Transport Equation for Dilute Binary Electrolyte

Let us discuss about the governing equation for motion of dilute binary electrolyte with charged species. Dilute binary electrolyte is a combination of an unionized solvent and dilute fully ionized salt. The salt is composed of one negatively charged species and one positively charged species that do not enter into any reactions in the bulk of the fluid (r, = 0). The solution is also assumed to be electrically neutral. For example, NaCl have Na+ and Cr species. For the solution to be electrically neutral, we have 

This equation states that there is no accumulation of charge, that is, V / i = 0. If the positive ions are denoted by subscript + and the negative ions by subscript -, the electroneutrality condition is expressed by 

We have described the species conservation equation for individual species in the previous chapter as 

the mass average velocity is defined as pu = LpiUi and molar flux with respect to the mass average velocity is defined as / = c, (H - ). The expression for molar flux with respect to stationary coordinate system has been expressed as (equation (6.17)) 

The molar flux with respect to the reference velocity has been expressed as 

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