Abstract
We investigated the conditions, characteristics, and outcomes of liquid droplet interaction in the gas medium using video frame processing. The frequency of different droplet collision outcomes and their characteristics were determined. Four interaction regimes were identified: bounce, separation, coalescence, and disruption. Collision regime maps were drawn up using the Weber, Reynolds, Ohnesorge, Laplace, and capillary numbers, as well as dimensionless linear and angular parameters of interaction. Significant differences were established between interaction maps under ideal conditions (two droplets colliding without a possible impact of the neighboring ones) and collision of droplets as aerosol elements. It was shown that the Weber number could not be the only criterion for changing the collision mode, and sizes and concentration of droplets in aerosols influence collision modes. It was established that collisions of droplets in a gaseous medium could lead to an increase in the liquid surface area by 1.5–5 times. Such a large-scale change in the surface area of the liquid significantly intensifies heat transfer and phase transformations in energy systems.
Highlights
Over the recent years, optical techniques, cross-correlation systems, high-speed photo, and video recording have made it possible to obtain unique experimental results and extend the concepts of the physics of hydra-dynamic and thermal processes in the area of a large group of gas-droplet systems [1,2,3,4].Non-contact optical methods are of special note here
Droplet coalescence is crucial for high-temperature gas-vapor-droplet flows due to heat exchange intensification [20,21]
The algorithm performed a preliminary screening of all the droplets with a smooth change in the intensity from the edge to the center. This way, we excluded the droplets in which size could be significantly reduced by the binarization as compared to the actual size
Summary
Non-contact optical methods are of special note here These include particle image velocimetry (PIV) [5,6], particle tracking velocimetry (PTV) [7,8], stereo particle image Velocimetry (Stereo PIV) [9,10], interferometric particle imaging (IPI) [11,12] and shadow photography (SP) [13,14]. Droplet coalescence is crucial for high-temperature (above 1000 ◦ C) gas-vapor-droplet flows due to heat exchange intensification [20,21]. Based on the video frames of the experiments in [22] and the obtained velocity fields of droplets and high-temperature gases, using PIV, Stereo PIV, and PTV, we have formulated a hypothesis that the droplets moving first significantly alter the heat exchange conditions of all the subsequent droplets with gases. A similar assumption was made from the numerical simulation results [22] of a consecutive motion of several droplets through high-temperature (800–1000 ◦ C) gases
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