旋轉鼓中顆粒表面粗糙度對於潛變流動影響之研究;Influence of particle surface roughness on granular creeping motion in rotating drum

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题名:	旋轉鼓中顆粒表面粗糙度對於潛變流動影響之研究;Influence of particle surface roughness on granular creeping motion in rotating drum
作者:	張威慶;Chang,Wei-Ching
贡献者:	機械工程學系
关键词:	顆粒流;潛變流;旋轉鼓;核心;流動層;粗糙度;granular flow;creeping motion;rotating drum;core;flowing layer;roughness
日期:	2014-07-22
上传时间:	2014-10-15 17:18:47 (UTC+8)
出版者:	國立中央大學
摘要:	本論文以旋轉鼓為實驗對象，研究在旋轉鼓中的流動層下方的潛變流區域，在高填充率下可以發現核心的產生，隨著時間的增加核心會不斷地縮小，被稱為侵蝕現象，且核心的轉速相較於旋轉鼓轉速稍快，稱為相位領先。本研究欲透過實驗了解顆粒表面粗糙度對於潛變流的影響，利用混合碳化矽與玻璃珠，透過球磨機製造出表面較粗糙的玻璃珠，與表面光滑的4 mm玻璃珠進行不同表面粗糙度對於旋轉鼓中潛變流之影響分析，分別在五個不同填充率下使用光滑顆粒與粗糙顆粒進行實驗，利用攝影機進行長時間的影像紀錄，利用高速攝影機拍攝影像透過PIV進行速度場分析，核心分析的結果顯示，顆粒表面粗糙度對於核心侵蝕和相位領先有存在著相關性，填充率越大，侵蝕越快，且粗糙顆粒有較大的侵蝕率；填充率越大，相位領先率越快，且光滑顆粒有較大的相位領先率。本文利用速度場分析出相關參數且利用數學模型對其現象進行討論，透過剪應變率、流動層厚度、特徵長度，剪應變率隨著填充率越大而越小，且粗糙顆粒有較小的剪應變率，特徵長度隨著填充率越大而越大，且粗糙顆粒有較大的特徵長度。剪應變率將主導相位領先的過程，而特徵長度將主導核心縮小的趨勢，改變顆粒粗糙度將會影響剪應變率及特徵長度，進而改變潛變流中的運動行為，包含核心的侵蝕和相位領先，最後本文將透過數學模型的預測比較理論的核心之相位領先和侵蝕和實驗結果，結果顯示實驗與理論趨勢相同。;This thesis is aimed to the effect of particles surface roughness on granular flow in a quasi-two dimensional rotating drum. The dynamic behavior of creeping flow under the flowing layer is discussed. The core is found in the center of rotating drum as fill ratio lager than 50%. The size of the core in the center of the rotating drum decreases as the drum rotating number increasing. This is so-call core erosion. The rotating speed of the core is larger than the rotating speed of the drum. This is so-call core precession. Two different surface roughness of glass particles with 4mm diameter are used in the experiment. The rougher particles are roughened by a ball mill equipment with silicon carbide grit. The experiments are performed in five different fill rates in a 50 cm diameter rotating drum. A model from the literature based on the two regions of velocity profile is adopted to investigate the core dynamic. Depend on this model, the experimental results show that the characteristic length yR0R and the shear rate in the flowing layer both are dependent on the particles surface roughness. The characteristic length is larger for the rough surface of particle and larger at high fill rate. The shear rates are smaller for the rough surface of particle and smaller at high fill rate. The shear rates dominate the core precession and the characteristic length dominates the core erosion. Therefore, dynamic behavior of the core in the rotating drum is also different with different surface roughness of particles and different fill ratio. Core precession rate is smaller for the rough surface of particles and larger at high fill ratio. The core erosion rate is larger for the rough surface of particles and larger at high fill ratio. Although there exists discrepancies between core dynamic model predictions and experimental measurement for the values of core precession rate and core erosion rate. The tendencies of the results from model prediction are in agreements with the experimental data for core precession and erosion.
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