臺灣博碩士論文加值系統

本實驗使用平均粒徑193 ，密度2635 kg/m 的砂為床體粒子，並藉由壓力擾動訊號的量測，探討砂在床高2.95 m和床徑5.2 cm的流體化床中，形成快速流體化的操作條件與判斷指標。並由不同探針位置所取得的壓力擾動訊號，利用自我相關係數的圖形及冪次頻譜的分析，分辨不同的流體化狀態。
在增大氣體流速下，由駐塞流體化進入紊流流體化的臨界氣體流速UC，可以壓力擾動訊號的標準差來決定。UC的大小，和床中砂量的多寡或壓力訊號量測的位置均無關。在固定固體流量，增加氣體流速下，由快速流體化進入非勻相稀相輸送之流態轉變，以當床中各段之壓力梯度約相等時之氣體流速UCA為指標。而繼續增大氣體流速，床中壓降呈現遞減趨勢，而流態由非勻相稀相輸送進入勻相稀相輸送，以當達最小壓力梯度之氣體流速Ump 作為非勻相稀相輸送和勻相稀相輸送之轉換速度。
以床中單點壓力擾動訊號經自我相關係數處理所獲得的圖形特徵顯示氣相輸送之週期性較快速流體化低，且相關度也較小，故可區分快速流體化與氣相輸送兩種不同的流體化狀態。由床中兩點間的壓差擾動訊號經冪次頻譜分析發現，床頂的壓差訊號經冪次頻譜圖類似像空床時所得之頻譜圖且不易判斷其主頻的位置，而和床底所得之頻譜圖中有一明顯主頻有所差異，故可區分出在快速流體化中之濃相、稀相之兩相分佈。

In this study, the operating criteria and hydrodynamic characteristics of circulating fluidized bed were investigated in a 2.95 m height 5.2 cm i.d. riser, by using pressure fluctuation signals. The solid particles used was sand with a mean particle size 193 . From the autocorrelation coefficient and power spectrum of pressure fluctuation signals, the flow regimes were classified.
It was found that for the transition from slugging to turbulent fluidization, standard deviation of pressure fluctuation signals indexed to pinpoint the transition velocity UC. The magnitude of UC was independent of the solid inventory in bed and pressure tap position. For the transition from fast fluidization to pneumatic transport, the transition point was determined by plotting pressure gradients measured both at the top and the bottom of the riser. As the gas velocity exceeded UCA, the pressure gradient for the top section was identical to that for the bottom section. This indicated that a transition from fast fluidization to heterogeneous dilute phase flow had occurred. As the gas velocity was increased to reach the minimum pressure gradient point, the transition between heterogeneous dilute phase flow and homogeneous dilute phase flow occurred at transition velocity Ump.
Because the autocorrelation coefficient of absolute pressure fluctuation signals in fast fluidization was bigger than that in pneumatic transport, from the autocorrelation coefficient of absolute pressure fluctuation signals, the regimes of fast fluidization and pneumatic transport were classified. At fast fluidization, the power spectrum of differential pressure fluctuation signals in the top region of dilute phase did not have well-defined determinant frequency, but there was well-defined determinant frequency in the bottom region of dense phase. So the region transition from dense phase to dilute phase was determined by the power spectrum of differential pressure fluctuation signals.

第一章 緒論 1
1-1.前言 1
1-2.循環式流體化床的應用及發展 3
1-3.研究目的 9
第二章 文獻回顧 10
2-1.由氣泡流體化轉變成紊流流體化之情況 10
2-2.由快速流體化床轉變成氣相輸送之情況 13
第三章 實驗裝置與步驟 28
3-1.實驗裝置 28
3-2.實驗步驟 34
3-2.1. L-valve的控制 34
3-2.2.循環流體化床之操作 35
3-2.3.由氣泡流體化進入紊流流體化的流態變遷 35
3-3.固體流量的量測與控制 36
3-4.實驗材料 39
3-5.數據分析 39
3-5.1.Fourier transform 40
3-5.2.自我相關函數（autocorrelation function） 40
第四章 結果與討論 42
4-1.由氣泡流體化轉變成紊流流體化之流態變遷 42
4-2.由快速流體化轉變成氣相輸送之流態變遷 46
4-2.1.流態轉變的操作與流態描述 46
4-2.2.壓力降落之軸向分佈 53
4-2.3.截面平均床空隙度之軸向分佈 56
4-2.4.壓力擾動訊號與固體分佈 58
A.單點壓力擾動訊號的分析 58
B.兩點間壓差擾動訊號的分析 65
第五章 結論 79
第六章 符號說明 82
第七章 參考文獻 84
附錄 LabVIEW數據截取程式 88

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