Principles and descriptions of three liquid supply methods of evaporator in refrigeration system

In the refrigeration system of the cold storage, the evaporator is the core heat exchange device, and its liquid supply method directly affects the system efficiency and stability. Currently, the mainstream liquid supply methods include three forms: direct liquid supply, gravity liquid supply and liquid pump liquid supply. This article conducts a comprehensive analysis of three methods from the aspects of technical principles, system characteristics and applicable scenarios for reference.

1. Direct liquid supply system

Technical principle: The direct liquid supply system realizes throttling and pressure reduction of the refrigerant through a thermal expansion valve, and the throttling low-temperature liquid refrigerant directly enters the evaporator for evaporation and heat exchange. The system relies on the pressure difference between the compressor and the evaporator to drive the refrigerant circulation without additional power equipment.
Structural advantages: the system structure is simple, the equipment investment cost is low, and the maintenance is high.
Control characteristics: Thermal expansion valve is used to achieve flow regulation, but the liquid supply is greatly affected by fluctuations in the evaporation load, which may lead to uneven distribution of the liquid refrigerant in the evaporator.
Heat transfer performance: Some flash steam generated after throttling may enter the evaporator, reducing the effective heat transfer area, resulting in a lower heat transfer coefficient than other methods.
Applicable scenarios: Widely used in household air conditioners, small commercial refrigeration equipment and low-temperature brine preparation systems that require a simple system, especially suitable for situations where the evaporation load is relatively stable.

2. Gravity fluid supply system

Technical principle: The gravity liquid supply system realizes homogeneous distribution of refrigerant through a gas-liquid separator. The system requires that the normal liquid level of the gas-liquid separator is at least 1.5m higher than the top of the evaporator, and the low-temperature liquid is driven into the evaporator by using the gravity of the liquid column.
The refrigerant process is as follows: the outlet liquid of the high-pressure liquid reservoir is reduced by a float valve or a manual throttle valve and then enters the gas-liquid separator; the bottom of the separator gathers low-temperature liquid, and the upper part is flash steam; the low-temperature liquid flows into the evaporator by gravity, and the evaporated gas-liquid mixture returns to the compressor together with the flash steam.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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