An example of a convective-diffusion system the rotating disc electrode

9 An example of a convective-diffusion system the rotating disc electrode 

A rotating disc electrode12,13 consists of a disc electrode embedded in the middle of a plane surface (theoretically of infinite extent) that rotates around its axis in a fluid, the disc being centred on the axis. In practice the electrode bodies usually have the form of a cylinder, with the sheath around the disc significantly larger than it is, so as to approximate a surface of infinite dimension (Fig. 8.2). We assume in these calculations 

The first step consists in deducing the velocity profile. This fluid dynamics problem was solved by von Karman14 and Cochran15 and gives 

Levich10 introduced the approximation that, close to the electrode, 

in the steady state at constant rotation speed, the convective diffusion equation is 

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