本文選題：接觸式粘性力 + 流化床　； 參考：《東南大學》2016年博士論文

【摘要】：流化床反應器因其高效的傳熱傳質(zhì)與連續(xù)處理大量顆粒的能力,在不同工業(yè)領域中得到了廣泛的應用。伴隨著流化床處理對象與手段的多樣化,顆粒性質(zhì)經(jīng)常發(fā)生改變,其中較為常見的是顆粒間出現(xiàn)以液橋力和固橋力為代表的接觸式粘性力。粘性力的存在降低了顆粒的流動性,導致其流態(tài)化行為有別于傳統(tǒng)的無粘顆粒,從而影響了流化床內(nèi)的反應效率以及反應器的穩(wěn)定運行。因此,揭示顆粒間接觸式粘性力對流化特性的影響規(guī)律和機理,對此類流化床反應器的設計和運行具有重要的指導意義。但是,相較于無粘顆粒流態(tài)化豐富且逐漸完善的理論體系,對于接觸式粘性力的研究仍然較為零散,缺乏系統(tǒng)深入的認知。本文基于實驗手段,在顆粒層面和顆粒體系層面上開展了接觸式粘性力對流態(tài)化的影響機理研究,旨在加深對于此類顆粒體系運動特性的認知。全文主要的研究內(nèi)容和成果如下：(1)顆粒層面上,設計并搭建顆粒-平板含液膜碰撞系統(tǒng),其中顆粒與平板間的粘性力通過調(diào)節(jié)液膜的粘度與厚度實現(xiàn)：提出采用橫向擾動風賦予顆粒水平運動速度,實現(xiàn)顆粒與覆蓋液膜的有機玻璃平板進行斜向碰撞的目標,克服了傳統(tǒng)的傾斜平板法只能應用高粘度、低厚度液膜的缺點；借助布置在平板底部的透射光源,清晰地捕捉液膜和液橋幾何形態(tài)的變化,同時基于圖像處理技術(shù)準確獲取了顆粒的運動軌跡和速度等動力學參數(shù),為顆粒碰撞模型的構(gòu)建奠定了堅實的基礎。與準靜態(tài)過程不同,碰撞中液橋的形成和發(fā)展呈現(xiàn)滯后性,而且液體慣性在碰撞中所占的比重越大,滯后效果越明顯。液橋力對于反彈顆粒在法向方向上的動能損耗影響較大,對切向方向的影響較小。通過比較顆粒在碰撞全過程中發(fā)生的能量損耗可以發(fā)現(xiàn),液橋力造成的動能耗損遠小于其他阻力。在法向方向上,顆粒的能量耗損隨液膜粘度和厚度的增加而增加,隨碰撞速度的增加而減小；在切向方向上,能量耗損過程主要由液膜厚度主導：厚度較大時,液體主要起阻力作用,而當厚度較小時,液體主要起潤滑作用。鑒于液膜厚度在碰撞中的重要作用,本文將其引入,對傳統(tǒng)的表征碰撞過程的Stokes數(shù)進行修正,并結(jié)合液體彈性動力學理論和經(jīng)典的流體力學理論首次提出了用于判斷顆粒是否反彈的臨界Stokes數(shù)模型以及用于衡量顆粒動能耗損的碰撞恢復系數(shù)模型,獲得了較為準確的預測結(jié)果。(2)顆粒體系層面上,利用“多聚物涂層”法引入接觸式粘性力,通過調(diào)節(jié)涂層表面溫度,改變多聚物粘性,實現(xiàn)控制顆粒間粘性力的目標,克服了傳統(tǒng)引入方法粘性力分布不均且復現(xiàn)性差的缺點,同時基于圖像處理技術(shù)提取不同粘性力作用下二維可視化鼓泡流化床中氣泡的靜態(tài)和動態(tài)特征參數(shù)。與無粘顆粒體系相比,粘性力的存在抑制了氣泡在床中段的合并過程,促進了氣泡在床層頂部區(qū)域的分裂過程。粘性力對床內(nèi)整體的流化特性呈階段式影響：在粘性力增加的初始階段,乳化相的持氣能力提高,氣泡通過頻繁的縱向合并從近似圓形過渡到豎橢圓形,減弱了床兩側(cè)顆粒的運動強度,導致當粘性力繼續(xù)增大時,顆粒率先向床兩側(cè)粘結(jié),床層膨脹比迅速降低,并最終以溝流的形式造成流化失效,而且當床內(nèi)布置有埋管時,流化失效的進程加快。埋管的存在削弱了粘性力對氣泡參數(shù)的影響,埋管周圍的局部氣泡分布特性同時受到顆粒間粘性力及埋管位置的制約。(3)利用荷蘭代爾夫特理工大學搭建的多源復合X射線斷層掃描系統(tǒng),首次重構(gòu)出粘性顆粒在三維鼓泡流化床中的氣泡形態(tài),同時結(jié)合壓力波動分析技術(shù)獲取了豐富的流態(tài)化信息。實驗結(jié)果表明,粘性力的存在促進了氣泡合并,導致氣泡尺寸上升,頻率下降,最終在高粘性力作用下引發(fā)節(jié)涌,導致流化失效。與無粘顆粒流化不同的是,節(jié)涌產(chǎn)生的料栓在粘性力作用下能夠完成“自我生長”,使得流化失效區(qū)域逐漸向布風板方向擴張。伴隨著料栓的破碎,節(jié)涌與正常流化在床內(nèi)交替產(chǎn)生,而且相較于自由氣泡,節(jié)涌產(chǎn)生的氣栓對粘性力更加敏感。由于氣泡尺寸是觸發(fā)節(jié)涌的關鍵參數(shù),因此高粘性力、高流化風速等促進氣泡生長的因素都將直接導致節(jié)涌持續(xù)時間的延長。與之相伴的氣泡破裂、床層波動等相關性現(xiàn)象所激發(fā)的壓力波主導了床內(nèi)的壓力波動,而且高粘性力下壓力波沿高度方向的耗散規(guī)律與流化風速緊密相關。通過比較二維床與三維床的實驗結(jié)果可以發(fā)現(xiàn),粘性力的存在降低了顆粒的流動性,使流化質(zhì)量發(fā)生惡化。兩種床型下,發(fā)生流化失效的粘性力區(qū)間基本一致。但是,流化床不同的幾何特征直接導致了流化參數(shù)變化規(guī)律以及流化失效方式的差異,說明反應器幾何尺寸對粘性顆粒體系流態(tài)化特性具有重要影響。
[Abstract]:Fluidized bed reactor has been widely used in different industrial fields because of its high efficiency of heat and mass transfer and continuous treatment of large quantities of particles. With the diversification of the object and means of fluidized bed treatment, the properties of particles often change, and the more common is the contact type between the particles, which is represented by the bridge force and the solid bridge force. Viscous force. The existence of viscous force reduces the fluidity of the particles, resulting in its fluidization behavior different from the traditional cohesive particles, which affects the reaction efficiency in the fluidized bed and the stable operation of the reactor. Therefore, it reveals the regularity and mechanism of the influence of the indirect viscous force on the fluidization characteristics of the particles, and the setting of this kind of fluidized bed reactor. However, compared with the rich and gradually