Finned surfaces plates

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.

In this section we limited our consideration to tube banks witli base surfaces (no fins). Tube banks with finned surfaces are also commonly used in practice, especially when the fluid is a gas, and heat transfer and pressure drop correlations can be found in the literature for tube banks with pin fins, plate fins, strip fins, etc. 

R. K. Shah, Temperature Effectiveness of Multiple Sandwich Rectangular Plate-Fin Surfaces, ASMEJ. Heat Transfer, Vol. 93C, pp. 471-473,1971. 

Increased heat transfer of surface area in contact with the coolant is accomplished by the use of extended surfaces, plates or pin fins, giving the heat transfer rate Qy by a fin or fin structure as... 

Reference 9- 58 provides a summary of open literature for heat transfer and pressure drop correlations/test data for offset strip and wavy fin surface geometries. Only one set of test data for a fixed offset strip geometry have been identified for HeXe gas mixtures in the PrandtI/Reynolds regime being considered for the recuperator. Reference 9- 59 provides a summary of test data for various gas mixtures of HeXe for an interrupted plate fin geometry. 

For extended surfaces, which include fins mounted perpendicularly to the tubes or spiral-wound fins, pin fins, plate fins, and so on, friction data for the specific surface involved should be used. For details, see Kays and London (Compact Heat Exchangers, 2d ed., McGraw-HiU, New York, 1964). If specific data are unavailable, the correlation by Gunter and Shaw (Trans. ASME, 67, 643-660 [1945]) may be used as an approximation. 

Here I /G. is the heat exchanger contact resistance. The reason for rhe contact resistance is that there exists a resistance to heat flow between the outer surface of the pipe and the collar of the plate tins. Normally, the fins are attached to the pipes by mechanical expansion of the tubes out into rhe plate-fin collars. Because of this manufacturing method, the contact will not be ideal. Small gaps between the pipe surface and rhe collar of the tins will occur. 

Figure 10-10E. A cutaway section of plate-type fins showing the continuous surface contact of the mechanically bonded tube and fins. (Used by permission The Trane Co., La Crosse, Wis.)...

Hall, D. E. Electrodeposited Zinc-Nickel Alloy Coatings —A Review , Plating and Surface Fin., 59-65 (Nov. 1983)... 

Above this size, the flow of air over the condenser surface will be by forced convection, i.e. fans. The high thermal resistance of the boundary layer on the air side of the heat exchanger leads to the use, in all but the very smallest condensers, of an extended surface. This takes the form of plate fins mechanically bonded onto the refrigerant tubes in most commercial patterns. The ratio of outside to inside surface will be between 5 1 and 10 1. 

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