Harmony Search Applications in Mechanical, Chemical and Electrical Engineering - Music-Inspired Harmony Search Algorithm: Theory and Applications - page 72

2.2 Air-Cooled Heat Exchangers
Atmospheric air has been used for many years to cool and condense fluids in areas of
water scarcity. During the 1960s, the use of ACHEs grew rapidly worldwide. In
Europe, where seasonal variation in ambient temperature is relatively small, ACHEs
are used for the greater part of cooling process [9]. ACHEs are increasingly being
used nowadays due to significant increase in water cost, lack of water supplies, and
concern for water pollution.
A typical ACHE includes a tube bundle, which generally has spiral-wound fins
upon the tubes, and a fan, which moves air across the tubes and is provided with a
driver. Electric motors are the most commonly used drivers. A typical ACHE is
shown in Fig.2.
Fig. 2. Schematic of an air-cooled heat exchanger
Compared to the shell and tube exchangers, however, there are more parameters to
be taken into account, with the most important ones being tube diameter, tube length,
tube rows, number of tubes per row, air velocity, fan type, fan diameter, number of
fins, fin height, tube pattern and tube material. Similar to the shell and tube heat ex-
changers, an ACHE design problem has different variable types. Tube rows, number
of tubes per row and number of fins are integer variables, whereas tube diameter, fin
height, and tube pattern are discrete variables and can be chosen only from prespeci-
fied standard values.
In the last few decades, several methods for optimization of heat exchangers have
been developed. These methods can be classified into three main groups, namely ther-
modynamic approaches, mathematical programming methods and stochastic methods.
Thermodynamic approaches are based on Second Law Analysis. The aim of these
approaches is to minimize the exergy destruction or irreversibility. Mathematical