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

1. Direct liquid supply

Direct liquid supply refers to the direct entry of low-temperature refrigerant from the outlet of the throttle valve into the evaporator. The refrigeration system of this liquid supply method is simple, and the throttle valve often uses a thermal expansion valve.

2. Gravity liquid supply

In the gravity liquid supply system, a gas-liquid separator is used, and the evaporator is located at the bottom of the gas-liquid separator. Generally, the normal liquid level of gas-liquid separator 3 is required to be more than 1.5m higher than the top of the evaporator.

The process of refrigerant is as follows: the refrigerant liquid from the high-pressure storage tank 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 accumulates at the top. The low-temperature liquid in the gas-liquid separator flows into the evaporator by gravity, and the refrigerant vapor returned from the evaporator is sucked back by the compressor along with the flash vapor generated by the throttle valve.

In this way, all the refrigerant liquid entering the evaporator is low-temperature. Compared with the direct liquid supply system, the heat transfer coefficient of the evaporator is higher. The gas-liquid separator plays a role in supplying low-temperature liquid to the evaporator and preventing compressor liquid shock. But the disadvantage of this liquid supply method is that the evaporator is not easy to return oil. Usually, the lubricating oil inside the evaporator is discharged by regularly defrosting the hot refrigerant in the evaporator.

3. Schematic diagram of gravity liquid supply system

The liquid pump supply system is a system that uses low-pressure circulation buckets and liquid pumps to supply liquid to the evaporator. The low-pressure circulation buckets are arranged in the equipment room and are not limited by the height and position of the evaporator.

The process is as follows: the low-temperature refrigerant at the outlet of the throttle valve first enters the low-pressure circulation bucket, and then the ammonia pump pressurizes the low-temperature liquid with 3-4 times the evaporation capacity and sends it to the evaporator. A part of the refrigerant in the evaporator evaporates and absorbs heat. The refrigerant liquid that has not been completely evaporated and the evaporated vapor return to the low-pressure circulation bucket together. The low-pressure circulation bucket separates the refrigerant gas and liquid, and the vapor returns to the compressor. The low-temperature refrigerant liquid is then re entered into the evaporator through the liquid pump.

This system has a large refrigerant circulation, high heat exchange efficiency of the evaporator, and is easy to return oil; Low circulation drums and ammonia pumps are centrally arranged in the equipment room for easy management, and are currently widely used.