The need to measure the thickness of thin liquid films is evident from thenumber of methods that have been developed to do so. Many of these methodshave significant drawbacks, such as intrusive probes or the dependenceon a conductive liquid. A non-intrusive, automated, optical film thicknessmeasurement technique has been developed to be used with a wide range offluids and with virtually any flow configuration. In this method, light is reflectedfrom the surface of a liquid film flowing over a transparent wall. Thisreflected light generates an image on the outside of the wall which is capturedand digitized using a CCD camera and framegrabber card in a desktop computer.The image is processed to determine the positions of the reflected lightrays, with which the film thickness and film slope are calculated. The entireprocess is automated and can be performed in less than 9 seconds on a 486PC, allowing many data points to be collected efficiently. Film thicknesses assmall as 0.03 mm can be determined using inexpensive components, with thepossibility of greater precision using more advanced imaging equipment. Anautomated calibration procedure allows for the determination of the necessaryphysical parameters automatically, so the index of refraction of the test fluidor the test section wall need not be known a-priori. A prototype of the automatedsystem generates static liquid measurements that agree to within 3%of measurements made using the needle-contact method. Film thickness dataare also presented for an air-water system in cylindrical, annular, two-phaseflow and compared with data from the literature.
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