The finned tube is divided into an integral finned tube, a welded finned tube, a high frequency welded finned tube, and a mechanically connected finned tube.
The integral finned tube is cast, machined or rolled, and the fin is integrated with the tube. Like the low-pressure boiler, the economizer uses an integrally cast finned tube. These finned tubes have no contact thermal resistance, high strength, thermal shock resistance and mechanical vibration, and have good heat transfer, mechanical and thermal expansion properties, but are high in manufacturing cost and are suitable for low finned tubes having a fin ratio of less than 5.
The welded finned tubes are manufactured by brazing or inert gas welding. The fins of different materials are welded together with the tubes. The finned tubes are easy to manufacture, have good heat transfer and mechanical properties, and are widely used in industry. Since the residue in the weld is not conducive to heat transfer, the quality of the weld must be guaranteed.
The high-frequency welded finned tube is a high-frequency electric induction generated by a high-frequency generator, so that the surface of the tube is in contact with the fin to generate a high temperature and partially melted, and then the fin is integrated with the tube by pressurization. No soldering, no soldering, simple manufacturing, excellent performance, and the most common process in industrial applications.
The mechanical connection of the finned finned tube is poor, mainly due to the existence of contact thermal resistance. Especially during operation, the tension of the finned fin is rapidly decreased with the increase of temperature, so that the contact thermal resistance also increases rapidly. Solder sheet heat transfer performance is best. The performance of the sleeve type is also better because the fins are tightly coated with the surface of the tube and then hot-dip galvanized. The heat transfer performance of the bimetallic rolled sheet is similar to that of the insert type, which is to roll the fins after the set.