Journal of Applied Physiology, Vol 69, Issue 2 562-569, Copyright © 1990 by American Physiological Society
Periodic flow at airway bifurcations. III. Energy dissipation
A. Tsuda, B. J. Savilonis, R. D. Kamm and J. J. Fredberg
Worcester Polytechnic Institute, Massachusetts 01609.
We measured the energy dissipation associated with large-amplitude periodic
flow through airway bifurcation models. Each model consisted of a single
asymmetric bifurcation with a different branching angle and area ratio,
with each branch terminated into an identical elastic load. Sinusoidal
volumetric oscillations were applied at the parent duct so that the
upstream Reynolds number (Re) varied from 30 to 77,000 and the Womersley
parameter (alpha) from 4 to 30. Pressures were measured continuously at the
parent duct and at both terminals, and instantaneous branch flow rates were
calculated. Time-averaged energy dissipation in the bifurcation was
computed from an energy budget over a control volume integrated over a
cycle and was expressed as a friction factor, F. We found that when tidal
volume was small [ratio of tidal volume to resident (dead space) volume,
VT/VD less than 1], F was independent of branching angle and fell with
increasing alpha and VT/VD. When tidal volume was large (VT/VD greater than
1), F increased with increasing branching angle and varied less strongly
with alpha and VT/VD. No simple benchmark flow represented the data well
over the entire experimental range. This study demonstrates that only two
nondimensional parameters, alpha and VT/VD, are necessary and are
sufficient to describe time-averaged energy dissipation in a given
bifurcation geometry during sinusoidal flow.
