Effect of ion mobility on electro-thermal convection: Linear stability analysis and numerical simulation

Abstract

In this work, a comprehensive investigation of Rayleigh-Bénard convection in an electric field is implemented based on linear stability analysis and numerical simulation. The effect of ion mobility represented by the ratio of negative and positive ion mobility (K_r) on the onset of flow instability and heat transfer enhancement is investigated. The stability analysis reveals that higher K_r values lead to a lower critical Rayleigh number (Ra_c), promoting earlier convection onset. A series of numerical simulations using the finite volume method with the EHD module is conducted across different K_r and Ra values, showing that a change in K_r not only initiates the flow without increasing the energy input, but also leads to the transition of the flow pattern and the structure of thermal plumes. Additionally, K_r significantly influences heat transfer efficiency: at Ra = 30000, increasing K_r from 1 to 10 leads to a 29 % increase in the Nusselt number (Nu). However, it is worth noting that the maximum velocity and heat transfer efficiency do not monotonically increase with K_r, suggesting that selecting an optimal working fluid is essential for practical applications. These findings highlight the critical role of ion mobility in driving convection and enhancing heat transfer in electro-thermal systems.