High and low temperature test chamber -40 ° C model can be used in a single-stage refrigeration cycle, or a reset refrigeration cycle system, Yashilin high cryogenic test chamber -40 ° C and below It uses a two-machine cooling because the single-stage refrigeration cycle is the expansion valve opening degree of the small compressor, reducing the refrigerant flow rate to lower the evaporation pressure, thereby obtaining a lower evaporation temperature, which affects the compressor The life. At the same time, the single-machine refrigeration has the following limitations:
(1) limitation of single-stage compressed vapor refrigeration cycle pressure
single-stage vapor compression refrigerator ZUI low evaporation temperature, depending on its condensation pressure and compression ratio, the cooling pressure of the refrigerant is determined by the temperature of the refrigerant and the temperature of the environment (such as air or water), in general, it is at 0.7 to 1.8 MPa In the range, the compression ratio is related to the condensed pressure and evaporation pressure, when the condensed pressure is constant, as the evaporation temperature is lowered, the evaporation pressure also decreases, and thus the compression ratio rises, it will cause an increase in the exhaust temperature of the compressor, The lubricating oil is thin, making the lubrication conditions, and even a combine and pull-tuplex phenomenon occurs when it is severe.
(2) Restriction of thermophysical characteristics of refrigerant.
High and low temperature test chamber
The medium temperature refrigerant in medium temperature refrigerant is R404A in a high-temperature refrigerant, and its evaporation temperature is -46.5 ° C under an atmospheric pressure (R22 / 40.7 ° C), but air cooled condenser heat transfer temperature difference usually takes about 10 ° C (under the forced air cooling cycle, the temperature difference of the evaporator and the inner box), that is, only the low temperature of -36.5 ° C in the box, Of course, by lowering the evaporation pressure of the compressor, the ZUI low evaporation temperature of the R404A refrigerant can be lowered to -50 ° C; so it is necessary to obtain a medium temperature refrigerant and a cryogenic refrigerant Refrigeration cycle, a low temperature of -50 ° C ~ -80 ° C, cryogenic refrigerant generally selected R23 which is -81.7 ° C in an atmospheric pressure.
(3) Restrictions on compressor coils
When the single-stage compressor is working, the compressor is around, because the coil of the compressor is inverse In the middle of the compressor, this generates a problem, -35 ° C, the low pressure of the compressor is a negative value, that is, an vacuum, so that the top heat of the coil does not have a way, so that the surface of the compressor is It is very cold, but in practice, his temperature is very high, (because the vacuum is the insulation medium)!