Plate-fin heat exchangers are usually composed of baffles, fins, seals, and guide vanes. Fins, guide vanes, and seals are placed between two adjacent baffles to form a sandwich, called a channel. Such sandwiches are stacked up according to different fluid flow patterns and brazed into a whole to form a plate bundle. The plate bundle is the core of the plate-fin heat exchanger.
Features of plate-fin heat exchangers
(1) High heat transfer efficiency. Since the fins disturb the fluid, the boundary layer is constantly broken, so it has a large heat transfer coefficient. At the same time, since the partitions and fins are very thin and have high thermal conductivity, the plate-fin heat exchanger can achieve a very high efficiency.
(2) Compact. Since the plate-fin heat exchanger has an extended secondary surface, its specific surface area can reach 1000㎡/m3.
(3) Lightweight. The reason is that it is compact and mostly made of aluminum alloy. Now steel, copper, composite materials, etc. have also been mass-produced.
(4) Strong adaptability. The plate-fin heat exchanger can be used for: gas-gas, gas-liquid, liquid-liquid, heat exchange between various fluids, and phase change heat exchange with collective state changes. Through the arrangement and combination of flow channels, it can adapt to different heat exchange conditions such as countercurrent, crossflow, multi-stream flow, and multi-pass flow. Through the combination of series, parallel, and series-parallel between units, it can meet the heat exchange needs of large equipment. In industry, it can be standardized and mass-produced to reduce costs, and interchangeability can be expanded through building block combination.
(5) The manufacturing process requirements are strict and the process is complicated.
(6) It is easy to clog, not corrosion-resistant, and difficult to clean and repair. Therefore, it can only be used in occasions where the heat exchange medium is clean, non-corrosive, not easy to scale, not easy to deposit, and not easy to clog.
From the perspective of heat transfer mechanism, the plate-fin heat exchanger still belongs to the partition heat exchanger. Its main feature is that it has an extended secondary heat transfer surface (fin), so the heat transfer process is not only carried out on the primary heat transfer surface (partition), but also on the secondary heat transfer surface. In addition to the heat from the high-temperature side medium being poured into the low-temperature side medium from the primary surface, part of the heat is also transferred along the height direction of the fin surface, that is, along the height direction of the fin, the partition pours heat, and then the heat is transferred to the low-temperature side medium by convection. Since the fin height greatly exceeds the fin thickness, the heat conduction process along the fin height direction is similar to the heat conduction of a homogeneous slender guide rod. At this time, the thermal resistance of the fin cannot be ignored. The highest temperature at both ends of the fin is equal to the partition temperature. As the fin and the medium release heat by convection, the temperature continues to decrease until the medium temperature in the middle area of the fin.
Application of plate-fin heat exchangers
Plate-fin heat exchangers have been increasingly widely used in various industrial sectors due to their superior performance and mature technology.
1. Air separation equipment: The use of plate-fin heat exchangers in the main heat exchanger, subcooler, condenser evaporator and other low-temperature heat exchangers of air separation equipment can save equipment investment and installation costs, and reduce unit energy consumption.
2. Petrochemical: Plate-fin heat exchangers have the advantages of large processing capacity, good separation effect and low energy consumption. They have been used in processes such as deep cold separation of ethylene, synthetic ammonia nitrogen washing, natural gas, oilfield gas separation and liquefaction.
3. Engineering machinery: After more than 20 years of research and practice, countries around the world have mass-produced and used plate-fin heat exchangers on automobiles, locomotive radiators, excavator oil coolers, refrigerator radiators, and high-power transformer radiators.
4. Superconductivity and space technology: The development of low-temperature superconductivity and space technology has provided a new way for the application of plate-fin heat exchangers. Plate-fin heat exchangers have been used on both the US Apollo spacecraft and the Chinese Shenzhou spacecraft.