本文選題：微流體　切入點：液滴　出處：《天津大學》2015年博士論文　論文類型：學位論文

【摘要】：多相流廣泛存在于多種工業(yè)過程中,其通常伴隨著界面現(xiàn)象與流體力學相互耦合。近年來,將多相流與微流控技術結合已逐漸成為一種前沿技術,具有廣泛的應用前景。微通道內兩相流是該領域的重要研究內容。本文利用高速攝像儀研究了微通道內液滴(氣泡)的生成,破裂及聚并過程。具體研究內容包括:第一部分主要研究了磁場調控下聚焦型微通道內磁流體液滴的生成過程。重點關注了磁流體液滴在通道內的擴張及破裂動力學行為�？疾炝肆黧w流速、磁場強度及磁場方向對擴張及破裂的影響。研究并比較了無磁場(NM)、徑向磁場(RM)和軸向磁場(AM)下的液滴形成過程。結果發(fā)現(xiàn),磁流體液滴的體積可通過所施加的磁場來進行有效調控。徑向磁場和軸向磁場分別通過影響液滴的擴張階段和破裂階段來影響液滴的尺寸。磁流體破裂過程的頸部最小寬度與剩余時間呈冪指數(shù)關系。第二部分研究了磁場對磁流體液滴破裂的影響以及反饋作用對氣泡破裂的影響。首先研究了勻強磁場及非勻強磁場下T型微通道分叉處磁流體液滴破裂動力學。研究發(fā)現(xiàn)在勻強磁場下,可以通過改變磁場強度來調控液滴破裂方式以及液滴破裂頻率。在非勻強磁場下,通過改變磁場強度可以調控液滴破裂的不對稱度從而使液滴的臨界破裂點發(fā)生遷移。此外,還研究了氣泡在T型微通道分叉處的不對稱破裂行為。氣泡不對稱破裂行為主要歸因于破裂所形成的子氣泡在下游通道內動力學行為的反饋作用�？疾炝讼掠螀R聚口處子氣泡碰撞以及交替通過出口時的反饋作用對破裂的影響。結果表明,當流速較小且子氣泡不發(fā)生碰撞時,反饋作用可以忽略。當子氣泡在下游匯聚口出發(fā)生碰撞時反饋作用較為明顯。此外,在高流速下通道瑕疵所帶來的影響亦不可忽略。第三部分研究了衛(wèi)星液滴(氣泡)的生成過程。本章前半部分主要關注聚焦型和T型微通道內液-液界面收縮破裂過程中形成的衛(wèi)星液滴。實驗結果表明,在頸部夾斷后期,由于粘性力和表面張力的平衡和強弱轉換,液滴的頸部不可避免從快速夾斷區(qū)進入慢速斷裂區(qū)。研究發(fā)現(xiàn)在慢速夾斷區(qū)頸部的體積幾乎保持不變,最細頸部位置也由中間過渡到頸部細絲的兩側,最后在頸部細絲兩側發(fā)生斷裂并形成衛(wèi)星液滴。在實驗范圍內衛(wèi)星液滴尺寸隨連續(xù)相毛細數(shù)的增長而增長。其后研究了直通道內剪切力引起的液滴(氣泡)尾部斷裂過程。重點關注了液滴(氣泡)尺寸及流速對尾部尖端流的影響。結果表明,隨著液滴(氣泡)的尺寸或毛細數(shù)的增長,其形變愈發(fā)顯著。存在一個臨界毛細數(shù),當大于這一數(shù)值,液滴(氣泡)尾部將發(fā)生破裂并產生尖端流。由尖端流所生成的衛(wèi)星液滴的尺寸通常比主液滴小三個數(shù)量級。論文的最后部分研究了液滴(氣泡)的聚并過程。首先研究了氣泡在T型微通道匯聚處的聚并行為。在不同的毛細數(shù)及氣泡尺寸下,實驗觀測到了三種主要行為:碰撞式聚并、擠壓式聚并及不聚并。實驗結果表明,中等粘度下不論是碰撞式聚并還是擠壓式聚并,其聚并效率都隨兩相表觀流速的增加而降低。兩相表觀流速的增加將致使碰撞式聚并過渡到擠壓式聚并,同時聚并效率小幅增加。此外,連續(xù)相粘度的增加或者氣泡尺寸的減小都會降低聚并效率。此外,研究了磁流體液滴在不同磁場強度下的聚并過程。兩個同軸的磁流體液滴在磁場作用下相互吸引并變形為圓錐體。實驗重點關注了兩個圓椎體液滴相互靠近相繼發(fā)生聚并及斷裂的過程。通過高速攝像儀發(fā)現(xiàn)當液滴之間的距離在10微米左右時液滴相互靠近的界面會形成柱狀突起并在兩個液滴間形成搭橋。實驗結果表明,磁流體液滴聚并的推動力為慣性力而不是表面張力,磁流體液滴聚并后會形成液柱。存在一個臨界磁場強度,高于臨界磁場強度磁流體液柱將變得不穩(wěn)定甚至發(fā)生破裂,液柱破裂的形式與磁場強度有關。
[Abstract]:Multi phase flow widely exists in many industrial processes, it is often accompanied by interfacial phenomena and hydrodynamic coupling. In recent years, the multiphase flow and combination of microfluidic technology has gradually become a new technology, has a wide application prospect. In the micro channel flow is an important research in this field. This paper use high speed camera is studied in micro channel drops (bubble) generation, rupture and coalescence. The research contents include: the first part is to study the magnetic field generating process of magnetic fluid droplet focusing control in micro channel. Focusing on the expansion and rupture of magnetic fluid droplets inside the channel dynamics effects of fluid velocity, magnetic field intensity and magnetic field influence on expansion and rupture. Study and compare the magnetic field (NM), radial magnetic field (RM) and axial magnetic field (AM) of the droplet formation process. The results show that the magnetic fluid The volume of the droplet by the applied magnetic field can effectively control the radial magnetic field and axial magnetic field respectively. Through the expansion phase of droplet impact and crack stage to affect the droplet size. The magnetic fluid rupture exponent and the minimum width of the neck of the remaining time. The second part studied the influence of magnetic field on magnetic rupture the fluid droplet and the influence of feedback effects on the bubble rupture. Firstly, study the T type magnetic field and nonuniform magnetic fields under the micro channel bifurcation of magnetic fluid droplet rupture dynamics. The study found in the magnetic field, can change the intensity of magnetic field to control the droplet breakup and droplet breakup in frequency. Non uniform magnetic fields, by changing the magnetic field strength can control the droplet rupture asymmetry so that the nanotest droplet transfer. In addition, also study the bubbles in the T type micro channel bifurcation Asymmetric rupture behavior. Feedback dynamics in the downstream channel