Filter Material Effects on Particle Absorption Characteristics
Cary Presser, Joseph M. Conny, Ashot Nazarian
The absorption coefficient and mass specific absorption cross section were determined for nigrosin-laden quartz, Teflon, and polycarbonate filters in inert surroundings at different steady-state temperatures and particle mass loadings. The objective was to investigate the effect of absorption enhancement for different filter types, including fibrous and porous substrates. Nigrosin particles were used as the reference since the particles are known from the literature to be highly absorbing. An apparatus was assembled to generate particles from a de-ionized water suspension and coat the filters, using an ultrasonic mist generator, heated line, and filter mounting. Sample absorptivity was determined using a novel laser-heating technique, which is based on perturbing the sample temperature from a pre-selected steady-state temperature, and monitoring the thermal response during decay back to steady state, along with a model for thermal energy conservation. In addition, transmissivity measurements were carried out to enable determination of the sample absorption coefficient. Measurements with clean and particle-coated filters enabled identification of the isolated nigrosin (without the substrate). Absorption enhancement effects were investigated by comparing the absorption coefficient obtained for the different filter types. The absorption coefficient was found to decrease with steady-state temperature and increase with mass loading and filter pore size. Comparing the absorption coefficient for both the isolated nigrosin and nigrosin-laden filters indicated that the effect was most significant for the Teflon filters and least significant for the polycarbonate filters. The effect became more significant as the pore size decreased, steady-state temperature increased, and particle mass loading decreased.