Gas permeability measurement in porous graphite under steady-state flow

Abstract

Abstract Porous graphite is employed for the development of air bearings used in the ultraprecision machine tools. The static performance of this new bearing type depends on the permeability and inertia coefficient of the porous graphite inserted in it. In this study, an experimental fitting method was used in conjunction with computational fluid dynamics (CFD) modeling to determine the permeability and inertia coefficient of three types of porous graphite with porosity of 16%, 13%, and 8% respectively. The experimental results show that the Compressible-Darcy-Forchheimer equation can fit the experimental mass flow rate and pressure drop well. The average permeability of SG-3, SG-5 and SG-8 porous graphite are 5.74 × 10 − 14 m2, 3.65 × 10 − 15 m2 and 1.85 × 10 − 15 m2 respectively. SG-5 and SG-8 porous graphite have good permeability consistency and can be used to make porous media air bearing. The PPSM (number of pores per square millimeter) of SG-3 and SG-8 are similar, but the permeabilities are very different. For low permeability porous graphite, samples with different sizes from the same material should be tested and the averaged inertia coefficient can be used. The accuracy of the pore-scale FVM (finite volume method) is highly dependent on the quality of the pore microstructure image.