Characterization of aerosol emission from single-film rupture in a tube

Abstract

The generation of aerosols during “silent” tidal breathing via the bronchiole fluid film burst (BFFB) mechanism, which involves the rupturing of mucus meniscus or film in terminal bronchioles, has been described in recent studies. To replicate the BFFB mechanism and identify the characteristics of aerosol generation during normal breathing, this study set up a single-film generation system employing tubes ranging from 0.7 to 2.94 cm in diameter that simulated the bronchioles. A liquid film of artificial mucus or soap solution was applied on the bottom of each tube and moved upward by filtered carrier air, which eventually led to the rupturing of the film. The resultant airborne particles (> 7 nm) were then counted with a condensation particle counter, and the number size distributions (0.6–20 µm) were measured with an Aerodynamic Particle Sizer. The experimental results show that the film’s rising velocity, rise distance and surface tension in addition to the tube diameter all affected the total particle count and the size distribution. The total particle count increased with the rising velocity until the latter reached 3 cm s–1 and then decreased as the velocity continued growing—a phenomenon that was mainly due to the curvature of the film increasing with the velocity. Moreover, the larger the tube diameter, the higher the particle count. When a 0.9% NaCl solution was added to increase the surface tension of the film, the total particle count decreased as the surface tension increased, regardless of whether artificial mucus or soap solution was used. This approach to reducing the propagation of infectious diseases in healthcare facilities seems to merit further exploration.