本文關鍵詞：顆粒流體系統(tǒng)中聚團的形成過程與結構特征研究　出處：《中國科學院大學(中國科學院過程工程研究所)》2017年碩士論文　論文類型：學位論文

  更多相關文章： 聚團 結構特征 生長與破碎 機理 DPM

【摘要】：顆粒流體系統(tǒng)是一個具有時空多尺度結構的復雜系統(tǒng),其中顆粒聚團是一種常見的非均勻結構。聚團的特性對于流化床等各類反應器的正常運行具有重要影響。目前對于聚團的研究大多針對尺寸和濃度分布等宏觀統(tǒng)計性質,而對其形成過程與結構特征的研究非常有限。本論文利用離散顆粒模型(DPM)模擬了含有數(shù)百萬個粘附性顆粒的液固體系,提出了一種適用于DPM模擬結果分析的聚團識別和量化方法。這種方法可以充分發(fā)揮DPM模擬能夠精確量化任意時刻每一個顆粒的速度和位置的優(yōu)勢,從聚團的尺寸、形狀、穩(wěn)定性角度表征其結構特征;通過跟蹤顆粒進入或離開聚團的狀態(tài)量化聚團生長和破碎的過程,并從顆粒受力的角度探究其機理。在論文第一章的文獻綜述的基礎上,第二章分析并確定了本論文中DPM的具體設置、模擬對應的實驗裝置及主要參數(shù),進而在實驗和模擬中均觀察到了聚團現(xiàn)象。在實驗可觀測的反應器中心區(qū)域,顆粒平均速度與體積分數(shù)與模擬吻合良好。第三章提出了聚團的識別與量化方法,并以此探究了反應器厚度、進料狀態(tài)、粘附力強度對模擬結果的影響,從尺寸、形狀、穩(wěn)定性三個角度考察了聚團的結構特征。研究表明,聚團內(nèi)顆粒數(shù)可以有效表征聚團的尺寸,而聚團內(nèi)顆粒的平均配位數(shù)及配位數(shù)分布可以表征聚團的形狀,配位顆粒表面間的平均距離及顆粒在聚團內(nèi)的平均停留時間可以表征其穩(wěn)定性。第四章提出了量化聚團生長與破碎的方法,并以此分析模擬結果表明:這些過程存在漸進或突變兩種方式,并以前者為主;而粘附力、曳力、碰撞力的非均勻分布能顯著影響聚團的凈變化率、尺寸和形狀。第五章總結了全文工作并展望了今后的研究方向。
[Abstract]:Granular fluid system is a complex system with space-time and multi-scale structure. Particle agglomeration is a common nonuniform structure, and the characteristics of agglomeration have an important effect on the normal operation of various reactors such as fluidized bed. At present, most of the studies on clusters focus on macro systems such as size and concentration distribution. Calculated nature. However, the formation process and structural characteristics are very limited. In this paper, a discrete particle model (DPMM) is used to simulate a liquid-solid system containing millions of adherent particles. A cluster recognition and quantization method suitable for the analysis of DPM simulation results is proposed. This method can give full play to the advantages of DPM simulation which can accurately quantify the velocity and position of each particle at any time. The structure of the cluster is characterized by its size, shape and stability. By tracking the state of particles entering or leaving the cluster, quantifying the process of cluster growth and fragmentation, and exploring its mechanism from the point of view of the force of particles, based on the literature review in the first chapter of the paper. The second chapter analyzes and determines the specific setting of DPM in this paper, simulates the corresponding experimental device and main parameters. The particle average velocity and volume fraction agree well with the simulation in the center of the reactor. In the third chapter, the recognition and quantification methods of the cluster are proposed. The effects of reactor thickness, feed state and adhesion strength on the simulation results were investigated. The structure characteristics of the clusters were investigated from three aspects: size, shape and stability. The number of particles in the cluster can effectively characterize the size of the cluster, while the average coordination number and the distribution of the coordination number of the particles in the cluster can characterize the shape of the cluster. The average distance between the surface of the coordination particles and the average residence time of the particles in the cluster can be used to characterize the stability of the coordination particles. In Chapter 4th, a method of quantifying the growth and fragmentation of the clusters is proposed. The simulation results show that there are two modes of evolution or mutation in these processes, and the former is the main one. However, the non-uniform distribution of adhesion force, drag force and collision force can significantly affect the net change rate, size and shape of the cluster. Chapter 5th summarizes the full text and looks forward to the future research direction.
【學位授予單位】：中國科學院大學(中國科學院過程工程研究所)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ021.1

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