A first assessment of an aerodynamic barrier layer for filtering airborne hygroscopic particles

Abstract

In this work consideration is given to an aerodynamic concept for filtration of small water droplets such as those caused by an infected person when coughs or sneezes and including airborne hygroscopic particle, and with particular application to medical masks. Nowadays, the efficiency of such masks is strongly reduced for airborne particles and increasing the efficiency implies either increasing the thickness of the filtering layers or decreasing the aerodynamic equivalent diameter of the pore, both measures in clear detriment of its breathability. Here, a novel strategy is proposed in which efficiency is increased, not by decreasing the diameter of the pore but actually by increasing the diameter of the water droplet itself. We called this concept as the aerodynamic barrier layer. In this concept a layer with parallel arrangement of micro fibers in the direction of the flow is located just before the traditional filtering layer and being able to promote lift forces which induce clustering, coalescence and growth of water droplets at the center of the aerodynamic channel. The enlarged drop after passing though the aerodynamic barrier layer is now easy captured by a conventional filtering layer. Utilizing a simplified geometrical model, an expression for the required length of the aerodynamic barrier layer was derived