Double stage semi closed compressor | Pressure ratio control scheme for deep cold working conditions in -60 ° C cold storage.
The double stage semi closed compressor splits the total pressure ratio into two stages, with a single-stage pressure ratio control of ≤ 3.5, achieving stable operation in -55 ° C to -65 ° C -60 ° C cold storage.
The two-stage semi closed compressor consists of a low-pressure stage and a high-pressure stage piston cylinder connected in series, with a cooling circuit added in the middle to reduce the intake temperature of the high-pressure stage. Under the evaporation condition of -60 ℃, the volumetric efficiency is maintained at over 54%. This model is mostly used for quick freezing tunnel matching. The minimum recommended thickness for the insulation layer of a cold storage at minus 60 degrees Celsius is 120mm polyurethane board. When the insulation is insufficient, the heat leakage of the enclosure will increase by 40%. The compressor will operate at full load for a long time, and the risk of exhaust overheating will significantly increase. R23 refrigerant is commonly used in ultra-low temperature scenarios below -60 ℃. This refrigerant has a higher pressure rating and cannot be used with R404A models for matching refrigeration oil and seals. Mixing them will result in seal leakage within 200 hours. The selection of two-stage compressors cannot be directly compared to single-stage horsepower. The theoretical displacement of two-stage models with the same cooling capacity is 1.9 times larger than that of single-stage low-temperature models. Many engineering companies are prone to directly using single-stage selection tables, resulting in insufficient cooling capacity. Low pressure stage return oil is a key focus of operation and maintenance for two-stage units. Under cryogenic conditions, the viscosity of the frozen oil increases, and the return oil flow rate is not less than 0.8m/s. The diameter of the return oil pipeline needs to be enlarged by one size according to cryogenic specifications. Many frozen tunnel compressors use two-stage semi enclosed models. When the frozen tunnel is opened for picking up goods, the heat invasion is large, and the load fluctuation range can reach 45%. The unit needs to be equipped with an energy regulation mechanism to ensure stable output. The growth of cold storage projects at minus 60 degrees Celsius in Central Asia is significant. The local outdoor low temperature in winter can assist in condensation, but in summer when the ambient temperature is 42 ℃, the load on the high-pressure side will increase by 28%, and sufficient condenser capacity should be reserved. Compared with low-temperature screw models, the two-stage semi closed compressor has a 42% lower procurement cost for the same refrigeration capacity, and has strong universality in maintenance parts, making it suitable for overseas engineering sites with weak maintenance resources. The compressor valve plate wears out faster under cryogenic pressure differential conditions, and the inspection cycle of the two-stage unit valve plate is shortened to 6000 hours. If deformation or cracks are found, they must be replaced in a timely manner to avoid liquid impact damage to the cylinder body. The export of dual level models for foreign trade requires the provision of CE certification test reports. For pharmaceutical cold storage and freeze-drying machine supporting projects, the purchaser shall additionally request high and low temperature continuous operation test curves.
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FAQ
What is the upper limit of single-stage pressure ratio control for a two-stage semi closed compressor? When designing the working conditions, the single-stage pressure ratio should not exceed 3.5.
What is the minimum thickness of insulation board for cold storage at minus 60 ℃? Recommend polyurethane board thickness ≥ 120mm to reduce enclosure heat leakage.
Can R23 refrigerant seals be interchangeable with R404A? No, the material has different pressure resistance and refrigerant resistance characteristics.
How often is the valve plate of the two-stage unit inspected? Under cryogenic conditions, the recommended valve inspection cycle is 6000 hours.
Why prioritize two-stage compressors for frozen tunnels? The load fluctuates greatly, and two-stage compression can stably maintain the cryogenic evaporation temperature.
How much is the difference in displacement between a two-stage engine and a single-stage engine with the same cooling capacity? The equivalent cooling capacity and exhaust capacity are about 1.9 times that of a single-stage low-temperature machine.
What are the risks of summer working conditions in Central Asian deep cold storage? The environment is at a high temperature of 42 ℃, and the load on the high-pressure side has increased by about 28%.
2026-11-09 12:14:29
