Bolus Contaminant Dispersion in Oscillating Flow in Curved Tubes

[+] Author and Article Information
D. M. Eckmann

Department of Anesthesia, University of Pennsylvania Medical School, University of Pennsylvania, Philadelphia, PA 19104

J Biomech Eng 120(2), 238-244 (Apr 01, 1998) (7 pages) doi:10.1115/1.2798307 History: Received December 27, 1996; Revised April 03, 1997; Online October 30, 2007


The investigation of longitudinal dispersion of tracer substances in unsteady flows has biomechanical application in the study of heat and mass transport within the bronchial airways during normal, abnormal, and artificial pulmonary ventilation. To model the effects of airway curvature on intrapulmonary gas transport, we have measured local gas dispersion in axially uniform helical tubes of slight pitch during volume-cycled oscillatory flow. Following a small argon bolus injection into the flow field, the time-averaged effective diffusion coefficient 〈Deff /Dmol 〉 for axial transport of the contaminant was evaluated from the time-dependent local argon concentration measured with a mass spectrometer. The value of 〈Deff /Dmol 〉 is extracted from the curve of concentration versus time by two techniques yielding identical results. Experiments were conducted in two helical coiled tubes (δ = 0.031, λ = 0.022 or δ = 0.085, λ = 0.060) over a range of 2 < α < 15, 3 < A < 15, where δ is the ratio of tube radius to radius of curvature, λ is the ratio of pitch height to radius of curvature, α is the Womersley parameter or dimensionless frequency, and A is the stroke amplitude or dimensionless tidal volume. Experimental results show that, when compared to transport in straight tubes, the effective diffusivity markedly increases in the presence of axial curvature. Results also compare favorably to mathematical predictions of bolus dispersion in a curved tube over the ranges of frequency and tidal volume studied.

Copyright © 1998 by The American Society of Mechanical Engineers
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