Thermal performance analysis of hydromagnetic Al₂O₃-water nanofluid flows inside a concentric microannulus considering nanoparticle migration and asymmetric heating

Direction and intensity of nanoparticle migration are able to tune thermophysical properties of nanofluids to improve thermal performance of heat exchange equipment. In this paper, thermal performance of hydromagnetic alumina/water nanofluid inside a vertical microannular tube is investigated numerically considering different modes of nanoparticle migration. The model used for the nanofluid is able to consider nanoparticle migration originating from the thermophoresis and Brownian motion. In order to study the thermal performance, the figures of merit for different range of parameters including the ratio of Brownian motion to thermophoresis (N_BT), slip parameter (λ), mixed convective parameter (Nr), Hartmann number (Ha), bulk mean nanoparticle volume fraction (ϕ_B), radii (ζ) and heat flux (ε) ratios are investigated in detail. It is revealed that increasing the slip velocity and magnetic field strength intensify the thermal performance, whereas increasing the ratio of inner wall to the outer wall radius, nanoparticle volume fraction, and heat flux ratio decrease it.