Available at: https://digitalcommons.calpoly.edu/theses/2412
Date of Award
MS in Mechanical Engineering
College of Engineering
College of Engineering
All materials in dust form pose an increased risk of accidental deflagration, or explosion. For workplace safety, this risk of deflagration for a solid particulate sample is characterized through specialized dust explosibility testing systems. These systems disperse a cloud of powder inside a spherical chamber via a pressure gradient, where a timed ignition occurs. The accuracy of measurements taken during this process are predicated upon the assumption that the cloud of powder is uniformly distributed during the ignition period. Metal additive manufacturing (AM) is a rapidly expanding technology that, in some cases, involves heavy metal powders that do not disperse well in standard explosibility testing vessels. Consequently, there is a need to validate explosibility data for heavy metal powder blends to ensure that the dust sample is adequately dispersed in the chamber at the time of ignition.
This thesis provides a method for employing optical dust probes to determine the concentration of a tungsten metal AM powder cloud inside an enclosed vessel. Optical dust probes are devices that measure light transmission through an attenuating medium, in this case a cloud of powder, and utilize Bouguer-Beer-Lambert (BBL) law to determine the concentration of particles. This thesis summarizes and synthesizes the assumptions and limitations of BBL law when used with optical dust probes, drawing from multiple published works with varying applications. The bounds of the average extinction efficiency are discussed, especially with respect to when the extinction paradox can be applied. Ultimately, it is determined that the BBL law can only be applied in this study to determine extinction coefficients, and that calculating a specific mass concentration value is theoretically misguided without specific modifications to the experimental setup. The extinction coefficients measured via an optical dust probe and a separate image analysis method are compared. Although no correlation could be established due to the limitations of this experimental setup, specific modifications are suggested that would enable this methodology to be used in future applications.