Determination of Settling Velocity of Airborne Metal Debris
WILLIAM CASPINO, Enrica Viparelli, Shamia Hoque, University of South Carolina
Abstract Number: 302
Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts
Abstract
Transport and deposition of debris are sources of environmental and public health concern. Controlled laboratory experiments and modeling are in progress to determine how deposition velocity distribution varies with particle type. Results will aid in field tests on contamination by metal debris generated from a radioactive fallout. The tests will be conducted in a rural environment by releasing the particles at a specific height under varying atmospheric conditions. This study performs laboratory experiments in a controlled environment consisting of a 1.2 m tall, scaled test chamber with a 0.5 m squared base within which particles are released under stagnant conditions. Electron microscopy images of the particles revealed that the particles are not spherical, and the size range is between 400 and 1000 μm. Transport through the column was tracked utilizing a Phantom v7.3 camera. Particles were categorized into three size bins with deposition velocity ranging from 1.71 m/s to 2.67 m/s depending on particle diameter. Size bin one contained particles with diameters finer than 500 μm, size bin two contained particles with diameters ranging from 500 μm to 800 μm, and size bin three contained particles with diameters larger than 800 μm. For size bin one, velocity estimates of five particles ranged from 1.71 m/s to 2.09 m/s. For the second size bin, the velocity measurements of six particles varied between 2.28 m/s to 2.38 m/s. For the third bin, nine velocities were measured with values between 2.47 m/s and 2.67 m/s, confirming that particle velocity increased with size. Preliminary results further indicated that steady-state conditions might have been achieved for the finest particles. Finally, Reynolds number estimates, as well as the irregular particle shape, suggest that Stokes’ law assumptions cannot be applied to determine the deposition velocities of these particles.