Bubble Size Reduction in a Fluidized Bed by Electric Fields
Bubble Size Reduction in a Fluidized Bed by Electric Fields
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DOI：
10.2202/1542-6580.1059
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发表时间：
2003-07
影响因子：
1.6
通讯作者：
F. K. V. Willigen;J. van Turnhout;J. V. Ommen;C. M. Bleek
中科院分区：
文献类型：
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作者：
F. K. V. Willigen;J. van Turnhout;J. V. Ommen;C. M. Bleek
在气固流化床中，减小气泡尺寸可以提高选择性和转化率。结果报告的减少气泡尺寸的应用电场不带电，极化颗粒在流化床中。它示出了如何平均气泡直径可以大大减少，床层膨胀的变化很小。文献综述表明，为了保持平稳的流化，在气流方向上的电场，具有相对低的交变频率，是最佳的。为了测量平均气泡直径，使用压力脉动时间序列的谱分解技术。使用这种基于非侵入式测量的方法，可以找到气泡直径的特征长度尺度。使用视频分析的实验表明，对于给定的床料和床尺寸，该长度尺度具有恒定的比例关系。长度尺度与气泡直径的比例与测量高度或气体速度无关。有了这个，我们就有了一个测量二维和三维流化床中气泡直径的工具。电场施加到流化床使用细线电极放置在列内。2-D和3-D柱都在一定范围的频率和场强下进行了测试。对于Geldart A玻璃珠，确定了5-20 Hz和400-1600 V/cm场的最佳范围。气泡直径的减小被测量为对于该系统高达25%。较大的Geldart B玻璃颗粒显示气泡直径的较大减小-高达85%。对于这些颗粒，最佳频率是在更高的范围内，20-70 Hz。在较高的频率（高达100 Hz）下，气泡尺寸减小较少，但仍然很大。在3-D柱中使用GeldartA颗粒的实验显示出类似的气泡直径减小。
The reduction of the size of bubbles can improve both selectivity and conversion in gas-solid fluidized beds. Results are reported of the reduction of bubble size by the application of electric fields to uncharged, polarizable particles in fluidized beds. It is shown how average bubble diameters can be drastically reduced, with little change of the bed expansion. A literature review shows that to maintain smooth fluidization, electric fields in the direction of the gas flow, with a relatively low alternating frequency, are optimal. To measure average bubble diameters, a spectral decomposition technique of pressure fluctuation time series is used. Using this method, based on non-intrusive measurements, a characteristic length scale for bubble diameters can be found. It is shown experimentally, using video analysis, that this length scale is of constant proportionality for a given bed material and bed dimensions. The proportionality of the length scale to bubble diameter is independent of measuring height or gas velocity. With this, we have a tool for measuring bubble diameters in both 2-D and 3-D fluidized beds. Electric fields were applied to fluidized beds using thin wire electrodes placed inside the column. Both 2-D and 3-D columns were tested over a range of frequencies and field strengths. For Geldart A glass beads, an optimal range was determined at 5-20 Hz and 400-1600 V/cm fields. The reduction of bubble diameter was measured to be up to 25% for this system. Larger Geldart B glass particles show a larger reduction of bubble diameters - up to 85%. For these particles, the optimal frequency was at a higher range, 20-70 Hz. At higher frequencies (up to 100 Hz), bubble size reduction is less, but still substantial. Experiments in the 3-D column using Geldart A particles show a similar reduction in bubble diameters.