Question: Since plate heat exchangers are so effective, why can’t they be used in evaporators?

Plate heat exchangers are compact and have high heat transfer efficiency; moreover, their plate design is specifically intended for liquid-liquid heat exchange, so they can be used as condensers without any modifications, and their heat transfer performance is also better than that of tubular heat exchangers. However, when plate exchangers are used as evaporators or condensers in refrigeration, air conditioning, heat pump, and hot/cold water systems, the following issues should be taken into consideration: 1. Generally, both condensation and boiling can take place within the same process; therefore, the phase-change side is often designed as a single-pass system, while the liquid side can be arranged as a single-pass or multi-pass system depending on the requirements. In the field of HVAC refrigeration, the water side is generally also single-pass for most applications. 　　2. For plate condensers, it is generally not advisable to have both a condensation section and a subcooling section in the design. Since the heat exchange efficiency of the subcooling section is low, if subcooling is required, a separate subcooler should be used in principle. 　　3. The design of plate condensers and evaporators also faces the issue of allowable pressure drop. A high pressure drop within the condenser reduces the condensation temperature of the steam, resulting in a small logarithmic mean temperature difference ； A high pressure drop inside the evaporator leads to an increased superheat of the outlet steam; both factors result in a larger heat exchanger area, which is detrimental to heat exchange. Therefore, when selecting a plate evaporator, it is advisable to choose plates with low resistance, and the number of plates per unit should not be too large ； Try to ensure even distribution of the liquid supply. Plate condensers should use intermediate partitions to separate the liquid on both sides. 　　4. When selecting a model, plate condensers and plate evaporators should be given priority; if no suitable model is available, conventional plate heat exchangers can be used. 　　5. For plate heat exchangers used in refrigeration and air conditioning equipment, due to the high pressure of the refrigerant and its tendency to leak, brazed plate heat exchangers are preferred. 　　The issues that need to be taken into account when using plate heat exchangers as condensers and evaporators are the ones mentioned above. Users who purchase plate heat exchangers for such purposes must pay special attention to these issues in order to maximize their performance, reduce project costs, and ensure that their service life is not affected.

It depends on the specific process requirements. The principle is the same; it’s just a matter of terminology.

Evaporation belongs to boiling heat transfer, not convective heat transfer; the heat transfer efficiency of other types of heat exchangers is no worse than that of plate heat exchangers

I’ve always wondered why the evaporator and condenser units in chillers are of the shell-and-tube type. I asked some people why plate-type designs, which are smaller in size, aren’t used But I didn’t get a very good answer.

There are plate evaporators. But it is viscous and prone to crystallization, making it unsuitable for use. When used in falling-film or rising-film evaporators, the cost becomes too high due to the length of the tube side, making it uneconomical in terms of cost-performance

For small volumes, a plate heat exchanger can be used as an evaporator; however, the diameter of the gas outlet in an evaporator is usually large, and using a regular plate heat exchanger results in higher overall costs. It is more appropriate to use a specialized evaporator.

There are both plate-type evaporators for material evaporation and plate-type evaporation-condensation units for refrigeration. Both types excel in terms of space efficiency in the heat exchange industry, and they are widely used; they’re not anything rare. Those who have prejudices against plate-type designs simply have flawed understanding. Of course, everything has its advantages and disadvantages: plate-type designs require a small spacing between plates, have high demands on the materials used, involve gaskets, and are not suitable for highly hazardous materials. There are also limitations regarding temperature and pressure. If a material can be processed using a plate-type evaporator, then no other evaporation method can compare to it, whether in terms of efficiency, space required, maintenance needs, or cost. Additionally, evaporation crystallization and plate-type crystallization are two different concepts – plate-type systems cannot achieve crystallization as they may get clogged, but they do offer high evaporation efficiency. A combination of plate-type evaporation and tubular crystallization can save money and space, as well as make maintenance easier. Some people claim that plate-type systems cannot facilitate crystallization, thereby dismissing their evaporation capabilities; those who blindly reject plate-type designs may simply not understand their advantages