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Plate-fin heat exchangers are heat exchangers that use plates and fins as heat transfer elements. It is mainly composed of plate bundles and end caps, etc. (see figure). There are several channels in the plate bundle. Fins are placed between the two plates in each channel layer, and sealed on both sides with seals. Depending on the flow pattern of the fluid, the cold and hot fluid channels are stacked, arranged, and brazed together to form a plate bundle. The two-fluid flow patterns include counterflow, crossflow, and mixed countercrossflow. Fluids A and B are introduced into their respective plate bundle channels through the inlet head via guide vanes in a distribution section, and then guided to the outlet head through guide vanes in another distribution section; the two fluids exchange heat across a partition in counterflow. Common fin types include straight, porous, serrated, and corrugated forms. The main advantages of plate-fin heat exchangers are: ① High efficiency. Due to the disturbance of the fluid caused by the fins, the boundary layer that constitutes the thermal resistance is continuously renewed, resulting in a heat transfer coefficient that is generally three times that of shell-and-tube heat exchangers; moreover, good heat (cold) recovery efficiency is achieved at small temperature differences (1.5–2°C). It performs best when used for gas-to-gas heat exchange. ②Compact. Since most of the heat is transferred through the fins to the flat plate, the heat transfer area per unit volume of the device can reach 1500 m²/m³. ③When the heat transfer area is the same, its weight is nearly 1/5 that of a shell-and-tube heat exchanger. ④Rugged. Since the plate bundle is a single unit and the fins serve as a support between the two plates, it can withstand high operating pressures. Furthermore, simultaneous heat exchange of multiple fluids can also be achieved in the same device. However, plate-fin heat exchangers have narrow channels that are prone to clogging, making cleaning and maintenance difficult, and their manufacturing process is complex. It is mostly made of aluminum alloy, but it can also be made from copper, stainless steel, titanium, and others. Due to its excellent low-temperature performance and low weight, aluminum plate-fin heat exchangers are particularly suitable for cryogenic equipment such as oxygen, ethylene, and helium liquefaction, and can also be used in power systems. Aluminum plate-fin heat exchangers are generally used in applications with a design pressure of less than 6.3 MPa and design temperatures ranging from +200 to -270°C. Countries such as China, the United States, the United Kingdom, and Japan have already produced plate-fin heat exchangers. The development trends of plate-fin heat exchangers are: improving the precision of the fins and the quality of brazing, expanding the range of types and specifications, and enhancing research on the performance of the fins as well as the heat transfer mechanisms under multi-flow and phase-change conditions.