Measurement of Droplet Size and Velocity in the Mist Flow Using Digital Image Analysis
|關鍵字:||熱傳;薄霧流;液滴大小;Heat transfer;Mist flow;Droplet size|
Cooling by mist flow can achieve higher heat transfer rate than cooling by forced convection of single phase flow. The mist flow is produced by mixing the dispersed water droplets with air stream. The heat transfer is affected by the water droplet size and the mist flow velocity. In this investigation, digital image analysis method was used to obtain the droplet size and velocity. The droplet size and velocity were determined by pixel counting and particle tracking method, respectively. Droplets were illuminated with laser light and images were captured by the camera with microscope lens. Noise reduction and image sharpening were applied before image segmentation. The digital images were segmented using thresholding method, and the threshold algorithm used in this study included mean value method, mode method, iterative method, and Otsu method. The channel used in the investigation had the cross-section of 40mm×40mm and the heated length was 240mm. The images were taken at two observation points at the entrance and exit of heated region. Droplet sizes ranging from 30µm to 80µm were produced by adjusting the water and air flow rate. Larger droplets can be generated by combining higher water flow rate and lower air rate. Measurement of droplet size and velocity in the mist flow can be used to analysis the mist cooling performance.