Conventional filtration theory for HEPA filter based on fan model filter was tested by using model filters consisting of two distinct fiber sizes. As a result, it was found that small content of coarse fibers introduces a considerable change in the particle penetration predicted by the conventional theory while the pressure drop remained almost unchanged, suggesting that the polydispersity of fiber size affects the pressure drop and collection efficiency in a different manner. In general, owing to the polydispersity of fiber size, the conventional theory overestimates the collection efficiency in diffusion regime while underestimates it in interception regime, and hence predicting a larger most penetration particle size.
Ultra-fine Zinc oxide (ZnO) particles were prepared by pyrolyzing and oxidizing zinc bisdipivaloilemethanate (Zn(DPM)2) vapor using atmospheric pressure CVD method. Control of particle preparation was carried out experimentally under various operating conditions, such as temperature setting of the reactor, and volume flow rates of N2 and air carrier gases. As a result, ZnO fine particles having wurtzite structure with diameter from 0.06 to 0.5 μm were prepared by the optimizing these conditions. The crystallinity of prepared particles was found to improve at high reactor temperatures and low volume flow rate of carrier gas. Moreover, the diameter of prepared particles was smallest at the reactor temperature of 1073 K, from which it was inferred that their diameter was dominated by the growth of the crystallites below 1073 K, and by the sintering of the agglomerate above 1073 K. From the spectroscopic analysis, it was found that prepared ZnO ultra-fine particles had a high transparency in the visible range and a high shielding ability in the ultraviolet range.
This paper relates to an experiment of removing aerosols using a radiation effect by γ-ray with a TRAPOL (trapping of aerosol by pole) in Ar-gas stream. If either positive or negative ions produced by the radiation are caused to act on aerosol, the aerosol charge becomes unipolar. The charged aerosol is trapped on an electrode of the opposite polarity, and removed onto HEPA filter with a high efficiency. The DF (decontamination factor) in TRAPOL exceeds to 103 in a particle range above 0.4 μm, and the DF of HEPA filter is improved upto 1,000 times compared with the inherent DF value of the filter, where DF is defined as the ratio of particle number concentrations at the entrance to those at the exit.