臺灣博碩士論文加值系統

本實驗是在內徑0.108m、高5.76m、頂端接有1.5m高擴大管的流體化床中，以FCC
及數種粒徑的Sand為研究對象，利用不同軸向位置的壓力探針及熱傳探針，同時量測相對
或絕對壓力擾動及床-壁間熱傳隨氣體表面速度變化的情形。藉由各別壓力擾動平均振幅
的統計分析來決定床中粒子的流態轉移速度，以作為氣泡床轉移至紊流床的判斷指標，並
由此了解流態轉移對不同熱傳探針高度之床-壁間熱傳係數的影響。由壓力擾動的分析可
知，利用相對壓力擾動可以得到Uc及Uk；但是利用絕對壓力擾動只能得到Uc。而且，兩者
所得Uc或Uk皆隨粒子粒徑的增加而增大。更進一步，隨著相對壓力探針間距的增加，其結
果會和絕對壓力擾動所得漸趨一致。因此，絕對壓力擾動其實只是相對壓力擾動測量方式
的特例，並非文獻所提僅為相對壓力擾動測量方式下的特殊點，而是確實為紊流床的起點
。在轉變到紊流床的過程中，Geldart A類粒子在密相床床-壁間的熱傳係數，會隨氣體表
面速度的增加，由逐漸趨緩的走勢再度上升；Geldart B類粒子則由下降的走勢再度上升
；且兩者的稀相床床-壁間熱傳係數，皆隨氣體表面速度的增加而逐漸趨緩，甚至進入一
變動不大的區域。床-壁間熱傳係數雖然在Uc位置上未發生明顯的轉折，但卻在紊流床起
點Uk的位置出現，故吾人認為床-壁間熱傳會隨流態的轉變而改變。另外，熱傳探針在床
中軸向位置越高，其床-壁間熱傳係數會越小，而且對於Geldart A、B類粒子，在氣泡床
到紊流床的區間，床-壁間熱傳係數皆隨粒子粒徑的減小而增加。

Gas velocities at which transition occurred from bubbling to turbulent
fluidization were determined by the measurement of pressure fluctuations at va
rious axial positions in a 0.108m i.d., 5.76m high expanded-top fluidized bed
. By the method of statistical analysis, mean amplitude of
pressure fluctuations
were used to determine the transition velocity from bubbling to turbulent
flow regimes. On the other hand, the effects of different flow regimes on bed
wall heat transfer coefficients were also determined. The results showed tha
t Uc and Uk could be obtained by the method of relative pressure fluctuations,
but only Uc obtained by the method of absolute pressure fluctuations. Further
more, Uk would disappear when the distance between two pressure probes of rel
ative pressure fluctuations was far enough. So Uk was not the artifactby the m
ethod of relative pressure fluctuations, but really the onset point ofturbulen
t fluidization. For the heat transfer, the results showed that when the superf
icial gas velocity increased beyond Uk, the bed-wall heat transfercoefficient
would increase again for Geldart A or B particles in a dense-phase part of the
bed and would be gradually leveling-off for both kinds of particles in a lean
-phase part of the bed.