Stokesian particles impaction

For Stokesian particles, rvi o impaction regimes are similar when the Stokes, interception, and Reynolds numbers are the same. The impaction efficiency. as in the case of diffusion, is defined as the ratio of the volume of gas cleared of particles by the collecting element to the total volume swept out by the collector. (Refer to Fig. 4.5 for the case of the cylinder.) If all panicles coming within one radius of the collector adhere, then we obtain... 

This analysis provides a lower anchor point for curves of impaction efficiency as a function of Stokes number. It applies also to non-Stokesian particles, discussed in the next section, because the point of vanishing efficiency corresponds to zero relative velocity between particle and gas. Hence Stokes law can be used to approximate the particle motion near the stagnation point. This is one of the few impaction problems for which an analytical solution is possible. 

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