A TAXONOMY OF CURVE SHAPES IN TRANSITIONAL DUST LOADING OF AIR FILTERS

摘要

Maintaining an acceptable level of the quality of indoor air usually requires adequate maintenance of the filters within ventilation systems. Filters that collect dust particles eventually reach a point when the particle loading restricts the flow enough to require filter replacement. Understanding this process of loading can aid in the improved design and maintenance of such filtration systems. This study seeks to provide a taxonomy of the different shapes of the pressure drop loading curves (pressure drop vs. volume of particles loaded) that result from loading a variety of air filters with solid aerosol dust particles. For a good part of a century now, pressure drop loading curves have been presented in the literature that show a variety of different basic shapes depending on the combination of the type of filter media and the loading aerosol characteristics. As yet, few published studies have investigated the shapes of the transitional loading curves in order to correlate them with the details of what is occurring microscopically within the filter media. In this study, experimental filter loading results are presented to illustrate the four main curve shapes. The four shapes are concave-up, s-shaped, concave-down, and straight. These shapes form points along a continuum of decreasing porosity and enhanced collection towards the upstream surface of the media. At one end of the continuum there is the concave-up curve that corresponds to an open filter with a high clean media porosity. At the other extreme, there is the straight curve shape that corresponds to cake (or surface) filtration with no significant depth filtration. The s-shaped and concave-down curves correspond to different degrees of media openness between these two extreme conditions. The specific curve shapes also depend on the percent open area of individual layers within the filter media and also on the variety of ways the fibers can be arranged through the depth of the filter. All the curves eventually reach the straight cake-loading condition where the surface cake is formed and the pressure drop rises linearly.