分野別セミナー

Using long-wave theory and direct numerical solutions of the Navier-Stokes equations, we investigate nonlinear dynamics of thermocapillary flows arising in a two-layer system consisting of a thin liquid film and an overlying gas layer with the liquid film covering a heated solid substrate with a non-uniform temperature in the form of traveling thermal waves. Our results indicate that unidirectionally propagating interfacial waves are formed in the liquid film. The interfacial waves transport liquid, thereby creating a net pumping effect. We show that the frequency of thermal waves leading to the most efficient pumping is defined by their wave length and weakly depends on other system parameters.

In the case of a stationary thermal wave with sufficiently large amplitude and Marangoni number, liquid film rupture takes place with a flattish wide trough. For moderately small frequencies of the thermal wave, a periodic structure consisting of localized drops interconnected by thin liquid bridges emerges with virtually no mass exchange between the adjacent drops. This train of drops travels along the heated substrate following the thermal wave. For larger thermal wave frequencies, the thickness of the bridges increases enabling fluid flow between the neighboring drops. The drop-train regimes may be utilized in microfluidic applications for directed transport of liquid content enclosed in drops formed by thermocapillary forces.