Evaporator Three Ways of Feeding Liquids

2024-08-31

There are three forms of liquid supply from the refrigeration system of cold storage to the evaporator: direct liquid supply, gravity liquid supply, and liquid pump liquid supply.

Direct liquid supply
In direct liquid supply, the low-temperature refrigerant at the outlet of the throttle valve directly enters the evaporator. This liquid supply method has a simple refrigeration system, and the throttle valve often uses a thermal expansion valve.
Gravity liquid supply
In the gravity liquid supply system, a gas-liquid separator is used. The evaporator is located at the lower part of the gas-liquid separator. Generally, the normal liquid level of the gas-liquid separator 3 is required to be more than 1.5 meters higher than the top of the evaporator.
The refrigerant flow is as follows: The refrigerant liquid from the high-pressure receiver enters the float valve (or manual throttle valve) for throttling and pressure reduction.
The low-temperature refrigerant at the outlet of the float valve (or manual throttle valve) enters the gas-liquid separator. The low-temperature liquid is at the bottom of the gas-liquid separator, and the vapor gathers at the upper part. The low-temperature liquid in the gas-liquid separator flows into the evaporator by gravity. The refrigerant vapor returning from the evaporator and the flash vapor generated by the throttle valve are sucked back by the compressor together.
In this way, all the refrigerant entering the evaporator is low-temperature liquid. Compared with the direct liquid supply system, the evaporator has a high heat transfer coefficient. The gas-liquid separator plays the role of supplying low-temperature liquid to the evaporator and preventing liquid hammer of the compressor. However, the disadvantage of this liquid supply method is that the evaporator is not easy to return oil. Generally, the lubricating oil in the evaporator is discharged by regularly defrosting the evaporator with hot refrigerant.
Liquid pump liquid supply system
The liquid pump liquid supply system is a system that uses a low-pressure circulation drum and a liquid pump to supply liquid to the evaporator. The low-pressure circulation drum is arranged in the equipment room and is not limited by the height position of the evaporator.
Its flow is as follows: The low-temperature refrigerant at the outlet of the throttle valve first enters the low-pressure circulation drum. Then, the ammonia pump pressurizes and sends the low-temperature liquid of 3 to 4 times the evaporation capacity into the evaporator. In the evaporator, part of the refrigerant evaporates and absorbs heat. The unevaporated refrigerant liquid and the evaporated vapor return to the low-circulation drum together. The low-circulation drum separates the refrigerant gas and liquid. The vapor returns to the compressor, and the low-temperature refrigerant liquid re-enters the evaporator through the liquid pump.

This system has a large amount of refrigerant circulation and high heat exchange efficiency of the evaporator, and it is easy to return oil. The low-circulation drum and ammonia pump are centrally arranged in the equipment room for easy management and are widely used at present.