气液两相流中上升气泡体积的计算方法

通过高速摄像机拍摄气液两相流中上升气泡的运动过程,分别记录不同直径的气孔所产生的单个气泡上升过程的连续图像,结合数字图像处理技术,提取了气泡的面积、当量直径、几何中心、速度、加速度等特征参数.并在此基础上,应用两种计算气泡体积的方法:几何方法和受力分析法,实现了气泡体积的初步计算.几何方法计算气泡体积是根据图像中气泡的形状构造一个与气泡体积相当的椭球体,进而计算椭球体的体积;而受力分析的方法则是通过分析气泡在垂直方向上的受力情况,根据牛顿第二定律推导出气泡体积的计算公式.并对两种方法计算出的气泡体积值进行分析对比,阐明了这两种方法适用情况,计算出单个气泡上升情况下的气相体积含气率.

Calculation method for bubble volume in gas-liquid two-phase flow

A suit of visualized experimental device was designed. Single bubble rising in stagnant liquid in a translucent rectangular tank was studied using a high-speed video system. Bubbles generated by four orifices with different diameter (1 mm, 2 mm, 3 mm, 4 mm) were recorded respectively. Sequences of the recorded high-speed images were processed by digital image processing method. Several parameters of bubble could be obtained from the processed image, such as bubble area, equivalent diameter, geometric center, bubble velocity, bubble acceleration, and so on. Two methods for bubble volume calculation were applied. The first method is geometric method, in which the bubble volume is calculated by reconstructing an ellipsoid based on the shape of bubble in an image. Another one is force analysis method, in which the bubble volume is calculated by analyzing the forces exerted on the bubble in vertical direction, and then the formula of the bubble volume could be derived from Newton's second law. Calculation results of the two methods are analyzed and compared to illuminate the situations they adapt to. Finally, the gas volume fraction of a single bubble in its rising condition in water is calculated.