Experimental Study on the Effect of Fiber Orientation on Filter Quality

Abstract

Most filtration models assume that the air stream runs perpendicularly to the orientation of the filter fibers. However, cigarette filters remove aerosol particles apparently by a different filter configuration in that the fiber orientation almost parallels the air streamlines. To focus on the effect of fiber orientation, cellulose acetate filters were used in this work to facilitate the filter performance comparison. A piece of original round cigarette filter was molded to form a cube. The same piece of filter was used for both perpendicular and parallel orientations, to avoid the variability caused by the non-uniform filter media distribution. DOP aerosol particles used in the tests were generated by either a constant output aerosol nebulizer or an ultrasonic atomizing nozzle. A Po-210 radiation source was used to neutralize the challenge aerosols to the Boltzmann charge equilibrium. A scanning mobility particle sizer (for < 0.8 μm) and an aerodynamic particle sizer (for > 0.8 μm) were used to measure aerosol number concentrations and size distributions upstream and downstream of the cigarette filters. The results showed that parallel and orthogonal filters behave similarly. However, the pressure drop across parallel filter was lower than for the perpendicular filter, indicating that the airflow is more laminar passing through the parallel filters. Possibly for the same reason, aerosol penetration through parallel filter was higher than the orthogonal filter, although the difference may not be statistically significant. When a comparison of the fiber orientation is based on filter quality, orthogonal filter performs better than parallel filter, if face velocity is lower than 60 cm/s. Parallel filter performs better only when the particles are smaller than the most penetrating size and under high face velocity.

The authors would like to thank the National Science Council (Grant No. NSC90-2320-B-002-191) for the financial support.