Dušan P. Sekulić

The objectives of Part 1 of HEDH is to set the scene for HEDH as whole, to present the basic theory of heat exchangers, and to give information relating to the utilization of heat exchangers in process plants. The first objective is met by discussing the basic nature of the quantities involved and the definition of the nomenclature adopted by HEDH is based entirely on SI Units. Though it could have been reasonably expected that SI units would have been universally adopted in the period since the first publication of HEDH in 1983, one has to recognize that other unit systems are still widely used, particularly those based on the former British system (pound mass, pound force, foot, Btu, etc.). The latter units are no longer used in Britain itself, but live on as U.S. customary units. It was important to continue to provide unit conversion information.

Section 1.1 provides a general introduction to heat exchangers covering flow configurations and thermal interactions between streams (Section 1.1.1 and Section 1.1.2), basic stream temperature patterns (Section 1.1.3), and the commonly used classifications for heat transfer, heat transfer surfaces, and heat exchanger device configurations (Section 1.1.4, Section 1.1.5, Section 1.1.6, and Section 1.1.7).

Section 1.2 deals with the theoretical background for heat exchangers with Section 1.2.1 introducing the thermodynamics concepts and conservation principles, Section 1.2.2 constitutive and flux relationships, and Section 1.2.3 the basic transfer coefficient dependencies. The overall balance equations are introduced in Section 1.2.4 and the differential equations governing heat transfer process are presented in Section 1.2.5 and Section 1.2.6.

In Section 1.3, simplified models for design are introduced. In Section 1.3.1 design problems are listed, in Section 1.3.2 the analytical models are discussed, and in Section 1.3.3 and Section 1.3.4 a set of solutions to these models for a wide variety of heat exchanger configurations and the engineering representation of these solutions are provided.

Modern computational tools, and specifically computational fluid dynamics (CFD) models, are increasingly used in heat exchanger design and this subject is introduced in Section 1.4. This starts with a general introduction to CFD (Section 1.4.1) and then deals with cases where the flow pattern is assumed to be known (Section 1.4.2). It is shown that CFD methods not only predict the analytical solutions given in Section 1.3 but also allow investigations of the basic assumptions of these solutions. The application of CFD models to the prediction of shell-side in shell-and-tube-heat exchanges is presented in Section 3.3.14.

In an ideal countercurrent flow heat exchanger exchanging heat between two single-phase streams with constant heat capacity, the average temperature difference is the logarithmic mean value. Deviations from this ideal case occur, for instance, in shell-and-tube exchangers having more than one pass, in heat exchangers with cross flow, etc. These deviations can be dealt with using correction factors, and a wide range of information on such factors is presented in Section 1.5. The correction factors are estimated using a number of assumptions. One of the assumptions for shell-and-tube heat exchangers is that the flow is 1D; some relaxation of this assumption can be obtained using the “cell method” as described in Section 1.6.

Section 1.7, Section 1.8, and Section 1.9 address the broader issue of optimal utilization of energy in process systems. In Section 1.7, the pinch analysis method for the design of heat exchanger networks so as to achieve the maximum heat recovery is presented. Spectacular energy savings have been achieved using this technology but there also has to be concern not only about the quantity of energy but also its quality (or capacity to be converted into useful work) as represented by available energy or exergy. Discussions of the minimization of entropy generation and of the analysis of processes in terms of exergy are given in Section 1.8 and Section 1.9.