Effect of Magnetic Field on Growth Rate of Aragonite in a Stirred Tank
Date Issued
2007
Date
2007
Author(s)
Yeh, Shih-Wei
DOI
zh-TW
Abstract
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.
Subjects
碳酸鈣
磁場
溫度
結垢
calcium carbonate
magnetic field
temperature
aragonite
scale formation
Type
thesis
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