Experimental investigation of consecutive water droplets falling down through high-temperature gas zone

• Consecutive motion features of water droplets at high-temperature gas were established.
• Velocities and evaporation rates of each droplet were measured.
• Conditions for coalescence of droplets in high-temperature gases were determined.
• Distance between consecutive droplets influences chiefly on their evaporation.

An experimental investigation of the motion of water droplets falling down in series of 2, 3 and 4 through high-temperature gas (about 1100 K) was carried out. Sizes of droplets (radii 1–3 mm), initial distances between them (4–36 mm), initial speeds (0.5–2 m/s), as well as up-flow gas velocities (1.5 m/s) are varied within ranges corresponding to some advanced applications. Velocities and evaporation rates of each droplet were measured by high-speed video camera “Phantom” (up to 105 frames per second), associated with the software packages “Tema Automotive” and “Phantom Camera Control” while varying the distance between droplets within wide range. Conditions for coalescence of droplets, their slowing down and acceleration in high-temperature gases were determined. Influence of the initial droplet sizes, the distance between droplets, their temperatures as well as their number during motion in an upstream flux of high-temperature gases on the intensification of evaporation was analyzed. One of the most typical mechanisms of droplet coalescence in high-temperature gas zone was experimentally confirmed.