Modeling the Effect of Buoyancy and External Heating on the Flame Spread in Fire Resistant Fabrics
Alonso Ipiña, Alain
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Spacesuits are fabricated with Nomex, Kevlar and other fire resistant fabrics. The flammability behavior of these materials has been widely studied experimentally, mostly under standard sea level atmospheric conditions. However, future human space exploration vehicles and habitat environments will very likely have different environments, i.e. reduced pressure and enriched oxygen concentration. Experiments under these conditions, particularly in microgravity, can become a difficult and expensive task. Numerical investigations of the flammability of high performing fibers/fabrics may be a viable alternative to experiments. Here we present a numerical model formulated to understand the effect of environmental conditions on the flame propagation characteristics of thin fire-resistant material such as Nomex. Moreover, the effect of external radiant heating on material flammability is also studied. Thermogravimetric analysis (TGA) experiments were performed with Nomex to estimate the kinetic parameters, which were then used to model the thermal decomposition of the fabric sample using a Computational Fluid Dynamics (CFD) code, Fire Dynamics Simulator (FDS6). Two-dimensional simulations are performed using finite-rate single-step combustion kinetics in the gas phase and an Arrhenius reaction mechanism with multiple steps for the solid phase decomposition. The model results are then compared to previous experimental results at high oxygen concentrations and/or reduced pressure conditions. It is shown that with the appropriate kinetic parameters the model is able to capture the main physical aspects of the flame spread of a thin solid fuel and it provides a basis for future modeling of fire resistant fabrics for space exploration.