On the importance of fibers' cross-sectional shape for air filters operating in the slip flow regime

In this paper, we investigate the effects of fibers' cross-sectional shape on the performance of a fibrous filter in the slip and no-slip flow regimes. The slip flow regime is expected to prevail when fiber diameter is comparable in size to the mean free path of the gas molecules (about 65 nm at normal temperatures and pressures), whereas the no-slip flow regime describes the aerodynamic condition of flow through media with large fibers. Our numerical simulations conducted for flow around single fibers with different geometries indicate that, while the collection efficiency is only weakly affected by the cross-sectional shape of nanofibers, the fiber drag (i.e., permeability of the media) can be considerably influenced by the fiber's shape. Simulating the flow field around nano- and microfibers with circular, square, trilobal, and elliptical cross-sections, it was found that the more streamlined the fiber geometry, the lower the fiber drag caused by a nanofiber relative to that generated by its micron-sized counterpart.

We simulate the influence of fibers' cross-sectional shape on the pressure drop and capture efficiency of filters made up of circular or non-circular fibers. It was found that, the more streamlined the fiber geometry, the lower the fiber drag caused by a nanofiber relative to that caused by its micron-sized counterpart.Figure optionsDownload as PowerPoint slideHighlights
► We modeled the slip flow over circular, square, elliptical, and trilobal fibers.
► We compared pressure drop and collection efficiency of these fibers.
► We compared performance of these fibers in slip and no-slip flow regimes.
► We concluded that the influence of fiber shape is more important in the slip flow regime.
► Fiber shape influences pressure drop more than collection efficiency.