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Properties of commonly used refrigerants in supermarket refrigerated showcase
Properties of commonly used refrigerants in supermarket refrigerated showcase
1) Ammonia, a commonly used refrigerant in supermarket refrigerated showcase, symbol is R717, chemical formula is NH3, standard boiling point -33.4℃, freezing temperature -77.7℃ . Ammonia is flammable and explosive. When the ammonia content in the air reaches 11% to 14% (volume fraction), it can be ignited (yellow flame), and when the content reaches 16% to 25%, it can cause an explosion. In order to prevent explosions, exhaust temperature and pressure must be limited, and water cooling measures must be taken to the cylinder. In addition, the ammonia refrigeration system in the supermarket refrigerated showcase must be equipped with an air separation device to remove the air and other non-condensable gases in the system in time. Ammonia is highly toxic, colorless, and has a strong irritating odor; when the content of ammonia in the air (volume fraction) reaches 0.5% to 0.8%, it will cause serious damage to the human body. Therefore, ammonia vapor in the working area of the supermarket refrigerated showcase The mass concentration shall not exceed 0.02mg/L.
Ammonia and water can be miscible in any ratio. The formed ammonia solution will not precipitate from ammonia at low temperatures. Therefore, the ammonia refrigeration system in the supermarket refrigerated showcase may not be installed in the dryer, but the ammonia solution will increase metal corrosion, and the evaporation temperature will be slightly Therefore, the mass fraction of water content in ammonia solution cannot exceed 0.2%. Ammonia is not easy to dissolve in the lubricating oil. In order to reduce the lubricating oil from entering the supermarket refrigerated showcase condenser and evaporator, so as not to affect the heat transfer effect, the supermarket refrigerated showcase ammonia refrigeration device must be equipped with an oil separation device, and in the condenser and evaporator And the bottom of the reservoir is provided with an oil drain hole to drain the oil regularly. Pure ammonia does not corrode steel, but it corrodes zinc, copper and other alloys when it contains water, except for phosphor bronze, so copper and copper alloys are not allowed in supermarket refrigerated showcase ammonia refrigerators, and only high tin phosphor bronze can be used when necessary. The unit volume of ammonia cooling capacity qv is larger than R12 and R22, so when the cooling capacity is the same, the volume of the supermarket refrigerated showcase ammonia refrigerator is smaller, and the price of ammonia is the cheapest. Ammonia has a moderate working pressure and is one of the most widely used supermarket refrigerated showcase medium temperature refrigerants. Especially suitable for large piston, rotary and centrifugal supermarket refrigerated showcase refrigerators, which can be used in ice making, cold storage, chemical industry and other industries. However, it is toxic, so ventilation safety must be paid attention to. When looking for leaks, you can apply soapy water to the joints and welds. If bubbles are generated, it means that there is leakage. You can also use litmus paper or phenolphthalein paper. If there is ammonia leakage, the litmus paper turns from red to blue. The phenolphthalein test paper turns rose red.
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