Integrity test for porous structures using acoustic emission

Abstract

A rapid, highly sensitive determination, in-situ, of the integrity and/or pore size distribution of a porous membrane structure (e.g. a pleated membrane filter cartridge) is disclosed. The identification of the integrity and/or pore size characteristics involves interpreting the residence time distribution (RTD) of the membrane structure under test and includes using a tracer gas in mixture with a carrier gas as part of a diffusion or bubble-point test. The tracer gas mixture exiting the downstream surface of the membrane becomes moisturized and is excited with a pulsed (or otherwise modulated) light source at a wavelength corresponding to the absorption line of the tracer gas. The frequency of modulation is chosen such that the tracer gas preferentially generates a photo-acoustic emission while the emission due to the absorption of water present is suppressed. The detected pressure pulse is processed to produce electrical signals indicative of the concentration of tracer gas that passes through the membrane. A non-integral (or incorrect pore size) device will demonstrate a characteristic RTD that differs from an integral (or correct pore size) device in either/or (or both) the onset time prior to tracer gas detection and the rate of change of tracer gas concentration with time.