Refractive index and mole fraction field of the vapor evaporated from ethanol-water mixture droplet

Abstract

In this study, effect of the ambient relative humidity on the vapor concentration of ethanol-water mixture droplet on PTFE substrate was observed. Ethanol-water mixtures were prepared at 100 vol% (pure ethanol), 75 vol%, 50 vol%, 25 vol%, and 0 vol% (Pure water) by ethanol volume fraction. Relative humidity inside the test chamber was controlled at 33%RH, 52%RH, and 75%RH using saturated salt solution technique. Vapor concentration field was acquired by both applying Abel inverse transform to the Schlieren image and simulating with OpenFOAM source code. Pure ethanol had smaller value of mole fraction at the center than ethanol water mixture which was similar to the refractive index field. Two peaks of the mole fraction value were observed at the side of droplet in the case of pure ethanol from the concentration field, which was due to the presence of the droplet that blocked the downward movement of the ethanol vapor which was heavier than air and forced it to horizontally move to the edge of the droplet. On the other hand, one peak at the middle was found in the case of ethanol-water mixtures. Comparison of the concentration field between experimental result and simulation showed consistency in pure ethanol case and deviation became larger as ethanol portion decreased. Results of pure water and low ethanol concentration case (25 vol%) were obtained from simulation alone due to the limitation of Z-type Schlieren.

Methanol–water mixture evaporation-induced self-assembly of ZIF-8 particles

“…Given that the evaporation flux is the highest at the three-phase contact line, the methanol inside the droplet is supposed to flow toward the contact line to increase the evaporation rate because it is more volatile than water. 25 Due to the uneven distribution of methanol along the gas-liquid interface, the surface tension near the droplet apex should be higher than at the droplet edge. The thermal and concentration gradients can lead to circulating flows driven by surface-tension gradient Marangoni flows and the resulting Marangoni flow moves towards the center of the droplet.…”