rupture behavior of bubbles is mainly due to asymmetry formed by rupture of bubbles was studied. The convergence of downstream export debut bubble collision and alternating through feedback effect on the export effect of rupture. The results show that when the flow rate is small and the bubbles do not collide, feedback effect when the bubble can be ignored. The more obvious role in the convergence of downstream feedback mouth collision. In addition, effects in high speed channel defects can not be ignored. The third part studies the satellite droplets (bubble) formation process. The first part of this chapter, the main focus and T in micro channel the liquid-liquid interface contraction of the satellite droplets formed in the process of rupture. The experimental results show that in the neck pinch off late, due to the viscous force and surface tension balance and strength of the conversion, drop the neck The Ministry of the inevitable from fast pinch off region into slow rupture zone. The study found that the size of the neck pinch off region in the slow almost unchanged, the most narrow neck position from both sides of the intermediate filaments to the neck, finally in the neck fracture and the formation of filaments on both sides of the satellite droplets. In the experimental range of satellite droplet size with continuous phase the breakdown of hair growth and growth. Then study the droplet in straight channel shear stress (bubble) tail fracture process. Focus on the droplet size and velocity (bubble) effect on the tail tip flow. The results show that, with the droplet size (bubble) or capillary growth in the number, the more deformation significant. There is a critical capillary number, when greater than this value, the droplet (bubble) will rupture and tail tip flow. Satellite droplet sizes generated by tip flow is usually higher than the main drop orders. The mistress The last part of the droplet (bubble) coalescence process. Firstly, the bubble in the T type micro channel sink at the coalescence behavior. The capillary number and bubble size under different experimental observation to three kinds of behavior: collision coalescence, extrusion and coalescence coalescence experiments. The results show that medium viscosity both collision coalescence or extrusion coalescence, the coalescence efficiency of the two-phase flow and reduce the increase of apparent increase. Two apparent velocity will cause collision coalescence and transition to squeeze together and at the same time, the efficiency of coalescence increased slightly. In addition, even. Continuous phase viscosity increase or bubble size will reduce the coalescence efficiency. In addition, the Research on magnetic fluid droplet under different magnetic field intensity of the coalescence process. The magnetic fluid droplet two coaxial in magnetic field and attract each other is a cone. The experiment focuses on the deformation of two cone The droplet coalescence process occurred near each other and fracture. By the high speed camera found that when the distance between the droplets in the 10 micron droplet interface will be close to each other to form columnar protrusions and formation of bypass in two drops. The experimental results show that the magnetic fluid droplet coalescence and impetus for inertia instead of surface tension force, magnetic fluid droplet coalescence will form the liquid column. There exists a critical magnetic field strength is higher than the critical magnetic field strength magnetic fluid column will become unstable or even rupture, rupture of the liquid column form associated with the magnetic field strength.

【學位授予單位】：天津大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TQ021.1
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本文編號：1642341