Characteristics of the Smith Turbine Impeller in an Aerated Stirred Vessel

本研究同時以實驗與模擬的方法來探討Smith盤式攪拌翼的特質並將結果與Rushton盤式攪拌翼相比較。吾人以CFD的模擬方法來估算攪拌翼周圍的氣體再循環速率、拖曳漩渦結構與相對應的氣體分散力並將結果與量測所得氣穴周圍不同位置的氣泡大小分佈結合來討論攪拌翼的氣體分散機制。最後吾人量測不同操作條件下Smith盤式覺拌翼與Rushton盤式攪拌翼功率消耗與質傳係數分佈以凸顯Smith盤式制拌翼的優點。由研究結果得知，無論實驗與模擬結果均顯示進入攪拌翼的氣體乃由氣穴尾端分散。針對Smith盤式制拌翼而言，覺拌翼葉片上下兩端的小漩渦有助於氣體分散。雖然Smith盤式制拌翼的功率消耗隨著通氣速率增大有些微下降的趨勢，但相對於Rushton盤式制拌翼而言較為平緩且在很小的通氣量時便達到定值。當通氣數NA＞０．０３，Rushton盤式制拌翼後的氣穴結構轉變為大氣穴；然此時Smith盤式攪拌翼的氣穴依舊屬於漩渦氣穴，顯示Smith盤式覺拌翼在高通氣量下具有較佳之氣體分散能力，因而有較佳的質傳表現。

關鍵字

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並列摘要

The characteristics f the Smith turbine impeller were studied both experimentally and numerically, and the results were compared to those of the Rushton turbine impeller. The gas recirculation rate around the impeller was examined and the structure of ventilated cavities behind blade as well as the values of forces related to gas dispersion was calculated through the CFD simulation. In addition, the sizes and distributions of dispersed bubbles were determined experimentally at various locations around ventilated cavities to examine the gas dispersion mechanism. Finally, the gassed power and local mass transfer coefficient for both impellers were measured and the results were related to the cavity structure. Both the results after the CFD simulation and bubble size measurements show that most of the total gas is dispersed at the cavity tail. For the Smith turbine impeller, the small-vortex pair attaching to the leading blade makes an additional contribution to gas dispersion. Although the gassed power drawn by the Smith turbine impeller decreases slightly with the increase in aeration rate, the trend is much flatter and tends to be leveling off at a much smaller aeration number as compare to the Rushton turbine impeller. As the aeration number NA ＞0.03, the cavity structure of the Rushton turbine impeller changes into the large cavity, while the vortex cavity still clings to the Smith turbine impeller. This fact indicates that the Smith turbine impeller has a better gas handling capability under a higher gassing condition and provides a better mass transfer performance.

並列關鍵字

Pressure Distribution ； Gas Dispersion Mechanism ； Trailing Vortex ； Bubble Size ； Stirred Vesse

國際替代計量

Characteristics of the Smith Turbine Impeller in an Aerated Stirred Vessel

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