本文選題：雙乳液 + 微流控��； 參考：《東南大學(xué)》2016年博士論文

【摘要】：單分散的高品質(zhì)雙乳液在聚變能源利用、化學(xué)化工、醫(yī)藥等行業(yè)中有著廣泛的應(yīng)用。傳統(tǒng)的雙乳液生產(chǎn)工藝通常伴隨強烈的振蕩過程,制備過程的重復(fù)性差,系統(tǒng)的可控性與原料消耗率等指標(biāo)不盡人意,所生成的雙液滴中內(nèi)、外液滴的尺寸均一性都難以得到保證。近年來,微流控技術(shù)的蓬勃發(fā)展為單分散的高品質(zhì)雙乳液制備提供了一條有效途徑。特別是,軸對稱三維微流控裝置作為被動式乳化系統(tǒng)的代表,具有高度的可控性和原料利用率,所制備的雙乳液單分散性好、均一度高、球形度佳,表現(xiàn)出了優(yōu)越的流變特性,可用于多種流體的乳化,相比傳統(tǒng)工藝有了很大進(jìn)步,該方向的研究現(xiàn)已成為工程熱物理微尺度多相流學(xué)科的一個前沿研究熱點。目前,雙乳液的生成過程及其流體動力學(xué)行為仍然缺乏深入、系統(tǒng)的研究,尤其是各相流體之間的相互作用方式、界面的運動與破裂的規(guī)律、流動狀態(tài)對乳化過程的影響機(jī)理等尚未得到完全揭示。為此,本文基于VOF相界面追蹤方法,建立了流動聚焦式微通道和協(xié)流式微通道中乳化過程流體動力學(xué)行為特性的理論分析模型。數(shù)值研究了兩種系統(tǒng)中雙液滴的形成過程；給出了典型乳化模式的流型演化；分析了流體物性、流動狀況對雙液滴形成過程的影響；對比了協(xié)流結(jié)構(gòu)與流動聚焦結(jié)構(gòu)的中液滴形成過程的異同；探討了微通道局部結(jié)構(gòu)的變化對乳化模式及其轉(zhuǎn)換的影響。同時,本文還設(shè)計并搭建了協(xié)流式與流動聚焦式兩套微流控乳化裝置實驗臺,制備了多種形態(tài)的雙乳液,采用高速動態(tài)攝像裝置觀測并記錄了兩種系統(tǒng)中雙液滴的生成過程,分析了各相流量對乳化過程的影響,對比了兩種微流控裝置所生成的雙液滴尺寸、生成頻率以及多分散度等特性。概括起來,本文的研究內(nèi)容及獲得的主要研究結(jié)論如下：開展了流動聚焦式微通道中雙乳液生成過程的理論建模和數(shù)值模擬研究,復(fù)現(xiàn)了滴式與噴式兩種典型乳化模式,對比了單、雙乳液生成過程的異同,建立了流量比、粘度比、界面張力比與所生成的雙液滴尺寸間的定量聯(lián)系,并闡明了流動狀況與流體物性對乳化過程的影響機(jī)理。數(shù)值研究表明：滴式模式下液滴脫離的驅(qū)動力是界面張力,而噴式模式下則是外流體粘性力,因此兩種模式具有不同的界面形狀與流體動力學(xué)行為。雙乳液的生成過程相比單乳液更復(fù)雜,內(nèi)界面的形變與破裂加速了外界面的形變過程。在滴式模式下,增大外流體的流量將引發(fā)乳化模式向噴式的轉(zhuǎn)換,所生成的雙液滴的尺寸與壁厚都隨之減小,但流型轉(zhuǎn)換時尺寸的變化有不連續(xù)的突增。中間流體流量在很大范圍內(nèi)只對雙液滴的壁厚起到?jīng)Q定性的作用,對液滴生成模式和內(nèi)液滴尺寸影響均不明顯。滴式模式下,改變中間流體的粘度直至超過其他流體粘度時,液滴生成模式由滴式突然轉(zhuǎn)變?yōu)閲娛?所生成的液滴尺寸減小。界面張力系數(shù)的改變對相界面的形狀有顯著的影響,但對所形成的液滴尺寸幾乎不起作用�；谳S對稱微通道中的雙乳液生成過程的數(shù)值研究,對比了協(xié)流系統(tǒng)與流動聚焦系統(tǒng)中典型乳化模式,分析了外流體毛細(xì)數(shù)、通道局部結(jié)構(gòu)對乳液乳化過程的影響機(jī)理。數(shù)值研究結(jié)果表明：協(xié)流式微通道中,外流體毛細(xì)數(shù)的增大也會引起乳化模式從滴式向噴式的轉(zhuǎn)換,但轉(zhuǎn)換的臨界毛細(xì)數(shù)要遠(yuǎn)大于流動聚焦式系統(tǒng)中的臨界毛細(xì)數(shù),并且雙液滴尺寸與壁厚對外流體毛細(xì)數(shù)的變化更敏感。在相同物性與流動參數(shù)條件下,流動聚焦式微通道中雙液滴的脫離位置總是比協(xié)流式微通道中更靠近下游,并且所生成的雙液滴尺寸與壁厚更小,單分散性稍遜,但這一差異隨著外流體毛細(xì)數(shù)的增大逐漸減弱。與協(xié)流式微通道相比,流動聚焦式微通道中聚焦孔的存在在滴式模式下起到了促進(jìn)相界面變形、加速雙液滴脫落的作用,在噴式模式下則起到了促進(jìn)噴射段形成的作用。聚焦孔半徑較小的情況下雙液滴更容易在噴式模式下生成,所生成的液滴尺寸較小、多分散度較高；隨著聚焦孔半徑增大直至流動聚焦結(jié)構(gòu)變成協(xié)流結(jié)構(gòu),水力聚焦作用逐漸減弱,雙液滴的脫離位置向上游移動、所生成的液滴尺寸增大、多分散度降低。此外,聚焦孔深度的變化不對雙乳液生成模式造成任何影響,并且對所生成的雙液滴尺寸、壁厚以及單分散性的作用也不明顯。設(shè)計搭建了基于協(xié)流結(jié)構(gòu)的雙乳液制備與可視化觀測實驗臺,開展了油包水包油雙乳液的制備實驗,獲得了單核雙乳液、多核雙乳液、單乳液和雙乳液混合乳液等多種形態(tài)的乳液,分析了多個典型工況中界面的形變過程,獲得了各相流量與雙液滴尺寸、液滴生成頻率、多分散度的定量關(guān)系。實驗研究結(jié)果表明：內(nèi)液滴的個數(shù)、雙液滴的尺寸、液滴生成模式與生成頻率等均可以通過外流體流量進(jìn)行精確控制,雙液滴壁厚則通過中間流體與內(nèi)流體流量進(jìn)行調(diào)整。低流速的滴式模式下所制備的單核雙乳液和單、雙乳液混合的二元乳液尺寸均一性好,多分散度能夠控制在3%以內(nèi)。而滴式模式下制備的多核雙乳液外液滴的多分散度能夠控制在8%以內(nèi),但每一個內(nèi)液滴在脫離時均受到前-個內(nèi)液滴的影響,因而內(nèi)液滴尺寸是多分散的。設(shè)計搭建了基于流動聚焦結(jié)構(gòu)的雙乳液制備與可視化觀測實驗臺,同樣開展了油包水包油雙乳液的制備實驗,獲得了多種形態(tài)的乳液以及流量與液滴尺寸、生成頻率、多分散度的定量關(guān)系,并對比分析了協(xié)流系統(tǒng)與流動聚焦系統(tǒng)中乳化過程。實驗研究結(jié)果表明：在與協(xié)流式系統(tǒng)相同的實驗條件下,聚焦孔的存在促進(jìn)了相界面的形變與破裂,因而低外流體流速下的流動聚焦系統(tǒng)中通常不會生成多核雙乳液。流體在通過聚焦孔后的減速使得雙液滴在外流體通道中的排列更緊密,合并的可能性較大。在同樣的流量與物性參數(shù)條件下,相比協(xié)流式微通道,采用流動聚焦式微通道所制備的雙乳液雖然單分散性稍遜,但是其中液滴生成頻率相對較高,在高效制備小尺寸雙乳液的場合具有更好的效果。本文工作較為系統(tǒng)地揭示了軸對稱微流控裝置中雙乳液生成的流動形態(tài)演化、乳化模式轉(zhuǎn)換機(jī)理以及通道結(jié)構(gòu)的影響,相關(guān)研究成果可為乳液制備微流控裝置的設(shè)計與優(yōu)化提供有力的理論與關(guān)鍵技術(shù)支撐,同時,也是對微小結(jié)構(gòu)內(nèi)液液多相流動、界面相互作用及其流體動力學(xué)行為基礎(chǔ)理論的重要補充和完善。
