Cascade Compression Refrigeration Working Principle
Oct 15, 2025
Cascade compression refrigeration mainly consists of two independent refrigeration cycles and a heat exchanger connected to them. The high-temperature stage recycles medium-temperature refrigerants, high-temperature stage compressors, high-temperature stage condensers, expansion valves, and evaporative condensers. The low-temperature stage recycles components such as low-temperature refrigerants, low-temperature stage compressors, and expansion valves.
The work mainly includes four processes: compression, condensation, throttling and evaporation.
Low-temperature stage cycle: The low-temperature refrigerant is compressed in the low-temperature stage compressor, with its pressure and temperature increasing. The high-temperature and high-pressure low-temperature refrigerant vapor then enters the evaporative condenser. Here, it is not cooled by ambient air or cooling water, but by the refrigerant liquid that evaporates and absorbs heat in the high-temperature stage cycle, thereby releasing heat and condensing into a high-pressure liquid. This is the core of the cascade system! Subsequently, the high-pressure low-temperature refrigerant liquid passes through the low-temperature stage throttling valve, where the pressure drops sharply, transforming into a low-temperature and low-pressure gas-liquid two-phase mixture. This gas-liquid mixture enters the low-temperature stage evaporator, absorbing the heat of the object to be cooled (such as the heat inside the freezer), and completely evaporates into low-temperature and low-pressure vapor, thereby achieving the purpose of refrigeration. The low-temperature and low-pressure vapor after evaporation is once again drawn into the low-temperature stage compressor to complete the cycle.
2. High-temperature stage cycle: The high-temperature refrigerant is compressed in the high-temperature stage compressor, with its pressure and temperature increasing. The high-temperature and high-pressure refrigerant vapor enters the condenser (usually cooled by air or water), releasing heat to the ambient medium and condensing into a high-pressure liquid. The high-temperature refrigerant liquid under high pressure passes through the high-temperature stage throttling valve, causing a sudden drop in pressure and transforming into a medium-temperature and low-pressure gas-liquid two-phase mixture. The mixture enters the evaporative condenser, absorbing the heat released by the refrigerant vapor from the low-temperature stage cycle (i.e., serving as the cold source for the low-temperature stage), and evaporates into low-pressure vapor. The low-pressure vapor after evaporation is once again drawn into the high-temperature stage compressor to complete the cycle.
Cascade refrigeration can reach a temperature range of -60°C to -150° C. Each stage of the cycle operates within its own reasonable compression ratio range, ensuring high compressor efficiency and reliable operation. Compared with the single-stage cycle that barely achieves low temperatures, the cascade system has a higher energy efficiency ratio under the design conditions.
At the same time, it avoids problems such as excessively high exhaust temperature and deterioration of lubricating oil in single-stage systems at high compression ratios, and enables the selection of the most suitable refrigerants for the temperature zones of the high and low-temperature stages respectively.
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