A Novel Equivalence Approximate Model for Second Law Based Optimization of Three-Fluid Cross-Flow Plate-Fin Heat Exchanger Using Genetic Algorithm

Number of entropy generation is a significant performance evaluation factor for heat exchanger as it results in trade-off between heat transfer and pressure drop. Optimization of the three-fluid heat exchanger (⁠$3−FHX)$ for minimum number of entropy generation unit requires $ε−NTU$ relation which is unavailable for three-fluid cross-flow heat exchanger due to various complexities involved. A new approximate methodology for the optimization is presented by proving the equivalence of $3−FHX$ with a coupled two-fluid heat exchanger (⁠$2−FHX$⁠) followed by using $ε−NTU$ relationship for $2−FHX$⁠. The experimental and numerical validation of the equivalence model is presented. Three-fluid cross-flow compact heat exchanger with offset strip fins is optimized for minimum number of entropy generation units using genetic algorithm (GA). Optimum design variables including heat distribution factor are determined for different cross-flow arrangements of $3−FHX$ with heat duty and pressure drop as constraint for both even and uneven fin dimensions case in all the passages. The present complex model including large number of continuous design variables can be handled well by GA. Validation of the results is carried out by using graphical techniques and very good agreement is observed. Additionally, sensitivity of the heat exchanger dimension has also been checked on the number of entropy generation along with the pressure drop in all the three fluids.