[Abstract]:The single dispersed high quality double emulsion is widely used in the field of fusion energy utilization, chemical industry, medicine and other industries. The traditional double emulsion production process is usually accompanied by strong oscillation process, poor reproducibility of the preparation process, unsatisfactory indexes of system controllability and raw material consumption, and the formation of the inner and outer drops in the double droplets. In recent years, the rapid development of microfluidic technology has provided an effective way for the preparation of monodisperse high quality double emulsion. In particular, the axisymmetric three-dimensional microfluidic device, represented by the passive emulsion system, has high controllability and raw material utilization, and the prepared double emulsion has good monodispersibility. It has a high degree of uniformity and good sphericity, showing a superior rheological property, which can be used in the emulsification of various fluids. Compared with the traditional technology, the research of this direction has become a frontier research hotspot in the subject of Engineering Thermo physics microscale multiphase flow. At present, the process of producing double emulsion and its hydrodynamics are still short of depth. The study of the system, especially the interaction mode of each phase fluid, the law of the movement and rupture of the interface, the influence mechanism of the flow state to the emulsification process, has not been fully revealed. Therefore, based on the VOF phase interface tracing method, the fluid dynamics of the flow focusing microchannel and the co flow microchannel are established. The theoretical analysis model of behavior characteristics is studied. The formation process of double droplets in the two systems is numerically studied. The flow pattern evolution of the typical emulsion mode is given. The effects of fluid physical properties and flow conditions on the formation of double droplets are analyzed, and the similarities and differences of the formation of the droplets in the flow focusing structure are compared with the flow focusing structure. The influence of the change of the local structure of the channel on the emulsification mode and its conversion. At the same time, this paper also designed and built a two set of micro fluidic emulsification device experiment platform, which is co flow and flow focusing. A variety of double emulsion forms are prepared. The formation process of double droplets in the two systems is observed and recorded by high speed dynamic camera. The effect of flow on the emulsification process is compared with the characteristics of the double droplet size, generation frequency and multi dispersion generated by two kinds of microfluidic devices. Two typical emulsification modes of drop type and spray type are presented, and the difference between single and double emulsion production processes is compared. The quantitative relation between flow ratio, viscosity ratio, interfacial tension ratio and the size of the produced double droplets is established. The mechanism of the flow situation and the effect of fluid property on the emulsification process is clarified. The driving force is the interfacial tension, while the spray mode is the viscous force of the external fluid, so the two modes