Design optimization of prismatic rib turbulators in a rectangular channel based on multi-objective criterion

Abstract

A multi-objective shape optimization of truncated prismatic ribs in a rectangular channel has been performed to optimize simultaneously, heat transfer and pressure loss. The numerical analysis was performed using Reynolds-averaged Navier-Stokes equations with eddy viscosity-based models for turbulence closure. The optimization was performed using multi-objective genetic algorithm technique, and the fitness functions for the objectives were obtained using surrogate modeling. Using literature survey and preliminary parametric analysis, three design variables related to prismatic ribs viz. ratio of rib-height (e) to hydraulic-diameter (Dh) of a rectangular channel, ratio of rib-pitch (p) to rib-height (e), and ratio of rib-height at end (ep) to rib-height at center (e) were selected. The augmentation Nusselt number (FNu) and friction factor (Ff) ratios were chosen as the multi-objective functions for heat transfer and pressure drop, respectively in the rectangular channel. Numerical analysis and multi-objective optimization have been done at fixed Reynolds number, Re = 42,500. Using the proposed optimization framework, Pareto-optimal front design (POD) signifies the trade-off between the obtained objective functions, and among them, five PODs have been chosen using K-means clustering technique. In the paper, results indicated that the POD which offer high blockage effect to the incoming flow lead to high heat transfer performance, but accompanied by greater pressure losses. The blockage effect is discussed using spatial flow and thermal patterns. An optimum design with a relative thermal performance enhancement of 168.60% compared with the reference design is reported.