Numerical Simulation and Experimental Study for the Impact of In-Flow Nozzle on Spray Characteristics.

Abstract

The impact of the in-flow characteristics inside the injection nozzle on atomization has been experimentally and computationally studied. Measurements are carried out using a transparent glass nozzle. Pulsed laser sheet with a synchronized charge-coupled device (CCD) camera and image processing, together with a particle image velocimetry (PIV) setup have been used as measuring techniques. Images and relevant image processing are used to visualize and quantify the rate of generation of cavitation bubbles inside the nozzle, the spray particle size distribution, and cone angle. Velocities inside and outside the injection nozzle are measured using PIV. The experimental investigation has been extended to include a wider range of the injection nozzle geometrical aspect ratios and working parameters. The computational model is a three-dimensional, two-phase, turbulent model to solve both the in- and out-nozzle flows. A novel coupling mathematical model is proposed for the definition of the probability density function of the issuing droplet size distribution, based on the in-flow developed conditions. A good agreement between both the experimental and computational results has been found under all conditions. According to both the experimental and computational results, it has been found that the onset of cavitation inside the injection nozzle, its location, collapse, and consequently the issuing spray configurations depend on the flow cavitation number, the nozzle geometrical characteristics, the liquid temperature, and the injection and back pressures. According to the quality of the obtained results from the model, it can be used to extend the study to cover a wider range of spray applications.