Optimization of Microparticle Suspensions for Shock Accelerated Particle Studies

At Los Alamos National Laboratory’s Horizontal Shock Tube (HST) facility we are studying the acceleration of shocked isolated micron-scale liquid and solid droplets in a gas. Unsteady forces on microparticles driven by a shock wave are not well understood and difficult to model and therefore standard drag coefficients may not predict the motion of particles. Since drag coefficient is dependent on particle diameter, controlled seeding of flow field is required. This work details how we optimized our microparticle seeding systems and monitored resulting distributions for both liquid and solid particles. Controlling the polydispersity of the size distribution proved critical for minimizing random and systematic uncertainty of resultant drag measurements.  This was done for liquid droplets by carefully optimizing the spray injector and particle solution concentration, and for the solid particles by sifting. Additionally, for solid particles, moisture and electrostatic forces caused clumping which we are addressing by redesigning the particle circulation system using grounded stainless steel tubing. As a result, we saw substantial reductions in estimated drag, which can be attributed to reduction in uncertainty and spread of particle diameters used in drag coefficient analysis.