Conference Year

2016

Keywords

Heat Exchanger, Performance, Optimization, Decision-Making, Utility Function

Abstract

The Performance Evaluation Criteria (PEC) constitutes a set of metrics that quantifies geometrical characteristics, and performance of a Heat eXchanger (HX) under design and off-design conditions. There is a vast literature describing different PEC methods and it can be separated into two main categories: energy-based and entropy-based metrics. The first include all metrics that directly measure the thermal-hydraulic performance and geometry features such as surface density, face area and aspect ratio. The second approach entails a more fundamental perspective by employing the second law of thermodynamics to determine the best and worst heat transfer surfaces in terms of entropy generation and/or exergy destruction. Usually the second approach brings a broader perspective when evaluating the HX in a system context. From a design viewpoint the choice of PEC is really a matter of preference, as long as the problem specifications are being met. A more challenging task, however, is the selection of the best HX amongst multiple alternatives. More recently, with the great advances in computational tools, a large number of novel HX concepts and multi-objective optimization (MOO) studies are being undertaken. When performing MOO analysis one must be able to understand why did the optimizer selected those optimum designs, and be able to know which one to select from a set of Pareto Optimal designs. In other words, from a decision-making viewpoint the use of PEC’s is less trivial. In this paper we provide a brief review of the available PEC in the literature for HX design. Additionally we present a set of PEC metrics that should be used for selecting a HX amongst multiple optimum designs, sized to perform the same job, i.e. same heat load capacity and fluid states. We developed a utility function, using such metrics that will better assist the decision-maker in selecting the best alternative. This utility function was specifically developed for single-phase air-to-refrigerant HX application, and applied to a case of study consisting of multiple optimum Pareto sets for different surfaces. Additional CFD analysis is also carried out for completeness and to illustrate the underlying physics of the airflow on different surfaces that lead to the differences in performance between different surfaces.

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