Simple Model for Diffusion-Limited Drop Evaporation of Binary Liquids from Physical Properties of the Components: Ethanol–Water Example

Abstract

The understanding of the evaporation process of drops consisting of binary mixtures, in particular ethanol–water drops, is important in many industries such as ink-jet printing, cooling of microelectronics, and alcohol-added pesticide spray applications. The theory of the diffusion-limited drop evaporation process for pure liquids has been investigated thoroughly, and linear (dV (2/3)/dt) slopes were obtained for most of the cases. However, the evaporation of binary liquid drops was found to be much more complicated than that of the pure liquids due to the change of the composition of the drop by time and there is a need for the development of a new model. The experimental results on the diffusion-limited drop evaporation behavior of ethanol–water binary drops initially containing 25 and 50% ethanol by wt and having a volume of 7 μL were reported on a flat hydrophobic Teflon-FEP substrate under the constant relative humidity of 54% and 25 °C temperature conditions, together with pure liquids. The change of contact angles, heights, and contact radius of the drops by time were monitored with a camera. In a parallel study, the concentration changes in the bulk composition of ethanol–water binary drops of 7 μL (25 and 50% ethanol by wt) by time in the same evaporation conditions were monitored using a refractive index–ethanol concentration calibration curve. Then, the parameters affecting the drop evaporation process, such as total vapor pressures, average diffusion coefficient of binary vapors, average molecular weights, and densities of the liquid drops, were calculated using well-known physical chemistry approaches from the previously published data. These parameters were used to estimate the rate of binary ethanol–water drop evaporation, and it was determined that the proposed model fitted the (dV (2/3)/dt) slopes obtained from experimental data points with lower than 5% error when the surface cooling of the drops was considered.

An Experimental Investigation of Evaporation of Ethanol–Water Droplets Laden with Alumina Nanoparticles on a Critically Inclined Heated Substrate

“…A model based on diffusion-limited evaporation is developed particularly for the ethanol−water binary mixture to predict the evaporation rate. 25 The sliding angle of a droplet on an inclined surface depends on the nature (wettability) of the substrate via the contact angle and surface tension. 13 Thus, many experimental and theoretical studies have been conducted on droplet migration on different hydrophobic and super-hydrophobic surfaces by considering natural surfaces, such as that of a lotus leaf, 26 surface texturing, 27 and by imposing temperature and concentration gradients.…”

“…This leads to an increase in the evaporation time of the droplet. A model based on diffusion-limited evaporation is developed particularly for the ethanol–water binary mixture to predict the evaporation rate …”

Volatile Aroma Surfactants: The Evaluation of the Adsorption–Evaporation Behavior under Dynamic and Equilibrium Conditions

“…Analysis of evaporating droplets (spherical, pendant, or sessile) of simple liquids − or drops consisting of binary mixtures , is an intensive research field. Theoretical models of evaporation involve consideration of heat as well as mass transfer as a result of the convective transport and evaporation flux. , Evaporation of binary liquid drops was found to be much more complicated than that of pure liquids.…”

Review of the binary mixture droplet evaporation studies

“…( 2). The well-developed diffusion model has been widely used in recent studies for the evaporation dynamics of BMD, and some modified models have been developed to accurately predict the diffusive evaporation rate [55][56][57][58]. Even if these diffusion models were developed based on the experimental data of the single-component droplet evaporation, the diffusion models have been widely used to predict the diffusive evaporation rate of BMDs.…”