Multiscale Model for Hydrogen Chloride Uptake on Aluminum for Spacecraft Fire Safety

Abstract

An electrical fire within spacecraft environments often produces poisonous gases, such as hydrogen chloride (HCl). These gases adsorb on the interior materials of the spacecraft, primarily treated aluminum surfaces. A safe design of the spacecraft can be facilitated by modeling the spacecraft compartment. In this study, a multiscale model is developed to predict HCl uptake by anodized aluminum, which has a thick oxide layer covering its surface compared to other treatments. X-ray photoelectron spectroscopy revealed that aluminum chloride is found deep in the oxide layer of anodized aluminum, implying that the pore-scale transport and reaction of HCl within the oxide layer covering the aluminum surface must be considered. Hence, a multiscale approach is warranted. A pore-scale model is first developed, wherein the HCl reacts with the aluminum oxide pore walls to create an aluminum chloride layer. The HCl then diffuses through that layer for further reaction, until the layer (diffusion resistance) grows too large and the uptake of HCl stops. This pore-scale model is coupled with a reactor-scale model to predict overall HCl uptake. Results show that this new multiscale approach predicts the uptake of HCl far more accurately when compared to experimental data than previously used single (reactor)-scale models.