Investigating the thermal performance of nanofluids in curved microchannels: effects of curvature, viscosity models, and Reynolds numbers

The present study investigates the complexities of thermal performance in nanofluids within curved microchannels of varying radii of curvature by examining the bending effects on convective heat transfer at different flow rates. Employing the finite element method, the study assesses existing viscosity and thermal conductivity models for steady-state, non-isothermal incompressible nanofluids. A parametric analysis is conducted to determine Nusselt numbers at varying Reynolds numbers and angles of curvature, utilizing Maiga’s empirical model and contrasting the findings with Batchelor’s and Brinkman’s theoretical models. The results consistently show that empirical models yield Nusselt numbers significantly higher than theoretical predictions. With respect to flow rate, empirical models exhibit a 4.58–6.11% enhancement in heat transfer for nanofluid concentrations ranging from 1 to 4 mass%. Instances with identical Dean's numbers but different Nusselt numbers demonstrate that higher Reynolds numbers substantially elevate the Nusselt number concerning microchannel curvature. It is also found that at Re ≤ 10, the impact of channel curvature on nanofluid thermal performance was less than 0.1%. A novel expression for the Nusselt number as a function of the Dean number is proposed. The study highlights the potential to achieve similar heat transfer outcomes by strategically adjusting the microchannel curvature and nanofluid flow rate, offering opportunities to enhance thermal efficiency in curved microchannels.