Separator-type HEPA filters are composed of the elements which have square cross section bounded by the two separator walls and partitioned by the filter medium. Therefore, it is possible to characterize the pressure drop of a separator type air filter unit by studying the pressure drop of this filter element. In the present work, air flow distribution and the pressure drop of the filter element were studied through numerical calculations and experiments with the three-dimensional model filter. It was found that an optimum separator height is about 3.0 mm being independent of filter inlet air velocity. At a small separator height, the pressure drop significantly decreases with increasing separator pleating angle, while at a large separator height the pleating angle little affects the pressure drop. The separator-pleating angle and the media resistance coefficient affect the distribution of airflow velocity through the filter media only in the direction of the main air flow.
To estimate the deposition fraction of submicron aerosol particles in a long sampling pipeline, an estimation equation was proposed and its applicability was experimentally verified. The equation proposed in this paper was found to give relatively good estimation of deposition fractions for submicron particles in both the laminar and the turbulent airflows. It was found that the deposition fractions from turbulent airflow could be obtained by considering a sampling pipeline composed of a horizontal, a vertical and a bent pipes with a total length.
We have been researching air cleaning technology using gas-to-particle conversion of atmospheric gaseous pollutants by UV light irradiation. We measured removal efficiency of NOx and typical aromatic hydrocarbons ; benzene, toluene and o-xylene(BTX) , by the irradiation with a high power UV (with 184.9 nm wavelength) lamp. The removal efficiencies of NOx and BTX increased with increasing water vapor concentration. And 78-91 % NOx removal efficiencies were achieved in 50 % RH. The removal efficiencies of benzene, toluene and o-xylene in 50 % RH were 64 %, 82 % and 90 %, respectively, which could be related to their chemical reaction rate with OH radicals. Larger particles were formed in NO-BTX-air systems than in a NO-air system. The decrease in the removal efficiency of NOx by the addition of BTX could be ascribed to the competitive reaction of OH radicals with NOx and BTX. The obtained experimental results suggest that hybrid air cleaning systems to remove both paniculate and gaseous pollutants from the air could be built in conjunction with catalyst and air filters.