THERMOCAPILLARY DYNAMICS OF A LIQUID PLUG INSIDE A CAPILLARY TUBE: EXPERIMENTS AND MODELING

摘要

The dynamics of a liquid plug actuated due to the thermocapillary phenomenon in a capillary tube is studied in the present work. A plug in a capillary tube forms two menisci. When the temperature is increased at one end of the plug, the surface tension decreases at that corresponding meniscus. The reduced surface tension induces a capillary pressure difference causing motion of the plug. The velocity accelerates to a peak and then decelerates to a creeping velocity. A theoretical model is developed based on the balance of surface tension, viscous and inertial forces. The prediction of migration dynamics by the model agrees well with the experiments. The effect of the length of the plug, heat flux applied to the heater, and viscosity of silicone oil on migration dynamics is studied experimentally. The heat flux augments the migration phenomenon; whereas, the length and viscosity depreciate it. The reasons for various migration characteristics are explained. The predictions of the magnitude of peak velocity made by the theory across the change of parameters also agree well with the experimental observations. The model is then used to study the effect of radius and thermal conductivity of the capillary tube on the migration phenomenon. It is observed that the radius has proportional dependence on the magnitude of peak velocity; whereas, the thermal conductivity has a nonmonotonic dependence. The understanding developed from this work finds applications in the various fields of droplet's science and especially in the area of microfluidics.