液珠之熱能階振盪行為研究

Thermal-Quantum Oscillation of a Droplet

莊程媐(Cheng-Hsi Chuang)

指導教授 ： 楊鏡堂 ； 陳榮順

國立清華大學/工學院/動力機械工程學系/碩士(2010年)

摘要

摘要
本文主旨是研究液珠於加熱盤上之振盪行為與物理現象，探討液珠體積、液珠振盪模式與頻率及液珠內部流場之關係，分析重力、浮力、表面張力、黏滯度等物理因子對於液珠振盪模態之影響，並依據研究結果提出簡易的「液珠熱能階振盪理論」。由於熱懸浮液珠底層的氣液界面具有類似蓮葉複合表面微結構之特性，因此本文亦探討了濱海植物表面複合微結構之疏水特性，希望作為仿生研發之參考。
本文藉由高速攝影機觀測並歸納液珠在受熱狀態下之振盪模式與輪廓變化，並以無因次化分析法整理出各種力效應的影響。在液珠振盪且呈現動態平衡的情形，根據泰勒不穩定理論和邊界層理論可以知道底層氣膜提供初始振盪的波動能量，振盪時黏滯力和重力兩者分別為(R,θ)方向和Z方向的主導力，對於振盪頻率及模態的影響很大。本文也使用粒子影像測速儀(PIV)量測液珠振盪時的速度場、渦度和流線，深入探討加熱盤上液珠之振盪行為與液珠內部流場關係。
為探討蓮葉效應的複合表面結構，本文量測黃瑾、馬鞍藤、海桐、林投、蔓荊和月桃等濱海植物葉片表面的接觸角，藉由SEM影像觀察到葉片表面結構有「革質」、和「星狀結構」，這些葉面皆屬疏水性質，具有自清及保護作用，未來可考慮解析結構及材質機能。

關鍵字

液珠 ； 振盪 ； 萊氏溫度

並列摘要

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.

並列關鍵字

droplet ； oscillation ； Leidenfrost temperature

參考文獻

Adachi, K., and Takaki, R., “Vibration of a flattened drop I. Observation,” Journal of the Physical Society of Japan, vol. 53, pp.4184-4191, 1984.

Barthlott, W. and Neinhuis, C., “Purity of the sacred lotus, or escape from contamination inbiological surfaces,” Planta, vol. 202, pp. 1-8, 1997.

Berenson, P.J., “Film-boiling heat transfer from a horizontal surface,” J. Heat Transfer, vol.83, pp.351-358, 1961.

Bleiker, G. and Specht E., “Film evaporation of drops of different shape above a horizontal plate,” International Journal of Thermal Sciences, vol. 46, pp. 835-841, 2007.

Bojarevics, V., and Pericleous, K., “Droplet oscillations in high gradient static magnetic field,” Microgravity Science Technology, vol. 21, pp. 119-122, 2009.