Automated optical liquid film thickness measurement method

A nonintrusive, automated, optical film thickness measurement technique has been developed to be used with a wide range of fluids and flow configurations. 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 charge coupled device 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 is calculated. The entire process is automated, allowing for the collection of 600 data points in about 4 min using a personal computer with a 486 microprocessor. Film thicknesses on the order of 0.01 mm may 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, so the index of refraction of the test fluid or the test section wall need not be known a priori. Static liquid measurements agree to within 2.2% of measurements made using the needle-contact method. Film thickness data are presented for both round and square test sections operating under annular, two-phase flow conditions with air and water.