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Droplet entrainment from the surface of a gas-sheared liquid film increases the interfacial area, thus enhancing heat and mass transfer in the flow, Due to entrainment, the pressure drop increases; reduction of film thickness, impacts of depositing droplets and entrapment of bubbles may lead to formation of dry spots on heat walls of the duct. In [1] it was observed for the first time that the entrainment occurs due to disruption of small-scale waves on the surface of large-scale “disturbance” waves. Nonetheless, no systematic quantitative studies of the entrainment process were carried out yet. In the present work, such a study is carried out in a horizontal rectangular duct with height of 26 mm and width of 166 mm, in a wide range of gas and liquid flow rates, for three working liquids with different viscosity and surface tension. The study of entrainment events was carried out using stereoscopic modification of Laser-Induced Fluorescence technique. This method enables one to get instantaneous fields of film thickness resolved along two spatial coordinates and time, together with the vertical position of liquid objects above the film surface, such as droplets and overturning waves. Recently [2] this approach was used to investigate the impacts of high-speed droplets depositing from the gas stream onto the liquid film under small angles. The main regularities of such impacts with formation of craters and furrows were identified, including the bubbles entrapment, secondary entrainment and partial survival of the impacting droplets. In the present work, a quantitative study of three-dimensional spatiotemporal evolution of fast ripples on top of disturbance waves …