Longitudinal mixing by the human larynx

Both the characteristics of the velocity field and the longitudinal dispersion of helium, oxygen and sulfur hexafluoride in air flowing through a cast of a cadaveric human larynx have been studied. The larynx cast was mounted in the center of a 5 m long, 1.6 cm diameter tube through which air was admitted at 206, 425 or 775 ml/s, corresponding to fully-developed laminar (Reynolds number = 1110), transitional (2310), and fully-developed turbulent (4210) flow conditions, respectively. A significant enhancement of longitudinal mixing was detected immediately downstream of the glottis, presumably because of the jetting of air in the vicinity of the constriction. This enhancement did not depend upon the flow rate of air but was inversely related to the molecular diffusivity of the tracer gas; this indicates the importance of Taylor dispersion in the jet. The glottis generated intense local turbulence which propagated as as 110 cm from the constriction. This turbulence caused a flattening of the velocity profiles resulting in a reduction in the rate of downstream longitudinal mixing. The reduction was so great that, in spite of mixing enhancement in the jet, the overall mixing was less with the larynx in place than in the empty tube.