RECENT ADVANCES ON FRAGMENTATION AND EVAPORATION OF DROPLETS IN AIRFLOW

Cold gas dynamic spraying is an efficient and low-cost solution to build nanocomposite electrodes. However, there is a serious bow shock near the substrate causing a sudden drop in velocity when nano powder is directly deposited by traditional cold spraying methods. Nano powder carried by micro droplets has become one of the most potential solutions to deposit nano powder. In high-speed flow, droplets will deform, break up, and evaporate under the influence of airflow. In terms of fragmentation characteristics, the fragmentation of droplets in the airflow is dominated by inertial force, surface tension, and viscous force, resulting in various fragmentation modes such as bag fragmentation and multi-bag fragmentation. In terms of evaporation characteristics, the evaporation of droplets is affected by diffusion phenomenon, Marangoni effect, etc. Therefore, the fragmentation and evaporation behaviors of droplets will affect the acceleration of droplet flow, and further affect the impact velocity and deposition effect of nano powders. Based on this, this article reviews the recent advance of droplet fragmentation and evaporation in airflow in recent years, summarizes the dynamic mechanism of droplet fragmentation in airflow and the heat and mass transfer characteristics of droplet evaporation; Summarized the main influencing factors of droplet fragmentation and evaporation, including droplet properties such as viscosity, composition, and particle size, as well as airflow states such as temperature, pressure, velocity, humidity, and shock waves; At the same time, the main experimental schemes for the fragmentation and evaporation of droplets in airflow were introduced. Finally, prospects were made for the study of fragmentation and evaporation of droplets in the air, and further issues that need to be addressed and possible future research directions were proposed.