Multi-objective optimization of corrugated tube with loose-fit twisted tape using RSM and NSGA-II

A multi-objective optimization of corrugated tube with loose-fit twisted tape (CLT) is conducted to obtain the optimal performance, using Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm (NSGA-II). A series of simulation runs are performed to optimize the design variables on the objective functions. The corrugation parameters are fixed at constant values. The design variables include the Reynolds number (Re), twisted ratio (Y), and clearance ratio (CR). The objective functions involving the Nusselt number ratio (Nu/Nu_s), friction factor ratio (f/f_s), and overall heat transfer performance (η) are calculated from numerical simulations. Regression models for Nu/Nu_s, f/f_s, and η are tested, the statistical importance of each is assessed by means of the analysis of variance (ANOVA), and the models are expressed in quadratic polynomial forms. The multi-objective NSGA II is adopted to obtain the Pareto-optimal fronts. The results show that the most significant factor is the linear term of Y for Nu_c/Nu_s and f_c/f_s, while that for η is the linear term of Re. Pareto optimal solution can be obtained with the optimum Nu_c/Nu_s = 2.484 and f_c/f_s = 3.324. The corresponding values of the design variables are Re = 4000.08, Y = 2.79, and CR = 0.20. The optimal design variables against Re are also obtained, which possesses practical significances for designing heat exchanger.