濕顆粒體的動態特性與混合機制 ; The Dynamic Properties and Mixing Mechanisms in Wet Granular Matter

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題名:	濕顆粒體的動態特性與混合機制;The Dynamic Properties and Mixing Mechanisms in Wet Granular Matter
作者:	廖俊忠;Chun-Chung Liao
貢獻者:	機械工程研究所
關鍵詞:	流動層厚度;混合速率;轉鼓;液橋力;自擴散;剪細帶;間隙流體黏度;剪力槽;Shear;Interstitial fluid viscosity;Shear cell
日期:	2010-12-23
上傳時間:	2011-06-04 15:01:09 (UTC+8)
出版者:	國立中央大學
摘要:	本篇論文為研究探討濕顆粒材料物質的動態運動行為與混合的機制。本篇研究以實驗方法去量測剪力顆粒流體的傳輸性質，並探討在不同的間隙流體黏度下顆粒流體的流動行為。並利用影像分析方法，成功的量測到粒子的平均速度、擾動速度、粒子溫度以及粒子的擴散係數。由實驗結果指出，間隙流體在顆粒流體的傳輸特性上扮演著重要的角色，在乾系統時(間隙流體為空氣)，粒子的運動更為隨機且粒子間的互相碰撞也更為激烈。當間隙流體的黏滯度越大，相對的也產生越大的黏滯阻力，因此粒子的擾動速度及粒子溫度也相對的變小。隨著間隙流體黏度的減小，剪細帶的厚度大約從三顆粒子的粒徑成長到八顆粒子的粒徑。本篇研究也針對粒子的擴散係數做討論，並發現到粒子的擴散係數與粒子溫度皆隨著剪率的變大而提升，且在流場方向整體平均的擴散係數及粒子溫度會隨著史托克數與貝格諾數的增加而變大。藉由添加微量液體於顆粒物質，並探討濕粒子間液橋力對於剪力顆粒流動態行為的影響。由實驗的結果，可以發現當添加微量液體於顆粒材料以及改變轉速皆會對顆粒的動態運動特性有很明顯的影響，這主要原因是粒子間由於液橋的形成與斷裂過程中粒子的能量被消散所致。且由於液橋的建立與斷裂所造成的能量消散會隨著轉速的提升與添加液體黏度的變大而增加。液橋力對於濕顆粒物質動態運動性質的影響強弱皆會受到添加微量液體的黏滯度與顆粒系統的動能大小而定。最後本篇論文也研究間隙流體的黏度對於轉鼓中顆粒動態運動過程下混合速率的影響。實驗過程中，藉由固定轉速使流場落在滾動的流態，此時在自由表面的流動層的粒子流動是一個連續的流動。從實驗結果發現，粒子的特徵速度會隨著間隙流體黏度的變大而變慢，但粒子的混合速率卻會隨著間隙流體黏度的提升而變快。這些發現跟我們所提出的一個簡單物理模式相吻合，並發現粒子的混合速率主要是跟流動層厚度的大小有關。另外，由實驗結果指出當史托克數減小時，可能存在一個轉折點從慣性力主導的流態轉變為黏滯力主導的流態。整體而言，當改變粒子間微觀的作用力時，顆粒系統宏觀的物理量也會受到很大的影響，且效應會由於不同的顆粒系統而有所差異。 This thesis investigates the dynamic behaviors and mixing mechanisms in wet granular materials. The experimental measurements of transport properties in sheared granular materials with different interstitial fluids are reported by image processing technique and particle tracking velocimetry. The results indicate that the interstitial fluid plays an important role in determining the transport properties of the granular flow. The values of fluctuations and granular temperatures are smaller as the interstitial fluid is more viscous resulting in the larger viscous drag force. The thickness of shear band is about three to eight particle diameters and increases with the decrease of the interstitial fluid viscosity. The self-diffusion coefficient of granular materials is also discussed in this study. Both the self-diffusion coefficients and the granular temperature increase with increasing the shear rate. The average streamwise self-diffusion coefficient and granular temperature increase with the increase of Bagnold number. To quantify the effect of the liquid bridge force on dynamic properties in wet granular systems. A series of experiments are also performed to measure the dynamic properties of wet granular matter in a shear cell. The results show that adding small amounts of liquid with different viscosities and changing the wall velocity, both have significant influences on the dynamic properties of wet granular matter due to the formation and rupturing of liquid bridges. The energy dissipation due to the formation and rupturing of the liquid bridges increases with increasing the wall velocity and the increase of liquid viscosity. The effect of the liquid bridge force on the dynamic properties is not only dependent on the liquid viscosity but also on the kinetic energy of the granular system. Finally, the effects of interstitial fluid viscosity on the mixing rates of dynamical processes in a quasi-2D thin rotating drum half-filled with monodisperse glass beads are studied. The flow behavior is fixed at the rolling regime. While the characteristic speed of a bead in the flowing layer decreases with the fluid viscosity μ, the mixing rate of the beads is found to increase with μ. These findings are consistent to a simple model related to the thickness of the flowing layer. In addition, the results indicate a possible transition from the inertial limit regime to the viscous limit regime when the Stokes number is reduced. The overall of thesis, changing the microscopic mechanics between particles has significant influences on macroscopic physical quantities of granular systems. Additionally, the effects are not the same with different granular systems.
顯示於類別:	[機械工程研究所] 博碩士論文

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