On evaporation of thin liquid films subjected to ultrasonic substrate vibration

Theoretical and experimental studies on evaporation of thin and ultrathin liquid films (all volatile or liquid solutions) are desirable, but scarce. In this context, excitation of thin liquid films by (ultrasonic) vibration is also an interesting theoretical and applied research direction affecting the hydrodynamics, stability, and evaporation of thin liquid films. In this study, the evaporation history of drop-cast stationary and excited thin liquid films subjected to vertical and horizontal ultrasonic vibration is studied, and unprecedented results are obtained and discussed. The evaporation history of two model thin liquid films is captured using video camera and high precision digital balance. Since evaporation of excited thin films by substrate vibration resembles forced convection, the convective heat transfer coefficient and consequently the evaporation rate of the excited thin films are expected to increase compared to those of non-excited thin films. Experimental results substantiate this hypothesis. It is further shown and discussed that the films excited by horizontal ultrasonic substrate vibration evaporate faster than those excited by vertical vibration.