Dry Type and Flooded Type evaporator structure, principle, difference and advantages and disadvantages 2019-03-20

As we all know, the four major components of the refrigeration system are: compressor, evaporator, condenser, and throttling device. Among them, the type and characteristics of the compressor as the heart of the refrigeration system are more well known than the other three components. In addition, the evaporator is another key component. Do you know about the type and characteristics of the evaporator?

Shell and tube condenser working process:

Dry Type and Flooded Type evaporator


Dry evaporator structure and working process:

Dry Type and Flooded Type evaporator

The dry evaporator refrigerant 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 is relatively low, and the heat transfer coefficient is only about twice the heat transfer coefficient of the light pipe, but The advantage is that it is easy to return oil, and the control is relatively simple, and the charging amount of the refrigerant is about 1/2 to 1/3 of the filling amount of the full liquid type unit.


Structure and working process of Flooded Type evaporator:

Dry Type and Flooded Type evaporator

The operation mode of the Flooded Type evaporator and the dry evaporator is exactly opposite. The cold water passes through the heat exchange tube, the refrigerant completely immerses the heat exchange tube, and absorbs heat and evaporates outside the heat exchange tube. The surface of the heat transfer tube of the flooded evaporator has a plurality of needle-shaped holes, and a spiral protrusion on the inner surface of the tube enhances the heat exchange on the cold water side. The high-efficiency heat transfer tube that simultaneously enhances the boiling outside the tube and the heat transfer inside the tube, the heat transfer coefficient is increased by about 5 times compared with the light tube.


Comparison of structure of Flooded type and dry evaporator

Dry Type and Flooded Type evaporator


Advantages and disadvantages of Dry Type and Flooded Type evaporators

The Flooded Type evaporator draws water in the tube and the refrigerant evaporates outside the tube cluster, so the heat transfer surface is substantially in contact with the liquid refrigerant. Generally, the amount of refrigerant charged in the casing is about 55% to 65% of the effective volume of the cylinder, and the refrigerant liquid is heated and vaporized and then returned to the compressor through the liquid separator at the top of the cylinder. Easy operation and management, high heat transfer coefficient.


Disadvantages:

1. When the evaporation temperature of the refrigeration system is lower than 0 °C, the water in the pipe is easy to freeze and destroy the evaporation pipe;

2. Large amount of refrigerant charge;

3. Influenced by the height of the refrigerant liquid column, the evaporation temperature at the bottom of the cylinder is high, which will reduce the heat transfer temperature difference;

4. The lower part of the evaporator cylinder will accumulate oil, and there must be reliable oil return measures, otherwise it will affect the safe operation of the system.

The refrigerant of the Dry Type evaporator flows inside the tube, and the water flows outside the tube cluster. There are usually several processes for refrigerant flow. Due to the gradual gasification of the refrigerant liquid, the higher the flow rate, the more the number of process tubes. In order to increase the water side heat exchange, a plurality of baffles are arranged on the outer side of the tube heat transfer tube, so that the water flows across the tube cluster multiple times.


Advantage:

1. Lubricating oil enters the compressor with the refrigerant, there is generally no problem of oil accumulation

2. There is less refrigerant in the filling, generally only about 1/3 of the full liquid type;

3. When T0 is around 0 °C, the water will not freeze.


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