Numerical Investigation and Multi-Objective Optimization of Attached and Detached Inclined Ribs in an Annular Channel for Enhanced Heat Transfer

Abstract This study presents a detailed numerical investigation into local heat transfer enhancement in a double-pipe heat exchanger (DPHE) using attached and detached ribs as turbulence promoters. Ribs are a simple device for turbulence generation, but their effects in annular channel flow have been rarely investigated. The rib configurations analyzed include rib-to-wall gap (h), rib inclination angle relative to the flow direction (θ), rib-to-rib pitch (P), and rib height (e). Numerical simulations were performed in ansys fluent using the shear–stress transport (SST) k–ω model, and the methodology was validated against experimental data and correlations. Results show that detached ribs induce two classes of secondary flows and enhance the local heat transfer, however, at the cost of increased pressure drop. Conversely, inclined ribs reduce pressure loss but lead to a decrease in turbulence intensity and associated heat transfer. Taguchi-based design of experiments (DOE) with analysis of variance (ANOVA) is proposed to identify the optimum rib configuration to maximize heat transfer while minimizing pressure drop. ANOVA revealed that rib inclination angle and rib-to-wall gap predominantly influence the heat transfer. The optimized configuration (Re = 6000, P/e = 6, e/Dh = 0.14, h/e = 0.167, θ = 75 deg) achieved a maximum Nusselt number (Nu) of 2.35 times that of a smooth channel and a performance evaluation factor (PEF) of 1.25. These findings provide insights for designing rib turbulators in DPHEs and similar compact heat exchangers, enabling significant heat transfer enhancement with controlled pressure losses.