Extended or Finned Surfaces

Finned-Surface Appbcation Extended or finned surfaces are often used when one film coefficient is substantially lower than the other, the goal being to make hjAj. A few t ical fin config-... 

By using an extended or finned heat transfer surface to increase the area of heat transfer... 

There are various WT and FT boiler economizer designs, classified as either steaming economizer and nonsteaming economizer types according to thermal performance. These economizers are constructed in either bare tube or finned tube (extended surface) patterns. They may be positioned horizontally or vertically within the boiler system, in either cross-flow or counterflow arrangements. 

Figure 8.6. Examples of extended surfaces on one or both sides, (a) Radial fins, (b) Serrated radial fins, (c) Studded surface, (d) Joint between tubesheet and low fin tube with three times bare surface, (e) External axial fins, (f) Internal axial fins, (g) Finned surface with internal spiral to promote turbulence, (h) Plate fins on both sides, (i) Tubes and plate fins.

This chapter discusses one-dimensional steady-state heat conduction in three different coordinate systems. There is a discussion on temperature-dependent thermal conductivity. Extended surfaces or fins are treated exhaustively. 

This differential equation covers all forms of extended surfaces, as long as the aforementioned assumptions are met. The different fin or pin shapes are expressed by the terms Aq = Aq(x) for the cross sectional area and Af = Af(x) for the fin surface area over which the heat is released. So for a straight fin of width b perpendicular to the drawing plane in Fig. 2.11, with a profile function y = y(x) we obtain the following for the two areas... 

Free Convection. The topic of finned surfaces in free convection is covered in Sec. C.2 of Ref. 368. From the standpoint of enhancement, much interest has focused on interrupted extended surfaces such as the wire-loop fins used for baseboard hot water heaters or con-... 

The heat transfer surface is a surface of the exchanger core that is in direct contact with fluids and through which heat is transferred by conduction. The portion of the surface that also separates the fluids is referred to as the primary or direct surface. To increase heat transfer area, appendages known as fins may be intimately connected to the primary surface to provide extended, secondary, or indirect surface. Thus, the addition of fins reduces the thermal resistance on that side and thereby increases the net heat transfer from/to the surface for the same temperature difference. The heat transfer coefficient can also be higher for fins. 

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