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  • 學位論文

旋轉填充床中填充物對質傳影響之研究

The Effect of Packing on Mass Transfer in a Rotating Packed Bed

指導教授 : 劉懷勝

摘要


摘 要 本論文主要目的在於研究旋轉填充床中,填充物型態對質傳以及液體流態的影響。實驗中以氮氣氣提水中溶氧為實驗系統,比較液膜質傳係數(kLa)數值大小以得知質傳效率的優劣,在填充物的部分則選用了13種不同尺寸大小、材質、形狀、親疏水表面及構造型態的填充物進行研究。 經由實驗結果發現,填充物比表面積的大小與質傳係數間並無明顯正比關係;在材質方面,陶瓷材質填充物具有最佳的質傳效果;在幾何形狀的部份,由於拉西環及矩鞍容易造成液體流動的死角,因此質傳效果較圓珠為差;此外,親水表面填充物質傳效率優於疏水表面填充物,其質傳係數可比填充疏水表面填充物高11%~43%;在 Structured packing部分,填充金屬絲網的質傳效果較葉片及鋼圈為好。 經由實驗結果迴歸修正,提出不同的填充物的液膜質傳係數填充物修正因子,但修正因子與填充物特性,諸如:比表面積、孔隙度、水力半徑,並未發現明顯之關係。此外,本研究初步建立液膜流模型與液滴流模型,探討旋轉填充床內液體流態與轉速及填充物型態間的影響,並進一步分析液膜流與液滴流對質傳的貢獻比例。 將各種類型填充物的氣提水中溶氧實驗結果以及流態模型結論作一整理分析可以得知,質傳效果最佳的填充物必須同時具有親水表面,以增加液膜流的質傳效率,且其結構須能幫助液體碎裂成更多粒徑小、總表面積大的小液滴,以增加質傳有效界面積,提高液滴流的質傳效率。

關鍵字

旋轉填充床 填充物 質傳

並列摘要


Abstract In this study, the packing effect in rotating packed bed was investigated. The mass transfer coefficients (kLa) were obtained for deoxygenation from water by nitrogen stream. Random packings were used with the variation in sizes, materials, shapes, surface properties together with some structured packings. According to the experimental results, there was no obvious strong relationship between packing specific surface area and mass transfer coefficient. As to materials, ceramic packings had superior mass transfer efficiency. And probably because the shape of Raschig rings and saddle type might hinder liquid distribution, the mass transfer efficiency of spherical packings was higher than those of Raschig rings and saddle type. Besides, the kLa values for hydrophilic packings were generally higher by about 11%~43% than those of hydrophobic packings. Moreover, the mass transfer of wire mesh was better than that of blades and steel rings. We proposed a so-called packing factor to correct the mass transfer coefficient due to the discrepancy among experimental data. However, there is no obvious relationship between packing factors and packing characteristics, including specific surface area, porosity and hydraulic diameter. Furthermore, we developed preliminary film flow model and droplet flow model to investigate how rotor speed and packing characteristics influence flow pattern within rotating packed bed. Also, we analyzed the contribution of film flow and droplet flow to mass transfer in the rotating packed bed. Based on experimental and theoretical results, the superior performance of packings could be obtained with the hydrophilic surface for enhancing mass transfer caused by film flow and the conformation of breaking liquid into smaller droplets that raise effective interfacial area.

並列關鍵字

Rotating packed bed packing mass transfer

參考文獻


陳昱劭,旋轉填充床中黏度對質傳影響之研究,台灣大學化學工程研究所
Chen, Y. H., C. Y. Chiu, C. Y. Chang, Y. H. Huang, Y. H. Yu, P. C. Chiang, J.L.
Atlanta, G.. A.; ASHRAE handbook. Equipment, pp.11-16, American Society of Heating, Refrigerating, and Air-Conditioning Engineers (1983)
Basic, A. and M. P. Dudukovic; "Liquid Holdup in Rotating Packed-Beds - Examination of the Film Flow Assumption," AIChE J., 41, 301 (1995)
Burns, J. R., J. N. Jamil and C. Ramshaw; "Process Intensification: Operating Characteristics of Rotating Packed Beds - Determination of Liquid Hold-up for a High-Voidage Structured Packing," Chem. Eng. Sci., 55, 2401 (2000)

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