Time-dependent analysis of heat transfer enhancement and entropy generation of hybrid nanofluids in a tube with a solid and elliptical‑cut twisted tape insert with non-uniform heat flux

Abstract

ABSTRACT This numerical study investigates the improvement of transient heat transfer in a plain tube using hybrid nanofluids consisting of solid particles and twisted tapes with elliptical cuts, under non-uniform heat flux conditions. The analysis includes the calculation of the Bejan number and entropy production. Different working fluids, including water, CuO/water nanofluid, and a hybrid nanofluid with a 2% volume concentration of Al2O3-Cu/water, are used with varying concentrations of the hybrid nanofluid ranging from 1% to 4%. Effects of heat flux distribution and local concentration ratio (LCR) are investigated. The computational results indicate that conventional and elliptical cut twisted tapes enhance transient heat transmission. A slight rise in the heat transfer coefficient is observed when the fluid has higher thermal conductivity. The flow velocity gradually stabilizes over time. The hybrid nanofluid of (Al2O3-Cu/water) significantly affects transient heat transmission, reducing the maximum temperature difference by approximately 4.1% compared to water and 6.2% compared to the nanofluid. Transient heat transmission is further intensified by TECT. Moreover, frictional entropy production dominates the system’s irreversibility. This study contributes to the understanding of transient heat transfer enhancement and its dependence on hybrid nanofluids, providing insights for engineering applications.