Optical Methods for Conducting Nondestructive Testing of Fuel Filter Elements

摘要

Two optical methods have been investigated for use as a nondestructive test method for use with filter-separator coalescer elements. Shadowgraphs and holographic interferograms have been shown to be useful for examining the flow variations of a gas flowing through a filter element. The test gas, having an index of refraction substantially different from that of air, refracts the light near the filter surface and permits gas flow variations through the filter media to be observed. It is anticipated that the shape of the test gas boundary layer and the boundary layer thickness will provide information on the media's porosity, voids, and plugged areas. Initial experiments have confirmed the sensitivity of the two optical methods, because a 1/16-inch diameter hole drilled through an element was easily detected. However, additional work is needed to establish correlation between the optical-gas flow, nondestructive test method and naturally occurring filter-element defects. (Author)