Bubble vortex at surfaces of evaporating liquids.

Air bubble in volatile liquid on exiting to the surface spins a vortex maintaining integrity of the film over an indefinite period of time. The shear stress associated with the surface tension increase in the adiabatic evaporation cooling drags the warmer liquid inwards into the film counteracting its capillary drainage out under gravity. The chaotic patterns, visualized with the aid of light interferometry, depend on liquid volatility, degree of vapor saturation, and air convection. The circulation intensifies and the frequency of hydrodynamic instabilities in the multiphase flow increases on the transition to strong turbulent regimes with increasing evaporation rate. Self-consistency of the physical mechanisms of solute and evaporation inhibition of bubble coalescence is verified through dimensional parametric analysis.