Liquid-Solid Mass Transfer Coefficient and Coupling of the Electrode Processes

3 Liquid-Solid Mass Transfer Coefficient and Coupling of the Electrode Processes 

In a small-gap parallel-plate reactor with laminar liquid flow (without gas evolution), infinitely wide electrodes and a constant electrode surface concentration, the average Sherwood number over the electrode length is given by Leveque s equation [21]  

Equation (17.27) describes a developing mass transfer boundary layer in a fully-developed laminar flow. However, if the mass transfer boundary spans the whole electrode gap, the Sherwood number attains a limiting value which is independent of flow hydrodynamics. The limiting Sherwood number is given, for a uniform mass flux at the electrode surface by [21] 

Equation (17.28) holds if the mass transfer boundary layer is fully developed, which is verified for the following condition (see [22] for the case of the heat transfer boundary layer)  

The combination of Equation (17.27) or (17.28) with the definition of NTU [Equation (17.26)] permits NTU to be expressed in the case of a non-developed [Equation (17.30)] or a developed [Equation (17.31)] concentration profile. 

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