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

In this work, a comprehensive investigation of Rayleigh-Be<acute accent>nard 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 (Kr) on the onset of flow instability and heat transfer enhancement is investigated. The stability analysis reveals that higher Kr values lead to a lower critical Rayleigh number (Rac), promoting earlier convection onset. A series of numerical simulations using the finite volume method with the EHD module is conducted across different Kr and Ra values, showing that a change in Kr 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, Kr significantly influences heat transfer efficiency: at Ra = 30000, increasing Kr 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 Kr, 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.