The structure of a full liquid shell and tube evaporator is similar to that of a horizontal shell and tube condenser. Its outer shell is a cylinder welded with steel plates, and tube plates are welded at both ends of the cylinder. Steel pipes are fixed to the tube plates by welding or expanding. The refrigerant vaporizes in the space outside the pipe, and the refrigerant carrier flows inside the pipe. To ensure that the refrigerant carrier has a certain flow rate in the pipe, separators are cast in the covers at both ends to allow the refrigerant carrier to flow through the evaporator in multiple processes.
After being throttled by the expansion valve, the refrigerant liquid enters the outer space of the tube from the inlet, filling 70% to 80% of the cylinder space. The refrigerant vapor after heat absorption and gasification rises to the liquid separator, and the separated vapor is sucked in by the compressor, while the refrigerant liquid droplets still fall into the evaporator. In order to observe the liquid in the evaporator, a bypass pipe is installed between the liquid separator and the housing. The frosting on the bypass pipe indicates the liquid level in the evaporator.
The bottom of the ammonia evaporator is welded with an oil collector, which can regularly discharge the lubricating oil trapped therein.
This form of evaporative crying has the advantages of good heat transfer performance and compact structure. However, when using water as the refrigerant carrier, improper operation can easily lead to freezing accidents.
This type of evaporator can also be used in Freon refrigeration systems. In order to improve the boiling heat release coefficient on the refrigerant side, most heat transfer tubes use low rib steel tubes. However, due to the large amount of liquid filled and the difficulty in returning the lubricating oil in the evaporator to the compressor, it is recommended to use a dry shell and tube evaporator in the Freon refrigeration system.
The structure of a dry shell and tube evaporator is the same as that of a full liquid evaporator. The main differences between the two are: in the dry shell and tube evaporator, the refrigerant vaporizes and absorbs heat in the heat transfer tube, and the refrigerant carrier flows outside the tube. In order to improve the flow rate of the refrigerant carrier, multiple baffle plates are installed in the cylinder.
Due to the refrigerant flowing in the pipe, the liquid filling amount is small; The high flow rate easily solves the problem of lubrication returning to the compressor; In addition, the dry shell and tube evaporator also has the advantages of less cold loss and no frost cracking of the heat transfer tube.