Selective evaporation rate modeling of volatile binary mixture droplets

Abstract Despite numerous studies about droplet evaporation dynamics, the development of an accurate model to estimate the evaporation rate has been under debate for several decades. In particular, the selective evaporation characteristics of binary mixture droplets (BMD) have not been investigated well, in spite of its importance in many applications. The present study examines the selective evaporation characteristics of BMDs and develops a corresponding evaporation rate model. Surface plasmon resonance imaging (SPRi) and long-working distance microscopic imaging methods are applied to simultaneously measure ethanol concentration and droplet geometry, respectively, over the droplet lifetime. The evaporation rates of each BMD component are calculated based on concentration measurement. In this study, the Rayleigh number is employed to analyze the effect of free convection on evaporation dynamics. A new evaporation rate model is suggested as a function of the Rayleigh number by involving diffusive and convective evaporation effects. This model shows a strong correlation with the observed selective evaporation behavior over the droplet lifetime.