固氣兩相流在懸浮床與旋迴流管之研究

Abstract

本研究主要以固氣兩相流為對象，一方面採用實驗方法分別針對懸浮床與旋迴流管中兩系統之氣固兩相之流動現象與特性進行探討；另一方面，透過數值解析方法與實驗之結果做比較，確認數值解析之可行性與應用性。於單段懸浮床系統中，選用單粒徑2 mm之D族固體粒子（PS, millet, glass bead, zeolite）研究多孔板式懸浮床之形成機制與穩定操作範圍。經由實驗觀察，若達到一穩定氣泡懸浮床，其形成過程將歷經誘發期(induced stage)、第一成長期(first growing stage)、振盪淺床暫態期(oscillating shallow stage)、第二成長期(second growing stage)及穩定期(stable stage)等五個階段。此外，改變操作變數(氣體流速、固體粒子進料速率、開孔比、銳孔徑/粒徑比、粒子密度、孔板設計等)探討針對單段懸浮床穩定操作之影響並歸納出D族粒子之實際操作範圍。同時，對於操作變數進行無因次分析，且利用線性迴歸方式可求得操作條件與操作範圍之間的關係式。於數值解析中，以有限容積法求得氣相之速度分布，結合固體粒子之運動方程式計算兩相流之流動，所得結果與實驗數值相符，也確認此數值方法之可行性。 於旋迴流管系統中，以實驗與模擬方法針對單相氣體之流動進行研究，由實驗結果得知氣體切線速度隨著軸向方向而逐漸衰減，而其速度之高峰值則由靠壁端往軸心移動。此外，由於進口具有切線速度之故，於操作範圍內進口處有迴流區之產生，於模擬計算結果中也可確認此現象之存在。而在固氣兩相流方面，固體粒子在旋迴流管之流動，經由滯留時間分佈，可確定流態近似於栓流。而旋迴流管內固體粒子的平均滯留時間隨氣體流速與固體粒子濃度增加而降低。此外，氣固兩相在旋迴流管中的壓力損失僅為氣相在旋迴流管的45%左右，且含固體粒子時，壓力降並不受固體粒子大小或濃度的影響。最後，以熱傳實驗作為旋迴流管之應用，實驗之結果迴歸可得Nup=0.126Rep0.46(Fs/Fg)-0.53之關係式。

This thesis is mainly focused on the solid-gas two-phase flow and experimentally discussed with flow characteristics and flow phenomena in two systems (suspension bed & swirling flow tube), and proved the validation of the simulation results with experimental data. For the system of single-stage suspension bed, Geldart D group particles(PS,millet,glass bead,zeolite)with mono size (dp=2 mm) were used to study the mechanism of formation, stable operation range and characteristics of suspension beds. Given the typical formation of a stable bubbling bed in the experiments, total five stages will be observed here and defined here: the induced, the first growing, the oscillating shallow bed, the second growing and the final stable stage. The influences of the operation variables on the formation of single stage suspension beds were discussed separately in the study including of the air velocity through the hole (Uo/Ut), the particle feeding rate (Fv’), the opening ratio of the plate (m), the ratio of the diameter of the hole to the diameter of the particle (do/dp) , the density of particles and design of perforated plate. In addition, the correlation between operation variables and operating range was also investigated using dimensionless analysis and regression equation. Compared with experiments, the numerical analysis is calculated by finite volume method (FVM) for velocity distribution of gas combined with the motion equation of particles. Sequentially the results of simulation are well agreed with experimental results and prove its application. On the other hand, for investigating the solid-gas two-phase in a swirling flow tube, the single gas phase was studied at first to understand the flow pattern and flow characteristics. From the experiments, the results are shown that the decay of tangential velocity along axial distance and the maximum of velocity was moved from the wall to the center of tube. It is caused recirculation zone near the inlet zone due to the swirling velocity, and the results of simulation also show the phenomena. Meanwhile, in the case of PS particle, the flow pattern in the swirling flow system can be seen as a plug flow according the residence time distribution and the residence time distribution of particles decreases as the gas velocity and loading of particles increase. Pressure drop of solid-gas two phase mixtures was found approximately 55% less than that of only air flows through the system. At last, the heat transfer between gas and particles was taking as a application of swirling flow tube, and the relationship between Nup and Rep was obtained as Nup=0.126Rep0.46(Fs/Fg)-0.53.