Harmony Search Applications in Mechanical, Chemical and Electrical Engineering - Music-Inspired Harmony Search Algorithm: Theory and Applications - page 70

2 Design Optimization of Heat Exchangers
Design optimization of Heat exchangers is a complex task due to the coupled nature of
the design parameters involved. This section will focus on design optimization of heat
exchangers from an economic point of view and review some real-world examples.
2.1 Shell and Tube Heat Exchangers
Shell and tube heat exchangers (STHE) are the most common types of heat exchang-
ers in oil refineries and other large chemical processes, and are suited for a wide range
of operating temperatures and pressures. This type of heat exchanger consists of a
shell with a bundle of tubes inside. One fluid runs through the tubes and another fluid
flows over the tubes (through the shell) to transfer heat between the two fluids [1]. A
typical STHE is illustrated in Fig. 1. From a design point of view, STHEs represent a
complex process containing an integrated whole of design rules and empirical knowl-
edge of various fields. In fact, there are several parameters, such as tube diameter,
tube length, tube pitch, tube pitch pattern, tube passes, baffle cuts, baffle spacing, and
tube material, which need to be taken into account in design of STHEs.
Similar to most thermal systems, different types of variables including real, integer
and discrete types take part in design problem of heat exchangers. Integer variables
appear when the quantity of some identical components is a variable, such as the
number of tubes or tube passes in heat exchangers. Discrete variables usually arise
from discrete standard sizes of materials, such as the standard tube diameter, shell
diameter and tube pitch pattern.
Fig. 1. Schematic of a shell and tube heat exchanger
2.1.1 Problem Formulation for Design of STHEs
The objective function in heat exchanger design problems is normally the total annual
cost of the exchanger which includes the capital cost and pumping costs. However,
there are some studies in the literature which consider the rate of entropy generation
as the objective function as well [2-4]. Capital cost is usually approximated based on