Particle Size Determination from DPIs

Particle size impactors operate at constant flows. The aerosol output from DPIs has often been studied by abruptly increasing the flow through the DPI in a stepwise fashion. That is, the rise time from zero to desired flow is extremely short and does not necessarily ntimic patient inhalation. How acceleration at the start of inhalation is probably more important in terms of aerosol dispersion than the actual flow achieved (see below) (25). 

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On the other hand, from the earlier discussion, component i should have an equivalent packing ameter dpi, the values of which can be determined by eqn.(5). Therefoiie, if the sizes of all the components in the considered system are represented by their equivalent packing diameters respectively, then we will have an equivalent packing system composed of spherical particles only. This concept may be schematically illustrated by Figure 9. The porosity of this equivalent spherical packing system should be express as... 

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