Characterization of evaporation kinetics and wettability using a quartz crystal microbalance
Authors
Murray, Brandon
ORCID
https://orcid.org/0000-0001-8955-666X
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Other Contributors
Borca-Tasçiuc, Theodorian
Zhang, Lucy T.
Keblinski, Pawel
Narayan, Shankar
Zhang, Lucy T.
Keblinski, Pawel
Narayan, Shankar
Issue Date
2022-05
Keywords
Mechanical engineering
Degree
PhD
Terms of Use
Attribution-NonCommercial-NoDerivs 3.0 United States
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute (RPI), Troy, NY. Copyright of original work retained by author.
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute (RPI), Troy, NY. Copyright of original work retained by author.
Full Citation
Abstract
Evaporation of water is ubiquitous, found in a multitude of natural processes and industrial applications. While scientific studies of water evaporation have been performed for over a century, there exists continued interest in determining the fundamental transport phenomena at the liquid-vapor interface. Improved understanding of the rate-limiting transport mechanisms at the liquid-vapor interface would allow designing more efficient thermal systems for electronics cooling, energy storage, and other critical applications. However, the phenomena occurring in the interfacial region are extremely challenging to probe experimentally, often occurring across only a few nanometers to micrometers. High precision sensing techniques are needed to elucidate transport phenomena at the liquid-vapor interface.This thesis develops a megahertz frequency piezoelectric sensing technique using a quartz crystal microbalance (QCM) to quantify evaporation rates with high precision. It identifies the difference in QCM’s frequency response to changes in the droplet contact area and contact angle using a multiphysics computational model validated using experimental measurements. The QCM contact area sensing technique is then combined with side-view contact angle measurement to study sessile droplet evaporation under different conditions. This hybrid QCM-imaging technique provides a higher precision than imaging alone and is used to determine the evaporation rate of water droplets in a dry nitrogen flow at different temperatures.
With the QCM-imaging measurement technique, this thesis studies a series of nominally pure water droplets in a nitrogen cross-flow. The experimental observations are combined with a multiscale computational model to investigate the mass accommodation at the liquid-vapor interface. The computational model combines the macroscopic flow field with the kinetic theory of gasses near the interface to determine the mass accommodation coefficient (AC) during the evaporation process. Further, the QCM determines the amount of non-volatile impurities in the nominally pure water droplets, indicating how challenging it can be to obtain impurity-free water and keep it clean. This research obtains an AC close to 0.001 across multiple droplets in the dry nitrogen (diffusively-limited) environment. This model can provide predictive capabilities for evaporation in non-condensable gas streams. This thesis also extends the model to analyze water droplets with non-volatile impurities. Specifically, the evaporation of aqueous potassium chloride droplets into nitrogen flow was analyzed over a wide range of molality (10-5 – 1 mol/kg). Under these conditions, the accommodation is relatively stable around 0.001. This result indicates that potassium chloride does not strongly influence the accommodation during evaporation.
The QCM is also employed to study nanoscale phenomena, including electrochemical fabrication of nanomaterials and evaporation of liquids confined in nanopores. A two-step anodization approach is used to obtain an ordered array of cylindrical alumina nanopores. The creation of these nanopores is monitored during the fabrication process using the QCM to obtain and control the pore geometry. Our analysis indicates that a mass resolution of approximately 20 ng/s can be achieved using the QCM to elucidate the nanoscale phenomenon. Finally, the evaporation of water into pure vapor confined in single-ended nanopores is studied. A one-dimensional theoretical model based on the kinetic theory of gasses is developed that links the far-field temperature and pressure to the QCM measurement of mass flux from the nanopores to determine evaporation kinetics and mass accommodation at the liquid-vapor interface. This modeling approach allowed investigation of the meniscus shape and the tensile pressure in the condensed phase. It was found that confinement in the pore produces high tensile pressure when the liquid meniscus recedes far into the pores, strongly affecting the mass accommodation at the liquid-vapor interface.
Description
May 2022
School of Engineering
School of Engineering
Department
Dept. of Mechanical, Aerospace, and Nuclear Engineering
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection
Access
CC BY-NC-ND. Users may download and share copies with attribution in accordance with a Creative Commons
Attribution-Noncommercial-No Derivative Works 3.0 license. No commercial use or derivatives
are permitted without the explicit approval of the author.