Nano-Alumina Accommodation Coefficient Measurement Using Time-Resolved Laser-Induced Incandescence

It has recently been suggested that the accommodation coefficient of nano-aluminum/alumina particles may be significantly smaller than previously assumed. This result has significant implications on the heat transfer and performance of the nanoparticles in combustion environments. Currently, the accommodation coefficient has been deduced only after assuming a combustion model for the nano-aluminum particle and changing the accommodation coefficient to fit experimental temperature data. Direct measurement is needed in order to decouple the accommodation coefficient from the assumed combustion mechanism. Time-resolved laser-induced incandescence (TiRe-LII) measurements were performed to measure the accommodation coefficient of nano-alumina particles in various gaseous environments. The accommodation coefficient was found to be 0.03, 0.07, and 0.15 in helium, nitrogen, and argon, respectively, at 300K and 2 atm in each environment. These values represent upper limits for the accommodation coefficient as it is expected to decrease with increasing ambient temperature. The values are similar to what has been seen for other metallic nanoparticles and significantly smaller than values used in soot measurements. The results will allow for additional modeling of the accommodation coefficient extended to other environments and support previous measurements of high combustion temperatures during nano-aluminum combustion.