Falling film thickness measurement using air-coupled ultrasonic transducer

In this work, a new, non-intrusive, increased sensitivity technique based on air-coupled ultrasonics was developed to measure the falling liquid film thickness. Air-coupled transducer of frequency 1 MHz was used to make static and dynamic measurements of water level/film thickness. The air-coupled method were compared with a metal-side contact ultrasonic approach as well as calculating water levels in the collection tank. The falling film thickness measurement over inclined plate was used in this study. Measurement of film thickness was taken at flow rates in the range of 0.34-0.9 lpm. Relatively good agreement was found between the readings, which validates the dynamic measurement capability of the new technique. The technique was applied to measure the: horizontal tube falling film thickness for falling film Reynolds number ranging from 130 to 350, at different circumferential angles ranging from 40 degrees to 130 degrees and at tube spacing of 5 mm and 15 mm. Measurements were compared with correlations available in the literature and found to be in good agreement.