Abstract
ABSTRACTThere is an increasing demand of air filters with a high collection performance, i.e., high collection efficiency and low pressure drop, for the application to indoor air cleaning. Air filters consisting of nanofibers have attracted great interests since they may have a low pressure drop because of slip flow effect and high collection efficiency due to interception. Although various nanofiber filters are available on the market, their collection performance is not as high as expected by the conventional filtration theory because non-uniform packing of fibers plays a significant role. In the present work, the collection performance of nanofiber (780 nm) and microfiber (11.2 µm) mixed filters with various mixing fractions was studied in order to maximize the quality factor of filter, qF, as a function of mixing fraction of nanofibers. The collection performance of mixed fiber filters was predicted by using theoretical equations reported by Bao et al. (1998) for bimodal distribution of fibers. As a result, it was found that the mixed fiber filters had a uniform fiber packing compared to laminated filters and that the collection efficiency was well predicted by introducing the inhomogeneity factor calculated for the filter consisting of two distinct fiber sizes. Furthermore, we found that the mixed fiber filter with the nanofiber mixing fraction of 5% in mass had the highest quality factor.
Highlights
Recent progress in manufacturing technology of polymer fibers enables us to produce nanofibers in large quantity at a relatively low cost
The packing densities of nanofibers and microfibers in the mixed fiber filter cannot be measured after the fabrication of mixed fiber filters
Other than the filter with the mixing fraction of nanofibers 5%, the filters prepared at the mixing fractions above 10% have almost the same thickness of 237 m
Summary
Recent progress in manufacturing technology of polymer fibers enables us to produce nanofibers in large quantity at a relatively low cost. Sambaer et al (2014) and Podgorski et al (2011) introduced the inhomogeneity factor in the prediction of collection efficiency of a laminated nanofiber filter, which was originally proposed by Kirsch et al (1975), and reported that the predicted collection efficiency agreed well with the experimental data by the correction with the inhomogeneity factor. They reported that the inhomogeneity factor of nanofiber filter was high compared to HEPA filters
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