| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2005: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
The micro-bubble generator which consisted of a liquid pump and a special line mixer, was installed at the bottom of the bubble column made from transparent acrylic resin. The inside diameter was 0.10 m and the height was changed in the range of 1.00 - 4.00 m. A heat exchanger was equipped at the liquid pipe to keep the liquid temperature constant. The mass transfer characteristics were measured at the system of air and water, and the decomposition performance was examined by using gas including ozone and di-methyl sulfonic acid (DMSO) aqueous solution. The gas velocity was changed, and the bubble behavior was observed by using the high-speed video system combined with a hard mirror and a strong light source. By a treatment of the photos with a graphic analyzing soft, the distribution and average value of bubble diameter were obtained. The volumetric mass transfer coefficient was estimated from the change in dissolved oxygen with time, and the decomposition rate constant was calculated
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from the change in DMSO concentration with time. For the comparison, also the sintered glass gas sparger, which produced milli-bubbles, was used.
When milli-bubbles were sparged in the bubble column dispersed with micro-bubbles, micro-bubbles were observed to be absorbed into the wake of milli-bubbles. As a result, the amount of micro-bubbles became smaller at the higher position of the column. The average diameter of micro-bubbles from the present micro-bubble generator was 30-40 μm. At the higher gas velocity, also bubbles with several hundreds μm in diameter were generated. At the same gas velocity, the volumetric mass transfer coefficient for micro-bubbles was much higher than that for milli-bubbles. However, the mass transfer coefficient, which was estimated from the average diameter of bubble, for the former was about 1/10 times of that for the latter. From these results, it was concluded that the specific interfacial area largely contributed to the enhancement in mass transfer.
In the DMSO decomposition, no striping was found. The decomposition rate constant was much higher for micro-bubbles than for milli-bubbles, and it depended strongly on the volumetric coefficient. It was recognized that micro-bubbles were effective for the enhancement in decomposition performance when the mass transfer was a controlling step. This is considered because of special properties of micro-bubbles. Less
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