顆粒剪力流體之傳輸現象探討; Transport Phenomena in Sheared Granular Flows

NCUIR > Engineering College > Graduate Institute of Mechanical Engineering > Electronic Thesis & Dissertation > Item 987654321/2217

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/2217

Title:	顆粒剪力流體之傳輸現象探討;Transport Phenomena in Sheared Granular Flows
Authors:	楊文龍;Wen-Lung Yang
Contributors:	機械工程研究所
Keywords:	內聚力;應力規;剪力槽;顆粒流;stress gage;granular flows;shear cell;cohesion
Date:	2005-09-16
Issue Date:	2009-09-21 11:41:06 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本論文研究關於顆粒體於剪力流場中動態行為，這種流動方式在流體機械稱之為Couette flow，本論文主要研究兩種不同的顆粒體Couette flow型態，一種是無內聚力的顆粒流，另一種是加入微量水或矽油的顆粒流。實驗裝置是一環狀剪力槽，以玻璃珠當顆粒體，並且使用高速攝影機拍攝顆粒體運動情形，再運用影像處理技術與追蹤顆粒體程式，算出剪力流場中水平跟垂直方向的平均速度與變動速度，並借由長時間的追蹤粒子畫出粒子均方擴散位移量與時間的關係圖，進而求得自我擴散係數，使用三枚雙向應力規，裝置在實驗設備的上壁面，用以量測上壁面所受到的應力大小。在粒子顆粒流中，顆粒體間相互的碰撞造成顆粒流動行為並且導致顆粒體的隨機運動，再本論文的第一部份將探討粒子佔有體積比對顆粒流傳輸性質的影響，在較密的顆粒流場中，剪率、粒子溫度、壁面應力值、有效黏滯係數以及能量的損失都會比較大，然而在較密的顆粒流場中有較小的自我擴散係數值。在顆粒流中粒子間的內聚力包含凡得瓦力、燒結力、液橋力以及靜電力，然而在一個高濕度的系統中，液橋力相較於其他的作用力就變的很重要，我們做了一系列的實驗在顆粒流中加入不同含量的水，在本論文中的第二部份探討水的無因次化液體體積對顆粒流場的影響，由於周圍濕度影響下，粒子間的摩擦非彈性碰撞以及黏性阻力增加造成剪力槽內能量的消散，因此能量消散隨著增加無因次液體體積而增加。因為剪力槽內能量消散是由於黏滯阻力造成，因此外加液體的黏性強度影響著濕粒子系統的行為，所以在本論文的第三部分探討加入不同黏度矽油的影響，此外粒子Bond Number與Collision Number也將被用來討論濕粒子流系統的行為。本研究結果有助於發展研究剪力顆粒流的內部流場，特別是濕粒子流系統，期待本論文研究可以提供新的資訊給予研究界甚至是工業界。 This thesis examines the dynamic behavior of a granular material sheared in a shear cell. This type of flow is known as a Couette flow in fluid mechanics. In this thesis, we study two different kinds of granular Couette flows. One is the cohesionless granular material flow and the other is the cohesive granular material flow with adding little amount of water or silicone oils. Experiments are performed in a shear cell device. The glass spheres are used as granular materials. The motions of the granular materials are recorded by a high-speed camera. The image processing technology and particle tracking method are employed to measure the average and fluctuation velocities in the streamwise and the transverse directions. By tracking the movements of particles continually, the variation in the mean-square diffusive displacements with time is plotted and the self-diffusion coefficient is determined. Three bi-directional stress gages are installed to measure the normal and shear stresses along the upper wall. In granular material flows, the interactive collisions between particles are the dominant mechanism affecting the flow behavior and cause the random motions of particles. In the first part of this thesis, the influence of solid fraction of granular material on the transport properties is discussed. For the denser granular flows, the shear rate, the granular temperature, the wall stresses, the effective viscosity and the energy dissipation are greater. However, the denser granular flow has the smaller self-diffusion coefficient. In granular flow, the cohesive forces between particles include Van Der Waals force, sintering force, liquid bridge force and electrical force. The liquid bridge force is more important than the other forces in a high moisture system. A series of experiments were performed by adding different amount of water to the granular material system. The influence of the dimensionless liquid volumes of water added is studied in the second part of this thesis. The energy dissipations in the shear cell device are generated from the friction and inelasticity between particles and viscous resistance due to surrounding moisture. The energy dissipation increases monotonously with the increase of the dimensionless liquid volume. Because the energy dissipations in the shear cell are also contributed from the viscous resistance, thus the viscosity of the adding liquids have strongly influence on the behavior of wet granular system. The third part of this thesis discusses the influence of adding different silicone oils with different viscosities. The Granular Bond Number and the Collision Number are used to discuss the behaviors of the wet granular flow system. The works in this thesis are relatively fundamental. However, these issues are important for developing the insides of sheared granular flows, especially wet systems. We wish that the results will bring some new information to the research field and also be contributed to the related industries.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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