Abstract
In the present study, a new method measuring a thin liquid film in a small and curved channel by using an Optical Fiber Probing (OFP) is proposed. The OFP has highly spatial resolution due to its sensing-tip of 6-μm diameter. Hence, it can be highly adaptive for measuring a thickness of a micrometer-order and wavy liquid film. We simultaneously measured a thickness and maximum amplitude of a thin and wavy liquid film by using the OFP and a high-speed video camera. The OFP detects liquid film surfaces based on a difference in refractive indices between the gas and liquid phases. A fraction of liquid phase (integrated time while the sensing tip is positioned in the liquid film) is calculated from the output signals of the OFP at every fixed position, and is compared with a wave height obtained from the visualization. Calibrating the experimental results via a numerical simulation, we found that the fixed position of the OFP corresponded with the average thickness of a liquid film when the fraction of the liquid phase was 0.52. We demonstrated effectiveness of the OFP measurement through applying this method to an annular liquid-film flow inside a small two-fluid nozzle that is impossible to visualize. As a result, the average thickness and amplitude of the liquid film in the nozzle were 61 μm and 28 μm, respectively. Our new method possesses high measurement accuracy and appropriateness satisfactorily for practical measurement.
