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Investigation of the effect of geometrical parameters of pressure swirl atomizer on the hollow cone spray

Tokgöz, Tolga
In this study, effects of geometrical parameters of pressure swirl atomizer on the hollow cone spray are investigated experimentally, and physical phenomenon inside the pressure swirl atomizer is investigated numerically. In the experimental studies, hollow cone spray properties are examined macroscopically and microscopically. Macroscopic spray properties are studied by a visual technique called high-speed shadowgraphy. The hollow cone spray images are captured for different geometrical configurations of the pressure swirl atomizer at different flow rates. Then, the mean spray cone angles are obtained using the image processing program and breakup lengths are measured using obtained images. Microscopic properties of spray are researched by Phase Doppler Particle Analyzer system. Microscopic properties of spray such as droplet diameters and velocity distributions are obtained for different geometrical configurations of the pressure swirl atomizer and different flow rates. Within the scope of numerical studies, two-dimensional axisymmetric swirl flow simulations are carried out to examine the internal flow and spray of the pressure swirl atomizer. In these simulations, a computational fluid dynamics tool based on volume of fluid is used. In consequence of experimental studies, it is obtained that spray cone angle is not much sensitive to the mass flow rate, nozzle length, and tangential port number. However, nozzle diameter has a remarkable impact on the spray cone angle. Increase in nozzle diameter leads to an increase in the spray cone angle. Decreasing nozzle diameter and increasing mass flow rate result in a shortening of the breakup length. On the other hand, nozzle length and tangential port number have minor effect on the breakup length. Microscopically, x-velocity and y-velocity of the droplets are dependent on the mass flow rate and nozzle diameter, and magnitudes of velocities increase with increasing mass flow rate and decreasing nozzle diameter. On the contrary, nozzle length and tangential port number has a negligible effect on the magnitudes of velocities. Sauter mean diameter of the hollow cone spray increases with increasing nozzle diameter and decreasing mass flow rate, but nozzle length has no significant effect on it. However, increasing tangential port number increases the uniformity of the particle and Sauter mean diameter distribution. As a result of numerical studies, complex two-phase flow and velocity distributions in the pressure swirl atomizer are studied. Numerical results show that spray cone angle and air core diameter remain nearly the same with increasing mass flow rate. On the contrary, increasing mass flow rate causes an increase in axial and swirl velocities.