Droplet capture with a wetted fiber

Abstract

The capture mechanism of fibrous filters in a wet condition is studied by focusing on the single droplet impact to an initial droplet attached to the fiber. High-speed photography and numerical simulation are conducted to study the collision phenomenon. The eccentricity between the mass center of the impacting droplet and the initial droplet is varied to evaluate the threshold capture velocity of the impacting droplet. The eccentricity is considered to be composed of two perpendicular components. The distance between the impacting droplet trajectory line and fiber axis is considered as one of the components of eccentricity ( $$e_{1}$$ ). The distance between the mass center of the impacting droplet and the initial droplet along the fiber axis is defined as the other component of eccentricity ( $$e_{2}$$ ). The initial droplet volume is also varied in our investigation. It is observed that increasing the initial droplet volume attached to the fiber as well as increasing the eccentricity $$e_{1}$$ reduces the threshold capture velocity of the impacting droplet. However, increasing $$e_{2}$$ increases the threshold capture velocity. Surprisingly, for an impacting droplet with a radius of R colliding with a small volume initial droplet of a radius of $$R_{i}$$ at $$e_{2}> 0.85$$ ( $$R+R_{i}$$ ), the threshold capture velocity is found to be higher than that of a droplet impacting on a dry fiber.