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Measurement of the Evaporating Liquid Film of a Urea-Water Solution using Diode Laser Absorption Spectroscopy
H-N. Yang, X-L. Guo, M-X. Su and X-S. Cai

Liquid film thickness is an important parameter in many industrial applications. Here, a single diode laser absorption spectroscopy (DLAS) sensor for film thickness measurement of urea-water solution was developed. The wavenumber position of the employed diode laser was chosen at 6613.25 cm-1, where the derivative of absorption coefficient with respect to concentration of urea-water solution was zero, therefore, the sensor was available for film thickness measurement of urea-water solution at different concentrations. The performance of the sensor was first validated in a calibration-tool experiment with liquid layers of known film thicknesses (100.0 to 1000.0 mm), it was found that the average deviation between the measured film thicknesses and preset values was 1.5%. Then experiments were presented for time-resolved thickness measurement of evaporating liquid films of urea-water solution on a transparent quartz plate.

Keywords: Diode laser, urea-water, liquid film, diode laser absorption spectroscopy (DLAS), thickness, aqueous solution, mass fraction, measurement, laser spectroscopy

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