Optimal Shell and Tube Heat Exchangers Design

Abstract

Due to their resistant manufacturing features and design flexibility, shell and tube heat exchangers are the most used heat transfer equipment in industrial processes. They are also easy adaptable to operational conditions. In this way, the design of shell and tube heat exchangers is a very important subject in industrial processes. Nevertheless, some difficulties are found, especially in the shell-side design, because of the complex characteristics of heat transfer and pressure drop. Figure 1 shows an example of this kind of equipment. In designing shell and tube heat exchangers, to calculate the heat exchange area, some methods were proposed in the literature. Bell-Delaware is the most complete shell and tube heat exchanger design method. It is based on mechanical shell side details and presents more realistic and accurate results for the shell side film heat transfer coefficient and pressure drop. Figure 2 presents the method flow model, that considers different streams: leakages between tubes and baffles, bypass of the tube bundle without cross flow, leakages between shell and baffles, leakages due to more than one tube passes and the main stream, and tube bundle cross flow. These streams do not occur in so well defined regions, but interacts ones to others, needing a complex mathematical treatment to represent the real shell side flow. In the majority of published papers as well as in industrial applications, heat transfer coefficients are estimated, based, generally on literature tables. These values have always a large degree of uncertainty. So, more realistic values can be obtained if these coefficients are not estimated, but calculated during the design task. A few number of papers present shell and tube heat exchanger design including overall heat transfer coefficient calculations (Polley et al., 1990, Polley and Panjeh Shah, 1991, Jegede and Polley, 1992, and Panjeh Shah, 1992, Ravagnani, 1994, Ravagnani et al. (2003), Mizutani et al., 2003, Serna and Jimenez, 2004, Ravagnani and Caballero, 2007a, and Ravagnani et al., 2009). In this chapter, the work of Ravagnani (1994) will be used as a base to the design of the shell and tube heat exchangers. A systematic procedure was developed using the Bell-Delaware method. Overall and individual heat transfer coefficients are calculated based on a TEMA (TEMA, 1998) tube counting table, as proposed in Ravagnani et al. (2009), beginning with the smallest heat exchanger with the biggest number of tube passes, to use all the pressure drop