Examination of convective heat transfer and entropy generation performance in twisted elliptical tubes using response surface method

In this paper, the convective heat transfer (CHT) and flow properties of twisted elliptical tubes (TETs) are numerically simulated within the range of Reynolds numbers (Re) 710 to 4790. The effects of design parameters such as twist ratio (P/D), aspect ratio (A/B), and Re on the CHT and flow resistance properties of TETs are highlighted. The response surface method (RSM) is used to research the effect of interaction between design parameters on the performance of CHT in TETs and establish the relationship between the objective function, i.e., Nusselt number (Nu), friction factor (f), and design parameters. The objective function fitted by RSM are optimized by the non-dominated sequential genetic algorithm (NSGA-II) to obtain the Pareto optimal solution. Besides, the entropy generation minimization principle explores entropy generation characteristics to reveal the mechanism of CHT enhancement in TETs. The results show that the CHT performance, flow resistance, and total entropy generation in TET increase, decrease, and increase with the growth of Re, respectively. They all increase with the reduction of P/D or the growth of A/B. The maximum values of Nu and pressure drop (ΔP) occur when A/B = 2.16 and P/D = 11.90; the minimum value of total entropy generation is reached when A/B = 1.34 and P/D = 26.33; and the Pareto optimal solution corresponds to the best combination of design parameters of Re = 3980, P/D = 13.32, and A/B = 1.82.