One, the working process is different
1, full-liquid evaporator, the liquid refrigerant through the throttling device into the evaporator, the liquid level in the evaporator to maintain a certain. The heat transfer tube in the evaporator is submerged in the refrigerant liquid. Heat absorption after evaporation of gas-liquid mixture still contains a large amount of liquid, so from the evaporator escaped from the wet vapors by gas-liquid separation and then back into the compressor.
2, dry evaporator by the thermal expansion valve or electronic expansion valve to directly control the liquid refrigerant into the evaporator tube, refrigerant liquid in the tube is completely transformed into a gas, and is cooled by the medium in the heat transfer tube outside the tube flow.
Two, different performance
1, heat transfer
Full-liquid evaporator evaporator tube surface for the liquid wetting, surface heat transfer coefficient is large
Dry evaporator evaporator tube surface for the part of the liquid wetting, the surface heat transfer coefficient is slightly lower
2, refrigerant side of the resistance
Full-liquid evaporator refrigerant side of the resistance is larger.
3, back to the oil performance
For the lubricant and refrigerant solubility, full-liquid evaporator back to the oil is more difficult and unstable, and back to the oil condition directly affects the unit's working condition and the working condition of the oil shift. Dry evaporator oil return is stable and convenient.
4, liquid charging volume
Full liquid evaporator shell full of refrigerant, liquid charging volume. Mostly used for refrigerant leakage of open compressor.
Dry evaporator refrigerant charging volume is only full liquid evaporator 1/2 ~ 1/3.
Three, the structure is different
1, full liquid evaporator in the tube to go water, refrigerant evaporation outside the tube cluster, so basically the heat transfer surface are in contact with the liquid refrigerant. Generally the amount of refrigerant charged in the shell is about 55% to 65% of the effective volume of the cylinder, the refrigerant liquid heat absorption gasification through the liquid separator at the top of the cylinder, back into the compressor. Easy operation and management, high heat transfer coefficient.
2, dry evaporator refrigerant flows in the tube, water flows outside the tube cluster. Refrigerant flow usually has several processes, due to the gradual vaporization of refrigerant liquid, usually the more upward, the more the number of tubes in its process. In order to increase the water side of the heat transfer, the outer side of the cylinder heat transfer tube is equipped with a number of folding plate, so that the water swept several times across the tube cluster flow.
Extended information
Features of full liquid shell and tube evaporator. Widely used in ammonia refrigeration system, also can be used in freon system. Compact structure, small footprint. Carrier refrigerant can adopt closed cycle, can adopt volatile carrier refrigerant. Agent. Easy to accumulate oil. Carrier refrigerant is easy to freeze; refrigerant goes to the shell process, water goes to the tube process.
The heat exchange process is always between liquid refrigerant and liquid water, the resulting refrigerant gas is directly suctioned from the compressor into the compressor, the heat exchange area is effectively utilized and the heat exchange efficiency of the unit is improved.
Precautions
(1) The refrigerant has more than one process, in the end cover turning place if not handled well will produce accumulation of liquid, which will make the liquid into the next process is not evenly distributed, affecting the heat transfer effect.
(2) the water side of the leakage problem, because the outer edge of the folding plate and the shell between the general 1 ~ 3mm gap, and the heat transfer tube between the gap of about 2mm, thus causing water leakage. It has been proved that water leakage will cause a reduction of 20% to 30% in the heat transfer coefficient on the water side and 5% to 15% in the total heat transfer coefficient.
Baidu Encyclopedia - full liquid shell and tube evaporator
Baidu Encyclopedia - dry shell and tube evaporator