Influence of droplet concentration on evaporation in a high-temperature gas

This paper presents the study of the evaporation of water droplets with initial sizes from 100 μm to 300 μm. The spray is falling down in high temperature gas counter flow with velocity of about 1.5 m/s at temperature of about 1100 K. The gas in this study is a mixture of air and combustion products of kerosene. The concentration of droplets in the gas flow varied in the range 0.2 · 10−4-1.2 · 10−4 m3 of water/m3 of gas. This concentration corresponds to wide group of high-temperature gas-vapor droplets applications (e.g., firefighting by water mist, fog and dropping veil; thermal treatment of liquids; using the flows of flue gases, droplets and water vapor to transport heat). With the use of cross-correlation and high-speed video cameras, panoramic optical flow visualization techniques (PIV, Stereo PIV, PTV, IPI, SP) and Tema Automotive software the main parameters of the droplets evaporation process were measured, allowing to calculate the mass vaporization rates. The obtained laws allow predicting the conditions and characteristics of evaporation in a wide range of different droplets concentrations in a gaseous medium. It is demonstrated that increasing the number of droplets per unit volume may reduce the evaporation rate.