顆粒動力行為：流體化、迴流與偏析; Granular Dynamic Behaviors: Fluidization, Convection, and Segregation

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题名:	顆粒動力行為：流體化、迴流與偏析;Granular Dynamic Behaviors: Fluidization, Convection, and Segregation
作者:	戴其璜;Chi-Hwang Tai
贡献者:	機械工程研究所
关键词:	顆粒動力行為;顆粒體;流體化;迴流運動;偏析現象;微量液體;粒子溫度;convection;segregation;fluidization;granular dynamics;liquid content;granular temperature
日期:	2010-01-11
上传时间:	2010-06-10 16:55:22 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	摘要本論文以實驗的方式探討顆粒體物質受到垂直方向的振動驅動力時，振動床內顆粒物質的動力行為，探究主題包含振動顆粒床的流體化、迴流運動以及振動床內顆粒的偏析現象。首先建構三維圓柱型容器以作為振動顆粒床，用以探討振動顆粒床的流體化現象，並深究振動床流體化與床內顆粒添加量和外加振動驅動力間相應關係，並獲得相關參數的整體相圖，其相圖中清楚描述各種相態間的臨界範圍，包含氣相，液相，固相，和靜止相等各種相態。之後建置二維矩型容器的振動顆粒床，配合利用影像處理技術和顆粒追蹤的方法，以相關物理參數定量分析顆粒振動床的流體化現象，並且深入探究振動床內顆粒添加量和顆粒物理性質對於振動床流體化的影響。並發現振動床流體化的重要無因次參數。其三以二維矩型容器探討振動顆粒床因置入顆粒的密度不同而造成的偏析現象，亦會探討此偏析現象與顆粒添加量和相互添加比例的關係。由研究中發現振動顆粒床內顆粒偏析現象，主要的影響機制與系統的運動型態有極為重要的相互關係，其中影響振動顆粒床的偏析機制，整體床內顆粒的迴流運動是一個影響振動顆粒床偏析相當重要的一種流場運動型態。最後，探討添加微量液體對於振動顆粒床內迴流現象的影響，其中研究變因包含微量液體的添加量、黏度和表面張力。藉由添加微量液體的實驗獲得振動顆粒床迴流現象的強度與修正無因次參數(BogM)的冪次關係。 Abstract The experimental methods were employed to investigate the granular dynamics under the vertical vibrated driving force. The main research topics include the fluidization, the convection, and the density segregation in a vibrated granular bed. As an ensemble of macroscopic particles is mechanically excited by vertical vibrations, the energy input is dissipated into the system by multiple inelastic collisions. As a result, when a mono-dispersed set of glass beads exceeds a critical number of particles, a phase transition can be condensed crystalline-like state. Systematic studies of the dependence of this critical number on the internal parameters as well as the external conditions (amplitude and frequency of the shaker) are presented. The measurements of the fluidization process in the vertically vibrated two-dimensional granular packing were reported. An initially close packed granular bed is exposed to sinusoidal container oscillations with gradually increasing amplitude. At first the particles close to the free surface become mobile. When a critical value of the forcing strength is reached the remaining crystal suddenly breaks up and the bed fluidizes completely. This transition leads to discontinuous changes in the density distribution and in the root mean square displacement of the individual particles. The dominant mechanism affecting the flow behavior of granular materials is the random motion of particles resulted from the interactive collisions between particles. The velocity fluctuations induce the segregation in granular flows. The different densities of granular material were used to investigate the segregation mechanisms in a vibrated granular bed. The convection behaviors of wet granular materials subjected to external vertical vibration were examined. Different types of liquids with different contents, viscosities, and surface tensions were added to granular materials (in this case glass spheres) to form cohesive materials. The effects of the content, viscosity, and surface tension of the additions on the convection dynamics of the wet granular materials in the vibrated bed are discussed in the study. The convection flow rate decreased in a power relation with the modified granular Bond number.
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