Estimation for Filtering Efficiency of Air Filter Consisting of Coarse and Fine Fibers

Abstract

The classical theory for filtering efficiency of air filters is useful in predicting filter performance and designing new air filters. For instance, the formula for filtering efficiency has been proposed based on the theory of the Fan model filter (FMF). The FMF theory has parameters, such as the single fiber diameter, because fiber diameter could determine packing density and thickness of filter media, which have enormous impact on filtering efficiency. However, there are some air filters consisting of coarse and fine fibers. The calculated filtering efficiency of these filters, based on the FMF theory, exhibited a significant difference from the measured value. The objective of this study is to accurately predict the filtering efficiency of an air filter consisting of coarse and fine fibers. To achieve this objective, an empirical formula for filtering efficiency was developed, taking into account the diameter and the weight of the coarse and fine fibers. The empirical formula was expressed as the sum of filtering efficiencies dependent on the coarse and fine fibers, respectively. Results demonstrated that there was little difference between the filtering efficiency predicted by the developed empirical formula and the measured value, falling within the range of deviation observed for commercial filters. Therefore, the developed empirical formula is deemed capable of precisely predicting the performance of commercial filters.