Modeling laser ignition and heat propagation in nanocomposite thermites

Nanocomposite energetic materials are a mixture of nano-scale fuel and oxidizer particles. When these compositions are ignited, reactions are highly exothermic and can exhibit widely tunable energy release rates. These materials show great potential as igniters, propellants and for energy generation applications. However an understanding of the ignition and thermal propagation of these materials has not been fully developed. The objective of this study is to model the heat transfer in a composite energetic material and identify the influence of particle size on the ignition energy, time and temperature. A two-dimensional, transient numerical model is described for the radiant heating and subsequent combustion. The numerical model is based on finite difference nodal equations and is calculated in terms of thermal resistances and capacitances. Boundary conditions are predetermined, including a laser energy source applied to a single surface. Interstitial heat generation is based on laser absorption and chemical kinetics. The effect of particle size on the transient heating and energy release rate has also been considered. The model uses a 250 W CO₂ laser to ignite a Magnesium/ Sodium-Nitrate pyrotechnic sample. Results also show the 2-D nature of heat propagation that results from the Gaussian energy distribution from the laser beam.