顆粒的流動行為中包含固體顆粒體與其間隙氣體的相互作用，當封閉儲槽 在排放微細的顆粒體時，間隙氣體及逆向空氣效應之影響將造成不穩定的排放行 為，在顆粒體粒徑小於200 μm的情形下可見氣體團聚以氣泡的方式穿越顆粒床 體，類似於氣泡式流體化床內的現象。 本論文旨在研究微細顆粒體於封閉儲槽之排放行為及此一自然形成之氣泡 現象，探討不同粒徑區間之顆粒床體之排放行為及氣泡現象之動態。本研究之實 驗採用可視化設計之類二維封閉儲槽，將大小介於32至212 μm之玻璃珠分為七組 不同粒徑區間之實驗顆粒體進行排放實驗，探討粒徑產生之影響，並量測其排放 流率、儲槽內之氣壓變化等因素進行分析及討論氣泡現象之成因、特性及各實驗 參數之關聯。 實驗結果說明顆粒粒徑的改變將影響氣泡現象及排放行為，當粒徑愈大，逆 向空氣便愈容易在顆粒床內部滲透流動，產生的氣體阻礙效應及氣泡現象也較弱， 所形成氣泡尺寸較小，以及氣泡更容易在顆粒床內部消散等。但在小粒徑的配置 下，氣泡甚至會移動至顆粒床頂端產生爆裂飛濺現象。氣泡之移動速度與顆粒床 之流動性有關，當顆粒床的流動性愈好，則氣泡具有愈快的移動速度加快，與顆 粒床的粒徑成正比的關係。 此外，本研究利用理想氣體方程式及影像分析方法計算空氣之進入率，在本 實驗之實驗架構下，空氣進入率的變動與氣泡現象的動態有著良好的對應關係， 進一步說明了氣泡現象的動態、顆粒床高的變化與內部的氣壓之間的相互關聯性。;The granular flow behavior includes the interaction of solid granules and interstitial fluid therein, usually as air or gas. The discharge rate of granules in a silo is affected by the reverse way interstitial fluid. In particular, unstable discharge rate and air bubble can be found in the discharge process of the particle size less than 200μm in a closed-top silo. The air bubble effect in a silo is similar to the air bubble in a fluidized bed. The purpose of this study is to investigate the discharge and the bubble effect of fine powder in a closed-top silo. The experimental particle size from 32 to 212 micron and a transparent closed top silo are used in the experiments of this study, and the experimental particles are sieved to seven different particle size ranges. The mass flow rate during discharge and the pressure in the silo above the granular bed were measured. A high speed camera was used to photograph the discharge process and the bubble dynamics. The air bubble effect in granular bed is a complex multiphase flow. The permeability of granular bed is affected by the particle size. Hence the experiment results showed that the change of particle size of granular bed affects the dynamic of air bubble and discharge behavior. Bubble burst behavior and particle splashing can be found when the air bubble moved to the top of granular bed in the discharge process. The results of this study showed that the particle size influences the bubble size and bubble velocity. Bubbles with faster velocity and smaller size are generated in granular bed with coarser particle size, and vice versa. We also calculated the air input rate into the silo and the permeability to explain the bubble dynamics and the effect of particle size.
