The development of a facility and diagnostics for studying shock-induced behavior in micron-sized aerosols
Aerosols, by definition, are composed of small particles that occupy minute fractions of the total volume in which they reside. Despite this, the effects they have on the system behavior can be far-reaching because of the momentum, heat, and mass transfer between the condensed and gas phases. Shock-wave interactions with two-phase mixtures have been studied for over fifty years. This has resulted in a significant body of theoretical and experimental work. Our literature review revealed that there has been no work focused on creating spatially-uniform aerosols that have been well-characterized with regard to the particle size distribution. We made filling this gap our primary objective.
To this end, we developed a suite of tools for studying aerosols behind shock waves. The first of these is a specially-designed aerosol shock tube. The tube has a square cross-section and incorporates large flush-mounted windows that provide viewing access from three sides of the tube. Second, we developed a wavelength-multiplexed Mie extinction particle sizing diagnostic. Five wavelengths ranging between 0.754 and 2.05 μm were used determine the particle size distribution before the shock arrival and to measure the effects on the aerosol after it passed by. Third, we developed a one-dimensional computational model of shock wave interactions with aerosols. This model incorporates non-continuum heat and mass transfer mechanisms since the Knudsen numbers of the micron-sized particles are significant.
After characterizing the facility and finding conditions where the aerosol non-uniformity is less than 6% RMS, we captured lightsheet images of shock waves propagating through aerosols and measured the behavior of water aerosols behind shock waves with temperatures between 450-600 K and pressures between 0.65-1.1 atm. We determined evaporation rates with this data and found a correlation that provides the non-continuum evaporation rate in terms of the d 2 (continuum) evaporation rate and a correction function. These experiments demonstrate only one potential application of the facility; chemical kinetics of low vapor pressure fuels, fundamental physics of large Knudsen number flows, and materials science problems, among others, are well-suited for future study.