The main objective of this study is to explore the effectiveness of Simulated Annealing technique in the design optimization of STHEs from economic point of view。 Ability of the SA based technique is demon- strated using different case studies and parametric analysis。 

The second objective of the present study is to design the optimum heat exchanger, which would  comply with tubular exchangers manufactures asso- ciation (TEMA) standards and obey the industrial re- quirement of geometric, velocity and pressure drop  constraints。 Most of the optimum solutions (say tube  diameter, tube length, baffle spacing, shell diameter,  etc。) found in the literature are not available as per  TEMA standard sizes and thus makes the  fabrication of heat exchanger costly due to nonstandard sizes。  Also, some practical design rules such as geometric constraints, velocity  and  pressure  drop  constraints  are usually ignored in the algorithms present in the literature, which restrains the effective application of design solutions found。 In spite of the new algorithmic developments applied to heat exchanger design in literature, the complexity of the task allows some cri- ticism of the effectiveness of optimization procedures for real industrial problems [13]。 In this context of the development of new design algorithms, this paper  presents an optimization procedure integrated with practical design guidelines, aiming to provide a fea- sible alternative in an engineering point of view。 

With the application of SA algorithm, it is    found in the present study that multiple heat exchanger con- figurations are possible with practically same cost or with little cost difference。 The lowest cost exchangers are not always performing best in actual shop floor。  Maintainability, ease of cleaning of tubes and shells, less fouling tendency, less flow  induced vibrations,  less floor space requirement, compactness of design etc are some of the criteria which must be considered in industrial scenario。 All these solutions are feasible and user has flexibility to choose any one of them based on his requirement and engineering judgment。 This paper collects some practical guidelines from li- terature regarding how to choose the  best exchan- gers among various alternatives。 

THE OPTIMAL HEAT EXCHANGER DESIGN PROBLEM 

The procedure for optimal heat exchanger de- sign includes the following step: 

a。 Estimation of the  exchanger  heat  transfer  area based on the required duty and other design specifications assuming a set of design variable。 

b。 Evaluation of the capital investment, ope- rating cost and the objective function。 

c。 Utilization of the optimization algorithm to se- lect a new set of values for the design variables。 

d。 Iterations of the previous steps until a mini- mum of the objective function is found。 

The entire process is schematized in Figure 1。 

User input。 Following parameters are required as a user defined input to calculate the heat exchanger area: 

1。 Mass flow rate and inlet/outlet   temperatures of shell side and tube side fluids。 

2。 Thermophysical properties of both fluids, e。g。, density, viscosity, heat capacity, thermal conductivity。 

3。 Fouling resistances, Rfoul, shell and Rfoul, tube。 

Input optimization variables。 The optimization  variables, with values assigned iteratively by the opti- mization techniques (e。g。 SA) are given in Table 1。 

Calculation sequence 

1。Assume overall heat transfer coefficient based on type of shell and tube side fluid。 

2。Based on the actual values of the design specifications and on the current values of the opti- mization variables, the exchanger design routine de- termines the values of the shell side and tube side heat transfer coefficients, the overall exchanger area, the number of tubes, the shell diameter and tube side and shell side flow velocities, thus defining all cons- tructive details of the exchanger satisfying the as- signed thermal duty specifications。