Experimental Study of Collision of Liquid Al2O3/Al Droplets

An experimental investigation is conducted to determine the collision of Al2O3/Al droplets for an aluminized composite propellant using an innovative apparatus at various impact velocities. Droplets before and after collision are collected by means of quench-bomb technique. The morphology, composition, and size of the collected particles are analyzed with the aid of a scanning electron microscope, an X-ray powder diffraction, and a Malvern Mastersizer 2000. It is found that collected particles of various sizes are all spherical with diameters from 0.03 to 200 mu m. Collected particles mainly contain Al2O3 and Al. In addition, collision/coalescence of smaller droplets with larger droplets occurs dominantly in the converging nozzle. For the relative velocities of collision ranging from 3.8 to 81.9 m/s, the mean particle diameters d(43) and d(50) decrease after collision. The higher the relative velocity of the collision is and the larger the droplet diameter is before collision, the fiercer the fragmentation will be. Furthermore, collision causes fragmentation of droplets with diameter larger than 10 mu m as well as a significant reduction in volume fraction. Collision causes little volume fraction changes for droplets with diameter of 2 similar to 10 mu m but results in large volume fraction increases for droplets with diameter smaller than 2 mu m.