Brazed spiral finned tubing
The processing of the brazed spiral finned tube has two steps. First, the steel strip plane perpendicular to the pipe axis in a spiral way wound on the outer surface of the pipe, and the steel strip ends welded on the steel pipe, and then to eliminate the gap between the steel strip, the use brazing method welded the strip and bare pipes together.
This method, because the cost is expensive, so commonly used another method is wrapped around good steel tube into zinc bath in the overall hot-dip galvanizing to replace. The entire hot dip galvanizing, although the bath is not necessarily good to seep into fin and tube between a minimum space, but in the outer surface of the fin surface and the outer tube is the formation of a a complete galvanized layer. The use of the overall hot galvanized spiral fin tube, due to the thickness of the zinc coating (galvanized layer thickness, the zinc layer is strong, easy to fall off), and the zinc liquid can not be all into the gap, so, the combination of fin and tube is still not high. In addition, the heat transfer coefficient of zinc is lower than that of steel (about 78%), so the heat transfer ability is lower. Zinc in acid and alkali, sulfide in the extremely vulnerable to corrosion, so, with galvanized spiral finned tube is not suitable for air preheater (recovery boiler flue gas waste heat).
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