The constant temperature and humidity test chamber uses a cascade refrigeration cycle system at a low temperature of 20 ° C or lower, while the -40 ° C model uses a single-stage refrigeration cycle, or a cascade refrigeration cycle system, but a single-stage refrigeration cycle. It is achieved by adjusting the opening degree of the expansion valve of the small compressor and reducing the flow restriction of the refrigerant to lower the evaporation pressure to obtain a lower evaporation temperature. This design is achieved by sacrificing the cooling capacity of the system, resulting in refrigeration. The efficiency is low and the load of the compressor is increased, and the compressor coil is easily overheated, which affects the life of the compressor.
The minimum evaporation temperature of a single-stage vapor compression refrigerator in a constant temperature and humidity test chamber depends mainly on its condensing pressure and compression ratio. The condensing pressure of the refrigerant is determined by the type of refrigerant and the temperature of the environmental medium. Any refrigerant, evaporation The lower the temperature, the lower the evaporation pressure. The too low evaporation pressure may sometimes make it difficult for the compressor to inhale or allow outside air to enter the refrigeration system.
The compression ratio of the constant temperature and humidity test chamber is related to the condensing pressure and the evaporation pressure. When the condensing pressure is constant, as the evaporation temperature decreases, the evaporation pressure also decreases accordingly, thus increasing the compression ratio, which will cause the compressor discharge temperature to rise. High, the lubricating oil is thinned, the lubrication condition is deteriorated, and even in the case of serious carbonization and cylinder pulling phenomenon; on the other hand, the increase of the compression ratio will result in a decrease in the gas transmission coefficient of the compressor, a decrease in the cooling capacity, and an actual compression process. The farther away from the isentropic process, the higher the compressor power consumption, the lower the cooling coefficient, and the lower the economy. The following effects will occur.
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