Selection of compressors for high and low temperature test chambers | Analysis of refrigerant tolerance and start stop tolerance under alternating temperature conditions
The high and low temperature test chamber needs to achieve rapid alternation between -40 ℃ and 85 ℃, with a cooling rate of 0.5~3 ℃/min. Generally, a two-stage semi closed compressor is used to build a cascade or two-stage compression refrigeration circuit.
Under alternating working conditions, the compressor frequently starts and stops, with a maximum of 12 starts and stops per hour. The motor insulation level should not be lower than Class F, withstand a temperature of 155 ℃, and reduce the rate of thermal aging.
The Xitelide two-stage semi closed piston compressor is suitable for small and medium-sized high and low temperature test chambers. With R404A and R23 cascade scheme, it can stably achieve ultra-low temperature test environments below -70 ℃.
The internal air duct of the test chamber has a high heat transfer density, and the heat transfer margin of the evaporator needs to be increased by 35%. During the rapid cooling stage, the heat load is instantly increased to avoid a significant drop in suction pressure causing protective shutdown.
The discharge pressure of the compressor will significantly increase during high-temperature testing. When the condensation temperature is 40 ℃, the upper limit of the pressure on the high pressure side of R404A is controlled at 19 bar. Long term overpressure will accelerate seal aging.
The export of high and low temperature testing equipment is mainly for industrial customers, and foreign trade procurement focuses on verifying voltage and frequency. The winding design of 460V/60Hz motor models in the European and American markets and the 50Hz version are not interchangeable.
The loss rate of valve plates in the test chamber compressor is higher than that of cold storage equipment. Under frequent alternating impacts, the inspection cycle of valve plates is shortened to 5000 hours. If abnormal noise occurs, it needs to be disassembled and inspected.
Many experimental equipment manufacturers easily confuse cryogenic compressors with ordinary cryogenic compressors. Single stage cryogenic compressors cannot maintain stable and rapid cooling below -40 ℃, with a cooling rate of less than 0.3 ℃/min.
The amount of refrigerant oil added must strictly follow the nameplate. If the amount exceeds the standard by more than 12%, excess oil will enter the air duct evaporator and adhere to the inner wall, reducing heat transfer efficiency.
The long tail demand of this track is concentrated in small-scale OEM manufacturing, and refrigeration unit factories support adjusting interface dimensions according to the drawings of the test chamber manufacturer to match the existing box pipeline layout.
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FAQ
What is the standard cooling rate range for high and low temperature test chambers? The common indicator range is 0.5 to 3 ℃ per minute.
What is the minimum requirement for the insulation level of the compressor in the test chamber? Suggest not lower than F grade and withstand 155 ℃.
3. Which two refrigerant combinations are generally used in the cascade scheme? R404A is commonly used in combination with R23 to achieve ultra-low temperature range.
How much shorter is the valve inspection cycle compared to cold storage units? It is recommended to inspect the valve disc for 5000 hours under alternating working conditions.
What are the consequences of adding too much refrigerant oil? Exceeding 12% can easily cause oil accumulation and poor heat transfer in the evaporator.
6. Can a single-stage low-temperature function achieve a cooling rate of 0.5 ℃ per minute? It's difficult, the cooling rate in the -40 ℃ range is insufficient.
What are the key points for confirming the voltage of the compressor in the export test box to Europe and America? Confirm whether it is the 50Hz or 60Hz power supply version.
