Estimation method for mass transfer coefficient distribution using near-infrared spectroscopy

Various experimental studies were conducted to reveal the distribution of the heat and mass transfer coefficients over complex geometries using classical techniques, such as the wet filter paper and salinity methods. However, such methods cannot determine the spatial distribution of the transfer coefficients with high resolution because they are based on area-averaged mass changes during a certain period. Therefore, we propose a new estimation technique for determining the distribution of the transfer coefficients by applying near-infrared (NIR) spectroscopy. In our method, NIR light is incident on a wet filter paper, and the reflection intensity of the paper is measured using a high-response NIR camera. The water mass content of the paper is determined by the reflection intensity based on a calibration equation that establishes the relationship between water mass content and the reflection intensity. The results showed the measurement error was less than 7%. In this paper, we report basic trials to confirm the accuracy and applicability of the technique for a boundary layer over a smooth surface.