Simultaneous Planar Droplet Size and Droplet and Gas Velocity Measurements in a Confined Spray

Abstract

A new appro ach for simultaneous planar measurement of droplet velocity and size with gas phase velocities is used based on a combination of the out -of -focus imaging technique ‘Interferometric Laser Imaging Droplet Sizing’ (ILIDS) for planar simultaneous droplet size and velocity measurements with the in -focus technique ‘Particle Image Velocimetry’ (PIV) for gas velocity measurements in the vicinity of individual droplets. The measurements are presented in a model co -flowing (0.017 m/s) unheated spray dryer (0.5 m diam eter, � 2 m high) with a single air -assist solid cone atomizer with a characteristic droplet diameter (SMD) of the order of 150 –200µm at liquid feed rates of the order of 1.4 -1.6 �10 -3 kg/s and air feed rate of the order of 0.12 �10 -3 kg/s. The particular me asurement location was 500 mm downstream and at a 120 mm off -axial location in the spray, the size of the viewing area being 8 mm × 12 mm. The experimental method, the image processing algorithm and the method of calculation of spatially averaged correlati on are briefly described. The main results include plo ts of mean droplet velocity based on three different representative size classes, with Stokes numbers much less than unity, the mean gas velocity, instantaneous droplet and gas velocities and the spatia lly averaged correlations. For both the droplets and gas, the mean velocities were found to be of the similar magnitude, � 0.2 m/s, with similar , though not identical, in direction . The one -time spatial correlation coefficient between the axial component o f droplet and gas velocities was found to be about 0.6 while that of the other correlations calculated from combinations of other velocity components between the droplet and gaseous phases was close to zero, as expected in this region of the flow.