Computational fluid dynamics was used to investigate particle aspiration efficiency in low-moving air typical of occupational settings (0.1-0.4 m s(-1)). Fluid flow surrounding an inhaling humanoid form and particle trajectories traveling into the mouth were simulated for seven discrete orientations relative to the oncoming wind (0 degrees, 15 degrees, 30 degrees, 60 degrees, 90 degrees, 135 degrees and 180 degrees). Three continuous inhalation velocities (1.81, 4.33, and 12.11 m s(-1)), representing the mean inhalation velocity associated with sinusoidal at-rest, moderate, and heavy breathing (7.5, 20.8, and 50.3 l min(-1), respectively) were simulated. These simulations identified a decrease in aspiration efficiency below the inhalable particulate mass (IPM) criterion of 0.5 for large particles, with no aspiration of particles 100 µm and larger for at-rest breathing and no aspiration of particles 116 µm for moderate breathing, over all freestream velocities and orientations relative to the wind. For particles smaller than 100 µm, orientation-averaged aspiration efficiency exceeded the IPM criterion, with increased aspiration efficiency as freestream velocity decreased. Variability in aspiration efficiencies between velocities was low for small (<22 µm) particles, but increased with increasing particle size over the range of conditions studied. Orientation-averaged simulation estimates of aspiration efficiency agree with the linear form of the proposed linear low-velocity inhalable convention through 100 µm, based on laboratory studies using human mannequins.
Fluids; Hydrodynamics; Aerosols; Air-flow; Particle-aerodynamics; Humans; Analytical-models; Simulation-methods; Mathematical-models; Breathing; Inhalants; Airborne-particles;
Author Keywords: aspiration efficiency; CFD inhalability; computational fluid dynamics; continuous inhalation; inhalable particulate mass; mouth breathing; orientation averaged; particle aspiration; particle transport; ultralow velocity
T. Renée Anthony, Department of Occupational and Environmental Health, University of Iowa, 105 River Street, Iowa City, IA 52242, USA