High-speed & Long-time Electrostatic Measurements of Fluid & Particle Interfaces Open Access

Harvey, Dana (Fall 2022)

Permanent URL: https://etd.library.emory.edu/concern/etds/m900nv78k?locale=en


Studying the inter-facial dynamics of complex systems requires non-invasive measurement techniques. During my time at Emory, I used electrostatic concepts to probe two separate systems: the dynamics of Leidenfrost vapor layers near collapse and charge decay on acoustically levitated particles. A Leidenfrost vapor layer forms between a sufficiently hot solid and an evaporating fluid. The gas-fluid and gas-solid interfaces are treated as capacitors to capture micro-second dynamics. Using this technique, a minimum Leidenfrost temperature, T-≈140°C, was found and determined to be caused by hydrodynamics alone. To expand upon experimental results, COMSOL Multiphysics simulations were conducted. Simulations uncovered a lower bound for T-, which matched the experimental results. It was determined that inertia, often assumed negligible in simulations, is paramount in determining the failure of Leidenfrost vapor layers. In the second experimental system, an acoustic levitator is coupled with an inductive Faraday cup to monitor charge decay in a non-contact manner. It was found that charge remained on particles in dry environments for weeks, contradicting the current theories. Furthermore, charge decay was found to be independent of particle composition, and instead determined by environmental factors. Finally, using a 1D sedimentation model it was determined that charge must be considered when determining how far particles can travel in Earth's atmosphere.

Table of Contents

(1) Introduction (1.1) History of the Leidenfrost effect (1.2) Acoustic levitation as a tool for isolating atmospheric particles (2) Minimum Leidenfrost Temperature on Smooth Metallic Surfaces (2.1) The failure temperature of Leidenfrost drops (2.2) Inverse Leidenfrost geometry as a reproducible experimental system (2.3) Chapter conclusions (2.4) Leidenfrost thickness measurement technique (2.4.1) Sampling protocol (2.4.2) Capacitor model of the vapor layer (3) Inertial Leidenfrost Collapse (3.1) Leidenfrost simulations couple many physics concepts (3.2) COMSOL simulation details (3.3) Lubrication model details (3.4) Chapter conclusions (4) The lifetime of charged dust in the atmosphere (4.1) Non-contact charge measurement technique (4.2) Schlieren imaging (4.3) Behavior determines the discharge behavior (4.4) 1-D sedimentation model (5) Conclusions

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