Экспериментальное исследование закономерностей испарения капель воды, движущихся последовательно в области высокотемпературных продуктов сгорания

Abstract

Introduction. The paper presents the results of experimental investigation of cross impact of water droplets in a flow while moving and evaporation in a medium of high-temperature gases, which cor¬respond in temperature to the typical combustion products due to a fire. We considered the sequential schemes of droplet movement and the schemes when the trajectories of droplet movement diverged relative to each other. Materials and methods. The area full of high-temperature (about 1000 K) combustion products was created using the model of fire source (hollow cylinder of height h = 1 m and diameter d = 0.15 m). Droplets moved in the opposite direction of the gas medium. In experiments we applied the tools of high-speed video recording (up to 106 frames per second) and also the optical diagnostic methods of two-phase gas flows (Particle Image Velocimetry, Particle Tracking Velocimetry, Stereoscopic Particle Image Velocimetry, Shadow Photography). Results. In experiments the decrease in typical radius R of water droplets and change in distance Ld between neighboring droplets was the main defining characteristics. From the experiments we deter-mined the velocity variation of droplets moving sequentially, distance, at which the subsequent droplet catches the next one in a flow, and there is a coalescence. The influence of initial distance between neighboring droplets in a flow on their approximation while movement in a channel with high-¬temperature gases at various values of initial speed of droplet was investigated. Also, we determined the impact scale of the vapor trace forming from evaporation of droplets moving ahead on the eva¬pora¬tion intensity of the next droplets. It was revealed that heating and evaporation of the next droplets in a vapor-gas trace of preceding ones are less intense. The influence of initial water temperature on the approach and the coalescence of droplets moving subsequently in a flow of high-temperature gases were determined. It was illustrated that the previous heat-up of water accelerates the droplet coales¬cence in a flow under conditions of relatively short initial distances between droplets. Also, the extreme distances between droplets were defined, in pro-viding which there is a coalescence of droplets when they pass the area of high-temperature combustion products. Conclusions. We illustrated the satisfactory correlation of experimental results with the data of nu¬me¬-rical simulation carried out previously. The theoretical hypothesis about the significant influence of water droplets moving ahead (through high-temperature gases) on the conditions of evaporation and movement of subsequent ones was proved experimentally.