ANALYSIS OF RESEARCH ON THE INFLUENCE OF SURFACE TENSION FORCES ON THE DISPERSITY OF DROPLETS DURING EXTINGUISHING FOREST FIRES BY AVIATION EQUIPMENT

Abstract

The literature review is carried out and regularities concerning changes of parameters of drops in the course of transformation of liquid massifs during free fall are defined. The main reason for the limited transverse dimensions of the transforming liquid mass and the cloud of small droplets formed after its destruction is determined. The correlation between the effect of compression of the water mass and the stages of its crushing depending on the high-temperature gaseous medium is established. There are 4 stages of the process of evolution the macro-volume liquid and 3 modes of coagulation of liquid droplets. Characteristic features of droplet collision taking into account the influence of convective flows are described. As a result of the analysis of videograms of experiments several modes of coagulation of drops at their movement through a flame are established. In particular, when monitoring the change in the distances between the drops and the temperature of the vapor-gas mixture in the trace of the drops, it was found that the coagulation of the latter can be realized in three modes:

• moving in the footsteps drops catch up with the previous ones;
• droplets change the direction of their movement to the opposite due to the resistance of the gas flow and coagulate with the droplets moving after them;
• droplets due to the implementation of phase transformations coagulate with droplets that move at some distance from them.

In the analysis of the modes of coagulation of water droplets in the field of high-temperature gases, the characteristic features of droplet collision are established. Experiments have shown that at «tangential» collision of two drops (especially at difference of their characteristic sizes several times) there is their short-term merger and then crushing into two drops with the sizes close to initial. At «frontal» collision of drops there is their merger and further movement. continues the «combined» drop. At the same time, experiments have shown that the characteristics of the processes of collision of droplets change significantly when varying the size and speed of movement of droplets, as well as the angles of intersection of the trajectories of their movement.