Temperature dependence of evaporation coeffcient of water in air and nitrogen under atmospheric pressure; study in water droplets

TL;DR

This study measures how water evaporation coefficients vary with temperature in air and nitrogen at atmospheric pressure, using levitated droplets and light scattering analysis, revealing a temperature-dependent trend consistent with Arrhenius behavior.

Contribution

It provides the first detailed temperature-dependent measurements of water evaporation coefficients in air and nitrogen at atmospheric pressure using levitated droplets and light scattering techniques.

Findings

Evaporation coefficients decrease from ~0.18 to ~0.13 between 273.1 K and 293.1 K.

Evaporation and condensation coefficients are equal within experimental error.

No dependence of coefficients on droplet charge or ambient pressure was observed.

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 \alpha in air and in nitrogen were found equal. \alpha 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 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 \pm 0.05.