Electric Field-Induced Instability in a Non-Newtonian Hybrid Nanofluid

Abstract

The influence of fluid rheology on the onset of thermal convection in a hybrid nanofluid layer subjected to a vertical alternating current electric field is investigated using linear stability theory with stress-free boundary conditions. The analysis incorporates the Buongiorno model for nanoparticle transport and the Maxwell model to describe non-Newtonian rheology, accounting for both thermophoresis and Brownian motion effects. Hybrid nanofluids — engineered by dispersing dissimilar nanoparticles in a base fluid — exhibit enhanced thermal conductivity and complex flow behaviour. An eigenvalue problem governing the onset of convection is formulated and solved analytically using a single-term Galerkin method, resulting in exact expressions for the critical thermal Rayleigh number for both bottom–heavy and top–heavy configurations. The comparative stability behaviour of ordinary nanofluids and hybrid nanofluids is examined, with articular emphasis on the enhancement of thermal transport properties. The effects of key dimensionless parameters — such as the Lewis number, nanoparticle Rayleigh number, electric Rayleigh number, and the modified diffusivity ratio — on the threshold for stationary convection are analysed both analytically and numerically. These values are numerically computed using software Mathematica 12. Results reveal the significant role of rheology and electric fields in modulating the convective stability of hybrid nanofluids, offering insights for thermal management in advanced electrohydrodynamic systems.