have different interface shape and hydrodynamic behavior. The formation of double emulsion is more complex than the single emulsion. The deformation and fracture of the inner interface accelerates the deformation process of the external interface. In the drop mode, the flow rate of the external fluid is increased. The size and wall thickness of the two droplets will decrease with the conversion of the emulsification mode to the spray type, but the change of the size of the flow pattern is incontiguous. The flow rate of the middle fluid only plays a decisive role in the wall thickness of the two droplets in a large range, and the droplet generation mode and the droplet size are not obvious. In the mode, when the viscosity of the intermediate fluid is changed until the viscosity of the other fluid is exceeded, the droplet generation mode is suddenly transformed from the drop type to the spray type, and the droplet size decreases. The change of the interfacial tension coefficient has a significant influence on the shape of the phase interface, but it almost does not play a role in the formation of the droplet size inch. The numerical study of the production process of double emulsion is compared with the typical emulsification mode in the coflow system and the flow focusing system. The influence mechanism of the number of outer body hair and the local structure of the channel on the emulsion emulsification is analyzed. The numerical results show that in the coflux microchannel, the increase of the number of outer body hair will also cause the emulsification mode from the drop to spray. However, the critical capillary number of the conversion is far greater than the critical capillary number in the flow focusing system, and the size of the double droplet is more sensitive to the change of the capillary number of the external fluid. Under the same physical and flow parameters, the removal of the double droplets in the flow focused microchannel is always closer to the lower than the covariance microchannel. The size of the two droplets is smaller and the wall thickness is smaller and the monodisperse is slightly inferior, but this difference decreases with the increase of the number of outer body hair. Compared with the coflow microchannel, the existence of the focusing hole in the flow focused microchannel is the effect of accelerating the phase boundary surface deformation and accelerating the drop off of the double droplets in the drop mode. When the radius of the focusing hole is smaller, the two droplets are more easily generated in the spray mode, and the droplets are smaller and have a higher dispersion. With the increasing of the radius of the focusing hole until the flow focusing structure becomes a cocurrent structure, the hydraulic focusing function gradually decreases and the dislocations of the double droplets are displaced. In addition, the change of the depth of the focusing hole does not affect the pattern of the double emulsion generation, and the effect on the size of the droplets, the thickness of the wall and the monodisperse is not obvious. The preparation and visual observation of the double emulsion based on the coflow structure are designed and built. The experimental platform has carried out the preparation of oil