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A numerical method for approximating the mass flux from a dissolving cylindrical drug compact, a tablet, is presented. The tablet consists of alternating layers of drug and inert material. The dissolution takes place in a non‐reactive medium using a standard stirring device and is considered to be two dimensional and steady. A finite difference scheme is used to generate an approximation to the concentration boundary layer. By integrating across the velocity* concentration profile at the trailing edge, the mass flux is estimated. This value differs by 0.9% from the recent estimate of Crane et al. who used a Pohlhausen approximation to the concentration boundary layer. The finite difference concentration profile at the trailing edge also agrees very well with the equivalent Lévêque exact solution. We conclude that the finite difference model is behaving as expected.

Straightforward analysis can show that it is difficult to implement a successful electrodynamic braking system for a small wind turbine system, i.e. of swept area less than 200 m2 and power rating of 50 kW. Two principal difficulties are: (i) the peak short-circuit torque of the electrical generator can be far too low to overcome the torques associated with the wind turbine rotor, even at wind speeds close to rated; (ii) the energy dumped into the generator during braking is significant and can cause swift heating to high temperatures. Transient electrical effects can also lead to electrical and electronic component failures. Documented failures in machines of up to 10 kW indicate that it is the case that electrodynamic braking is not well understood throughout the industry. Additionally, the academic literature on the topic is sparse. In this paper, we show how very straightforward analysis can shed light on the edge cases for electrodynamic brake systems and help to avoid expensive errors.

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