The evaporation and stability of a droplet in a finite system

grantor: University of TorontoThe results of recent experiments indicate that a temperature discontinuity exists at a liquid-vapour interface undergoing steady evaporation. In order to investigate this phenomenon in an unsteady situation, an experimental apparatus that can study the evaporation of a single one-component liquid droplet in a finite system has been built. The measured temperatures predict the existence of a temperature discontinuity at the liquid-vapour interface in agreement with the previous experiments. The 'D' 2-law of droplet evaporation gives a reasonable estimate of the evaporation rate when the temperature discontinuity is considered. Using the measured temperatures and droplet size, the pressure in the vapour during the evaporation process can be predicted using Statistical Rate Theory. For each of 80 sets of measurements, the largest difference between the prediction and the measured value is 9 Pa (less than 0.5%). Adsorption on the surface of the confining volume is found to play a significant role in the evaporation process. The stability of a droplet in a finite system has been investigated theoretically with consideration of the solid-vapour interface. The results indicate that a stable droplet can exist if the pressure at which film-wise condensation is predicted to occur is greater than the saturation pressure. The stable equilibrium size has not been observed with the experimental apparatus, and this is attributed to the nature of the solid surface. However, a quasi-steady state has been observed, which could serve as a well defined initial condition for an evaporation experiment.M.A.Sc