Heat exchangers, design

Similar considerations apply to the selection of pressure drops where there is freedom of choice, although a full economic analysis is justified only in the case of very expensive units. For liquids, typical values in optimised units are 35 kN/m where the viscosity is less than 1 mN s/m and 50-70 kN/m where the viscosity is 1-10 mN s/m for gases, 0.4 - G.8 kN/m for high vacuum operation, 50 per cent of the system pressure at 100-200 kN/m, and 10 per cent of the system pressure above 1000 kN/m. Whatever pressure drop is used, it is important that erosion and flow-induced tube vibration caused by high velocity fluids are avoided. 

The general approach is to calculate the area for cross-flow for a hypothetical row of tubes at the shell equator from the equation given in Section 9.4.4  

Using this equivalent diameter, the shell-side Reynolds number is then  

The pressure drop over the shell nozzles should be added to this value although this is usually only significant with gases. In general, the nozzle pressure loss is 1.5 velocity heads for the inlet and 0.5 velocity heads for the outlet, based on the nozzle area or the 

Using Kern s method, design a shell and tube heat exchanger to cool 30 kg/s of butyl alcohol from 370 to 315 K using treated water as the coolant. The water will enter at 300 K and leave at 315 K. 

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Synthesis and Detailed Heat Exchanger Design, Trans. IChemE, part A, 69 445, 1991. 

A numerical study of the effect of area ratio on the flow distribution in parallel flow manifolds used in a Hquid cooling module for electronic packaging demonstrate the useflilness of such a computational fluid dynamic code. The manifolds have rectangular headers and channels divided with thin baffles, as shown in Figure 12. Because the flow is laminar in small heat exchangers designed for electronic packaging or biochemical process, the inlet Reynolds numbers of 5, 50, and 250 were used for three different area ratio cases, ie, AR = 4, 8, and 16. 

A. P. Fraas, Heat Exchanger Design, 2nd ed., John Wiley Sons., Inc., New York, 1989. 

B = direct expansion coils, C = flooded evaporators, and D = special heat-exchanger designs. 

P, V, h, and 5 interpolated and converted from Heat Exchanger Design Handbook, vol. 5, Hemisphere, Washington, DC, 1983 and reproduced in Beaton, C. F. and G. F. Hewitt, Physical Propeity Data for the Design Engineer, Hemisphere, New York, 1989 (394 pp-)- Other values compiled hy P. E. Liley An enthalpy-pressure diagram to 1000 psia, 250—500 F appears in J. Chem. Eng. Data 7, 1 (1962) 75-78. 

Values interpolated and converted from Martin, J. J., 1977 (private communication), and from Heat Exchanger Design Handbook, vol. 5, Hemisphere, Washington, DC, 1983. Values of Ziegler, Chem.-lng.-Tech., 22 (1950) 229, apparently were also used in Landolt-Bornstein, IVa, (1967) 238-239, and in UUmans Enzyklopadie der technische Chemie, 9, Verlag Chemie, Weinheim, 1975 (317-372). 

Values interpolated and converted from Heat Exchanger Design Handbook, voL 5, Hemisphere, Washington, DC, 1983, and from various hterature sources. 

Especially at low temperatures, the thermal conductivity can often be markedly reduced by even small traces of impurities. This table, for the highest-purity specimens available, should thus be used with caution in apphcations with commercial materials. From Perry, Engineeiing Manual, 3d ed., McGraw-Hill, New York, 1976. A more detailed table appears as Section 5.5.6 in the Heat Exchanger Design Handbook, Hemisphere Pub. Corp., Washington, DC, 1983. f Parallel to basal plane. 

Another growing field is that of nonmetallic heat exchanger designs which typically are of the shell and tube or coiled-tubing type. The graphite units were previously discussed but numerous other materi- s are available. The materials include Teflon, PVDF, glass, ceramic, and others as the need arises. 

There are two basic approaches to heat-exchanger design for low temperatures (1) the effec tiveness-NTU approach and (2) the log-mean-temperature-difference (LMTD) approach. The LMTD approach is used most frequently when all the required mass flows are known and the area of the exchanger is to be determined. The effec-... 

Heat Exchangers. Several aspects of heat exchanger design should be reviewed at this stage of the study since they impact on workability and cost. 

A check should be made to be sure that the licensor has not included any temperature cross situations in shell and tube heat exchanger design. In Figure 1, the colder fluid being heated emerges hotter than the outlet temperature of the other fluid. This is an impossible real world situation, or close enough to impossible to be undesirable for the plant design. 

The assumptions hold so well that the F factor charts are standardized by TEMA for shell and tube heat exchanger design. 

Patankar, S. V., and D. B. Spalding. 1974. A calculation procedure for the transient and steady-state behavior of shell-and-tube heat exchangers. In N. H. Afgan and E. V. Schliinder (eds.). Heat Exchangers Design and Theory Sourcebook. New York McGraw-Hill, pp. 155-176. 

The factors that affect the evaporation process are concentration in the liquid, solubility, pressure, temperature, scaling, and materials of construction. An evaporator is a type of heat exchanger designed to induce boiling and evaporation of a liquid. The major types of evaporator are... 

Figure 10-37. Finding a counterflow weighted MTD. (Reprinted with permission Gulley, Dale E., Heat Exchanger Design Handbook, 1968 by Gulf Publishing Company, Houston, Texas. All rights reserved.)...

In heat exchanger design, the exchange of the heat between fluids is considered to be complete (i.e., 100%)... 

Gulley, D. L., How to Calculate Weighted MTDs, Heat Exchanger Design Book, Gulf Publishing Company, p. 13 (1968). 

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