Droplets size measurement of upward sprinkling nozzle based on photography

Abstract: 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.