可壓縮軟粒子之壓縮及過濾行為之研究

Abstract

本研究的主要宗旨，在於探討體積可變之可壓縮軟粒子受機械壓壓縮下之特性，以及此類物質在流體流動系統當中之流力行為。因此，本研究首先以單顆及二維平面上規則排列之多顆不可壓縮及可壓縮軟粒子，進行機械壓縮實驗，並推導出描述圓形軟粒子變形行為的圓球及橢圓壓縮模式，以分析單一軟粒子受壓後之型態；此外也將模式延伸至推估軟粒子於二維平面排列下，受壓時粒子間的孔隙度變化。實驗及分析結果顯示所推導之壓縮模式，可合理地描述軟粒子受壓下型態相關物理量(體積，表面積)之改變，並經比較而知不可壓縮軟粒子因受壓下具較大擴張量，而與可壓縮軟粒子之行為有所差異。 其次，為探討含可壓縮軟粒子之流體流動系統的行為，本研究採恆床壓力降及恆率操作方式，對可壓縮Ca-alginate粒子堆積床進行流力實驗，並以考量粒子體積可變而修正Ergun方程式，使其適於計算流體流經可壓縮軟粒子床之壓力降；同時，以此式為基礎，建立一套動態分析方法，運用於計算操作過程中堆積床之結構變化及水力行為。實驗結果顯示，恆壓力降操作下的床高有回彈之現象，與恆率操作下床高不斷下降的行為迥異；而由動態分析之結果可瞭解，若不考量粒子體積可變的影響，則在估算可壓縮軟粒子堆積床之床高變化上，將與實驗值間有相當大的偏差。 本研究第三部份，為探討含可壓縮軟粒子泥漿在恆壓及恆率操作下之過濾行為，同時針對童(1998)及Lu et al.(2001b)所提出之可變形軟粒子過濾行為之動態解析方法加以修正，針對其中的黏彈性模式，則引入粒子體積可變之概念，以對含可壓縮軟粒子泥漿之過濾行為加以解析。實驗結果顯示由於粒子在操作過程當中持續的壓縮行為，在恆壓及恆率過濾實驗曲線上，皆顯示了斜率不同的轉折，而反映出不同階段時粒子壓縮率過濾行為的影響。其次經由動態分析之結果，可瞭解雖不同過濾操作方式對於濾餅局部性質分佈有不同形式的影響，但亦可發現在同一系統壓力下，恆壓及恆壓操作所得之局部孔隙度與固體壓縮壓力之關係有相當一致的分佈。此外，以動態模擬所得之濾性值，反證恆壓過濾實驗之過濾曲線，結果顯示在過濾曲線尚未陡升前有合理的計算結果，但在轉折上升後的行為，則仍須有更進一步理論的探討。

The performance of the filtration of the compressible soft particle slurries is systematically studied in the following three aspects: First of all, the uni-axial compression of a single compressible(volume variable) or incompressible(volume invariable) soft particle without or with surrounded by other particles are studied to obtain the compression models for characterizing the properties of the soft particles in a deformation course. It is shown that the incompressible soft particle expands more significantly during compression and therefore interacts with the surrounding ones more effectively than the compressible soft particle. The results calculated by the models can properly describe the compression behaviors of the soft particles as well. Secondly, a method of dynamic analysis based on modified Ergun equation, which considering about the volume variation of the particles, was proposed to evaluate the structural and hydro-dynamic behaviors of the compressible soft particles bed under a constant pressure-drop or a constant rate operation. Experimental results show different mechanisms for bed-height variation of the constant pressure-drop and constant rate operations. The results of dynamic analysis indicate that without considering the volume variation of the particles, reasonable estimations of the properties of the compressible particle beds are not possible. In the third portion, compressible Sephadex and Ca-alginate particles are adopted for the cake filtration experiments under a constant pressure(CPF) and a constant rate(CRF) operation. The method of dynamic analysis of cake filtration proposed by Lu et al.(2001b) is modified by the consideration of the volume variation of the particles to investigate the local cake properties of compressible soft particles. From the experimental results, the filtration curve shows various stages due to the deformability of compressible particles. Results obtained by dynamic analysis show that although the cake structures obtained by CPF and CRF differ obviously, the relations between the local porosity and the solid compressive pressure of the two operations are approximately the same. The verification of the cake characteristic values obtained by dynamic analysis by the estimation of the CPF filtration curve agrees with the experimental value as the curves remain linear. More factors must be considered for evaluating the compression behavior of the cakes of compressible soft particles.