Method of Calculating the Fluid Permeability of Machined Skin-Covered Porous Sheets from Experimental Flow Data

Abstract

Porous polymer sheets created by the “solid state microcellular foaming process” possess an impermeable solid skin on the boundary. In order to experimentally determine the internal structure's fluid permeability, the skin is removed by machining a pattern of holes or channels so that fluid flow can be established when applying a pressure difference across the faces. In this work, a fluid flow model for this particular geometry assuming a Newtonian fluid and isotropic internal porous structure is established. This yields formulae used to compute the structure's Darcy permeability from experimental flow data. Experimental verification of the model is provided for a sample of Polyetherimide (PEI) nanoporous polymer sheet whose skin was drilled in various hole patterns, thus establishing the mathematical foundation for future work in investigating this class of porous materials.

Production of Cellular Polymers Without Solid Outer Skins by Gas Dissolution Foaming: A Long-Sought Step Towards New Applications

“…However, the polishing process destroys or damages several layers of the cellular structure leading to a new densified skin, avoiding the exposure and the interconnection of the cellular structure with the external medium [29]. Hence, other works [23,26,[30][31][32] which applied drilling or milling processes on the non-foamed surfaces to interconnect the cellular structure with the external medium also produced irreversible damages in the sample, and thus in the cellular structure. In particular, the application of mechanical attacks is strongly discouraged to remove the solid skin in thin films.…”