The refrigerant of the dry evaporator passes through the heat exchange tube, and the cold water runs outside the high efficiency heat exchange tube. The heat exchange efficiency of such a heat exchanger has a relative error, and its heat exchange coefficient is only about 2 times that of the bare tube. However, its advantage is that it can return oil and control expansion, while the refrigerant charge is about 1/2 to 1/3 of that of the full liquid unit.
The operation mode of the full liquid evaporator is just the opposite to that of the dry evaporator. Cold water passes through the heat exchange tube, and the refrigerant completely submerges the heat exchange tube and evaporates outside the heat exchange tube after absorbing heat. There are many needle shaped holes on the surface of the tube, and spiral protrusions on the inner surface of the tube enhance the heat transfer of the cold water side. This kind of high efficient heat transfer tube can simultaneously strengthen the boiling outside the tube and the heat transfer inside the tube, so the heat transfer coefficient is about 5 times higher than that of the smooth tube.
Falling film evaporator, also known as spray evaporator, is similar to full liquid evaporator, but it is different from full liquid evaporator. The refrigerant of this evaporator is sprayed from the upper part of the heat exchanger to the heat exchange tube. The refrigerant only forms a thin refrigerant liquid film on the heat exchange tube, so that the static liquid level pressure of the refrigerant is reduced during boiling evaporation, thus improving the heat exchange efficiency. Its heat exchange efficiency is about 5 times higher than that of the full liquid unit.
Falling film evaporation is flow boiling. Due to the small thickness of the liquid film layer on the outer surface of the tube, there is no increase in the boiling point caused by static pressure, and the heat transfer coefficient is high. The bubbles generated by full liquid evaporation (that is, immersion evaporation) tend to accumulate on the surface of the heat exchange tube, leading to a decline in heat transfer efficiency, and its heat transfer effect is not as good as falling film evaporation. Generally speaking, falling film evaporation is under the condition of small temperature difference, but scaling shall be prevented to affect heat transfer efficiency.
"Water chiller" is a customary nomenclature for a kind of refrigeration unit. This kind of "water chiller" is generally used for the cold source of the central air conditioner or the refrigeration under the working condition of the air conditioner. The output is low temperature cold water, usually called "chilled water", so it is named. Generally, those that can only cool are called chillers, while those that can heat at the same time are called "heat pump" units.
The "full liquid type" means that the "shell and tube evaporator" used by the unit adopts the form of "full liquid evaporator", which is a shell and tube type different from the "dry type" and "falling film type". The "shell side" uses refrigerant circulation, and the "tube side" uses chilled water circulation. From the profile, it seems that there is more than half a cylinder of refrigerant in the cylinder, and the water flowing tube bundle is immersed in the refrigerant. It is the opposite of the "dry evaporator". The dry evaporator uses refrigerant in the "tube side" and water in the "shell side", just like the refrigerant tube bundle is immersed in water.
The full liquid evaporator and the full liquid unit have higher heat transfer efficiency than the dry evaporator/dry unit. The approaching temperature difference between the outlet water temperature and the evaporation temperature is small, and the compression along the way is small. It is suitable for units with large circulation (compressor centrifuge), and the refrigeration effect is good. However, the refrigerant charge is required to be large, and a special oil return system is required to help the compressor return oil.
The full liquid type means that the refrigerant flows between the copper tube and the shell tube, while the chilled water flows inside the copper tube. The dry type is the opposite. The refrigerant evaporates in the copper tube, and the water flows between the copper tube and the shell tube. They mainly use the ordinary dry evaporator in the industrial low temperature chiller.
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