Optimization of enhanced heat transfer and flow resistance reduction in twisted petaloid helically coiled tube based on ZS-RSM and NSGA-II

The Pareto equilibrium of enhanced heat transfer and flow resistance reduction for 3 types of twisted petaloid helically coiled tubes (TPHCTs) was numerically studied. Firstly, the effects of torsion angle (θ), inlet Re and petal number (m) on the enhanced heat transfer and flow resistance performances were investigated. Secondly, the fitness function of Nu and |Δp| based on ZS-RSM method is constructed. Finally, the NSGA-II is utilized to acquire the equilibrium of enhanced heat transfer and flow resistance reduction. The results show that: the increases of torsion angle (θ), inlet Re and petal number (m) can intensify the integration effect of centrifugal force and torsion force, which leads to the enhancement of heat transfer but the deterioration of flow resistance. As the highest degree order (n) increases, there is a better aligned accuracy for the fitness function of Nu and |Δp|; however, it can be obtained the best fitness function for Nu and |Δp| when the overfitting occurs. The optimization results illustrate that the 3-lobe TPHCT with large torsion structure (m = 3, θ = 3548.44°, Re = 1597.71) can achieve a well Pareto equilibrium for enhanced heat transfer and flow resistance reduction of the TPHCT.