Temperature Dependence of the Evaporation Coefficient of Water in Air and Nitrogen under Atmospheric Pressure: Study in Water Droplets

Abstract

The evaporation coefficients of water in air and nitrogen were found as a function of temperature, by studying the evaporation of pure water droplet. The droplet was levitated in an electrodynamic trap placed in a climatic chamber maintaining atmospheric pressure. Droplet radius evolution and evaporation dynamics were studied with high precision by analyzing the angle-resolved light scattering Mie interference patterns. A model of quasi-stationary droplet evolution, accounting for the kinetic effects near the droplet surface was applied. In particular, the effect of thermal effusion (a short range analogue of thermal diffusion) was discussed and accounted for. The evaporation coefficient α in air and in nitrogen were found equal. α was found to decrease from ∼ 0.18 to ∼ 0.13 for the temperature range from 273.1 K to 293.1 K and follow the trend given by Arrhenius formula. The agreement with condensation coefficient values obtained with essentially different method by Li et al. 1 was found excellent. The comparison of experimental conditions used in both methods revealed no dependence of evaporation/condensation coefficient upon * jakub@ifpan.edu.pl 1 droplet charge nor ambient gas pressure within experimental parameters range. The average value of thermal accommodation coefficient over the same temperature range was found to be 1 ± 0.05.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume VI – heterogeneous reactions with liquid substrates

“…In contrast, Marek and Straub (2001) conclude in their review that the condensation and evaporation coefficients are different from each other, and a decline of both coefficients with increasing temperature and pressure is derived, in disagreement with theoretical predictions and the principle of microscopic reversibility. The data of Zientara et al (2008) obtained on a stationary droplet are consistent with a negative T dependence of α b and α t = 1. Other evaporation rate measurements were inconclusive about the temperature dependence (Smith et al, 2006;Drisdell et al, 2008).…”

An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds

“…Recent focus has been on experiments employing droplet trains or liquid jets Cappa et al, 2005;Smith et al, 2006), expansion cloud chambers (Winkler et al, , 2006, laminar diffusion flow reactors (Voigtländer et al, 2007) and electrodynamic levitation (Shaw and Lamb, 1999;Zientara et al, 2008).…”

Evaporation of Micro-Droplets: the "Radius-Square-Law" Revisited

“…Such is exactly the case in the vicinity of gasliquid interface, below the mean free path of the gas molecule from the surface. Customarily, however not with full exactness (see [31,4,32,2,13]), the transport of molecules in this region is treated as ballistic and thus governed by the HertzKnudsenLangmuir (HKL) equation.…”