長氣泡擠壓流型與前端驅動流場之研究

Liquid Flow Patterns in Front of a Long Gas Bubble

陳柏壯(Po-Chuang Chen)

指導教授 ： 許政行

中原大學/工學院/機械工程研究所/博士(2006年)

https://doi.org/10.6840/cycu200500800

摘要

本研究主要在探討一長氣泡穩定推擠黏滯流體的擠壓流型與其前端驅動流場。本文先以實驗驗證經驗氣泡輪廓式的準確性，之後再將其導入數值方法中來計算流場。採用一已知的氣泡輪廓可以有效降低以往必須同時在流場與自由液面（氣泡輪廓）間作反覆疊代的複雜程序。
在數值解析方法上，本研究採用有限差分法以及連續過-鬆弛法來解析其前端驅動流場。藉由改變λ值（氣泡漸進寬度與管徑的比）所模擬出的流場結果可發現三種流場，分別為完全過渡流、迴流與轉換流，其中完全過渡流與迴流即為以往研究文獻所解析出的兩種典型流場。
本研究除了在兩種典型流場的結果上與先前文獻相符合外，更精確的以停滯點的移動形式作判別並發現在兩典型流場之間存在著轉換流場。本研究亦進一步考量雷諾數（慣性力）對於驅動流場的影響，發現到當雷諾數大於32時轉換流場將消失不見。此外並發現在高雷諾數(Re>200)時於氣泡後端靠近下游邊界附近會產生局部的封閉的渦度環線。

關鍵字

雙相流 ； 長氣泡 ； 經驗氣泡輪廓式 ； 慣性力

並列摘要

This study investigates the steady-state flow pattern in a circular tube filled with a viscous fluid expelled by a long gas bubble. The interface (bubble profile) between the gas and liquid is measured with experimental apparatus to identify the empirical deduced bubble profile. The empirical deduced bubble profile is employed to simplify the complex computation of the interface shape between the gas and the viscous fluid.
The study uses a finite difference method (FDM) with successive over-relaxation (SOR) in the computation of the viscous fluid flows. By varying the ratio of the bubble width to the diameter of the circular tube (λ), the numerical simulation shows three fluid flow patterns: the complete bypass flow, the recirculation flow and the transition flow. The first two flow patterns of the viscous fluid are in agreement with other researches.
The transition flow pattern found in the present study shows a clear transition from the complete bypass flow to the recirculation flow, as well as the migration of the stagnation point. The results also clearly present the effects of the inertia force, which is represented by the Reynolds number (Re), on both the flow patterns and the vorticity distribution on the bubble interface. The transition flow disappears in the condition of Reynolds number higher than 32. The closed-loop vorticity lines in the fluid flow at the rear part of the bubble with higher Reynolds number (i.e.,Re>200) are found in the present study.

並列關鍵字

Two-phase flow ； Empirical bubble profile ； Inertia forces ； Long gas bubble

參考文獻

1. Belblidia F., Pittman J.F.T., Polynkin A. and Sienz J., 2005, “Gas displacing viscous shear thinning liquids from tubes: Effects of cooling before gas injection,” Chem. Eng. Sci., Vol. 60, pp. 4953-4956.

2. Brannock, D. and Kubie, J., “Velocity of long bubbles in oscillating vertical pipes,” Int. J. Multiph. Flow, Vol. 22, 1996, pp. 1031-1034.

3. Bretherton, F.P., “The motion of long bubbles in tubes,” J. Fluid Mech., Vol. 10, 1961, pp. 166-188.

4. Cox, B.G., “On driving a viscous fluid out of a tube,” J. Fluid Mech., Vol. 14, 1962, pp. 81-96.

5. Cox, B.G., “An experimental investigation of the streamlines in viscous fluids expelled from a tube,” J. Fluid Mech., Vol. 20, 1964, pp. 193-200.