Quantitative analysis of transverse non-uniformity of liquid film at the initial stage of annular-dispersed flow

A Comparative Analysis of Conductance Probes and High-Speed Camera Measurements for Interfacial Behavior in Annular Air–Water Flow

“…In this method, the excited species by the laser beam light will after only a few nanoseconds to microseconds, de-excite and emit light at a wavelength larger than the excitation wavelength. The most relevant optical techniques discussed are light absorption by photography, brightness-based laser-induced fluorescence (BBLIF) [26], planar laser-induced fluorescence (PLIF) [27] and some recent variants of the latter such as the PLIF40 and PLIF70 [10][11][12].…”

“…To avoid these errors, the LIF method has been ameliorated in recent years by two different approaches. The first one of these procedures is the brightness-based laser-induced fluorescence (BBLIF) technique developed by Alekseenko et al [25], which is based on measuring the brightness of the fluorescent light emitted by the dye in the liquid and then converting this local brightness 𝐼(𝑥, 𝑦, 𝑡 into film thickness ℎ(𝑥, 𝑦, 𝑡 , considering the following relationship between both magnitudes [26]: 𝐼(𝑥, 𝑦, 𝑡 = 𝐶(𝑥, 𝑦 1 − 𝑒 ( , , 1 + 𝐾𝑒 ( , , + 𝐷(𝑥, 𝑦…”

“…Figure 6 displays the application of BBLIF methods in cylindrical pipes as performed by Isaenkov et al [26] in a region of interest (ROI) of 80 × 12 mm for cylindrical pipes. Also, Isaenkov et al [26] performed measurements in rectangular ducts with a region of interest (ROI) of 200 × 50 mm. Based on these measurements, the authors concluded that the BBLIF technique can be used to measure film thickness in flat regions, but its sensitivity is smaller for thicker regions.…”

“…with x and y being the longitudinal and transverse coordinates, α the absorption coefficient of the fluorescent light in the dye, K the interfacial reflection index between phases, equal to 0.02 for moderate interface slopes, and, finally, C(x, y) is a compensation matrix created to compensate for the non-uniformity of laser illumination and to create a reference value of brightness corresponding to a reference value of film thickness. Figure 6 displays the application of BBLIF methods in cylindrical pipes as performed by Isaenkov et al [26] in a region of interest (ROI) of 80 × 12 mm for cylindrical pipes. Also, Isaenkov et al [26] performed measurements in rectangular ducts with a region of interest (ROI) of 200 × 50 mm.…”