In-situ characterization of droplets during free fall in the drop tube-impulse system

Powders of copper were produced using a drop tube-impulse atomization technique. In this system, molten metal is pushed through orifices, forming ligaments, which eventually break down and spherodize into droplets. A 3-D translation stage was designed, constructed and installed in the drop tube to allow for measurements of velocity and droplet size in flight using a Shadowgraph and radiant energy using DPV-2000. A mathematical model of the evolution of droplet velocity and temperature for different sized copper droplets at various heights was developed. The experimental results from the Shadowgraph and the DPV-2000 are compared to the model's results. In addition, the extent to which microgravity prevails during flight and droplet solidification was investigated by using the model and the Shadowgraph results. It was found that the acceleration of falling droplets near the melting point is close to gravitational acceleration and as a result the falling droplets do not reach their terminal velocity at their melting point. The results of in-situ measurements during the atomization of copper showed that the larger droplets have higher radiant energy than that of the smaller ones. Correlation between experimentally measured radiant energy and predicted temperature of falling droplets will be investigated. The current work is part of the NEQUISOL project supported by ESA within contract number 15236/02/NL/SH and CSA within contract number 9F007-08-0154 and SSEP Grant 2008.