A compressible advection approach in permeation of elastomer space seals

The preservation of air in manned spacecraft is of grave importance. It is imperative that a comprehensive understanding in the fundamental mechanics of compressible permeation be applied to research and development of elastomeric space seals. Current state of the art space seal designs have relied heavily on past experimental experience, where design iterations are accomplished through costly experimental evaluations alone. To this end, a compressible advection model of permeation in elastomeric space seals was accomplished through a porous media approach. The model allows for compressibility effects on permeation, enables gas dilation, and lumps both diffusion and the incompressible permeability constants. A one-dimensional analysis resulted in a Generalized Emden-Fowler Equation, to which an exact, analytical solutions exist. The analysis yielded two permeation parameters which are dependent of the material-fluid and independent of geometry: (1) the incompressible permeability coefficient, kinfinity, and (2) the Klinkenberg coefficient, b. A series of experiments, coupled with analytical analysis, resulted in material characterization of dry air in the silicone elastomer S0383-70, a candidate space seal material. The material characterization revealed that the permeation coefficients are temperature dependent, supporting conclusions of previous space seal research. An experimental investigation of a subscale candidate space seal established a baseline leak rate for the computational prediction at +23°C and +50°C. A detailed uncertainty analysis was performed on the leak rate methodology, resulting in uncertainties within 7.0%. A second order, computational analysis of the developed model was performed on a domain representative of the candidate, space seal profile and with test conditions similar to that of the experimental baseline evaluations. The predicted leak rate showed exceptional correlation with the experimental investigation, as the predictions were within the uncertainty bounds of the experimental results. This in-detail study of dry air permeation through a candidate space seal material and geometry provides researchers and designers with an accurate and proven methodology for the prediction the mass leak rate for future space seals.