Finned tubes, in heat exchangers

Design for Heat Transfer Coefficients by Forced Convection Using Radial Low-Fin tubes in Heat Exchanger Bundles... 

Zukauskas, A., Skrinska, A., Zingzda, J., and Gnielinski, V., Banks of Plain and Finned Tubes, in Heat Exchanger Design Handbook—1998, Hewitt, G. F., Ed., Section 2.5.3, Begell House, New York, 1998. 

The heat transfer area, A ft, in an exchanger is usually estahlished as the outside surface of all the plain or hare tubes or the total finned surface on the outside of all the finned tubes in the tube bundle. As will be illustrated later, factors that inherendy are a part of the inside of the tube (such as the inside scale, transfer film coefficient, etc.) are often corrected for convenience to equivalent outside conditions to be consistent. When not stated, transfer area in conventional shell and tube heat exchangers is considered as outside tube area. 

Figure 10-144. Approximate relationship of the overall coefficient fouled, and the fouling factor of inside tubes for predicting the economical use of finned tubes in shell and tube units. (Used by permission Williams, R. B., and Katz, D. L. Performance of Finned Tubes and Shell and Tube Heat Exchangers, 1951. University of Michigan. Note For reference only, 1950 costs.)...

For a double pipe exchanger (one finned tube in each of two shells), see Figure 10-4A, the heat flow resistances are ... 

Kern and Kraus (1972) give full details of the use of finned tubes in process heat exchangers design and design methods. 

In heat exchangers, fins are used on tubes (externally or internally) to enhance the available surface area for heat transfer. For a plain tube heat exchanger, the overall heat-transfer coefficient is given by ... 

The contact resistance is also affected by differential thermal expansion when the surfaces are at elevated temperatures or with large temperature differences in the two materials. The problem is aggravated by thermal cycling, especially if one material is heated above its elastic behavior range, and must be considered with finned tubes in air-cooled heat exchangers. 

Williams, R. B., and Katz, D. L., Performance of Finned Tubes in Shell and Tube Heat Exchangers, Tram. ASME 74, 1307-1320 (1952). 

Square Isothermal Fins on a Horizontal Tube. Square fins attached to a horizontal tube, as shown in Fig. 4.23e, are commonly used in heat exchangers. The experimental data of Elen-baas [88, 89] for square plates, without the tube, covered the range 0.2 < Ra < 4 x 104, for Pr = 0.71. These data are closely correlated by... 

W. E. Hilding and C. H. Coogan Jr., Heat Transfer and Pressure Loss Measurements in Internally Finned Tubes, in Symp. Air-Cooled Heat Exchangers, pp. 57-85, ASME, New York, 1964. 

For the precooler, the helical coil type heat exchanger which has proven results for various machine type has been selected and the low-fin tube has been employed to reduce the height. If a plate-firmed or fin-and-tube type heat exchanger is employed for the precooler, it can reduce the installation space for the precooler. This subject will be dealt Avith in the next stage of our research work. 

Thbe evaporators with thermosiphon circulation or continuous flow evaporators are mainly used in rectification facilities. Falling film evaporators or film evaporators are seldom used. The vapor is condensed in a horizontal liquid-cooled tube bundle heat exchanger or air-cooled finned-tube heat exchangers [2.135]. 

In the example shown in Figure 3.15 EHD is used to assist the draining of condensate from between fins on a heat exchanger tube (Butrymowicz et al., 2003). The main feature is the arrangement of the tube-electrode system. In this case the... 

Example 5.5, If the finned tube in Example 5.4 is placed inside another tube with an inside diameter of 30 mm to form a countercurrent concentric tube heat exchanger, determine the overall heat transfer coefficient for the exchanger when the mass flow rate of the return air at 0.101 MPa and 175 K is 0.094 kg/s. Base the overall heat transfer coefficient on the outside area of the finned tube. 

In petrochemical plants, fans are most commonly used ia air-cooled heat exchangers that can be described as overgrown automobile radiators (see HeaT-EXCHANGEtechnology). Process fluid ia the finned tubes is cooled usually by two fans, either forced draft (fans below the bundle) or iaduced draft (fans above the bundles). Normally, one fan is a fixed pitch and one is variable pitch to control the process outlet temperature within a closely controlled set poiat. A temperature iadicating controller (TIC) measures the outlet fluid temperature and controls the variable pitch fan to maintain the set poiat temperature to within a few degrees. 

Transverse fins upon tubes are used in low-pressure gas sei vices. The primary application is in air-cooled heat exchangers (as discussed under that heading), but shell-and-tube exchangers with these tubes are in sei vice. 

Low-fin tubes (Mfi-in-high fins) provide 2.5 times the surface per lineal foot. Surface required should be divided by 2.5 then use Fig. 11-41 to determine basic cost of the heat exchanger. Actual surface times extra costs (from Table 11-14) should then be added to determine cost of fin-tube exchanger. 

HumidiRcation Chambers The air-cooled heat exchanger is provided with humidification chambers in which the air is cooled to a close approach to the wet-bulb temperature before entering the finned-tube bundle of the heat exchanger. 

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