Thermodiffusion of a binary electrolyte situated in the microgap between two ion-selective surfaces under external electric field is theoretically studied. It is assumed that temperature gradient occurs only by Joule heating of the electrolyte; and the concentration gradient may trigger an inner gravitational instability. There are three types of instability in such setup: electrokinetic, thermoelectrokinetic and internal gravitational instability. The direct numerical simulation of the problem shows that for the typical salts solutions such as NaCl or KCl the termodiffusion effect is negligible, while for some salts with bigger values of the reduced Soret coefficients of ions (for example, for tetra-n-butylammonium fluoride) the thermodiffusion may significantly affect the voltage-current characteristic. It is also obtained, that the negative thermodiffusion leads to the destabilization of the one-dimensional steady state regime and shifts the critical values of governing parameters for each aforementioned type of instability. The thermodiffusion mostly influences the classical electrokinetic instability and less — the internal gravitational instability. Under effect of both types of thermodiffusion (normal and negative), the thermoelectrokinetic instability manifests at smaller values of Rayleigh numbers.

理论上研究了在外部电场下位于两个离子选择性表面之间的微间隙中的二元电解质的热扩散。假定仅通过电解质的焦耳加热发生温度梯度；然而，温度梯度仅通过焦耳加热而产生。浓度梯度可能会触发内部重力失稳。在这种设置中，存在三种类型的不稳定性：电动，热电动和内部重力不稳定性。该问题的直接数值模拟表明，对于诸如NaCl或KCl之类的典型盐溶液，其扩散效应可忽略不计，而对于某些具有降低的离子Soret系数值的盐（例如，对于四正丁基氟化铵而言） ）热扩散可能会严重影响电压-电流特性。也可以得到，负热扩散会导致一维稳态状态不稳定，并会改变上述每种类型的不稳定性的控制参数的临界值。热扩散主要影响经典的电动不稳定性，而较小的是内部引力不稳定性。在两种类型的热扩散（正态和负态）的影响下，热电不稳定性表现为较小的瑞利数值。