Effect of gravity on liquid plug transport through an airway bifurcation model

Abstract

In this study, gravitational and surface mechanisms determining the distribution of instilled liquids are examined experimentally using a bench top model of a symmetrically bifurcating airway. A liquid plug was instilled into the parent tube and driven through the bifurcation by a syringe pump. The effect of gravity was adjusted by changing the roll angle (phi) and pitch angle (gamma) of the bifurcation (phi = gamma = 0) deg was isogravitational). phi determines the relative gravitational orientation of the two daughter tubes: when phi not equal 0 deg, one daughter tube was lower (gravitationally favored) compared to the other gamma determines the component of gravity acting along the axial direction of the parent tube when gamma not equal 0 deg, a nonzero component of gravity acts along the axial direction of the parent tube. A splitting ratio R-S, is defined as the ratio of the liquid volume in the upper daughter to the lower just after plug splitting. We measured the splitting ratio, R-S, as a function of the parent-tube capillary number (Ca-p); the Bond number (Bo); phi; gamma; and the presence of pre-existing plugs initially blocking either daughter tube. A critical capillary number (Ca-c) was found to exist below which no liquid entered the upper daughter (R-S = 0), and above which R-S increased and leveled off with Ca-p. Ca-c increased while R-S decreased with increasing phi, gamma, and Bo for blocked and unblocked cases at a given Ca-p > Ca-c. Compared to the nonblockage cases, R-S decreased (increased) at a given Ca-p while Ca-c increased (decreased) with an upper (lower) liquid blockage. More liquid entered the unblocked daughter with a blockage in one daughter tube, and this effect was larger with larger gravity effect. A simple theoretical model that predicts R-s and Ca-c is in qualitative agreement with the experiments over a wide range of parameters.