[Experience] Constant temperature and humidity box refrigeration system

[Experience] Constant temperature and humidity box refrigeration system Constant temperature and humidity box refrigeration system: 1 Two single-stage refrigeration system cascade refrigeration cycle; 2 Cascade refrigeration cycle of two-stage compression system; 3 ternary cascade refrigeration cycle. Use-On the 20th, the Northeast low temperature cascade refrigeration cycle system. The reasons for low temperature and the use of two-stage compression cascade refrigeration cycle: The refrigerant thermophysical properties of the refrigerant at the temperature of the medium; 1 Constant temperature is limited. R404A is basically used for the single-stage refrigeration cycle of the constant humidity box. The evaporation temperature in the atmosphere is -46.5℃ (R22/-40.7℃), but the temperature difference of heat transfer of the air-cooled condenser usually requires about 10℃ ( In the thermal cycle of the forced air source, the temperature on the evaporator and inner box) is the only production low temperature -36.5℃, of course, the compressor through the reduction of the evaporation pressure can be reduced, the refrigerant with the lowest evaporation temperature R404A is- About 50℃, so to get -50, NE and below, you must use low-temperature refrigeration cycle to prepare the cascade of low-temperature refrigerant refrigerant, -50, NE-80, NE low-temperature, low-temperature R23 refrigerant is generally used in high-pressure evaporation The temperature is -81.7°C. 2 The pressure of the single-stage vapor compression refrigeration cycle is lower than the minimum evaporation temperature limit of the single-stage vapor compression refrigerator, and the condensing pressure mainly depends on its compression ratio. The refrigerant of the condensing pressure refrigerant, which is determined by the category and the temperature of the environmental medium (such as air or water), is generally in the range of 0.7~1.8MPA. In the compression ratio and condensing pressure and evaporating pressure, the condensing pressure is constant, and the evaporating temperature is reduced, the evaporating pressure is reduced, so that the increase of the compression ratio will lead to the increase of the compressor discharge temperature, the lubricating oil becomes thinner Conditions, even under severe coking and gluing phenomena; on the other hand, an increase in the compression ratio will lead to a reduction in the transmission coefficient of the gas compressor, which reduces the cooling capacity. The farther the actual deviation from the isentropic compression process, the lower the cooling coefficient. The energy consumption reduces the economy. There will be a certain impact. A. The evaporation temperature of any refrigerant decreases, and the evaporation pressure is lower. If the evaporating pressure is too low, the compressor may be sucked in, or outside air may enter the refrigeration system. B. When the evaporating temperature is too low, some commonly used refrigerants have reached the solidification temperature and cannot achieve the flow and circulation of the refrigerant. C. The evaporation pressure is lower than the volume increases, the refrigerant, the mass flow of the refrigerant decreases, and the cooling capacity is greatly reduced. In order to obtain the required refrigeration capacity, the suction volume of the compressor must be increased, which is too large. 3 The heat dissipation of the compressor coil limits the operation of the single-stage compressor. When this is done at -35℃, the coil of the rotary air compressor of the compressor is in the middle, which will cause a problem. At -35℃, the compressor pressure It is a negative value, which will form a vacuum, so that the top of the coil heat transfer cannot be dispersed, so that the surface of the compressor is very cool, but in fact, his temperature is very high, (because the vacuum insulation medium is the best Yes)! From the visible light: constant temperature and humidity box, then the model at -40 ℃ can be used in a single-stage refrigeration cycle circuit, can also be used in a cascade refrigeration cycle system, but the single-stage refrigeration cycle is reduced by the opening of the expansion valve For small compressors, the refrigerant flow is limited to reduce the evaporating pressure (0.7 atm) to obtain a lower evaporating temperature. This design sacrifices the cooling capacity of the system (the cooling capacity is only about 0.7~0.8), thus It leads to low efficiency and increases the cooling load of the compressor, and it is also easy to cause the compressor coil to overheat, affecting the service life of the compressor