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The refrigerant Freon in the display cases (2)
author: supermarket refrigerated showcase category: walk-in display coolers Views: 564Time: 2016-08-22
The refrigerant Freon in the display cases
The substitutes for R12 in the display cases are R134a, R152a and R600a.
R12 is the first refrigerant that appeared, used in large quantities, and has excellent performance, but it is not accepted by the environment now. The current substitutes for R12 are R134a and R600a, and possible substitutes are R152a. The ODP of R134a is O, GWP is 1430, the standard evaporation temperature is 26.2℃, and the freezing point is 101.0℃. Its refrigeration cycle characteristics are close to R12, the flow resistance loss is larger than R12, and the heat transfer performance is better than R12. In terms of oil solubility, R134a and R12 are very different in oil-soluble type and oil-soluble behavior. R134a has very little solubility in non-polar oils, such as mineral oil and alkylbenzene oil. Synthetic oils specially developed for R134a are mainly polyenol oils AGs (POlyalkylene), ester-based oils (Ester) and amino oils (Amides). Although R134a is mutually soluble with them, the dissolution characteristics are unusual: there are two dissolution critical curves, so that there is a layered zone in the high temperature zone and the low temperature zone. The solubility in the high temperature zone decreases with increasing temperature. This feature makes it difficult for the system to operate in a wide temperature and pressure range. The application of R134a/PAGs oil in automobile air conditioning systems shows that there is no stratification in the low-temperature side evaporator, but stratification occurs in the high-temperature side condenser, making R134a white turbid . But stratification does not affect the discharge pressure and cooling capacity. R134a does not contain Cl in its molecule and does not have lubricity by itself. Insufficient oil supply for the moving parts of the
machine will increase wear and even cause sintering. For this reason, it is necessary to add additives to synthetic oils to improve lubricity. In addition, it is necessary to improve the material and surface characteristics of moving parts, and improve the oil supply mechanism. R134a has a slightly stronger swelling effect on non-metallic materials than R12. PAGs/R134a can use hydrogenated nitrile rubber. The traditional CFC electronic leak detector is not sensitive to the reaction of R134a.
refrigerated showcase display cases A new type of fluorocarbon refrigerant leak detector has been produced, with a leak detection sensitivity of 10.6×10'-6Nml/s for R134a (corresponding to an annual leakage of 1..5g/ years). The greenhouse effect index of R134a is 1430. In the long run, it will be replaced. The ODP of R152a is 0, GWP is 124, and the security level is A2. In terms of environmental acceptability, it is better than R134a. R152a is a polar compound, and its compatibility with lubricating oil is similar to R134a. Its disadvantage is that it is highly combustible. R152a will catch fire when its volume concentration in the air reaches 4.5% to 2.21.8%. When the volume concentration is 10.5%, the minimum combustion value of R152a is 0:6mJ, which is about 10 times the ammonia combustion value. The standard evaporating temperature of R152a is -25℃, and the refrigeration cycle characteristics are better than that of R12d. Because it is flammable, R152a should be used. There are good security measures. In addition to R134a and R152a, based on standard boiling point considerations, freons that may replace R12 also include R124 and R134. But the research and development work on them is far less than R134a. The theoretical cycle characteristics of these substances at 50℃/-15℃. From the data in the table, the cycle indicators of these substitutes are compared as follows: COP from large to small is: R152a, R134, R124,R134a. SCD from small to large is: R152a, R134a, R134, R124; the pressure ratio from small to large is: R152a, R134a, R134, R124. R600a is a hydrocarbon, which exists in nature, with GWP=20 and safety level A30. R600a is miscible with mineral oil, is low in price and easily available, and can be directly filled into devices using R12. Because it is flammable, it is mainly used in refrigeration devices with a small charge, such as household display cases for refrigeration and freezing.
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