Date of Award

12-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Dr. Joshua Bostwick, Committee Chair

Committee Member

Dr. John Saylor

Committee Member

Dr. Daniel Fant

Abstract

A liquid drop placed on a heated surface above the Leidenfrost temperature will levitate on a vapor cushion. The static shape of these non-wetting Leidenfrost drops is that of a flattened sphere, reflecting the balance between gravitational, surface tension and lubrication pressures. In this thesis, we study Leidenfrost drops on curved substrates where we observe spontaneous star-shaped surface oscillations of characteristic frequency and mode number. Experiments are conducted using six different liquids and the temporal response of the observed modes n = 2 – 13 is analyzed to dene the oscillation spectrum. We observe that large drops oscillate with a constant frequency, while small drop frequencies are strongly dependent upon liquid volume. A simple mathematical model is developed using a hydrodynamic stability analysis and shows reasonable agreement with our large experimental data set. Scaling arguments are used to collapse the data which allows generalized statements to be made regarding the physics governing star oscillations. In addition, we observe more complex dynamics such as mode doubling where two distinct modes are simultaneously excited at different frequencies and modal dominance where one mode persists over large ranges of parameter space previously thought to be occupied by another mode. Lastly, we conclude by offering some qualitative observations of Leidenfrost shape instabilities in other complex substrate geometries.

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