| 摘要: | 顆粒流包含固體的顆粒體及間隙流體，通常是空氣。當儲槽排放過程的顆粒體尺寸小至數百微米以下，空氣與粉體彼此交互運動，屬於一種兩相流。顆粒體的流率與尺寸、密度、溼度、內聚力、環境壓力等有關。 Beverloo方程式在圓錐型儲槽對於流率的估算相當準確，然而當顆粒體尺寸小至數百微米以下，間隙氣體對於流率及流動型態的影響開始顯著，尤其頂端封閉式儲槽，由於空氣逆向填補顆粒排出的空間，有時甚至可見氣泡產生的現象，在此我們稱為氣體阻礙效應，故實際排放率較其預估為低。 本研究實驗採用粒徑範圍由90至1000微米的矽砂為實驗顆粒體，採用開放與封閉兩種系統，並改變三種開口直徑，以及儲槽環境壓力。量測排放過程的流率以及間隙氣體壓力資訊，驗證氣體阻礙效應與粒徑呈反比及與環境氣壓呈正比的關係，亦即當粒徑越小、環境氣壓高時氣體效應越明顯。 此外本研究定義一氣體效應被削減的臨界壓力，此臨界壓力與粒徑有反比的關係。Darcy Law在多孔介質是廣泛運用的理論，在本研究中我們以簡化的模組比較實驗也得到相當準確的結果。 The process of discharge in a silo includes granular material and interstitial fluid, usually as air, is belong to two-phase flow phenomenon. The discharge rate of granular material bases on size, density, humidity, cohesive force, and ambient pressure etc. Beverloo correction performs well in the conical tank for reasonably accurate estimation of flow rate. However, when the particle size is small than several hundred microns or less to. Interstitial gas flow impact the flow rate and flow pattern, especially in a closed-top silo. Due to air reversely fill the gap caused by particle discharge, sometimes we can see the phenomenon of bubbles produced, in which we call gases impede effect, so the actual discharge rate is lower than its forecast. This study used experimental particle size range from 90-1000 microns silica sand for the experiment. With changeable open or closed-top conical silo, and changed three diameters of orifice, as well as the ambient pressures of silo, we experimentally measure the discharge rate of sand and pressure variations of interstitial gas. This work proves the accuracy of Beverloo equation for open-top silo. Closed-top silo at atmosphere because of counter-current air fill the space of discharged sand, even seen bubbles generated, the discharge rate is much decreased. Experiments of closed-top silo at low ambient pressure demonstrate the gases impede effect is reduced. The effect of air obstacle is inversely proportion to particle size and directly proportion to ambient pressure. In addition, this study defines a critical pressure of reduced interstitial gas effect. This critical pressure has inverse relationship between particle size. Darcy Law is widely used in porous media theory, in this study, we compared a simplified experimental module has accurate results. |
