Hydrodynamical analysis of nanometric aluminum/teflon deflagrations

The hydrodynamics of deflagrations from reactive materials (RM) submerged underwater can be studied using a modified aquarium test. Normally loose powder RM will disperse after being submerged in water. Introducing hydrophobic materials such as Teflon into the reactant matrix, enables a barrier against permeation of water into the reactants. Also, ignition via resistance heating can be difficult underwater because significant energy is lost by convection off the wire into the water. Nano-Al particles require significantly less energy for ignition than their micron scale counterparts such that underwater ignition via resistance heating can be achieved. The objective of this study is to examine the reaction hydrodynamics from a submerged nano Al-Teflon mixture as a function of mixture composition and bulk density.

Submerged Aluminum/Teflon mixtures were ignited and the ensuing reaction was recorded with a high speed camera and a pressure transducer. The resulting bubble shape, size, and pressure histories along with the burn time and rate allow the analysis and comparison of different fuel/oxidizer compositions and powder packing densities. Results show that as the density of the powder decreases the reaction transitions from a slow jet of multiple bubbles to quick single bubble. One observation is that as the percentage of aluminum increases the bubble radius also increases even though there is less of the gas producing Teflon in the mixture. This could imply that the excess aluminum is reacting with water.