Figure 1:  Laser Doppler anemometry system used in wind tunnel experiments investigating velocity field

 

 

Particle Inhalability Studies

 

This research investigates the applicability of the ACGIH inhalable criteria for indoor work environments with low windspeeds. The study consists of two distinct phases:  experimental and computational.  Initial investigations of the velocity field and particle transport will be studied in wind tunnels to assess the appropriateness of using a simple geometric form as a surrogate for an inhaling human form. 

Following this determination of an appropriate model, a three-dimensional simulation will be conducted using computational fluid dynamics, where particle aspiration will be determined for inhalable particle sizes.  Although the work conducted here is limited in mannequin orientation relative to the wind, the method and computational mesh developed for this work can be used to fully explore particle inhalability

Results from the particle inhalability investigation will provide new criteria that will influence development of size-selective samplers.  With devices that sample only the inhalable fraction of ambient particles, better estimates of human exposure and, subsequently, risk will be available for the protection of workers.

 

Abstract:  “Effects of facial features on velocity fields for inhaling mannequins”

 

Although CFD and numerical investigations of particle inhalability and contaminant exposure have used simple geometrical surrogates for a breathing human form, the effect of eliminating facial features has not been investigated.  In this work, three-dimensional velocity measurements were made to determine the impact of facial features on velocity fields associated with inhaling surrogate human forms in a low velocity wind tunnel. 

 

Laser Doppler anemometry was used to obtain measurements for two scaled human forms, a simple geometrical representation and an anatomical form with facial features.  For both mannequins, the Reynolds number based on head diameter and freestream velocity was 1910, and the velocity ratio (Uo/Us) was 0.11.  Continuous inhalation through the mouth, with mannequin facing the wind, was the test condition.  Because the lasers and optics were obstructed close to the mannequin surface, the velocity measurement method could not identify the stagnation points to define the inhalation streamtube. 

 

However, significant velocity differences were identified.  Horizontal velocities were significantly different immediately in front of and below the mouth, as well as between the subnasal region and tip of the nose.  These effects were evident within lateral distances of less than +/-0.6 times the mouth width from the mouth center.  Significantly different vertical velocity components were identified within +/- 2.5 times the height of the mouth opening. Both vertical and horizontal velocity differences at and below the chin were significant between the mannequins, although this location has limited effect on contaminant inhalability.  At upstream distances greater than 5/16ths of the head diameter, velocity differences were insignificant, indicating that facial features affected the flow field only near the face surface. 

 

The results of this study should guide future research in computational fluid dynamic investigation of both fluid flow and particle inhalability.

 

 



 

 


Figure 2:  Velocity field in mid-sagittal plane (Y=0) upstream of the inhaling mannequin.   Difference between fields was insignificant further upstream than 20 mm.  Measurement location indicated by arrow tail; arrows in legend are scaled to 0.3 m s-1, the freestream velocity.  At X = -5 mm, velocities were available only with the elliptical form, as most of this volume was contained within the surface of the anatomical form’s face.