① Adopt thermal mixing plate
The geometric structure of the corrugation on both sides of the thermal mixing plate is the same. The plates are divided into hard plate (H) and soft plate (L) according to the angle of the herringbone corrugation. The angle (usually 120. About) is greater than 90. It is a rigid board, and the included angle (usually 70. About) is less than 90. For soft board. The surface heat transfer coefficient of the hard plate of the thermal mixing plate is high, and the fluid resistance is large, while the soft plate is the opposite. The combination of hard board and soft board can form high (HH), medium (HL), and low (LL) flow channels to meet the needs of different working conditions.
When the flow of cold and heat medium is relatively large, the use of a heat mixing plate can reduce the plate area than a symmetrical single-process heat exchanger. The diameters of the corner holes on the hot and cold sides of the heat mixing plate are usually the same. When the flow ratio of the cold and heat medium is too large, the pressure loss of the corner hole L on the side of the cold medium is large. In addition, it is difficult to achieve precise matching with thermal mixing plate design technology, which often results in limited plate area saving. Therefore, it is not advisable to use a hot mixing plate when the flow ratio of cold and heat medium is too large.
② Adopt asymmetrical plate heat exchanger
The symmetrical plate heat exchanger is composed of plates with the same corrugated geometry on both sides of the plate, forming a plate heat exchanger with equal cross-sectional areas of the cold and hot runners. Asymmetrical (unequal cross-sectional area type) plate heat exchangers, according to the heat transfer characteristics and pressure drop requirements of the cold and hot fluids, change the wave geometry on both sides of the plates to form a plate heat exchanger with unequal cross-sectional areas of the cold and hot runners , The angle L on the side of the wide runner has a larger diameter. The heat transfer coefficient of the asymmetrical plate heat exchanger decreases slightly, and the pressure drop is greatly reduced. When the flow of cold and heating medium is relatively large, the use of an asymmetric single-process heat exchanger can reduce the plate area by 15% to 30% compared to a symmetrical single-process heat exchanger.
③ Adopt multi-process combination
When the flow rate of the cold and heat medium is large, a combination of multiple processes can be used, and more processes are used on the side of the small flow rate to increase the flow rate and obtain a higher heat transfer coefficient. The large flow side uses fewer processes to reduce the resistance of the heat exchanger. Mixed flow patterns appear in the combination of multiple processes, and the average heat transfer temperature difference is slightly lower. Both the fixed end plate and the movable end plate of the plate heat exchanger with multi-process combination have takeovers, which requires a lot of work during maintenance.
④ Set the bypass pipe of the heat exchanger
When the flow of cold and heat medium is relatively large, a bypass pipe can be installed between the inlet and outlet of the heat exchanger on the side of the large flow to reduce the flow into the heat exchanger and reduce the resistance. To facilitate adjustment, a regulating valve should be installed on the bypass pipe. This method should adopt a countercurrent arrangement to make the temperature of the cold medium exiting the heat exchanger higher and to ensure that the temperature of the cold medium after the confluence of the heat exchanger outlet can meet the design requirements. The bypass pipe of the heat exchanger can ensure that the heat exchanger has a higher heat transfer coefficient and reduce the resistance of the heat exchanger, but the adjustment is slightly complicated.
⑤ Selection of the form of plate heat exchanger
The average flow velocity of the medium in the flow channel between the heat exchanger plates is preferably 0.3 to 0.6 m/s, and the resistance is preferably not more than 100 kPa. According to the flow ratio of different cold and heat media, different types of plate heat exchangers can be selected according to Table 1. The cross-sectional area ratio of the asymmetric plate heat exchanger in the table is 2. For symmetrical or asymmetrical, single-process or multi-process plate heat exchangers, heat exchanger bypass pipes can be installed, but detailed thermal calculations should be conducted.
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