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Supermarket refrigerated showcase commonly used refrigerants
author: supermarket refrigerated showcase category: commercial refrigeration Views: 566Time: 2016-08-22
At present, there are more than 80 kinds of substances that can be used as refrigerants in supermarket refrigerated showcase, of which only more than 10 are commonly used. The commonly used refrigerants for refrigerators and air conditioners are R12, R22, R502 and environmentally friendly Refrigerant.
1.R12 (CHCI2F2, difluoro=chloromethane)
It is a methane derivative, a medium pressure refrigerant, mainly used in medium and small refrigeration equipment. It is colorless, tasteless, non-flammable, non-explosive, and less harmful to the human body. Under normal circumstances, R12 is non-toxic and has no corrosive effect on metals. It will only decompose phosgene when the temperature is above 400℃ and contact with open flames: if the content of R12 in the air exceeds 25%~30% Time, two hours later, it will suffocate people.
R12 is characterized by being very soluble in oil but not soluble in water, and has strong penetrating power. Dissolving in oil reduces the performance of lubricating oil. It is not easy to dissolve in water. It is easy to freeze the system water and block the regulating valve and pipeline. When freon contains water, it is very corrosive to metals. R12 can also dissolve a variety of organic substances, so normal rubber gaskets cannot be used. R12 has a boiling point of -29.80°C and a freezing point of -1150Cg
2. R12 should be low. R22 is colorless, odorless, non-flammable, non-explosive, and slightly more toxic than R12, but it is still a safe refrigerant. R22 is low in solubility. R22 is colorless, odorless, non-flammable, non-explosive, and slightly more toxic than r22, but it is still a safe refrigerant. r22 is in oil and slightly soluble in water, but it is still insoluble in water.
R22 has similar effects on metals and non-metals as R12, and its leakage characteristics are similar to R12. It also requires high system sealing performance.
3.R502
It is a mixed solution composed of 48.8% R22 and 51.2% R12, the boiling point is -45.6°C, and the operating temperature is -600C~200°C. This kind of refrigerant with a certain boiling point formed by dissolving two or more refrigerants in a certain proportion is called azeotropic solution refrigerant. It has a certain evaporation temperature under a certain pressure, and the composition of the liquid and gas phase is constant.
R502 has the advantages of both R22 and R12. The discharge temperature of the compressor using R502 is about 10℃~15℃ lower than that of R22, and the cooling capacity per unit volume is higher than that of R22. In the case of the same evaporation temperature and condensation temperature, R502The suction pressure is high, the compression ratio of the compressor is small, and the coefficient of refrigeration is large. In low temperature conditions, the cooling capacity of R502 is larger than that of R22: if the evaporating temperature is higher than 0°C, the cooling capacity of R502 is smaller than R22. R502 has worse oil solubility than R22. R502 is mostly used in low-temperature refrigeration systems. If used in a small air conditioner, the refrigeration system must be improved as necessary. Although R502 is more expensive, it has gradually replaced R22 because of its excellent performance.
4. New refrigerant substitute
Because R12, R22 and R502 are all low-chlorinated fluorinated carbon substances, their molecules contain chlorine atoms, which will destroy the ozone layer and cause the chlorine atoms in the earth's molecule 5, 5 The more the number, the stronger the destructive effect. Therefore, the 1992 Copenhagen International Conference stipulated: Developed countries will ban R12 from January 1, 1996, and R22 from January 1, 2020, while the ban period in developing countries allows 10 years to be postponed to find the best CFCs Substitutes are a hot research topic worldwide.
(1) Replacement for R12. There are two more mature types: one is hydrofluorocarbons, represented by R134a; the other is hydrocarbons formed by propane and butane. Some companies in the United States, Japan and my country advocate the use of R134a. This substance does not destroy the ozone layer, is non-toxic, non-flammable, and has similar physical and chemical properties as R12: but it has a global warming greenhouse effect, and it is insoluble in mineral oil. A new ester lubricant compatible with R134a must be used. Oil, and the design of refrigeration components such as compressors and heat exchangers must be modified accordingly. European countries generally advocate the use of hydrocarbon refrigerants. Some use a 50% mixture of propane and butane instead of R12, and some use R600a (isobutane) instead of R12.
(2) Replacement for R22. Hydrofluorocarbons do not destroy the ozone layer. After repeated experiments and screening, it is found that replacing R22 with a mixture of R32/R134a not only has better thermal performance, but also saves energy, and the electrical insulation performance is better than R22, which improves the performance of the supermarket refrigerated showcase. But it only has compatibility with polyester lubricants, and this compatibility is also affected by the type and quantity of additives.
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