Vulcan's Helical Serrated Finned Tubes are produced by helically wrapping continuous serrated fin strip on edge around the tube circumference and continuously welding the fin strip to the tube.  Before being formed around the tube, the fin strip is cut (or "serrated") crosswise from one edge (which will become the outer edge of the fin segments) to within 1/4" of the other edge, leaving an uncut portion that will become a continuous base for the fin segments.  The interval between cuts (which determines the segment width after the strip is formed around the tube) may be specified as either 5/32" or 5/16".   After being cut, the fin strip is held under tension and confined laterally as it is formed around the tube, thereby ensuring forceful contact with the tube surface.  As the fin strip is formed around the tube its outer (serrated) edge spreads, opening the segments like petals of a daisy.   A continuous weld is applied at the point where the fin strip first begins to bend around the tube diameter, using the gas metal arc welding (GMAW) process.

For a given pipe or tube size, the desired heat transfer surface area per unit length of tube can be obtained by specifying the appropriate fin height and/or number of fins per inch of length.

Several claims have been made for the advantages of Helical Serrated finned tube over Helical Solid finned tube ...

• For some configurations, for a given tube diameter, fin height, and fin pitch the helical serrated configuration will have greater heat transfer surface area than the helical solid configuration. (However, this is not true for all combinations of pipe diameter and fin height -- see the tables included in Design Info.)

• For a given tube diameter, a greater fin height can be used for helical serrated than for helical solid (in other words, the ratio of fin height to tube outside diameter can be greater).  For configurations with large fin height/tube OD ratio, the solid fin strip must undergo significant deformation of its outer edge as it is formed around the tube -- its outer edge is stretched and its inner edge is compressed.   This deformation can cause thinning of the outer fin edge and/or wrinkling of the fin base and/or cupping of the fin.  In severe cases, the fin strip may tear at its outer edge and break during the manufacturing process.  In contrast, the serrated fin strip is free to spread from its outer edge down to its unserrated base (which is only 1/4" high) during the forming process.

• It has been claimed that the serrated segments allow some lateral flow of fluid along the tube axis (perpendicular to the fin), which serves to increase turbulence (thereby increasing heat transfer efficiency), and also slows the formation of fouling deposits between fins. 

The following table shows Vulcan's manufacturing capabilities for helical serrated finned tube ...

This welded steel finned tube configuration can be used for practically any heat transfer application, and is particularly suited to high temperature, high pressure applications.   The important features of this configuration are efficient, effective bond of fin to tube under all conditions of temperature and pressure, and ability to withstand high fin-side temperatures.

See Vulcan's "Standard Specifications for Welded Helical Serrated Finned Tubes"

© 2006 Vulcan Finned Tubes, L.P.