Let's continue the discussion on the last topic--Refrigeration Technology Of Constant Temperature And Humidity Test Chamber.
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(2) Limitation of thermal physical properties of the refrigerant
The medium temperature refrigerant used in the single-stage refrigeration cycle in the constant temperature and humidity chamber is R404A. The evaporation temperature is -46.5 °C (R22/-40.7 °C) at one atmosphere, but the heat transfer temperature difference of the air-cooled condenser is usually taken. Around 10 °C (in the forced air cooling cycle, the temperature difference between the evaporator and the inner box), that is, the box can only produce a low temperature of -36.5 ° C, of course, by lowering the evaporation pressure of the compressor, R404A can be cooled The minimum evaporation temperature of the agent is reduced to -50 ° C; therefore, to obtain a low temperature of -50 ° C and below, it is necessary to use a medium-temperature refrigerant and a low-temperature refrigerant cascade refrigeration cycle to obtain a low temperature of -50 ° C to -80 ° C, Low-temperature refrigerants are generally R23 which has an evaporation temperature of -81.7 ° C at one atmosphere.
(3) Restriction of heat dissipation of the compressor coil When the single-stage compressor is working, it is about -35 °C, because the coil of the compressor is swirled in the middle of the compressor, which causes a problem, at -35 ° C, the compressor The low pressure is a negative value, that is, a vacuum is generated, so that there is no way to dissipate the heat at the top of the coil, so the surface of the compressor is very cool, but actually the internal temperature is very high (because Vacuum is the best insulation medium).