Unsteady thermal convective transport of nanofluids with couple stress through a circular microchannel under the time-periodic pressure gradient and electromagnetohydrodynamic

This study investigates the unsteady thermal convective transport mechanism of nanofluids(Water-Al 2 O 3 ) with couple stress in a circular microchannel under the influence of electromagnetohydrodynamic(EMHD) and time-periodic pressure gradients. The Poisson–Boltzmann(PB) equation related to potential is derived using the Debye–Hückel approximation. The velocity and temperature distributions are obtained using the Green’s function method, and the Nusselt number and entropy generation are further derived. The effects of different dimensionless parameters are shown graphically and analyzed and discussed. The main results indicate that increasing the dimensionless couple stress parameters significantly increases the velocity, temperature, and convective heat transfer efficiency of the fluid. In addition, as the dimensionless frequency increased, the fluid flow rate decreased, energy transfer became more efficient, and thermal irreversibility and energy dissipation are notably reduced. It is also found that in nanofluids with low nanoparticle volume fractions, an increase in nanoparticle volume fraction enhanced the convective heat transfer capability of the fluid. The novelty of this study lies in providing a systematic theoretical analysis of the thermal convection mechanism of nanofluids with couple stress under complex flow conditions, especially under the effect of EMHD and time-periodic pressure gradients. This study not only offers a new perspective for understanding the thermal convective behavior of nanofluids under special flow conditions but also provides significant theoretical insights for the optimization design of microchannel heat exchangers and related devices, which can contribute to improving overall performance and optimizing fluid flow and heat transfer characteristics.