基于摄影法的上喷式喷头水滴粒径测量

Droplets size measurement of upward sprinkling nozzle based on photography

上喷式喷头喷洒的水滴粒径可达到毫米级别,且存在非球形的水滴,通常超出了基于光学衍射原理仪器的适用范围。为获取上喷式喷头水滴粒径数据,该文设计1种测试平台,基于摄影法,使用Canon EOS 7D Mark II相机进行照片采集,根据光学传播原理完成现实物体尺寸与照片像素之间的定标;应用Image Pro Plus软件进行照片处理,分析水滴粒径数据。对上喷式喷淋系统水滴粒径现场测试和数据分析,结果表明Canon EOS 7D Mark II相机能够对0.20 mm级别的物体进行准确成像,相对误差为4%;相机可以捕捉到运动的水滴并且清晰成像;Image Pro Plus软件可通过自适应灰度阈值和亚像素边缘检测算法分割脱焦的水滴成像,通过形态学参数的定量表征分割重叠、拖影的水滴成像;最终得到水滴粒径的概率密度数目分布和累计数目分布。该研究展现了基于摄影法进行上喷式喷头水滴粒径测量的新应用。

Sprinkling system plays an important role in many areas of industrial application, and the droplet size is the one of key parameter for analyzing sprinkling system. This study aimed to establish a method for droplet size measurement by upward sprinkling system. According to the industrial application, in the purpose of investigating upward sprinkling system, an experimental platform was created at the South China University of Technology in June of 2015. It consisted of water supply facilities, control valves, indicating instruments, sprinkling nozzle and camcorder devices. Based on the direct photography method, the DSLR camera Canon EOS 7D Mark II was used for photos collection, and the scaling between real sizes and image pixels was determined on the basis of optical propagation model. The image color histogram adjustment and regional segmentation were implemented by the Image Pro Plus software, and statistic data of droplets size were analyzed. What’s more, four basic dimension parameters including length, width, minimum radius, maximum radium and three dimensionless parameters including uniformity, roundness, and ellipticity were quantitated for the data filtration of out-of-focus droplets image based on the morphology. Results showed that a hair in diameter of 0.20 mm and a lead rod with diameter of 0.90 mm could be well identified respectively by the Canon EOS 7D Mark II from 3.5 m away, and the relative errors based on the present method were 4% and 0.6%, respectively. Moving droplets of upward sprinkling system could be imaged clearly. Based on morphological technique, four basic dimension parameters of length, width, minimum radius, and maximum radium were set as 3-20, 1-10, 5-40, and 3-15 pixel, respectively, and three dimensionless parameters of uniformity, roundness, and ellipticity were set as 0.1-0.2, 1-1.05, and 1-1.1, respectively. Then blurring and shadowy sports, which were invalid interference data, could be filtered by the Image Pro Plus software based on the adaptive gray level threshold and subpixel edge detection algorithm. To set parameters of grey range, brightness, contrast, gamma as 11-102, 80%, 200%, 0.9, respectively, comparisons between original photo and processed photo had been shown. Finally, the probability density of number distribution and the cumulative number distribution of droplets diameter had been given. The droplet diameters for cumulative number distribution corresponding to 10%, 50%, and 90% had been obtained as 1.309, 1.866, and 2.537 mm. Therefore, the present method is effective and convenient for the measurement of upward sprinkling nozzle droplets size, and can expand the scope of application on photography.