Resonant acoustic measurement of vapor phase transport phenomenon in porous media

Abstract

Diffusion of gases through porous media is commonly described using Fick’s law and is characterized by a gas diffusion coefficient modified by a media-specific tortuosity parameter. A phase-locked-loop resonance frequency tracker [J. Acoust. Soc. Am. 108, 2520 (2000)] has been upgraded with an insulated copper resonator and a bellows-sealed piston instrumented with an accelerometer. Average system stability (temperature divided by frequency squared) is about 180 ppm. Glass-bead-filled cores of different lengths are fitted into an o-ring sealed opening at the top of the resonator. The rate at which the tracer gas is replaced by air within the resonator is controlled by the core’s diffusion constant. Mean molecular weight of the gas mixture in the resonator is determined in real time from the ratio of the absolute temperature to the square of the fundamental acoustic resonance frequency. Molecular weight of the gas mixture is determined approximately six times per minute. Changes in the gas mixture concentration are exponential in time (within 0.1%) over nearly two decades in concentration. We will report diffusion constants for two different sizes of glass beads, in samples of five different lengths, using two different tracer gases, to establish the validity of this approach. [Work supported by ONR.]

Sonic gas analyzer for hydrogen and methane

“…Using an analyzer with a single resonator, Schuhmann used acoustical gas analysis to make non-invasive determination of gaseous diffusion rates through porous media [21,22]. This technique, with its higher accuracy and precision, provided new insights into the determination of tortuosity factors and generated corrections to the standard chromatographic analysis which produced results that were previously confounded by advection and non-equimolar effects [23].…”