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  • 學位論文

磁場對攪拌槽中文石成長速率的影響

Effect of Magnetic Field on Growth Rate of Aragonite in a Stirred Tank

指導教授 : 戴怡德

摘要


在工業上研究以磁場抑制管內結垢的方法已有數十年,頗多研究指出磁場既可預防結垢,亦有除垢的功用。而通常結垢問題都發生高溫系統,如熱交換器等,且本實驗室之前在探討有關磁場對結垢的影響方面,都是在常溫下進行,所以本實驗將就此重要的變數-溫度進行討論,又由於實驗在攪拌槽中進行會比在流化床中進行更容易控制溫度,故本實驗將在攪拌槽中,探討磁場與溫度對文石成長速率的影響。 本研究方法是在攪拌槽中,以恆溫水槽控制溶液溫度,然後用帝斯卡磁能防垢器將溶液受磁二十個小時,確定其完全受磁,之後丟入文石晶種開始成長實驗,利用恆鈣離子定組成法來量測其成長速率,進而討論磁場的有無及溫度的高低(25οC~40οC)各對文石成長速率的影響,並比較何者效應對文石成長速率的影響較大。 本研究在無磁場作用,過飽和度為0.95,pH為9.0,離子強度為0.018,離子活性比為5.54的條件下,探討溫度對文石成長速率的影響方面,首先發現溫度在25οC時,做出的文石成長速率接近零,而在溫度從30οC上升至40οC時,發現文石成長速率隨溫度增高而變大。而在有磁場作用之下,探討溫度對文石成長速率的影響,溫度從25οC上升至40οC時,亦發現溫度愈高,文石成長速率愈大,。另外,在有無磁場時,溫度對文石成長速率的比較方面,無磁場作用時,溫度從30οC上升至40οC,文石成長速率增加約100.2%,會比有磁場作用之下,溫度從30οC上升至40οC,文石成長速率增加的48.3%還高。而在磁場和溫度二種效應的比較方面,發現在每個過飽和度之下,在常溫及磁場作用下之成長速率比無磁場時40οC高溫下之成長速率大約高出10%至20%之間。而當磁場與溫度效應都存在的情況下,即在40οC並有磁場作用下,由其文石成長速率的比較可知,兩種效應具有加成性。另外,以總成長速率式(overall growth rate equation) G=Kg σn分析攪拌槽中文石的成長模式,在三種不同的條件下:25οC有磁場、40οC無磁場及40οC有磁場,找出在攪拌槽中文石成長的總反應階數n值都接近1.4。此三種條件均能促進文石成長,而從三種條件下的Kg值大小,得到40οC時有磁場的情況最能有效促進文石成長,其次為25οC時有磁場,影響最小的是在40οC時無磁場作用下。

關鍵字

碳酸鈣 文石 磁場 溫度 結垢

並列摘要


In industry, magnetic treatment has been installed to suppress the scale formation in pipes for decades. Many literatures reported that magnetic field was effective to prevent scale formation and remove scale. The scaling problem usually occurs in higher temperature systems, for example, heat exchanger. However, the previous studies in the subject of magnetic effect on scaling of our laboratory were proceeded under room temperature. Moreover, it is easier to control the temperature in the jacketed stirred tank than in the fluidized bed. In this research, the effects of magnetic field and temperature on the growth rate of aragonite in a jacketed stirred tank are studied. In this research, the temperature in stirred tank was maintained by a temperature controller. The solution was pumped through the Descal-A-Matic DC-3 and then back to the tank for 20h to make sure it was fully magnetized. After magnetized for 20 hours, the aragonite seed crystals were poured into the stirred tank. Then the crystal growth rate was evaluated by constant-composition method. The main subject of this research was to study the magnetic effects on aragonite crystal growth rate under different temperature, from 25οC to 40οC, and to compare the effect of magnetic field and temperature on aragonite crystal growth rate. Under the conditions of σara= 0.91, pH=9.0, I=0.018, R=5.54, without magnetic field, T=25οC, the aragonite growth rate approached to zero. When T was raised from 30οC to 40οC, the trend observed was that the growth rate of aragonite increased with an increasing in temperature level. This trend was the same as the result observed from conditions of σara= 0.91, pH=9.0, I=0.018, R=5.54, with magnetic field, T from 25οC to 40οC. The increase of temperature enhanced the aragonite growth rate both in the absence and presence of the magnetic field. When the temperature increased from 30οC to 40οC, the increasing percentage of aragonite growth rate was about 100.2% without magnetic field, greater than that obtained with magnetic field, 48.3%. The results showed that both magnetic field and high temperature environment increased the aragonite crystal growth rate. The magnetic field was more effective to aragonite crystal growth as compared with high temperature raising from 25οC to 40οC. Furthermore, the two effects were synergetic. On the other hand, the overall growth rate equation, G=Kgσn, was used to analyze the aragonite crystal growth kinetics. The overall reaction order of aragonite crystal growth, n, was found to be close to 1.4 in a stirred tank. Judging from Kg’s obtained in the kinetic analysis, the experimental condition under magnetic field at 40οC was most favorable to aragonite crystal growth; secondly, the experiment under magnetic at 25οC; the experiment without magnetic field at 40οC was not so advantageous as the former two.

參考文獻


林彥志,“溶液性質對碳酸鈣晶體成長之影響”,碩士學位論文,台大化工所(2005)。
Karpinski, P.H., J. Budz and M.A. Larson, “Influence of Cationic Admixtures on Kinetics of Crystal Growth from Aqueous Solution”, Industrial Crystallizaton, 84, Eds. S.J. Jancic and E.j. de Jong, 85-90, Elsevier, Amsterdam, Netherlands (1984)
Baker, J. S., and S. J. Judd, “Magnetic Amelioration of Scale Formation”, Water Research, 30, 247-260 (1996).
Berthoud, A., “Theorie de la Formation des Faces d’un Crystal”, J. Chem. Phys., 10, 624-635 (1912)
Busch, K. W., M. A. Busch, D. H. Parker, ”Studies of A Water Treatment Device That Uses Magnetiv Field”, National Association of corrosion Engineering, 42, 211-221, (1986)

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