多尺度气泡尺寸分布数字图像测量方法研究

鼓泡塔是一种广泛应用于能源和环境领域的多相流反应器,鼓泡塔中气泡的大小和浓度对于研究鼓泡塔中"三传一反"过程具有重要意义。采用高速摄像法和数字图像处理技术开展了鼓泡塔中内多尺度气泡尺寸分布测量研究,针对气泡识别过程中密集气泡易发生重叠的问题,提出基于曲率计算的凹点匹配与圆周拟合的重叠气泡分割与轮廓重构算法。搭建了鼓泡塔反应器实验装置,针对星型、均匀和方形3种不同进气孔形态的气泡分布器开展了实验研究,分析了不同尺度气泡的尺寸分布规律。试验结果表明:该算法不仅能够有效地从图像中提取轮廓清晰完整的气泡,而且能够对图像粘连重叠的气泡进行准确分割,从而可精确地获得多尺度气泡尺寸分布。随着气体流量的增加,小气泡的数量急剧增加,同时产生更大的气泡;气泡的最大直径和Sauter平均直径均随气体流量的增加而增大,且两者的比值基本保持不变,即分布器形式对气泡尺寸分布均匀性有影响,方形分布器产生气泡最均匀,气含率相对其他两种分布器更高。实验结果证明了图像分割与轮廓重构方法在气液两相流中气泡参数在线测量的可行性。

Multi scale bubble size distribution measurement by digital imaging technique

The bubble column is a multiphase flow reactor, which has been widely used in energy and environmental field. The size and concentration of bubbles are of great significance for studying the heat and mass transfer process in the bubble column. A digital image processing technique is proposed to measure the bubble size distribution in the bubble column. However, the dense bubbles are easy to overlap during the bubble recognition process. To solve this problem, the overlapping bubble matching and the circumferential fitting based on the curvature calculation are presented. The segmentation and contour reconstruction algorithm are further used to determine the size distribution of bubbles. Experiments are implemented in a bubble column. Experimental results show that the proposed algorithm can not only extract the clear and complete bubbles from the image, but also accurately segment the overlapping bubbles of the image. The multi scale bubble size distribution can be accurately obtained accordingly. As the gas flow rate increasing, the number of small bubbles increases sharply. At the same time, larger bubbles are also generated. The maximum diameter of the bubble and the average diameter of Sauter increase with the increase of the gas flow rate. But, their ratio remains basically the same. The configuration of the distributor has an influence on the uniformity of the bubble size distribution. The square distributor produces the most uniform bubble, and the gas holdup is higher than those of the other two types of distributors. These results verify the feasibility of the image segmentation and contour reconstruction method for the measurement of bubble parameters in gas liquid two phase flow.