Plate-fin

Compact brazed aluminum plate-fin heat exchangers can be used in most cryogenic hydrogen purification apphcations. The use of these relatively low cost heat exchangers, combined with low separation energy requirements, results in a highly economical process for hydrogen purification. 

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. 

FIG. 11-50 Expl oded view of a typical plate-fin arrangement. Trane Co.)... 

Design The economics usually work out in the favor of gas coolers when the centrifugal machines flow rate reaches about 5000 scfm. The pressure loss can Be kept to 7.0 kPa in most cases. When the ratio of A(ht lo Ajhs is 20 1, is another point to consider these plate-fin designs. Vibration is practically impossible with this design, and uses in reciprocating compressors are possible due to this. 

Marine and hydraulic-oil coolers use these characteristics to enhance the coefficient of otheiwise poorly performing fluids. The higher metallurgies in marine applications like 90/10 Cu-Ni afford the higher cost of plate-fin design to be offset by the less amount of alloy material being used. On small hydrauhc coolers, these fins usually allow one to two size smaller coolers for the package and save sldd space and initial cost. 

A common type of heat exchanger used in industrial ventilation is the plate fin-and-tube heat exchanger (Fig. 9.7). Liquid or gas flows in the tubes, with a gas or a liquid circulating outside the tubes between the plates. 

The complete study of annular ftns is essential in order to calculate the amount of conduction in the plate fin. A schematic diagram of annular fins is given in Fig. 9.8. 

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. 

It is very difficult to estimate the magnitude of the contact conductance G. Normally the total conductance of the heat exchanger is determined, and G - is calculated from Eq. (9.48). Only in the case that rhe plate fins are welded to the pipes with a metallurgical contact is the contact conductance infinite, leading to zero contact resistance, that is 1 /G,. = 0. 

Kim, N.-H, Yun, f.-H., and Webb, R. L. Heat transfer and friction correlations for wavy plate fin-and-tube heat exchangers. Journal of Heat Transfer 119 (1997) August, pp. 560-567,... 

Fan, Y. N., How to Design Plate-Fin Exchnagers, Heat Exchanger Design Handbook, Gulf Publishing Company (1968) p. 59. 

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. 

Siegel, R. and Howell, J. R. Thermal Radiation Heat Transfer, 2nd edn (McGraw-Hill, New York, 1981) Sparrow, E. M. and Cess, R. D. Radiation Heat Transfer (Hemisphere Publishing, New York, 1978) Taylor, M. (ed.). Plate-fin Heat Exchangers Guide to their Specification and Use (HTFS, Harwell, 1987). Tohloukian, Y. S. Thermophvsical Properties of High Temperature Solid Materials (Macmillan, New York. 1967)... 

Fig. 2.69a,b Coefficient of performance for aluminum plate fin array in forced convection (a) maximum heat transfer design, and (b) least material design. Reprinted from Bar-Cohen et al. (2006) with permission... 

Plate-fin heat exchangers. Another type of plate heat exchanger is the plate-fin heat exchanger. This is illustrated in Figure 15.17. The plate-fin heat exchanger consists of a series of flat plates, between which is a matrix formed... 

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