The steady propagation of an air bubble into a partially collapsed, fluid-filled, elastic tube.
The reopening of a partially collapsed, fluid-filled, elastic tube is investigated experimentally. The origin of this problem lies in the field of lung airway reopening. Airway closure can occur as a result of pulmonary disease and thus greater understanding of the reopening dynamics is essential in order to prevent damage during mechanical ventilation. The laboratory model consists of a 1m long, uniformly collapsed, fluid-lined tube into which air is injected at a constant flow rate. This leads to the steady propagation of an air bubble, whose velocity is characterised by the non-dimensional capillary number Ca.
Controlled experiments have been performed for 70% initial tube collapse, were the effect of viscosity on the reopening dynamics was investigated by using three different grades of silicone oil. A direct comparison between the experimental pressure dependence on Ca and the numerical simulations of the zero-gravity, three dimensional airway reopening model of Hazel and Heil (2005) highlighted some significant differences. Within the experimental parameter range, gravity was found to profoundly influence the reopening mechanics in several ways.
Recently, experiments have been performed to assess the effects of varying the initial level of tube collapse upon the reopening dynamics. At strong levels of collapse multiple steady reopening states were observed, including the propagation of an asymmetric air bubble, a double-tipped bubble and a low pressure pointed bubble.
A. Heap & A. Juel Multiple states of airway reopening.