H finned tube is also called square finned tube to recovers the waste heat of exhaust gas from power station boilers, industrial boilers, industrial kilns, ship power plants, etc., and effectively improves the utilization rate of fuel, and the enhanced heat exchange is arranged at the tail of the system flue element. Due to the characteristics of the convective heat transfer of the low-temperature flue gas-that is, the heat release coefficient a1 of the flue gas to the tube wall is much smaller than the heat release coefficient a2 of the tube wall to the steam and waterside, the use of an extended heating surface on the flue gas side is very effective necessary. The "economizers" (also called economizers) currently used in boilers include smooth tubes, spiral fin tubes, cast iron fin tubes, membrane wall tubes, etc. Except for the smooth tube type, the rest all Expand the heating surface structure.