Generating Uniform Sub-micron Particles for Laser-based Flow Diagnostics

Abstract

New laser-based flow diagnostic techniques such as Particle Image Velocimetry are an attractive method for characterizing the velocity field of high-temperature jet flows. PIV required particle seeding and many current seeding techniques are not feasible within a high temperature flow. This research focuses on developing a system to generate uniform sub-micron solid particles and to seed them into a jet system with a high temperature air flow using a pH stabilized colloidal dispersion. The pH stabilized technique was first developed at NASA’s John Glenn Research Center by Dr. Mark Wernet. This research covers the design and development of a system to use the pH stabilized technique to produce sub micron particles for laser based flow diagnostics. Seeding is the key to producing accurate laser based diagnostics results. The seed size and material must be chosen to balance the ability to follow the flow, reflect measurable amounts of light, and exist within the testing application. For this research, 0.6 µm aluminum oxide was chosen as a balance of these three characteristics. The system to introduce these particles into the flow was produced based on its storage ability, flow and pressure control, and seeding capabilities. The system consists of an 8 gallon stainless steel pressure vessel, a Tescom pressure regulator, stainless steel tubing, needle and ball valves, and injector nozzles. The system produces seed for laser based flow diagnostics. Experiments were run at Jet Mach 0.9, 0.83, and 0.73 and compared to a baseline case at Mach 0.9 to see how well the seeder seeded the flow. The results show that the seeder produces aluminum oxide seed particles, and each test showed steady improvement in seeding the flow homogenously. However, this first generation seeder never seeded the flow as well as the baseline case. Recommendations for running heated jet experiments, adding air atomizing nozzles, using a solenoid control valve, and running multiple injection points are made to increase performance of the system.