Introduction Some basic principles of hydrodynamics for electrochemistry

1 Introduction Some basic principles of hydrodynamics for electrochemistry 

The concentration distribution of species in the diffusion layer, SD, obeys the convective-diffusion equation  

Equation (10.3) represents Newtons second law of motion, where the left hand side of the equation denotes the product mass x acceleration, pL is the density of the fluid, and the right hand side represents the net force exerted on a volume element of the fluid, P is the pressure, /u. the viscosity and g the force per unit volume exerted on an element of the fluid by gravity. The term pV2u represents frictional forces. 

Equation (10.3) is generally simplified for electrochemical problems by assuming the absence of a pressure gradient and neglecting the effect of gravitational forces and hence can be written as equation (10.4)  

The equations are often written in terms of dimensionless variables which will become evident later. The two most important for this review are the Reynolds number, Re and the Schmidt number, Sc. The Reynolds number describes the flow characteristics of the system. It is directly proportional to some characteristic solution velocity and length (normally associated with the electrode, but for flow in a channel it is related to the 

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