Characterization of silica particles generated with Raskin nozzles and their application to air filter performance tests

Silica particles generated with Raskin nozzles are suggested as a substitute for DOP (dioctyl phthalate) particles for testing HEPA Filters. However. the generation characteristics of Raskin nozzles from the silica suspension are not well understood yet. The present work investigates the generation characteristics of Raskin nozzles for silica particles by measuring the size distribution, the mass or number concentrations of silica particles and their electrical charges. As a result, (i) although atomization pressure increases mass or number concentration. the size distributions remain rather unchanged, (ii) suspension of smaller primary silica particles generates smaller agglomerated particles with a higher mass concentration, and (iii) a higher concentration of suspension does not necessarily generate a higher concentration of particles. Further, the light scattering characteristics of silica particles by LPC were evaluated by classifying the silica particles according to the electrical mobility. The LPC underestimates the size of silica particles by a factor of about 1.6 compared to DOP particles, leading tu a serious deviation in particle penetration through air filters. Special caution is required for the light scattering characteristics and electrical charge when silica particles are used as a substitute of DOP particles for filter test.