Date of Award

2021

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Chang Kyoung Choi

Committee Member 1

Jeffrey S. Allen

Committee Member 2

Ezequiel Medici

Committee Member 3

Jae Yong Suh

Committee Member 4

Nenad Miljkovic

Abstract

The objective of this work is to identify the fundamental mechanism of dropwise condensation on a smooth solid surface by probing the solid-vapor interface during phase-change to evaluate the existence and structure of the thin film and the initial nucleus that develop during condensation. In this work, an automated Surface Plasmon Resonance imaging (SPRi) instrument with the ability to perform imaging in intensity modulation and angular modulation is developed. The SPRi instrument is used to probe (in three dimensions) the adsorbed film that forms on the substrate during dropwise condensation. SPRi with a lateral resolution of ~ 4-10 μm, thickness resolution of 0.1-1nm, and temporal resolution of 200-10,000 frames per second can measure water films that are monolayer to multilayer in thickness. The governing mechanism of dropwise condensation is investigated in detail for stable dropwise condensation on a smooth hydrophilic substrate. The study shows nucleation is the first step in dropwise condensation and no film greater than a monolayer exists between droplets during stable dropwise condensation. Our result confirms previous experimental works in support of nucleation theory as the mechanism of dropwise condensation. Our observation of unstable dropwise condensation of steam on a smooth hydrophilic surface shows presence of a several nanometers thick water film between droplets during dropwise condensation. This data matches with previous experimental work in support of film rupture theory. In summary, our results indicate nucleation theory or film rupture theory may be valid for special experimental settings. And, neither of these two theories are a comprehensive theory than can explain the physics of dropwise condensation.

Download

Share

COinS