Capillary instability of a two-layer annular film: an airway closure model

Coupled capillary and gravity-driven instability in a liquid film overlying a porous layer.

In this work, we study the problem of onset of thermal convection in a fluid layer overlying a porous layer, the whole system being heated from below. We use Brinkman's model to describe the porous medium and determine the corresponding linear stability equations. The eigenvalue problem is solved by means of a modified Galerkin method. The behavior of the critical wave number and temperature gr...

Forced instability of core-annular flow in capillary constrictions

Instability of a compressed elastic film on a viscous layer

A flat, compressed elastic film on a viscous layer is unstable. The film can form wrinkles to reduce the elastic energy. A linear perturbation analysis is performed to determine the critical wave number and the growth rate of the unstable modes. While the viscous layer has no effect on the critical wave number, its viscosity and thickness set the time scale for the growth of the perturbations. ...

Surfactant effects in model airway closure experiments.

The capillary instability that occurs on an annular film lining a tube is studied as a model of airway closure. Small waves in the film can amplify and form a plug across the tube. This dynamical behavior is studied using theoretical models and bench-top experiments. Our model predicts the initial growth rate of the instability and its dependence on surfactant effects. In experiments, an annula...

Extended annular capillary surfaces

The height of the surface of a fluid in an annular tube is explored using a shooting method to solve a boundary value problem where the radii and the contact angles are given. The contact angles on the inner and outer tube surface need not be the same. These surfaces are then extended so that they are no longer graphs. The extended surfaces are shown to solve a boundary value problem over an an...