Experimental Measurements and Numerical Simulation of the Hydrodynamics in an Airlift Reactor: Dispersed Bubbling Regime

本研究使用質點影像追跡儀(PIA)之量測與計算流體動力學模式之數值模擬來探討二維(32×100×1.2 cm)氣舉式反應器內分散氣泡區之流場。由量測結果發現在分散氣泡區下其瞬時與平均流場有以下共同特徵：(1)有一總體循環流動，此循環包含riser內向上之水流與downcomer內向下之水流；(2)兩對漩渦，分別在riser底部內側與在downcomer內draft tube之頂部邊上。而在riser內氣泡鏈上之氣泡大小相當均勻，以近似直線方式上升，且於氣泡鏈間產生小尺度之漩渦。由於氣泡尾流之拖曳與總體循環致使其平均垂直速度大於平均水平速度。又因兩對漩渦之擾動，使得底部與頂部有較大之平均正向剪應力。此研究使用CFX4.4套裝軟體配合尤拉－尤拉兩相流模式做為數值模擬工具，除了液體速度分佈有些微之差異外，其模擬與量測結果顯示相當吻合。

關鍵字

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並列摘要

The hydrodynamics of a two-dimensional airlift reactor (32×100×1.2cm) in the dispersed bubbling regime is investigated through experimental measurement using particle image analyzer (PIA) and numerical simulation using computational fluid dynamics model. The instantaneous and the averaged hydrodynamics in the dispersed bubbling regime have a similar flow structure: (1) a global circulation flow with an upstream in the riser and a downstream in the downcomer, (2)two pairs of vortices, one at the bottom sidewall of the riser and the other at the upper edge of the draft tube in the downcomer. The bubble streams rise roughly rectilinear with relatively uniform bubble size along the column and generate small-scale vorticities in between bubble streams. The bubble wake drifting and the circulation cause the averaged vertical velocity is relatively large than the averaged horizontal velocity for all locations. Due to the fluctuation of the vortices, the averaged normal stresses at bottom and upper locations are higher than those at middle location. A numerical simulation with the Eulerian-Eulerian two-phase model has been carried out using a commercial code, CFX4.4. A satisfactory agreement between the simulated and the measured results has been accomplished, although few slight discrepancies might have been found in the liquid velocity distribution.

並列關鍵字

Airlift reactor ； Computational fluid dynamics ； Particle image analyzer ； Hydrodynamics

國際替代計量

Experimental Measurements and Numerical Simulation of the Hydrodynamics in an Airlift Reactor: Dispersed Bubbling Regime

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