An Experimental Study of Discharge Coefficient with Non-Circular Effervescent Type Twin-fluid Nozzle

An experimental study was carried out to investigate the injection characteristics of non-circular effervescent type twin-fluid nozzles. For this purpose, two types of non-circular nozzles (E1, E2) and one kind of circular nozzle (C) were used. Two types of nozzles were machined with similar area of exit orifice. Three types of aerorators with hole diameters of 1.2, 1.7 and 2.1 mm were used. Each aerorator has a total of 12 holes. It is expressed as Area ratio which is ratio of exit orifice area and aerorator hole area. At this time, the aerorator mounted on the nozzle used three different diameters to match the aspect ratio with the nozzle exit area. Therefore, experiments were performed according to three aspect ratios for each nozzle, and total experiments were conducted. Experiments were carried out by controlling the amount of air flowing after fixing the flow rate of the liquid, and then the nozzle internal pressure and the droplet size (SMD) were measured. The jet image was taken from the nozzles. The discharge coefficients of the three kinds of nozzles were compared with the conventional equation and the Jedelsky’s equation, and the Jedelsky’s equation was found to be about 4 times larger. In addition, empirical formula based on ALR, which is the largest variable in Jedelsky’s equation, was derived, and it was confirmed that the coefficient is almost the same regardless of the exit orifice type. SMD injected from the nozzle was confirmed to be smaller in the non-circular shape than in the circular shape, which is expected to be caused by the difference of the discharge coefficient values.