Convection in the liquid at droplet squeezing out of the capillary

•Velocity in a suspended droplet falls from 90 mm/s to 5 mm/s over time.•Accumulation of impurities on a droplet interface is realized for 10 s.•With an increase in air temperature, the convection velocity increases. Experimental studies of droplet geometry and instantaneous velocity field in the liquid at a rapid change in the droplet shape are conducted. A droplet is squeezed out of the capillary in the presence of an external air flow. This article for the first time shows that when a droplet surface changes, impurities from the ambient air accumulate on the free surface within 10 s rather than instantly. Consequently, the average velocity in the drop varies from 90 mm/s to 3 mm/s. As the air temperature increases, the liquid in the drop heats up and the dynamic viscosity of both the drop and the air changes. Therefore, with an increase in air temperature from 20 to 100 ° C, the convection velocity in the drop increases almost two times from 0.1 to 0.2 ms. In practice we often have to deal with droplets and gas-droplet flows when fast-flowing processes are implemented. The lifetime of the droplet, after its formation from the nozzle, is a short time interval (0.001 s – 1 s). For correct modeling of the gas droplet flow, it is necessary to take into account the change in the convection velocity in the droplet, which changes with time.