Session BB1.5

10:30 AM BB1.5
IN-FLIGHT PARTICLE MEASUREMENTS WITHIN A TWIN-WIRE ELECTRIC ARC SPRAY PLUME. Donna L. Hale, David W. Swank, D.C. Haggard, Lockheed Martin Idaho Technologies Company, Idaho Falls, ID.

A real-time, nonintrusive measurement technique was successfully applied to a Tafa Inc. Model 9000 twin-wire electric arc thermal spray system to simultaneously measure particle size, velocity, and temperature within the spray plume. The purpose of these experiments was to gain an understanding of the physics of the particle-laden spray flowfield produced by a twin-wire electric arc spray (TWEA) system. Aluminum wire was sprayed with parametric variations of current from 100 to 300 amps and gun pressure (air flowrate) from 40 to 75 psia. For all cases, the average diameter of the molten aluminum particles range from 26 to 52 mm, with the largest particles concentrated at the center of the spray. As the molten metal is stripped from the wires and transported downstream, the droplets initially breakup and the smallest particles are flung to the edges of the spray. As expected, the largest velocities and temperatures are found at the center of spray due to entrainment from the quiescent, room temperature air. The particles accelerate to peak velocities between 130 and 190 m/s, then decelerate slightly as they travel downstream. The particles exhibit high superheat, with average centerline particle temperatures ranging from 2004 to 2056 oC , and the temperature profile remains fairly flat throughout transport to the substrate. A stagnation pressure probe was used to characterize the gas flow regime and shock structure in the plume without particles. The wires were found to have a pronounced effect on the flow, resulting in a complex three-dimensional flowfield with mixed regions of subsonic and supersonic flow.