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ACRC Technical Report 134PDF


Title:An Automated Optical Liquid Film Thickness Measurement Method
Author(s):Shedd, T.A.
Contributor(s):Newell, T.A.
Subject(s):refrigerant/oil flows
Abstract:The need to measure the thickness of thin liquid films is evident from the number of methods that have been developed to do so. Many of these methods have significant drawbacks, such as intrusive probes or the dependence on a conductive liquid. A non-intrusive, automated, optical film thickness measurement technique has been developed to be used with a wide range of fluids and with virtually any flow configuration. In this method, light is reflected from the surface of a liquid film flowing over a transparent wall. This reflected light generates an image on the outside of the wall which is captured and digitized using a CCD camera and framegrabber card in a desktop computer. The image is processed to determine the positions of the reflected light rays, with which the film thickness and film slope are calculated. The entire process is automated and can be performed in less than 9 seconds on a 486 PC, allowing many data points to be collected efficiently. Film thicknesses as small as 0.03 mm can be determined using inexpensive components, with the possibility of greater precision using more advanced imaging equipment. An automated calibration procedure allows for the determination of the necessary physical parameters automatically, so the index of refraction of the test fluid or the test section wall need not be known a-priori. A prototype of the automated system generates static liquid measurements that agree to within 3% of measurements made using the needle-contact method. Film thickness data are also presented for an air-water system in cylindrical, annular, two-phase flow and compared with data from the literature.
Issue Date:1997-12
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-134
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 77
Date Available in IDEALS:2009-04-29
Identifier in Online Catalog:4190430

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