液相中气泡群粒径分布的检测与分析

Detection and analysis of bubble size distribution in liquid phase

采用图像分析技术对液相中气泡群的粒径分布进行了研究.首先使用高速摄像机拍摄得到简易反应器内气泡的图片,再通过Matlab平台对图像进行预处理后将其转换为二值图像来提取周长和面积,并依据圆度值对气泡进行分类,分离单个气泡和黏连气泡,以防止分水岭算法对单个气泡的过度分割.然后利用改进的分水岭算法对黏连气泡进行分割,获得黏连气泡的粒径分布,将单个气泡与黏连气泡的粒径分布汇总得到整个气泡群的粒径分布.最后,将由气泡群的粒径分布计算得到的气含率与实验测得的气含率进行比较,得到不同表观气速下的测量误差,在此基础上得到了各表观气速下气泡群粒径分布的概率密度图.结果表明,误差随着表观气速的增大而增大,表观气速在1.2~1.8cm·s-1之间时,误差在10%以内.

The purpose of this work is to measure bubble size distribution of bubbly flows in the column by using image analysis technology.Firstly,images of bubbles for a range of superficial gas velocities are obtained by using high speed camera with lighting emitting diode（LED）as a light source.Air and water are used as gas-liquid bubbly flows.Then,the images are preprocessed and converted into binary images by employing Matlab.Thus,perimeters and areas as factors of roundness are extracted to classify bubbles into overlapping and solitary bubbles.Solitary bubbles are separated to prevent the software segmenting them mistakenly.The size distribution of solitary bubbles is achieved by the use of formula.Then the overlapping bubbles are segmented into solitary bubbles by the use of an improved watershed algorithm.Finally,the size distribution of all bubbles at different gas velocities is analyzed and compared with the distribution without watershed.It shows that the size distribution with watershed is more accurate than the size distribution without watershed.The gas hold-up has also been calculated by the use of size distribution.In order to check the accuracy of the result,the calculated gas hold-up and actual gas hold-up have been compared and the measurement error between those two is expressed in the form of figure.The error grows with the increase of superficial gas velocity,less than 10% at 1.2~1.8cm·s-1.But the size distribution obtained by the image analysis technology cannot describe the actual gas hold-up when the superficial gas velocity is more than2.0cm·s-1.In spite of this,the size distribution detected can help us to learn more rules of bubble motion.For example,the growth trend of the bubble＇s interfacial area slows down with the increase of superficial gas velocity.And the resulting bubble size distribution with the superficial velocity between 1.2cm·s-1 and 2.0cm·s-1 is shown in the form of probability density function（PDF）.