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This paper presents an approach based on genetic algorithms for the optimal design of shell-and-tube
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heat exchangers. The approach uses the Bell–Delaware method for the description of the shell-side flow
with no simplifications. The optimization procedure involves the selection of the major geometric param-
eters such as the number of tube-passes, standard internal and external tube diameters, tube layout and
pitch, type of head, fluids allocation, number of sealing strips, inlet and outlet baffle spacing, and shell-
side and tube-side pressure drops. The methodology takes into account the geometric and operational
constraints typically recommended by design codes. The examples analyzed show that genetic algo-
rithms provide a valuable tool for the optimal design of heat exchangers.1. Introduction
The transfer of heat between process fluids is an essential part of 5993
most chemical processes. To carry out such heat transfer process,
shell-and-tube heat exchangers are widely used because they are
robust and can work in a wide range of pressures, flows and tem-
peratures [1]. The traditional design approach for shell-and-tube
heat exchangers involves rating a large number of different exchan-
ger geometries to identify those that satisfy a given heat duty and a
set of geometric and operational constraints [2]. This approach is
time-consuming, and does not guarantee an optimal solution.
Jegede and Polley [3] reported a design approach based on sim-
plified equations that related the exchanger pressure drop, the sur-
face area and the heat transfer coefficient; theirmodelwas based on
the Dittus–Boelter correlation for the tube-side flow, and on the
Kern correlations for the shell-side flow [4]. The combination of
the pressure drop relationships with the basic exchanger design
equation gave rise to a simple design algorithmthat avoids the iter-
ative procedure required to test different geometries. However, the
use of the Kernmethodmay lead to significant errors in the calcula-
tions because of its simplified flow patternmodel for the shell-side.
Polley et al. [5] developed an algorithmusing the Bell–Delaware
method [6] to describe the flow pattern of the shell-side fluid. The
model accounts for leakage and bypass streams using the flow
model proposed by Tinker [6]. Although the model by Polley
et al. [5] provides better estimations than the one by Jegede and
Polley [3], some shortcomings can be mentioned. In order to keep
the accuracy of the Bell–Delaware method, Polley et al. [5] devel-
oped a rather complex relationship for pressure drop estimation
on the shell-side, which requires an iterative procedure that in-
volves detailed estimations of exchanger geometries. The algo-
rithm also shows some lack of flexibility for the shell-side,
because it is restricted by the assumptions that cross-flow areas
are equal to window flow areas, and that the spacings for end baf-
fles are equal to those for the central baffles. The second geometric
restriction ignores cases when large inlet and outlet nozzles make
it necessary to have higher inlet and outlet baffle spacings than
central baffle spacings [6]. Finally, the algorithm does not take into
account the end pressure losses on the tube-side due to contrac-
tions at the tube inlets, expansions at the exits, and flow reversal
in the headers.
Recently, Serna and Jimenez [7] presented an algorithm for the
rigorous design of segmentally baffled shell-and-tube heat
exchangers. The algorithm makes use of the maximum allowable
pressure drops of both streams without introducing geometric lim-
itations. In particular, the use of two compact formulations for
pressure drop estimations provides a simple algorithm with