Aerodynamics of porous screens and application to aerosol collection by textile
Textiles are often used to capture airborne droplets, for example for fog harvesting. Recently, we have shown that particular screens composed of pairs of vertical fibers are very efficient and provide an accurate measurement of the liquid water content of fog, with a fast response [1]. In these cases the flow of fog can go around and through the screen. The prediction of the capture efficiency of textile screens requires a quantitative description of the flow in the vicinity of the net. Such description is thus of great interest for many applications, including the development of effective facemasks to prevent respiratory virus transmission, or optimal fog collectors.
In this seminar we investigate first the three-dimensional free flow around and through a screen for various solidities and fiber diameters at high Reynolds number Re = O(104). We present a theoretical model based on three-dimension potential flow theory to calculate the velocities and pressures in the vicinity of a porous screen of any shape [2]. Then, we apply this model to the case of a rectangular geometry as used in most fog nets.
In a second part of the seminar, we focus on the aerosol collection by textiles. Using a wind tunnel producing microscopic water droplets, we measure experimentally the collection efficiency of many textiles from low solidity to high solidity. The collection efficiency strongly depends on the normal wind velocity at the screen that we measure accurately for different fiber diameters and screen solidities. This velocity, as well as the number of droplets deviated around the screen are influenced by the three-dimensional aspects of the flow around the screen and the viscous effects within the pores of the screen, which are not accounted for in previous models. We use the model of the flow obtained in the first part to solve numerically the trajectory of aerosols droplets ; this physics at the macroscopic scale is then combined to the microscopic scale of deposition on a single fiber to compute the efficiency, in good agreement with our experiments.
Contact Bruno Deremble for more information or to schedule a discussion with the seminar speaker.
- [1] A. Moncuquet et al., Atmospheric Research, vol. 277 (2022), https://doi.org/10.1016/j.atmosres.2022.106312
- [2] O. C. Marchand et al., Journal of Fluid Mechanics, vol. 987 (2024), https://doi.org/10.1017/jfm.2024.372