Water Droplet Evaporation in Air: Effects of Interfacial Thermal and Mass Diffusion Resistance

Abstract

Evaporation of water droplets in air is a process highly relevant to a variety of environmental, industrial, and biomedical applications. In conventional hydrodynamic modeling of droplet evaporation, it is usually assumed that thermodynamic equilibrium exists at the water-air interface. However, such an assumption could result in considerable errors in predicting the evaporation rate of micro/nanoscale water droplets in air. In this work, we use the combination of kinetic theory-based model and hydrodynamic model to study the effects of interfacial resistance on the evaporation behavior of water droplets in air. The interfacial thermal resistance and interfacial mass diffusion resistance predicted by the kinetic theory-based model are first validated by MD simulation results, and then incorporated into the hydrodynamic model to predict the influence of the water droplet size, air temperature, pressure and humidity on the water droplet evaporation rate and droplet temperature. The evaporation behavior of water droplets in air predicted by our kinetic-hydrodynamic model are corroborated by MD simulation results and the recent experimental data. Our modeling results show that, at normal temperature and pressure (i.e., 25 °C and 1 atm by NIST), the equivalent length of thermal resistance and mass diffusion resistance at water-air interface are both ∼200 nm. This indicates that, at normal temperature and pressure, the effects of interfacial thermal and mass diffusion resistance on evaporation of water droplets in air cannot be ignored if the droplet diameter is less than 20 μm. The thermodynamic equilibrium assumption is only valid if the droplet diameter is greater than 20 μm. Once the droplet size is greater than 100 μm, the radiation heat transfer and convection effects must also be taken into account to give a more accurate prediction of droplet evaporation rate.

Department(s)

Mechanical and Aerospace Engineering

Comments

National Science Foundation, Grant 2310833

Keywords and Phrases

Interfacial resistance; Kinetic and hydrodynamic combined model; Molecular dynamics; Water droplet evaporation

International Standard Serial Number (ISSN)

0017-9310

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Elsevier, All rights reserved.

Publication Date

01 Apr 2025

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