Working principle of multi-stage compression and stacking of refrigeration system

1. Collapsorted refrigeration system
A composite refrigeration is a refrigeration technology that uses two or more refrigerants and is composed of two or more single-stage (or two-stage) compressed refrigeration circulation systems. It is mainly used in facilities that require a low temperature environment of -120℃ to -60℃, such as ultra-low temperature cold storage, rapid freezing process equipment, as well as biological and chemical industries, low temperature boxes, etc. that require ultra-low temperature conditions.

The system structure of a composite refrigeration device is usually divided into two parts: high-temperature stage and low-temperature stage. The medium-temperature refrigerant is used for the high-temperature stage, while the low-temperature stage uses for the low-temperature stage. The evaporation process of the high-temperature refrigerant promotes the condensation of the low-temperature refrigerant, and the two parts are connected into a whole through a condensing evaporator. The condenser evaporator acts as both a high-temperature evaporator and a low-temperature condenser in the system

Low temperature workflow:
After the low-temperature refrigerant gas comes out of the evaporator, it passes through the low-temperature heat recycler, then is compressed by the low-temperature compressor and then enters the oil separator. In the oil separator, most of the lubricating oil is separated and returned to the compressor, and the refrigerant gas with very little oil content enters the precooler for precooling, and then enters the condensation evaporator. In the condensation evaporator, the heat emitted by the low-temperature refrigerant is absorbed by the high-temperature refrigerant. While the high-temperature refrigerant evaporates, the low-temperature refrigerant condenses. The condensed low-temperature refrigerant passes through a drying filter and a low-temperature recycler, and then enters the evaporator through a throttle valve

to complete a refrigeration cycle.

High temperature workflow:
The high-temperature refrigerant gas absorbed in the condensation evaporator is sucked in and compressed by the high-temperature compressor, and then enters the air-cooled condenser for condensation, releasing the heat to the cooling medium. The condensed high-temperature refrigerant liquid enters the reservoir, and then enters the condensation evaporator through the drying filter and the throttle valve to complete a refrigeration cycle.

Compared with ordinary single-stage compression refrigeration devices, the stacked refrigeration device has two special components: a condensation evaporator and an expansion vessel.

Condensation evaporator: Usually, casing or plate heat exchanger is used. In sleeve-type heat exchangers, high-temperature refrigerant evaporates in the tubes and low-temperature refrigerant condenses between tubes; in plate-type heat exchangers, high-temperature refrigerant inlets are usually equipped with liquid distributors to ensure that the liquid refrigerant flows evenly into each channel

Multi-stage compression refrigeration cycle process: After the low-pressure and low-temperature refrigerant vapor is generated in the evaporator, it is sucked in by the low-pressure compressor and compressed into superheated vapor of intermediate pressure, and then enters the intercooler of the same pressure, and is cooled into dry saturated vapor in the intercooler. The medium-pressure dry saturated vapor is then sucked in by the high-pressure compressor and compressed to the condensation pressure superheated vapor, and then enters the condenser and is condensed into a refrigerant liquid.

The liquid is divided into two channels: one passes through the expansion valve F and then goes into the intercooler and then goes into the intercooler; most of the liquid enters the coil of the intercooler from the other path and is super-cooled. Due to the heat transfer temperature difference, it is impossible for the liquid to be cooled to the intermediate temperature in the coil, but is higher than the intermediate temperature by △t=3-5°C. The supercooled liquid then passes through the main expansion valve to reduce the pressure to low-temperature and low-pressure supercooled liquid, and finally enters the evaporator to absorb heat and evaporate, creating a refrigeration effect.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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