General properties of refrigerants and requirements
a, refrigerant thermodynamic properties of
refrigerant in the refrigeration system is often in the two-phase region or close to saturation state.
2, chemistry, safety and environmental properties of refrigerants
2. 1, the thermal stability of the refrigerant
under certain conditions, the refrigerant heating temperature decomposition will happen, but in under normal operating conditions of refrigeration, due to the working temperature below the decomposition temperature of refrigerant, refrigerant is thermal stability. High used as refrigerant in the refrigeration system actual control temperature is affected by the kinds of working condition of cooling and lubricating oil, compressor materials and other factors limit.
2。 2, refrigerant and water solution
is not the same as the different refrigerant water soluble. Of aqueous ammonia soluble in water, generated by the freezing temperature is lower than 0 ℃, so in the ammonia refrigeration system by ice jams cooling pipe, but will contact with metal material corrosion. Halogenated hydrocarbon and hydrocarbon refrigerants is difficult to dissolve in water, when the refrigerant water content more than solubility, there will be free of water; When the cooling temperature is lower than 0 ℃, free water will throttle body channel ice jams. Hydrolysis happens after water dissolve refrigerants, generate acid, corrosion of metal materials, reduce the winding of electric insulation performance. In refrigeration system, therefore, does not allow to have the free water, generally set dryer in the system.
2。 3, refrigerant and oil solubility
different refrigerant liquid and the lubricating oil solubility is different, the same refrigerant oil with different solubility is different also, some complete miscibility, sometimes almost insoluble, dissolve and some parts.
in the refrigeration temperature range, and R717 R744 almost insoluble in mineral oil; R22, R152a, r114 miscibility with mineral oil part, they are in high temperature with complete miscibility, lubricating oil at low temperature stratification, a layer of oily, less a layer of oil. R11, R21, R500 complete miscibility with mineral oil, the formation of homogeneous solution. Everything with polyol esters ( POE) Synthetic lubricants are mutually soluble, and mineral oil is difficult to dissolve.
note: the refrigeration system of the lubricating oil is in liquid state, when the refrigerant and oil miscibility, its advantage is evaporating temperature is stable, and refrigerant in the refrigeration equipment and lubricating oil is divided into two layers, so easy to separate; Defect is in heat exchanger heat transfer surface, can form inhibit heat transfer oil film. When coolant and lubricant miscibility, won't form the oil film on the surface of the heat transfer. Lubricating oil can be infiltrated with refrigerant compressor parts, forming good lubrication conditions. However, attention should be paid to dissolve refrigerants lubricating oil viscosity decreases, the phenomenon such as evaporation temperature rises under the same pressure
2. 4, refrigerant effect on metal and nonmetal
ammonia for steel corrosion effect, the corrosion of copper, aluminum or copper alloy has a slight effect. But if the ammonia water, for copper and copper alloy ( In addition to the phosphor bronze) Have strong corrosion effects. Halogenated hydrocarbon non-corrosive effect of almost all metals, only for magnesium and magnesium are more than 2% of the aluminum alloy from corrosion. Halogenated hydrocarbon in the case of water will be hydrolyzed into acidic substances, have corrosion effect on metals. Therefore, water cut and oil mixture as refrigerant in the can dissolve copper. Halogenated hydrocarbon refrigerants is a good organic solvent, it is easy to dissolve the natural rubber and resin, polymer materials become soft. Inflation or bubbles. So, in the selection of refrigerating machine sealing materials and electrical insulation materials, without the use of natural rubber, resin compound, and to use halogenated hydrocarbon corrosion resistant chloroprene, chloroprene rubber, nylon, plastic and other materials. Hydrocarbon refrigerants without corrosion of metal material.
note: plating steel phenomenon: when the refrigerant in the system, when in contact with copper or copper alloy copper will be dissolved in the mixture, and then deposited on the higher temperature of steel components, form a layer of copper film, this is the so-called phenomenon of steel plating. Copper plating phenomenon in compressor crankshaft bearing surface, such as bright and clean surface of the suction and discharge valves in a particularly evident. It will affect the movement of the compressor parts fit clearance, and suction exhaust valve seal, serious when the compressor cannot work normally.
2。 5, electrical insulation of refrigerant
in closed compressor, motor coil, direct contact with refrigerator requirements refrigerant should have good electrical insulating properties. Said electric breakdown strength of refrigerant electrical insulating performance of an index. Worth mentioning is the presence of impurities, lubricating oil of the refrigerant electrical insulating strength will be reduced.
2。 6, the safety of the refrigerant
security including toxic and combustible.
2。 7, environmental performance and indicators
ozeme depletion potential ozone consumption ozeme depletion potential and global warming, overall atmospheric greenhouse effect value, life, life of climatic performance. 。
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