EFFECTS OF FLUID PROPERTIES ON THE CHARACTERISTICS OF IMPINGING-JET SPRAYS

This study is to investigate the effects of the physical properties (especially for viscosity and surface tension) of the working fluid on the atomization characteristics of a like-doublet impinging-jet spray. The injector orifices are constructed with a diameter of 0.5 mm and a length-to-diameter ratio of 10. The velocity of the jets in this experiment is as high as 50 m/s. Impingement angles of 60°, 90°, and 120° have been tested and the results of 90° are presented. Results show that the spray formed after jet impingement can be categorized into three major modes, i.e., closed rim, open rim, and fully developed. As many as 10 spray patterns for a like-doublet impinging-jet spray are observed in this work by changing the viscosity and surface tension of the working fluid, instead of only 4 patterns defined by Heidmann, Priem, and Humphrey (NACA TN 3835, March, 1957). An unforgettable pattern of "incredible periodical" can be formed only in fluid 2 condition in the closed-rim mode. The length-to-width ratio of the liquid film formed in the closed-rim mode remains nearly constant for each of the test fluids, which is the same trend as predicted by the theoretical approach (E. A. Ibrahim and A.J. Przekwas, Impinging Jets Atomization, Phys. Fluids A, vol. 3, pp. 2981−2987, 1991), although the ratio is underestimated. This ratio increases with increasing viscosity of the working fluid from 2.2 of fluid 1 to 2.9 of fluid 5. However, variation in surface tension has negligible effects. The viscosity effect is more significant than that of the surface tension. Slight changes in physical properties will scarcely affect the geometric shape of the film. The mean drop size approaches an asymptotic value of about 45 μm when jet velocity is higher than 30 m/s. These trends are all the same, regardless of the viscosity and surface tension of the working fluid.