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Basic classification of plate heat exchanger plates
Release time:
2022-08-08
The heat transfer coefficient and pressure drop are calculated according to the performance curves of the products of various manufacturers.
Basic classification of plate heat exchanger plates
Generally speaking, we mainly distinguish the plates of plate heat exchangers according to their structure, which is based on their appearance and can be divided into four categories: (1) removable plate heat exchangers (also called plate heat exchangers with sealing gaskets), (2) welded plate heat exchangers, (3) spiral plate heat exchangers, (4) coil tube-plate heat exchangers (also called honeycomb heat exchangers). The welded plate heat exchanger is divided into: semi-welded plate heat exchanger, fully welded plate heat exchanger, plate-shell heat exchanger and brazed plate heat exchanger.
Other commonly used classifications are: according to the amount of heat exchange area per unit space, plate heat exchanger is a compact type heat exchanger. Compared with shell-and-tube heat exchanger, the traditional shell-and-tube heat exchanger occupies a larger area. There are different names according to the process purpose: plate heater, plate cooler, plate condenser, plate preheater; According to process combination, it is divided into one-way plate heat exchanger and multi-directional plate heat exchanger; According to the flow direction of the medium, it can be divided into downstream (horizontal flow) plate heat exchanger, counter-flow plate heat exchanger, and cross-flow (cross flow) plate heat exchanger, the latter two are used more; According to the gap size of the flow passage, it can be divided into conventional clearance plate heat exchanger and wide clearance plate heat exchanger; According to the corrugated plate, the plate heat exchanger has a more detailed introduction, which will not be repeated. Please refer to the corrugated plate form of the plate heat exchanger.
The plate heat exchanger plate can be divided into single plate heat exchanger and plate heat exchanger unit according to whether it is a complete set of products. The selection of plate type or corrugated type shall be determined according to the actual needs of the heat exchange site. For the case of large allowable voltage drop, small resistance should be selected, and on the contrary, large resistance should be selected. According to the fluid pressure and temperature, the removable type or brazed type shall be selected. When determining the plate type, it is not advisable to select too small plate area to avoid too many plates, small flow between plates, and low heat transfer coefficient. Larger heat exchangers should pay more attention to this problem.
Selection of flow rate and flow path A group of parallel flow paths in the plate of plate heat exchanger with the same flow direction as the medium. The flow path is a medium flow path composed of two adjacent plates in the flow plate heat exchanger. Generally, several flow channels are connected in parallel or in series to form different combinations of hot and cold media channels. The flow combination form shall be determined according to the calculation of heat transfer and fluid resistance, and meet the requirements of process conditions. Try to make the convective heat transfer coefficients in the cold and hot water channels equal or close to each other, so as to obtain a good heat transfer effect. When the convective heat transfer coefficients on both sides of the heat exchange surface are equal or close, the heat transfer coefficient gets a larger value. Although the flow rates between plates of plate heat exchangers are different, the average flow rate is still used to calculate heat exchange and fluid resistance. Because the "U" type single flow pipe is fixed on the pressure plate, it is easy to disassemble.
In the design and selection of plate heat exchangers, there are certain requirements for pressure drop, which should be checked. If the check pressure drop exceeds the allowable pressure drop, it is necessary to redesign and type selection calculation until the process requirements are met.
The heat transfer coefficient and pressure drop are calculated according to the performance curves of the products of various manufacturers. The performance curve (standard correlation) is generally obtained from the product performance test. For the plate without performance test, the criterion correlation of the plate can also be obtained by using the reference dimension method according to the characteristic geometric size of the plate. This method is adopted by some international general software. For the type selection software of plate heat exchanger, generally each manufacturer has its own type selection software according to its own plate type. Software used internationally include HTRI, HTFS, etc. There are few general computing software on the market. Some domestic websites, such as heat exchange support website, provide online calculation software for plate heat exchangers for reference.
