Electro-thermo-convection in power-law fluids within a square enclosure with an inner cylinder

Abstract

This paper investigates the electro-thermo-convection of power-law non-Newtonian fluids between a square enclosure and inner cylinder subjected to the simultaneous actions of external thermal and electric fields via lattice Boltzmann method. We concentrate on the flow structure transition, heat transfer efficiency as well as the bifurcation criteria concerning the electric Rayleigh number T for various power index 0.6≤n≤1.4. In addition, in order to comprehensively examine the impacts of buoyancy, two different Rayleigh numbers (Ra=103,105) are considered, corresponding to the weak and strong buoyancy. The cases for Newtonian fluids are used as the basic result to compare with the non-Newtonian cases. Based on the simulations, it is found that the flow motion and bifurcation criteria depend strongly on the power-law index. Specifically, the shear-shinning characteristic decreases the bifurcation threshold and exhibits a smaller hysteresis loop compared with Newtonian fluid, and the opposite effect and more evolution details about the transformation of charge void region with different shapes can be captured for shear-thickening characteristic. Additionally, the flow motions with stronger thermal convection illustrate more complex bifurcation diagrams and hysteresis loops due to the cooperation and competition between the buoyant and Coulomb forces, while it is not obvious for shear-thickening fluids.