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  • 學位論文

流體流過可變形粒子床之現象觀察

Experimental Observation on Fluid Flow through the Deformable Particles Bed

指導教授 : 童國倫
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摘要


諸多固液分離程序中,經常遇到流體流過粒子床之流體力學問題,隨著生化科技的蓬勃發展,應用此程序的範圍更為廣泛,其中不乏含有可變形的固體粒子,所以探討粒子受外力而變形的行為刻不容緩,但迄今仍無一完整理論可供參考,尤其在預估流體流過可變形粒子床行為研究方面。 故本研究主要以實驗現象的觀察為主,針對流體流過可變形粒子床進行試驗,採用自行製備具有黏彈特性之藻膠酸化鈣粒子作為實驗物料,藉由改變不同入口流量、初始粒子床高及粒子強度,以探討流體流過可變形粒子床之流速、壓降及床高等改變情形隨時間變化的相互關係,以尋求可合理預估流體流過可變形粒子的流體力學行為之參考依據。 實驗結果發現,粒子的變形與否影響粒子床行為結果甚鉅,不同強度的可變形粒子在受到不同固定荷重,其平衡應變量會隨著改變,且其改變的量並不會隨荷重呈線性增加。隨著不同流速變化對粒子床會產生不同程度的壓降變化,粒子強度越大及初始粒子床較高者其壓降變化越大,反之相反;其主要變化來自於粒子本身的變形程度(抗壓強度)不同;在局部液壓分布部分,剛性粒子的局部液壓對位置關係圖中呈現出線性關係,表示其粒子不變形,所以床體結構受外力作用並不改變,粒子床內各位置的受力均一;然而可變形粒子則由於本身會變形,粒子床受到逐層累積的流體拉曳力影響,均導致其床高變化集中於底層,此時有一緻密層開始生成,故此層明顯阻力最大,局部孔隙度最小,隨著時間的增加,曲線變化幅度加大,表示此時粒子床之受力不再僅侷限於底層位置,此時粒子床受力開始向上層處分配,液壓分布對位置相對圖呈現非線性關係。 由於藻膠酸鈣粒子具有黏彈特性,當流體流過粒子床時,在相同流速下,由於不同強度的粒子其變形速率不一,表現在壓降、床高隨時間改變上,呈現緩慢變化的暫態行為;另外由粒子的本身黏彈特性,粒子床受力釋放後後,只有部分粒子彈性部分可回復,看出其具有遲滯行為。綜合以上結果得知,影響可變形粒子床之流體力學行為最顯著的因素為,外力作用大小及其來源(機械壓、水力壓)、粒子本身的變形特性和時間效應。

並列摘要


Many fluid hydrodynamic problems frequently occur when the fluid flows through the particle bed in solid-liquid separation procedure, and this procedure is widely applied in the biochemistry technology. The deformation behaviors of deformable particles are deeply concerned when the deformable particles under mechanical loading and hydraulic drag in particles bed. It is important to study on the particle deformation behaviors, but, still now, there is not a complete theory to refer to, especially in the hydrodynamic behaviors of fluid flowing though the particle bed composed of deformable particles. Therefore, this study focuses mainly on the experimental phenomenon observation and concentrates primarily on the hydrodynamic behaviors of fluid flowing through the particle bad composed of deformable particles. The Ca-alginate particle with viscoelastic property is used as a test material. A number of in stiu of different experimental conditions such as the entrance flow rate, the initial height of bed, and the strengths of deformable particles could help surveying the variations of the pressure drop, porosity, flow rate, bed height, and the correlation between these variations and that of time, which are to be discussed to seek the reasonable empirical equation of pressure drop when the fluid flows through the deformable particle bed. Experimental results show that the deformation dramatically influences the results of deformable particle bed behaviors. When the deformable particle is under the different intensity and loading, the constant proportion of Equilibrium Strain varies with time. And the progress decreases gradually in the particle bed height (porosity) while the stress on the bed is increased, with the particles being deformed into polyhedron on the bottom of bed. The more strength the deformable particles get and the more height the particle bed is, the bigger variation of the pressure drops occurs, and vice versa. The variation comes mainly from the distortion degree of the deformable particle itself. The effect of particle deformation due to cumulative friction drag on the reduction of porosity is studied to examine how this variation leads to increase in test. Results indicate that as the skin layer closing to the filter medium formed by the deformable particles, it exhibits a rapid increase in flow resistance and decrease in porosity due to deformation. The local hydraulic pressure distribution presents a linear relation in local liquid pressure distribution of rigid particles aspects, because the rigid particle shape remains unchanged. Thus, the bed body structure is nearly unchanged. The local hydraulic pressure is the same at any site. Because the Ca-alginate particle can deform itself, the hydraulic pressure distribution presents a curve tendency. The uneven stress of deformable particle causes its height of the bed to concentrate on the bottom of the bed. Apparently, the resistance becomes the biggest and the partial porosity is the smallest at the bottom of the bed. When fluid flows through the particle bed, the viscoelastic property of Ca-alginate particle rises with time as the pressure drops slowly. The Ca-alginate particle displays a transient behavior. The particle bed regains slightly of its original spherical shape upon releasing of stress after the flow rate reaching the maximum operating flow rate. The hysteresis behavior of the deformable particle can be verified. To summarize the above results, we know that the most apparent factors of hydrodynamic behavior to influence the particle bed are the size and source of external force function, the deformation characteristics of the particle itself, and the time effect.

參考文獻


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被引用紀錄


林昱燊(2008)。流體流過黏彈性凝膠粒子床之理論與實驗研究〔碩士論文,中原大學〕。華藝線上圖書館。https://doi.org/10.6840%2fcycu200800157

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