AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Effect of Secondary Aspiration on Low Velocity Human Aspiration Efficiency Estimates: Computational Fluid Dynamics Investigation
KIMBERLY ANDERSON, T. Renee Anthony, University of Iowa
Abstract Number: 373 Working Group: Aerosol Exposure
Abstract Background: Previous work using generic, uniformly applied non-zero coefficient of restitution (CoR) values on an inhaling humanoid found significant increases in low velocity aspiration as large as 90% compared to CoR=0. To improve modeling inputs, realistic CoRs for human facial skin were measured and applied to a CFD model used to examine the effect of particle bounce on human aspiration efficiency.
Objectives: The objective of this work was to examine the influence of human facial skin CoR estimates on secondary aspiration in human aspiration efficiency studies, using realistic values of CoR.
Methods: CFD simulations were conducted to examine airflow (standard k-epsilon turbulence) and particle transport (laminar) into a humanoid form, facing the wind (0.1 to 0.4 m/s), with constant mouth and nose inhalation. Values of CoR (0.55, 0.61 and 0.74) were applied to the forehead, nose and cheeks, respectively, corresponding to mean measurements obtained from 30 individuals using a ballistometer. Constant CoR measurements (1.0) and zero CoR were also evaluated. Aspiration efficiencies for particles ranging from 7-116 micrometers were computed for three freestream and two breathing velocities for three CoR schemes.
Results: Secondary aspiration using realistic CoR values were significantly greater than CoR=0 simulations (p <0.0001) for both nose- and mouth-breathing, with differences ranging from 0 to 80%. Secondary aspiration was more important with increased particle sizes (>52 micrometer) and with decreasing freestream velocity and decreasing breathing rate. No difference was observed between using contant CoR and regionally varied CoR values (p=0.06).
Conclusions: Secondary aspiration contributes significantly to human aspiration estimates in low velocity environments. Realistic CoR values should be incorporated into models, although constant values applied to the face provided similar results to regionally specific CoRs. Ignoring this phenomenon could result in a significant underestimation of aspiration efficiency, particularly in the facing-the-wind orientation.