The integral characteristics of the deceleration and entrainment of water droplets by the counter flow of high-temperature combustion products

• Necessary conditions of water droplet deceleration in counter gas were established.
• Comparison of non-stationary and nearly stationary heating conditions was done.
• Ranges of Weber and Reynolds numbers corresponding to droplets turn were found.
• Droplets sizes have the critical impact on the deceleration and entrainment.

This paper presents the results of experimental investigations on the deceleration and entrainment of water droplets during their motion in the counter flow of high-temperature combustion products (up to 1900 K). High-speed video cameras (105 frames per second), specialized software applications (with continuous tracking functions), as well as panoramic optical methods (Particle Image Velocimetry, Stereoscopic Particle Image Velocimetry, Particle Tracking Velocimetry, Shadow Photography) registered the processes under study. We used several typical oils, gasoline, kerosene, acetone, and industrial alcohol to generate combustion products with a controlled high temperature. The initial sizes (radius) of droplets and their velocities were varied from 0.05 mm to 0.35 mm and from 0.5 m/s to 5 m/s. The velocities of counter motion of combustion products were varied from 0.1 m/s to 2.5 m/s. In this paper we have also determined the characteristic trajectory length of the droplets of different sizes until their complete stop (and subsequent entrainment) in the counter flow of high-temperature gases. As a result of studies, we summarized the research results through the establishment of Weber and Reynolds numbers ranges for droplets and gases, when the full stop and entrainment of droplets may occur. This paper also covers a comparison of the characteristics of water droplet deceleration under the conditions of non-stationary (when the temperature of combustion products varies from 1900 K to 400 K in channel) and nearly stationary (when the temperature is 1100 ± 30 K) heat transfer. Thus, it has been found out that the values of these parameters correlate well (deviation did not exceed 7%) under such conditions (stationary and nearly stationary) during short heating (less than 0.5 s).