perfected theoretical system of cohesive particles, the study of contact viscous force is still scattered and lack of systematic understanding. Based on the experimental means, the contact viscous force is carried out on the particle and particle level. The main research contents and achievements of the full text are as follows: (1) the particle and plate liquid film collision system is designed and built on the particle level, in which the viscosity and thickness between the particles and the plate are realized by adjusting the viscosity and thickness of the liquid film. The wind gives the velocity of the particles horizontal movement and realizes the oblique collision between the particles and the organic glass plate covering the liquid film. It overcomes the shortcomings of the traditional inclined flat plate method, which can only apply high viscosity and low thickness liquid film. With the help of the transmission light source arranged at the bottom of the flat plate, the changes of the liquid film and the geometric shape of the liquid bridge are clearly captured and the results are based on the change of the liquid film and the liquid bridge. The image processing technology accurately obtains the kinetic parameters such as the motion trajectory and velocity of the particles, which lays a solid foundation for the construction of the particle collision model. Unlike the quasi static process, the formation and development of the liquid bridge in the collision is lagging, and the larger the proportion of the liquid inertia in the collision, the more obvious the lag effect is. The effect of the kinetic energy loss on the normal direction is larger and the influence on the tangential direction is smaller. The energy loss caused by the bridge force is far less than that of the other resistance. The energy loss of the particles increases with the increase of the viscosity and thickness of the liquid film in the direction of the normal direction. In the tangential direction, the energy loss process is mainly dominated by the thickness of the liquid film in the direction of the tangential direction: when the thickness is large, the liquid mainly plays the drag effect, and when the thickness is small, the liquid is mainly lubricated. In view of the important role of the thickness of the liquid film in the collision, the paper introduces it to the traditional Sto of the collision process. The kes number is modified and the critical Stokes number model used to judge whether the particles rebound or not, and the model of the collision recovery coefficient used to measure the kinetic energy loss of particles is first proposed in combination with the liquid elastodynamics theory and the classical fluid mechanics theory. (2) the use of "polymer" on the particle system level. The coating method introduces contact viscous force. By adjusting the surface temperature of the coating and changing the viscosity of the polymer, the viscosity of the particles is controlled, and the shortcomings of the traditional viscous force distribution are overcome, and the two dimensional visualization of the bubbling fluidized bed under the action of different viscous forces is extracted based on the image processing technology. The static and dynamic characteristic parameters