Water film thickness imaging based on time-multiplexed near-infrared absorption

Lubnow, Marc; Jeffries, Jay B.; Dreier, Thomas; Schulz, Christof

doi:10.1364/oe.26.020902

Cited by 17 publications

(7 citation statements)

References 20 publications

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“…At 343 K, the transmission increases by 1.7% compared to its ambient-temperature value. Lubnow et al [13] measured an increase of 6% at 338 K compared to room temperature value. A temperature-corrected absorption coefficient of k1450 = 27.7 cm -1 was used to calculate the droplet thickness at 343 K.…”

Section: Nira Absorption Coefficients and Temperature Dependencementioning

confidence: 92%

“…Equation ( 2), based on the Beer-Lambert law, describes the relation between the transmitted light intensity t λ , the water thickness d, the incident light intensity 0 λ , and the absorption coefficient λ . In equation ( 2), u describes elastic transmission losses like scattering or reflection on surfaces [13]. Thus, the term (1-u) represents the optical transmission efficiency.…”

Section: Nira Imagingmentioning

confidence: 99%

“…The results showed approximately the same thicknesses measured by Raman as by LIF, the latter with ethyl acetoacetate as a tracer excited at 266 nm. Lubnow et al [13] imaged water films sandwiched between a substrate and a transparent cover plate using NIRA. They used a fast-framing near-infrared (NIR) camera and a pair of time-multiplexed distributed feedback (DFB) diode lasers to switch between the absorption (1469 nm) and transmission (1353 nm) wavelength.…”

Section: Introductionmentioning

confidence: 99%

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Imaging of water droplet clusters on glass with simultaneous laser-induced fluorescence and near-infrared absorption

Mirschinka

Geiler

Kaiser

et al. 2021

ICLASS

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Water films and droplets on surfaces are important in the design of various processes. In the present work, two complementary non-invasive imaging techniques, laser-induced fluorescence (LIF) and near-infrared absorption (NIRA), were used simultaneously to quantify the deposited water mass in a simple spray-onto-plate experiment. LIF was applied in epiillumination with optical access from only one direction, but it requires the addition of a marker substance to the non-fluorescing water. Here, anisole (methoxybenzene) was used for this purpose. The present implementation of NIRA is based on the intensity ratio of light transmitted through the sample at two wavelengths, 1450 and 600 nm. Since water itself is the IR absorber, a tracer is not required. In a first step, in a thin-film cuvette the influence of temperature and film thickness on the measurement accuracy was investigated for both techniques. In a second set of experiments, water was sprayed onto a hot or cold quartz glass plate and simultaneously imaged with both techniques. From the measurements, advantages and weaknesses of both approaches were identified.

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Section: Nira Absorption Coefficients and Temperature Dependencementioning

confidence: 92%

Section: Nira Imagingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Imaging of water droplet clusters on glass with simultaneous laser-induced fluorescence and near-infrared absorption

Mirschinka

Geiler

Kaiser

et al. 2021

ICLASS

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“…For such a purpose, Fourier transform infrared (FTIR) spectrometers in combination with liquid cuvettes of known depth L are very commonly used for its convenience in revealing all the absorption peaks over a wide range of wavelengths from a single measurement [45][46][47][48][49][50][51]. This method, however, cannot provide quantitative information for wavelengths at which the absorption is very strong since the depth of the cuvette is typically in the range of millimeters and thus the transmitted signal is diminishing if the absorption coefficient is in the order of µm −1 , which, on the other hand, is the ideal choice of light wavelength for measuring liquid films with thicknesses of a few micrometers, e.g.…”

Section: Introductionmentioning

confidence: 99%

Calibration of absorption coefficients of liquid solutions for measuring liquid film thickness by absorptiometry

Zhao,

2024

Meas. Sci. Technol.

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Infrared absorptiometry is a widely used non-intrusive method for measuring the thickness of liquid films. The accuracy of that measurement depends crucially on having high-accuracy data of the absorption coefficient of the laser light used, which is, however, not easily available, especially for the wavelength range where the absorption is strong. Here we propose a method to calibrate the absorption coefficients in such cases. By measuring the light intensity reduction while scanning through a liquid film formed in a wedge, whose angle can be adjusted and determined a priori from interferometry, the absorption coefficient of the liquid can be accurately obtained without the need to create a flat liquid film with exact known thickness. The method is verified by calibrating the absorption coefficient of pure water at an infrared wavelength and the result agrees very well with the values found in the literature. As a demonstration of the application of the method, the absorption coefficients of soap solutions with different compositions were calibrated and used to measure the thicknesses of draining soap films. The results from the absorptiometry are in good agreement with the film thickness measured simultaneously from interferometry.

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“…In recent literature, Dupont and Lubnow et al focused their work on image analysis using the near-infrared measurement technique to determine film thickness [21,54]. Dupont only used one NIR wavelength narrowband filter.…”

Section: Introductionmentioning

confidence: 99%

Film Thickness and Glycerol Concentration Mapping of Falling Films Based on Fluorescence and Near-Infrared Technique

2022

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Falling film evaporation processes involve high fluid velocities with continuous variations in local film thickness, fluid composition, and viscosity. This contribution presents a parallel and complementary film thickness and concentration mapping distribution in falling films using a non-invasive fluorescence and near-infrared imaging technique. The experiments were performed with a mixture of glycerol/water with a mass fraction from 0 to 0.65 gglycgtotal−1 and operating ranges similar to evaporation processes. The measurement system was designed by integrating two optical measurement methods for experimental image analysis. The film thickness was evaluated using a VIS camera and high-power LEDs at 470 nm. The local glycerol concentration gglycgtotal−1 was determined using a NIR camera and high-power LEDs at 1050, 1300, 1450 and 1550 nm. A multiwavelength analysis with all NIR wavelengths was implemented with a better correlation for falling films at low flow velocity. The results show an improvement in the analysis of falling films with high flow velocities up to almost 500 mm/s by using only the 1450 nm wavelength and the fluorescence measurement. Simultaneous imaging analysis of film thickness and concentration in falling films provides further insight into understanding mass and heat transport and thus supports the optimization of falling film evaporators.

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Water film thickness imaging based on time-multiplexed near-infrared absorption

Cited by 17 publications

References 20 publications

Imaging of water droplet clusters on glass with simultaneous laser-induced fluorescence and near-infrared absorption

Imaging of water droplet clusters on glass with simultaneous laser-induced fluorescence and near-infrared absorption

Calibration of absorption coefficients of liquid solutions for measuring liquid film thickness by absorptiometry

Film Thickness and Glycerol Concentration Mapping of Falling Films Based on Fluorescence and Near-Infrared Technique

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