As we all know, dry evaporators and full-liquid evaporators are common evaporators. The difference between full-liquid units and ordinary chillers is that they use a full-liquid evaporator, while ordinary chillers use a dry type. Evaporator. In this article, Xiaobian mainly introduces the differences between them and their respective advantages and disadvantages.
The difference between dry evaporator and full liquid evaporator:
Full-liquid and dry evaporators are similar in appearance, but the two are significantly different in terms of refrigerant flow. The refrigerant in the flooded evaporator takes the shell, the refrigerant enters from the lower part of the casing, flows and boils outside the heat exchange tube, and the boiled steam is discharged from the upper portion of the casing.
The liquid level of the refrigerant in the flooded evaporator should be moderate. If the refrigerant charge is too full, the liquid level is too high, and a large amount of refrigerant droplets will be trapped in the steam when boiling. If it is not separated, it may cause the compressor to slam and damage the compressor; otherwise, the liquid level is too low. If the submerged heat exchange tube is too small, the heat transfer area is too small and the heat exchange capacity is limited. Therefore, there should be 1-2 rows of heat exchange tubes to expose the liquid surface, generally the liquid level is 55%-65% of the cylinder diameter. In the dry evaporator, the refrigerant travels through the tube, that is, the refrigerant flows into the heat exchange tube bundle from the lower portion of the end cap, flows and evaporates in the tube bundle, and the steam is discharged from the upper air outlet of the end cap. In addition, the dry water of the dry evaporator takes the shell side, so that the frozen water is generally flushed with the evaporator, the dry evaporator generally has several baffles, which is also a difference from the full liquid evaporator.
Advantages and disadvantages of a full liquid evaporator:
The biggest feature of the flooded evaporator is that it floods a large number of heat exchange tubes with liquid refrigerant and evaporates on the surface of the tube bundle to cool the frozen water. The surface-enhanced full-liquid evaporation tube is completely immersed in the refrigerant, so the heat transfer efficiency is high; and the refrigerant vapor does not need to be superheated, so that the evaporation temperature can be greatly improved. Under the condition that the frozen water returns to water at 12 ° C and the effluent at 7 ° C, the evaporation temperature can reach 5 ° C (while the evaporation temperature of the dry evaporator is only 2 ° C), and since the evaporation temperature is increased, the full temperature is greatly increased. The energy efficiency ratio of the liquid chiller saves energy.
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However, the flooded evaporator requires a large amount of refrigerant to be injected, and the separation of the lubricating oil is also a problem when using Freon.
Advantages and disadvantages of dry evaporators:
Compared to flooded evaporators, dry evaporators have the following advantages:
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1. The oil can be brought back to the compressor without the need for an oil return device.
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2. The refrigerant is used in a small amount, which is one-third of the full-liquid evaporator of the same cooling capacity.
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The disadvantages of dry evaporators are:
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1. When multiple processes are used, the gas-liquid two-phase refrigerant will separate when it is turned inside the end cover, which will cause the non-uniform distribution of refrigerant flow in each pipe in the next process. The more gas content, the more uneven the distribution, and even the lack of liquid or liquid in some tubes, so that these tubes lose the effect of evaporative cooling.
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2. Since there is generally a gap between the baffle and the casing, there is also a gap between the heat transfer pipe and the pipe hole on the baffle plate, so the frozen water leaks through these gaps (ie, short circuit of frozen water). Reduces the heat transfer effect on the water side.
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Since the evaporation temperature of the flooded evaporator can be increased to 5 ° C, the energy efficiency ratio (ie COP) of the flooded chiller is greatly improved, thereby saving energy and achieving energy saving.
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