In-situ measurement of permeability of a porous interface using the ultrasonic slow wave.

摘要

Porous materials are an important class of materials. They occur in natural substances such as oil or water bearing rocks, marine sediment, biological tissues (e.g. bones), granular materials and man made materials such as separation membranes, thermal insulators, ceramics and fuel cells. Porous materials have been used in many areas of applied science and engineering. Understanding of porous media plays an important role in areas such as experimental acoustics, geo-mechanics, geophysics, biophysics, material science. Among the number of parameters describing porous materials, the permeability is often the reason the porous structure is of interest. Permeability is a measurement of the ability of a porous material to transmit fluid. At an interface, permeability describes the flow of fluid into or out of a porous media;Ultrasound has been widely used for flaw detection and material characterization. Studies show that there are three waves that exist in porous materials: the longitudinal and shear wave that exist in other solid materials and the slow longitudinal wave that only exists in porous materials. This slow longitudinal wave can only be generated and propagated above a critical frequency. Measuring the critical frequency provides information about the intrinsic permeability of a porous interface. This thesis presents a new technique developed for an in-situ permeability measurement using measurement of slow wave.;In this work, an exact solution for the critical wave number for the slow wave has been developed and showed suitable for measuring the permeability of porous materials. A computer model of the reflection coefficient at the interface of fluid/porous media has been developed for the acoustic measurement. Ultrasonic experiments confirmed the sensitivity of this technique to changes in permeability and fluid viscosity. A flow cell test has been performed to show one potential industrial application of this technique by showing open pore and closed pore conditions in the test where comparisons were made to theory. This technique can be applied in a wide range of industries. For some applications, this special slow wave measurement could be the only possible method available to detect bio-fouling in water separation membranes or the permeability of marine sediments to nutrients.