Simple and cost-effective powder disperser for aerosol particle size measurement
Commercial dry powderdispersers needed in conjunction with particle size measurement equipment are usually quite expensive (of the order of thousands of dollars). We have found that a simple vacuum generator can be used as a cost-effective disperser (US$50). Comparison with other commercial dispersers, small scale powder disperser (SSPD) model 3433 (TSI, Shoreview, USA) and Scirocco dry powder disperser (Malvern, Worcs, UK), showed that our disperser worked as efficiently as these expensive dispersers. Crystalline mannitol (less than 1% moisture content) and amorphous BSA (8.5–9.2% moisture content) smooth spherical particles were used to test the dispersion capability of the unit. Smooth spherical particles were chosen because they are more cohesive than corrugated particles due to increased contact points. Therefore, sufficient dispersions of other less cohesive particles should be able to be achieved using the optimum conditions reported here. The effects of air pressure, sample weight, and nozzle size of the disperser were investigated. Comparison of the particle size distributions between wet and dry measurements were used to determine the dispersion efficiency. Quantitative comparisons were made using the values of D(v,0.5) and span. The best dispersion was found using a 1.00 mm nozzle and the maximum percentage differences in D(v,0.5) and span are 23% and 19%, respectively, with more than 200 mg mannitol powder dispersed with pressures of 50, 70, 90 psi. Using BSA powders, the maximum percentage differences of D(v,0.5) and span are 37% and 25%, respectively. As was the case for the commercial devices, the dispersion of BSA particles could not be improved even when the pressure of the compressed air was increased.