Performance enhancement of double-tube heat exchangers using nonuniformly twisted elliptical tubes: A CFD based multi objective optimization approach via RSM and NSGA-II

This study proposes an innovative nonuniformly twisted elliptical tube heat exchanger (NTETHEX) with unequal twist pitches to address the inadequacy of uniformly twisted tube designs in double-tube heat exchanger system. A numerical investigation was conducted in the laminar regime, evaluating nine CFD cases with twist ratios ranging from 1.0 to 2.0. The optimal configuration featuring an outer tube combination of (400-800-1400) achieved the highest Nusselt number ( Nu ) and thermal performance. Further, the numerical solutions are optimized by integrating Box-Behnken Design, Response Surface Methodology, NSGA-II and a weighted factor scalarization technique. The critical design variables such as Reynolds number ( Re ), twist pitch ( P ), and surface temperature ( T s ) were analyzed to enhance the Nusselt number ( Nu ), minimizing the friction factor ( f ), and improving the PEC . Also, Quadratic polynomial regression models are developed, and their significance are evaluated through analysis of variance (ANOVA). The objective functions fitted via RSM are processed with NSGA-II to identify the set of Pareto optimal solutions. The outcomes of this multi objective optimization study compared with uniformly twisted tube and the Nu increased by 52 % and frictional coefficient is reduced by 200 % . It is evident that raising Re markedly enhances Nu . The best-performing NTETHEX configuration was found at Re = 3940.54, T s = 365 K , and P = 1.90 demonstrates the potential of nonuniformly twisted tube for highly efficient heat exchangers in critical energy applications.