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.

Keywords

• inkjet printing
• ethanol-water mixture droplet
• z-type schlieren
• openfoam simulation
• abel inverse transform
• refractive index
• vapor concentration field