微米狹縫中之脈衝雷射誘發二維氣泡相互作用; Pulsed Laser Induced 2D Bubble Interaction in Micro-gaps

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/7374

Title:	微米狹縫中之脈衝雷射誘發二維氣泡相互作用;Pulsed Laser Induced 2D Bubble Interaction in Micro-gaps
Authors:	陳彥宏;Yen-Hung Chen
Contributors:	物理研究所
Keywords:	雷射;氣泡作用;cavitation;bubble interaction;laser
Date:	2005-06-03
Issue Date:	2009-09-22 10:56:43 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	我們利用高速影像系統觀察微米狹縫中的雷射誘發之二維氣泡相互作用，在充滿墨水溶液的狹縫中以脈衝雷射瞬間加熱產生氣泡(氣泡甲)，使其引發之衝擊波及流場影響鄰近的穩定氣泡(氣泡乙)，進而研究氣泡的動力學行為及碎裂的過程。在氣泡的相互作用實驗中，氣泡甲會先快速膨脹然後收縮，而氣泡乙會相對地被壓縮，然後重新膨脹，最後收縮至平衡狀態。由於周圍液體慣性較大的原因，氣泡界面呈現不穩定的狀態，在外在流場的影響之下，系統的不對稱性的造成特殊的氣泡形變。例如在氣泡乙壓縮的過程，微米噴流會順著衝擊波傳播的方向形成在氣泡的表面而穿出氣泡另一側，之後在氣泡乙重新膨脹的過程，噴流突出的表面形成蝴蝶狀的氣泡，當氣泡甲開始收縮時，氣泡間的壓力減小，而氣泡乙膨脹至最大體積，此時表面張力的效應使變形的氣泡表面平滑，最後被噴流分裂的氣泡冷卻下來且達到穩定的平衡狀態。當我們改變氣泡作用的強度或幾合條件，發現複雜的氣泡碎裂結果，這些規則與不規則的碎裂情形都是由兩側的橫向噴流切割氣泡的過程所決定的，造成橫向噴流的原因是因為兩側較強的流場會從蝴蝶狀氣泡的頸部流入，而這些噴流會直接連接已形成的中心噴流或改變方向連接至氣泡外側，因此造成各式各樣的氣泡碎裂圖樣。當氣泡間的距離縮短而使得作用加強時，我們發現氣泡反作用的行為，受到氣泡乙重新膨脹的影響，氣泡甲收縮時會産生一個反方向的噴流，經由實驗參數的改變，有趣的氣泡混和與排斥現象也被發現與探討。在以周圍液體作媒介的氣泡相互作用中，藉由體積的分析說明可壓縮氣泡間的能量交換情形。 The anisotropic bubble collapse under the symmetry-breaking process was well studied in the past few decades, such as cavitation erosion, underwater explosion and acoustic wave-bubble interaction. Recently, the developed bio-technology of cell lysis and the micro-surgery in the laser-microscope system are associated with the laser induced cavitation bubbles and shock wave. Nevertheless, the mutual bubble interaction between the micro-bubbles with the cavitation induced shock wave and flow field are not studied. Moreover there is no clear physical picture of the detailed bubble fragmentation evolution associated with the complicated hydrodynamic interaction. We experimentally investigate the pulsed laser induced two dimensional bubble interaction using high speed micro-photography. We address a new issue of the fragmentation dynamics about a strongly perturbed bubble with good reproducibility in a micro-gap. The topological patterns of the stationary bubble (B1) impacted by the nearby laser induced cavitation bubble (B2) are presented. Typical bubble (B1) deformations such as jetting, butterfly-shape pattern in fragmentation under various experimental conditions of geometry and laser power are studied. Due to the unstable liquid-gas interface of vapor bubble and the thermal effect of compressible bubble, the interaction process of B1 undergoes three stages, compression, re-expansion and collapse against the expanding and then collapsing B2. The forward liquid jet on B1 surface due to surface instability in the stage of compression protrudes the opposite bubble surface. The jet protrusion entrains vapor forward and leads to butterfly-like bubbles. In the stage of anisotropic re-expansion, the inward transverse jetting at the bubble neck fragments B1. Hence, the topology of bubble fragmentation is determined and then stabilized in the final stage of collapse. Furthermore, at short inter-bubble distance, the strong backward interactions for B2 are found, such as backward jetting and bubble mixing associated with the interplay between the collapsing B2 and the re-expanding B1. By the volumetric analysis, we explain the energy transfer between the two bubbles and the role played by B1 in the anisotropic liquid background compared with the free expansion of single bubble. In this thesis, the simplified 2D bubble interaction in the system without buoyancy force is studied first time, and the details are discussed.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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