Influence of evaporator distance of air cooler and frosting

As a common evaporator in refrigeration system, whether the air cooler is properly selected directly affects the efficiency of refrigeration system. As we all know, the air cooler will adopt different fin spacing according to the required ambient temperature.

Our common air coolers have fin spacing of 4mm, 4.5mm, 6~8mm, 10mm, 12mm, and variable fin spacing before and after. Small fin spacing, suitable for high temperature environment; The lower the cold storage temperature, the larger the fin spacing is needed. If the selection is unreasonable, the fins will frost quickly, which will soon block the wind passage, make it difficult to cool the cold storage, and the compressor efficiency will not be brought into play, resulting in an increase in power consumption of the refrigeration system.

According to the engineering experience, generally, in the environment of 0℃~20℃, such as workshop air conditioning, cool storage, cold storage hall, fresh-keeping storage, controlled atmosphere storage, ripening storage, etc., air coolers with a spacing of 4mm or 4.5mm are selected; In the environment of -16℃~-25℃, such as low-temperature freezing and cold storage, low-temperature logistics warehouse, choose air coolers with a spacing of 6mm~8mm; For quick-frozen warehouses at -25℃~-35℃, air coolers with 10mm and 12mm blade spacing are generally selected. If the quick-frozen goods have high humidity, air coolers with variable blade spacing will be selected, and the fin spacing on the air inlet side can reach 16 mm.

However, in some occasions, it is impossible to choose the fin spacing of the air cooler simply according to the temperature, such as the rapid precooling and acid discharge of meat and vegetables. Although the temperature in the cold room is generally set above 0℃, because the incoming temperature is high, the cooling speed is fast, and the humidity of the goods is high, it is not appropriate to choose an air cooler with a chip spacing of 4mm or 4.5mm, so it is necessary to use an air cooler with a chip spacing of 8mm or even 10 mm.

There are also fresh-keeping warehouses similar to those for storing garlic, apples and other fruits and vegetables. The suitable storage temperature is generally at -2℃. For fresh-keeping or controlled atmosphere warehouses with storage temperature lower than 0℃, it is also necessary to choose air coolers with a spacing of not less than 8mm to avoid air duct blockage and power consumption increase caused by rapid frosting.

Influence of frost on refrigeration system：

When the refrigeration system of cold storage is running normally, the surface temperature of evaporator is much lower than the dew point temperature of air, and the moisture in the air will precipitate and condense on the pipe wall. If the pipe wall temperature is lower than 0, water dew will condense into frost. Frosting is also the result of the normal operation of the refrigeration system, so a small amount of frost is allowed on the evaporator surface.

Because the thermal conductivity of frost is too small, it is one percent or even several hundred percent of that of metal, so the frost layer forms a large thermal resistance. Especially when the frost layer is thick, it is like heat preservation, which makes the cold energy in the evaporator difficult to radiate, affects the refrigeration effect of the evaporator, and finally makes the cold storage fail to reach the required temperature. At the same time, the evaporation of refrigerant in the evaporator should also be weakened, and the refrigerant that is not completely evaporated may be sucked by the compressor and cause liquid hammer accidents. Therefore, we must try to remove the frost layer, otherwise the frost layer will become thicker and thicker, and the refrigeration effect will become worse and worse.