Principle and description of three liquid supply modes of evaporator



There are three ways to supply liquid to evaporator in cold storage refrigeration system: direct supply, gravity supply and liquid pump supply.

1, Direct liquid supply

Direct liquid supply is the low temperature refrigerant at the outlet of the throttle valve directly into the evaporator. This kind of liquid supply refrigeration system is simple. The throttle valve often uses thermal expansion valve.

2, gravity liquid supply

In the gravity liquid supply system, gas-liquid separator is adopted, and the evaporator is located at the lower part of the gas-liquid separator. It is generally required that the normal liquid level of gas-liquid separator 3 is more than 1.5m higher than the top of the evaporator.

The refrigerant process is: the refrigerant liquid from the high pressure reservoir enters the floating ball valve (or manual throttle valve) throttling and lowering pressure, the low temperature refrigerant from the floating ball valve (or manual throttle valve) outlet enters the gas-liquid separator, the low temperature liquid is at the bottom of the gas-liquid separator, and the vapor is gathered in the upper part. The cryogenic liquid in the gas-liquid separator flows into the evaporator by gravity, and the refrigerant vapor from the evaporator is sucked back by the compressor together with the flash vapor generated by the throttle valve.

In this way, all the low temperature refrigerant liquid entered by the evaporator is. Compared with the direct liquid supply system, the heat transfer coefficient of the evaporator is high. The gas-liquid separator plays the role of supplying low temperature liquid to the evaporator and preventing the liquid strike of the compressor. But the disadvantage of this liquid supply mode is that the evaporator is not easy to return the oil. The lubricating oil in the evaporator is usually discharged by defrosting the evaporator with hot refrigerant regularly.

3, Schematic diagram of gravity liquid supply system

The liquid pump liquid supply system is a system that uses a low pressure circulation barrel and a liquid pump to supply liquid to the evaporator. The low pressure circulation barrel is arranged in the equipment and is not restricted 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 barrel, and then the ammonia pump pressurizes the low-temperature liquid with 3-4 times the evaporation capacity into the evaporator. Some of the refrigerant in the evaporator evaporates and absorbs heat. The refrigerant liquid that has not been evaporated and the vapor after evaporation returns to the low cycle barrel, the low cycle barrel separates the refrigerant gas and liquid, and the vapor returns to the compressor. The low temperature refrigerant liquid enters the evaporator through the liquid pump.

This system is easy to return oil because of the large refrigerant circulation, the evaporator heat transfer efficiency is high; Low cycle drum and ammonia pump are centrally arranged in the equipment room for easy management, and are widely used at present.