of the bubble. Compared with the inviscid particle system, the existence of viscous force inhibits the merging process of the bubble in the bed, and promotes the splitting process of the bubble in the top of the bed. The viscous force has a stage effect on the fluidization characteristics of the whole bed. The gas holding capacity of the emulsified phase is improved at the initial stage of adding viscous force. By the frequent longitudinal merging of the bubbles from the approximate circle to the vertical ellipse, the motion intensity of the particles on both sides of the bed is weakened. When the viscous force continues to increase, the particles are first bonded to the two sides of the bed and the bed expansion ratio decreases rapidly. Finally, the fluidization failure is caused by the form of the furrow flow, and the fluidization failure when the bed is buried in the bed. The process quickens. The existence of buried tube weakens the effect of viscous force on the bubble parameters. The distribution characteristics of local bubbles around the buried pipe are restricted by the viscous force between particles and the position of the buried tube. (3) using the multi source composite X ray tomography system built by the Technische Universiteit Delft in Holland, the viscous particles are reconstructed for the first time in the three-dimensional bubbling flow. The shape of the bubbles in the bed and the pressure fluctuation analysis techniques have been used to obtain abundant fluidization information. The experimental results show that the existence of viscous force promotes bubble consolidation, resulting in the increase of bubble size and the decrease of the frequency of the bubbles. The plug is able to complete "self growth" under the action of viscous force, making the flow failure region gradually expanding to the direction of the cloth wind plate. With the breakage of the bolt, the surge and normal fluidization are alternately produced in the bed, and the gas plugs produced by the gushing are more sensitive to the viscous force than the free bubbles. The factors such as high viscosity, high fluidization wind speed and so on will directly lead to the prolongation of the duration of the bubble growth. The pressure waves induced by the correlation phenomena such as bubble rupture, bed fluctuation and so on dominate the pressure fluctuation in the bed, and the dissipation law and fluidization along the high direction of the high viscosity pressure wave along the height direction The wind velocity is closely related. By comparing the experimental results of the two dimensional bed and the three-dimensional bed, it is found that the existence of viscous force reduces the fluidity of the particles and makes the fluidization quality worse. Under the two types of bed, the viscous force interval of the fluidization failure is basically consistent. However, the different characteristics of the fluidized bed directly lead to the change of the flow parameters. The difference of fluidization failure modes indicates that reactor geometry has important influence on fluidization characteristics of viscous particle system.
【學位授予單位】：東南大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TQ021

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本文編號：1901581