Lin Lin

Date of Award

2003

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Donald A. Grant

Second Committee Member

Richard C. Hill

Third Committee Member

Eric Landis

Abstract

Membranes are among the most important engineering components in use in many process industries. Examples of uses for membranes include water purification, industrial effluent treatment, recovery of volatile organic compounds, protein recovery, bio-separations and many others. Polymeric membranes are the most commonly used membranes. Membranes act as a barrier through which fluids and solutes are selectively transported. Quality assurance is a critical aspect of membrane module fabrication. In other materials, ultrasound has been widely used for materials characterization as well as flaw detection. Recently ultrasonic techniques have been used to detect the presence of defects in membranes. This thesis describes the use of guided waves in membrane applications to improve the ability to inspect large areas of membranes. Plate waves also have the potential to provide additional information in asymmetric membranes. The present effort focuses on developing techniques that make it possible to test microporous membranes using low frequency ultrasonic guided waves. The sensitivity of the material attenuation in polyvinylidene fluoride (PVDF) membrane material with frequency was investigated. The attenuation of the PVDF membrane increases with frequency, and does not appear linear. There is at least one inflection point occurs in the range considered. These measurements were verified using single frequency method. For these measurements the propagation distance and inspection area of a plate wave at different frequencies in porous PVDF membrane were estimated. The inspection ranged from 2.01cm2 at 2.25MHz to 7.69mm2 at 30MHz. The dispersion curve for the first mode was obtained using experimental data, and the single mode generated in the plate was shown to be dispersive.

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