含次微米級粒子懸浮液澄清過濾機制之研究

Study on the Mechanism of Deep Bed Filtration for Submicron Particle Suspension

賴正原(Jen-Yuan Lai)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/碩士(2003年)

https://doi.org/10.6840/cycu200300399

摘要

為了解次微米粒子於澄清濾床內部所受作用力機制，本研究基於計算流體力學模式，先以套裝軟體FLUENTTM求出規則堆積濾床中之流場變化，再以數值方法針對不同流場中次微米粒子所受作用力分別進行探討。由於澄清濾床內部依濾料不同堆積方式所得之流場分布會直接影響次微米粒子受力機制。因此本研究使用三種規則堆積濾床來控制流場，分別為面心立方、體心立方和簡單立方堆積。本研究針對次微米粒子進入規則濾床時，粒子所受作用力，求出粒子軌跡和隨著不同床高之捕捉率變化，在此探討作用力為淨重力，流體之拉曳力，粒子兩側不同速度差之慣性浮升力，水分子撞擊之布朗運動力和粒子與濾料間之凡得瓦力與電雙層斥力。
結果顯示次微米粒子較不受本身重力與流體之拉曳力及浮升力影響，主要因布朗運動力產生隨機移動之軌跡，碰撞濾料以提昇捕捉率，而與濾料間凡得瓦力則因粒徑太小所以並不如濾料表面所帶之負電性影響大，在粒子與濾料帶負電性大時，則會使得次微米粒子偏離濾料，降低捕捉率，此現象在粒子粒徑愈小時愈明顯；微米級粒子則主要受到重力、拉曳力和浮升力之影響。在三種堆積濾床中，面心堆積因為複雜之孔道變化且無垂流區域，所以水平流動分量大，使得粒子在濾床上層即被捕捉，而簡單堆積及體心堆積之垂直流動區域較大，粒子較容易流動至下層才被捕捉，所以捕捉率較差。

關鍵字

濾床結構 ； 捕捉率 ； 計算流力 ； 軌跡分析 ； 作用力分析

並列摘要

The mechanism of deep bed filtration for submicron particle suspension was conducted by force analysis on the suspended particles flow through order-packed granular filter beds. The flow field through the filter beds were calculated by using the commercial available CFD software － Fluent. Various types of granular packing structure, such as simple cubic packing, body-centered packing and face-centered packing structures were chosen for analyzing. The motion of suspended particle was tracked by considering the forces include net gravitational force, hydraulic drag force, lift force, Brownian force, van der Waals force and double layer force. Effects of granular bed packing structure, porosity of beds and suspended particle diameter on capture efficiency of a granular filter bed were examined.
Force analysis depicts that inertial effect and van der Waals force increased the capture probability of particles on the granular while lift force and Brownian force were to decrease particle deposition. Simulated results show that among the chosen packing structures, the face-centered packed granular bed gives the highest pressure drop and capture efficiency of particles due to the lowest packing porosity. The simple cubic packed filter bed showed the lowest pressure drop and capture efficiency of particles due to the highest packing porosity among the chosen packing structures. It is mainly due to the simple cubic packing exists free vertical downward flow path and thus exhibits higher packing porosity. Comparisons of simulated capture efficiency with experimental results depicted that the body-centered packed granular bed showed a best approximation of capture efficiency with that of random packed granular bed.

並列關鍵字

force analysis ； CFD ； granular packing structure ； trajectory analysis ； deep bed filtration ； capture efficiency

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