Capturing aerosol droplets with fibers

Capturing droplets from a stream with a fibrous material is a well-known and well-used process, from coalescence filters to fog harvesting. In this paper, we report experimental measurements of collection efficiency with a model system consisting in an array of vertical nylon fibers. In particular, we report precise measurements over a large range of parameters, and identify the key role played by the drop distribution on the overall collection efficiency. Due to a growth and coalescence process, this drop distribution evolves toward a regular pattern of uniformly distributed drops, and a balance between capillarity and gravity sets an average drop size. Accounting for these effects in a simple inertial impaction model allows predictive and quantitative comparisons with experiments. Drop growth can be suppressed by forming long continuous liquid columns between close fibers; incoming droplets immediately coalesce with these wet columns, and the capture efficiency is increased. In addition, we extend our model to take into account the interactions between fibers. Capturing droplets from a stream with a fibrous material is a well-known process, from coalescence filters to fog harvesting. The collection efficiency strongly depends on the drop distribution on the fibers, thus on their wetting properties.