Detailed Design Optimization of Three-Fluid Parallel-Flow Plate-Fin Heat Exchanger Using Second Law Analysis

Compact parallel-flow three-fluid heat exchanger (TFHX) of plate-fin type is optimized for attaining the minimum entropy generation unit. Four different types of plate-fins (plain rectangular, offset strip, corrugated louvered, and wavy fin (WF)) which are embodied within heat exchanger have been selected for the study under both cocurrent and countercurrent flow arrangements. The range of the decision variables are $0.3≤ma, mb, mc≤3$⁠, $0.1≤Ø≤0.95$⁠, $0.1≤Lx, Ly≤2$⁠, $0.015≤H≤0.033$⁠, $100≤n≤700$⁠, $0.0001≤tf≤0.0002$⁠, $0.001≤l≤0.009$⁠, $0.01≤Lwav≤0.09$⁠, and $0.001≤A≤0.005$⁠. Genetic algorithm is selected as an optimization tool that is apt in handling various continuous and discrete variables and the problems with the complexities in the objective function as well as in constraints. Validation of the optimization model is carried out by comparing the optimum results with that obtained from the experiments, particle swarm optimization (PSO) (under without heat duty constraint), and graphical method (under with heat duty constraint). It is observed that for a specified heat duty (180 kW) and given operating conditions, corrugated louvered fin (CLF) with countercurrent flow arrangement offers the minimum entropy generation among all. It is riveting to learn that the optimum results occur for most of the considered cases when the flowrate of the central hot fluid is lower than that of the adjacent fluids. At fixed Re = 3000 for all the fin types, off-set strip fin is the most favorable one, and plain rectangular fin (PRF) offers the worst solution comparatively.