The motion of droplets in a vertical temperature gradient

Abstract

The thermocapillary migration of single water droplets in butyl benzoate was investigated using the Plateau configuration. The droplets were injected below the level of equal density in the stably stratified butyl benzoate. Because of buoyancy and Marangoni force, the droplets rise until these forces balance each other. For seven different temperature gradients the final position of four to eight single droplets was determined. The reciprocal diameter was found to be a linear function of the deflection from the height of equal density. A systematic deviation from the theory of Young, Goldstein, and Block [J. Fluid Mech. 6, 350 (1959)] was observed. This deviation was attributed to the convective heat transport inside and outside the droplet not covered by the theory. The experimental data could be fitted by introducing an effective temperature gradient that decreases with the square of the applied gradient.