Heat exchangers design procedures

A logic diagram of a heat exchanger design procedure appears in Figure 8.13. The key elements are ... 

The structure of the process heat exchanger design procedure is shown in Fig. 13. The basic structure is the same whether hand or computer-based design methods are used all that is different is the replacement of the very subtle and complicated human thought process by an algorithm suited to a fast but inflexible computer. 

In many cases of industrial importance, heat is transferred from one fluid, through a solid wall, to another fluid. The transfer occurs in a heat exchanger. Section 11 introduces several types of heat exchangers, design procedures, overall heat-transfer coefficients, and mean temperature differences. Section 3 introduces dimensional analysis and the dimensionless groups associated with the heat-transfer coefficient. 

FIGURE 6.53 Logical structure of the process heat-exchanger design procedure. 

R. K. Shah, Plate-Fin and Tube-Fin Heat Exchanger Design Procedures, in Heat Transfer Equipment Design, R. K. Shah, E. C. Subbarao, and R. A. Mashelkar (eds.), pp. 255-266, Hemisphere Publishing Corp., Washington, DC, 1988. 

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 solution to this example illustrates the iterative nature of heat exchanger design calculations. An algorithm for the design of shell-and-tube exchangers is shown in Figure A (see p. 684). The procedure set out in this figure will be followed in the solution. 

Brown, R. (1978) Chem. Eng., NY 85 (March 27th) 414. Design of air-cooled heat exchangers a procedure for preliminary estimates. 

Considerable interest has been generated in turbulence promoters for both RO and UF. Equations 4 and 5 show considerable improvements in the mass-transfer coefficient when operating UF in turbulent flow. Of course the penalty in pressure drop incurred in a turbulent flow system is much higher than in laminar flow. Another way to increase the mass-transfer is by introducing turbulence promoters in laminar flow. This procedure is practiced extensively in enhanced heat-exchanger design and is now exploited in membrane hardware design. 

Figure 8.13. A procedure for the design of a heat exchanger, comprising a tentative selection of design parameters, rating of the performance, modification of this design if necessary, and re-rating to meet specifications (see also Bell, in Heat Exchanger Design Handbook, Section 3.1.3, Hemisphere Publishing Company, 1983).

Example 8.12 summarizes the results of such calculations made on the basis of data in Heat Exchanger Design Handbook (1983). Procedures for the design of kettle, thermosiphon and forced circulation reboilers also are outlined by Polley (in Chisholm, 1980, Chap. 3). 

TUBE-SIDE POWER COST IMMATERIAL. Optimization of the heat-exchanger design for this situation is based on the assumption that C, is zero and ht is constant. The procedure is similar to that for the case of shell-side power immaterial as described in the preceding paragraph. The optimum value of h0 can be determined from the following equation, which is obtained by setting the partial derivatives of Eq. (44) with respect to hQ and with respect to A, equal to zero ... 

The procedure for developing an optimum heat-exchanger design is simplified if the temperature of one of the fluids remains constant. This condition is often encountered when one of the fluidfc changes phase, as in a condenser or a steam heater. 

The concept of overall mass-transfer coefficients is in many ways similar to that of overall heat-transfer coefficients in heat-exchanger design. And, as is the practice in heat transfer, the overall coefficients of mass transfer, are frequently synthesized through the relationships developed above from the individual coefficients for the separate phases. These can be taken, for example, from the correlations of Chap. 3 or from those developed in later chapters for specific types of mass-transfer equipment. It is important to recognize the limitations inherent in this procedure [6]. 

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