillers have been replaced by R134a.

6、Freon 502 (R502): R502 is an azeotropic solution of 51.2% and 48.8% mixed with R12 and R22. Compared with R115 and R22, R502 has better thermodynamic properties and is more suitable for low temperature. The standard evaporation temperature of R502 is -45.6℃, and the normal working pressure is similar to that of R22. The cooling capacity per unit volume under the same working conditions is larger than R22, but the exhaust temperature is lower than R22. R502 is used in fully enclosed, semi-enclosed or some medium and small refrigeration equipment, and its evaporation temperature can be as low as -55℃. R502 is used more in refrigerators.

7、Freon 134a (C2H2F4, R134a): is a relatively new type of refrigerant with an evaporation temperature of -26.5°C. Its main thermodynamic properties are similar to R12, and it will not destroy the ozone layer in the air. It is an environmentally friendly refrigerant advocated in recent years, but it will cause the greenhouse effect. It is an ideal R12 alternative refrigerant.

8、The relationship between Freon and water: Freon and water are almost completely insoluble in each other, and their solubility in water is extremely small. The water entering the device from the low temperature side is in the state of water vapor. It is compressed together with the freon vapor and enters the condenser, and then condenses into liquid water. The water is mixed with the freon liquid as droplets, and freezes at the expansion valve due to low temperature. Ice blocks the valve and makes the refrigeration unit not work properly. Moisture can also hydrolyze Freon to produce acid, causing "copper plating" in the refrigeration system.

9、The relationship between Freon and lubricating oil: Generally, it is easily soluble in refrigerating oil, but at high temperatures, Freon will decompose from the refrigerating oil. Therefore, there are heaters in the oil tank of the large-scale water chiller, which are kept at a certain temperature to prevent the dissolution of Freon.

In actual production operations, when the system leaks or is upgraded or improved, a refrigerant recovery machine must be used to extract all refrigerant and oil, and special filters and oil separators are used. Separate and remove oil and various impurities, realize the reuse of refrigerant, environmental protection and economy.