Analysis of Fractal-Like Spore Aggregates Using Direct Simulation Monte Carlo

The work presented in this paper is a continuation of the authors' previous efforts to develop a realistic bioengineering model for predicting the survivability of anthrax spores subjected to a high-temperature gas environment. One of the major mechanisms of deactivating spores is to expose them to elevated temperatures, and careful, exposure-tube experiments have been carried out to ascertain the deactivation mechanism. Spores typically exist in nature as aggregates, but simulating the heat transfer to clumps of spores is difficult because of the highly irregular geometry of spore clumps. In this work, the tunable particle-cluster and cluster-cluster algorithms are implemented to generate fractal-like spore aggregates. The algorithm output as a function of algorithm parameter input is compared with a typical spore-clump image. Because the spore aggregate size is small and is on the order of the mean free path even at atmospheric conditions, the direct simulation Monte Carlo method is used to model the heat transfer to each of the spores in the aggregate. The shielding effect of aggregate spores on a single spore in the clump is studied, revealing that, for aggregates on the order of 100, the shielding effect is about 25% similar to 45% compared with a single, isolated spore.