流體流過澄清濾床之流態解析

Flow of Fluid through Granular Filter Bed

張雅鈴(Ya-Limg Chang)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200174

摘要

本研究基於流體力學模式，以微觀分析的方式對澄清過濾影響最顯著的兩個主要因素濾料填充結構與粒子補集作用力分析分別進行探討。由於濾床內濾料堆積出之不同孔隙度、截面積變化的濾床會直接影響流場的分布，若濾床結構阻力大將近一步影響出入口的壓降，因此本研究首先以規則堆積結構之粒子床依孔隙度遞減分別為簡單立方、體心立方與面心立方三種規則堆積進行探討，最後則以隨機產生濾料位置之濾料床與真實濾床最接近之濾床模式比較其差異性。
當粒子進入濾床時其運動軌跡、捕捉位置與濾床捕捉效率將由粒子受流體作用力之合力來決定，在此探討粒子所受之淨重力、流體與粒子間之拉曳力、粒子因周圍速度差而產生之慣性浮升力和粒子與濾料間的表面作用力，計算粒子於各種濾床中之捕捉效率。
研究結果顯示，在乾淨濾床的速度分布中，由於面心立方有最低之孔隙度，流體於孔道中產生較多噴擠的現象，阻力大使得壓降高而且孔道結構曲折變化率高致使流體方向水平分量較大，單位體積所含表面積較大，粒子與濾料碰撞機率高，因此於濾床中若存在較多之面心立方堆積形式的結構，將會有較佳之捕捉效率，而簡單立方與體心立方堆積有較多的垂流路徑，所以捕捉效率較差更證明流場較不均勻的面心立方有較高之捕捉效率。若只考慮重力時，粒子之軌跡將完全成直線往下運動，但加入流場拉曳力時，粒子之軌跡將依循流線方向運動；由於粒子相當的小，所以慣性浮升力對粒子運動影響相當不明顯。

關鍵字

計算流力 ； 濾料堆積結構 ； 澄清過濾 ； 電腦模擬 ； 軌跡分析

並列摘要

The mechanism of deep-bed filtration was conducted by analyzing a 3D model of granular beds using computational fluid dynamic technique. Various types of granular packing structures, simple cubic packing, body-centered packing and face-centered packing structures and random packing structure were chosen for analyzing. The flow field through the packing media was calculated by using the commercial available CFD software – Fluent. The motion of suspended particle was tracked by considering the forces exerted on the particle using the Lagrangian trajectory model. The forces exerting on the particles include net gravitational force, drag force, lift force, ven der Waal force and double layer force. The effects of packing structure, porosity on the efficiency of a depth filter were analyzed theoretically. Results show that among the chosen packing structures, the face-centered packing structure gives the highest pressure drop due to the lowest packing porosity. Among those close packing, say simple cubic packing and body-centered packing, there exist free vertical downward flow path except the face-centered packing structure. Force analysis depicts that inertial effect increased particle deposition while lift force was to decrease the particle deposition.

並列關鍵字

granular packing structure ； trajectory analysis ； deep-bed filtration

參考文獻

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