Evaporation Kinetics of Polyol Droplets: Determination of Evaporation Coefficients and Diffusion Constants

Abstract

In order to quantify the kinetics of mass transfer between the gas and condensed phases in aerosol, physicochemical properties of the gas and condensed phases and kinetic parameters (mass/thermal accommodation coefficients) are crucial for estimating mass fluxes over a wide size range from the free molecule to continuum regimes. In this study, we report measurements of the evaporation kinetics of droplets of 1‐butanol, ethylene glycol (EG), diethylene glycol (DEG), and glycerol under well‐controlled conditions (gas flow rates and temperature) using the previously developed cylindrical electrode electrodynamic balance technique. Measurements are compared with a model that captures the heat and mass transfer occurring at the evaporating droplet surface. The aim of these measurements is to clarify the discrepancy in the reported values of mass accommodation coefficient (αM, equals to evaporation coefficient based on microscopic reversibility) for 1‐butanol, EG, and DEG and improve the accuracy of the value of the diffusion coefficient for glycerol in gaseous nitrogen. The uncertainties in the thermophysical and experimental parameters are carefully assessed, the literature values of the vapor pressures of these components are evaluated, and the plausible ranges of the evaporation coefficients for 1‐butanol, EG, and DEG as well as uncertainty in diffusion coefficient for glycerol are reported. Results show that αM should be greater than 0.4, 0.2, and 0.4 for EG, DEG, and 1‐butanol, respectively. The refined values are helpful for accurate prediction of the evaporation/condensation rates.

Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles

“…[44][45][46][47][48][49][50][51][52][53][54] Many such studies are summarised in the review by Kolb et al 55 The determination of a M of various organic compounds, such as glycols, has also been the subject of several studies. 46,[56][57][58] Uptake coefficients of trace gases onto atmospheric aerosols, which are equal to the mass accommodation coefficients for Knudsen numbers c1, 17 are also discussed in reviews by Kolb et al 55 and Abatt et al 59 In this work we also assess the performance of singleparticle photoacoustic spectroscopy in retrieving mass accommodation coefficients of water vapour on tetraethylene glycol particles. In principle, the high sensitivity of photoacoustics allows for low laser powers to be used and hence restricts the temperature oscillation to just a few Kelvins.…”

The evaporation kinetics of pure water droplets at varying drying rates and the use of evaporation rates to infer the gas phase relative humidity

“…In this work, we apply the same analysis approach to the Liu and K-V-H models, analyzing their sensitivity to the thermophysical and kinetic parameters identified in section 2.2 and 2.3. The sensitivity of the K-V-H model predictions to the value of αM and αD are discussed below; the sensitivity of the Liu model to the value of M has already been discussed in a previous publication 32 . The impact of the uncertainties in the parameters Dv and Kg (± 6% and ± 2%, respectively) were also determined for both Liu and K-V-H models.…”

“…For a gas velocity of 3 cm s -1 , a droplet size of 25 m radius and a gas phase saturation ratio of 0.2, the surface temperature of the droplet can be estimated to be 281.1 K and the correction factor is 1.084. This factor has been used widely in previous publications 14,15,20,21,25,32 .…”

“…As would be expected given the results in Figure 3, the uncertainty in the retrieved RH is highest for the Liu model. The uncertainties in the RH extracted using the Liu and K-V-H models are given in equations (32) and (33) respectively, where the RH is given in the form of fractional…”

“…Ahn and Liu 31 developed a model (referred to as the Liu model) considering the coupled mass and heat transfer. This model was further modified by Su et al 32 As an additional benefit to providing a more comprehensive and accurate model framework for treating the evaporation of water droplets over a broader range of drying rates and environmental conditions, we anticipate that this refined model will improve the accuracy with which we are able to make hygroscopicity measurements. Our ability to measure the hygroscopic growth of a solute containing aerosol droplet (referred to as the sample droplet) to very high water activity and over very short time frame is dependent on an extremely accurate characterization of the gas phase RH 21,22 .…”