Title

Experimental Investigation of Condensation and Freezing Phenomenon on Hydrophilic and Hydrophobic Titanium Nanopillared Glass Surfaces

Abstract

Atmospheric condensation is very important for multiple practical applications such as heat transfer, thermal management, aerospace, and condensate harvesting. Water droplets heterogeneously nucleate on the surfaces when the temperature is below the dew point temperature. The nucleation energy barrier for a condensed droplet varies significantly with the humidity content in the operating environment. The freezing of this condensate is also dependent on the operating conditions and surface properties. This article presents an experimental study of condensation and freezing from humid air with the objective of understanding how the surface morphology and chemistry determines the droplet shape and wetting state. Hexagonal close-packed arrays of titanium (Ti) pillars are patterned using microsphere photolithography (MPL). The Ti nanostructured surface was tested with and without a Teflon© coating to reveal the condensate harvesting, passive freezing, and dropwise condensation applications, respectively. Condensation and freezing tests were conducted in the presence of non-condensable gases (air) with different relative humidity (RH) levels to control the nucleation site density. The experiments showed that droplet growth occurs in the following stages: initial nucleation, direct growth, and coalescence events. By pinning droplets, coalescence is suppressed for the Ti nanopillared surface altering the size distribution of droplets and significantly accelerating the freezing process.

Department(s)

Mechanical and Aerospace Engineering

Comments

Article in press

Keywords and Phrases

Atmospheric humidity; Coalescence; Condensation; Drops; Freezing; Heat transfer; Humidity control; Morphology; Nanopillars; Nucleation; Polytetrafluoroethylenes; Surface morphology; Titanium; Wetting, Dewpoint temperature; Dropwise condensation; Experimental investigations; Hexagonal close packed; Hydrophilic and hydrophobic; Nanostructured surface; Nucleation site density; Operating environment, Density of gases

International Standard Serial Number (ISSN)

0145-7632; 1521-0537

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2020 Taylor & Francis Ltd., All rights reserved.

Publication Date

01 Jan 2020

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