Liquid Supply Methods for Cold Storage Refrigeration Systems

The cooling methods include direct evaporation cooling and indirect cooling. Currently, the commonly used refrigeration system is the compression refrigeration system. The liquid supply methods of the refrigeration system are direct expansion liquid supply, gravity liquid supply, and refrigerant liquid pump liquid supply. These three liquid supply methods are determined according to the size of the small - scale cold storage and the type of cooling equipment.

The refrigerant is directly supplied from the condenser or liquid receiver to the evaporator or cooling coil through the expansion valve. This liquid supply method is called direct expansion liquid supply. This method is relatively simple, but it is difficult to control the appropriate liquid supply volume. The refrigeration effect is reduced due to superheat (insufficient liquid supply) and liquid hammer (excessive liquid supply). For the Freon refrigeration system of a small - scale cold storage, it is suitable to use the superheat control of the expansion valve, and this application is relatively common.

This method involves adding a gas - liquid separator between the evaporator and the expansion valve. After storing a certain amount of liquid, the static pressure of the liquid supply column supplies the liquid to the cooling equipment.

When ammonia passes through the expansion valve (manual) or float valve (automatic control) and throttles into the ammonia liquid separator, the flash gas generated by throttling is separated in the separator. The liquid enters the cooling coil through the liquid sub - regulating station. The gas that absorbs heat and evaporates flows into the ammonia liquid separator through the gas sub - regulating station.

Since the gas contains a certain amount of liquid droplets, it must be separated in the separator. The separated dry vapor and the flash gas generated by throttling are sucked into the refrigeration compressor through the suction pipeline, ensuring the effective evaporation area of the liquid in the coil and preventing liquid hammer in the compressor.
If supplying liquid to the top coil of a small - scale cold storage, the ammonia liquid separator should be installed at a position where the liquid level is 1.5m higher than the top coil, and the liquid enters the coil due to the static pressure of the liquid supply column.

This method uses a pump to send the low - temperature liquid refrigerant in the low - pressure circulating receiver to the refrigeration equipment for forced liquid supply.

It is mostly used in "ammonia cold storages" and is called the ammonia pump system.
There are two types of ammonia pump liquid supply methods: top - in bottom - out and bottom - in top - out. Each of these two methods has its own advantages and disadvantages. In the bottom - in liquid supply method, the low - temperature ammonia liquid enters the ammonia pump from the low - pressure circulating receiver through a filter. The ammonia pump transports the ammonia liquid to the main regulating station. This regulating station is equipped with multiple pipelines, which respectively supply liquid to the cold storage rooms, freezing rooms, etc. through the liquid sub - regulating stations. At the same time, a bypass pipe is provided, which can return the excess ammonia liquid to the circulating receiver to adjust the liquid supply volume. The return gas in the pipeline enters the low - pressure circulating receiver from the gas separation station. After separating the liquid droplets, it is sucked back by the compressor. The suction pipe is used to discharge the gas in the pump. The discharge pipe is used for draining liquid during hot ammonia defrosting, and the discharged liquid flows to the low - pressure circulating receiver.