package oil and oil double emulsion. A variety of emulsion forms, such as mononuclear double emulsion, multi core double emulsion, single emulsion and double emulsion mixed emulsion, have been obtained. The deformation process of interface in several typical working conditions is analyzed. The quantitative relation of phase flow and double droplet size, droplet generation frequency and polydispersity is obtained. The experimental results show that the number of internal droplets, the size of double droplets, the mode of droplet generation and the generation frequency can be accurately controlled by the flow rate of the external fluid. The thickness of the double droplets is adjusted by the intermediate fluid and the flow of the inner fluid. The mixture of mononuclear double emulsion and single, double emulsion prepared in the drop mode of low flow rate is two. The size uniformity of the emulsion is good, and the polydispersity can be controlled within 3%. The multi dispersion of the multi core double emulsion droplets prepared under the drop mode can be controlled within 8%, but the droplets in each of the internal droplets are affected by the droplets in the front and the inner droplets, so the internal droplet size is dispersed. The flow focusing structure is designed and built. The double emulsion preparation and visual observation test bench have also carried out the preparation experiments of oil package oil double emulsion. The quantitative relationship of various forms of emulsion, the flow rate and droplet size, the generation frequency and the dispersion degree are obtained, and the emulsification process in the coflow system and the flow focusing system is compared and analyzed. The experimental results show that: Under the same experimental conditions, the existence of the focusing hole promotes the deformation and fracture of the phase interface under the same experimental conditions. Therefore, the multi core double emulsion is not usually generated in the flow focusing system at the low flow velocity. The reduction of the fluid after the focusing hole makes the arrangement of the double droplets more closely arranged in the passage of the external flow body, and the possibility of merging is larger. Under the same flow and physical parameters, compared with the coflow microchannel, the double emulsion prepared by the flow focusing microchannel is slightly less monodisperse, but the droplet generation frequency is relatively high, and it has better effect in the high efficiency preparation of small size double emulsion. This paper has systematically revealed the axisymmetric microsphere. The flow morphology evolution, the mechanism of the emulsion mode conversion and the influence of the channel structure in the flow control device can provide a powerful theoretical and key technical support for the design and optimization of the emulsion preparation of microfluidic devices. At the same time, it is also the liquid and liquid multiphase flow, interface interaction and fluid dynamics in the micro structure. The important supplement and perfection of the basic theory of mechanical behavior.

【學(xué)位授予單位】：東南大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O35
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本文編號：1869954