| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 98 === Abstract
The goal of this thesis is to investigate the oscillation behavior and physical mechanisms associated with a droplet placed on a heated plate. The correlations between volume, oscillation mode and frequency, and interior flow-fields of the droplet are revealed. The impacts of gravity, buoyant force, surface tension, and viscosity on the oscillation mode of the droplet are analyzed. A simplified theorem of “thermal-quantum oscillation of a droplet” is proposed. Due to the structural analogy of the vapor-liquid interface underneath the suspended droplet and the micro surface-structure of lotus leaves, this thesis studies as well the hydrophobic characteristics of the composite micro surface-structure of strand plants, so as to provide a reference for biomimetic applications.
Experimental analysis and observations were carried out to characterize the oscillation modes and deformation of the heated droplet. Dimensional analysis is employed to dissect the extent of impact of various forces acting on the droplet.
It is found that, on the bases of both the Taylor instability theory and the boundary layer theory, the energy for initializing the oscillation of the droplet sources from the gas-film within the vapor-liquid interface underneath the droplet. Viscous force and gravity force are respectively the dominant forces for the (R,θ) and Z- directions. In addition, the interior flow-fields of the oscillating droplet are quantitatively visualized by Particle Image Velocimetry, rendering the fluid velocities and vorticity. The correlations between the interior flow-fields and oscillation modes of the droplet are discussed.
In order to explore the lotus effect of composite surface structure of strand plants, the contact angle intrinsic to the leaves of (Hibiscus tiliaceus, Dracaena angustifolia, Ipomoea pes-caprae, Vitex rotundifolia L. f., Scaevola sericea, and Alpinia zerumbet) are measured. Employing SEM, “stellate trichome” and “leathery structure” are recognizable on the surface of those strand plants. It is discovered that the surface of those measured leaves of strand plants are almost hydrophobic, possessing the capabilities of self-clean and protection. Future studies may focus on physical properties of structures of those strand plants.
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