Experimental study of the liquid droplet shape upon separation from a cylindrical nozzle

The dynamics of liquid droplet formation and separation in a periodic dripping regime was experimentally studied on tubes with an outer diameter in the range of 0.5 ÷ 4 mm. Water, ethanol, a 40 % water-ethanol solution, and glycerin were used as working fluids, which allowed us to cover a wide range of physicochemical properties (viscosity, surface tension, density). An analysis of the dynamics of droplet shape changes revealed three stages of the cyclic process. Dimensionless parameters were used for the analysis, allowing for a comparison of experimental data obtained under different operating conditions. It was found that throughout the entire period of droplet formation, a jet flow section with a liquid flow rate lower than that through the nozzle arises in central region of the droplet. This leads to the division of the droplet into two parts: the upper and the lower ones. The lower droplet separates directly from the forming jet. However, characteristics of this process differ significantly from similar processes of droplet separation under chaotic dripping faucet conditions.