Experimental investigation on the performances of a valve-based and on-demand droplet generator producing droplets in a wide size range

Many aspects of our daily lives are affected by the generation of water droplets, and it is important to controllably produce droplets with a wide size range in various applications. In this paper, we describe an on-demand droplet generating system based on a high-speed two-way solenoid valve. A nozzle made of stainless steel tubing is fit into one port of the valve, and the other port is connected to the fluid reservoir by which the pressure can be controlled via a pressure regulator. When the liquid is pressurized and the valve is opened with a short pulse voltage, trace amounts of liquid will be ejected from the nozzle to form a droplet. Droplet generation is captured using a high-speed camera to measure the dimension and velocity and to evaluate the performances of the generator, such as repeatability and stability. We demonstrate the influences of applied pressure and pulse width of driving voltage on droplet generation. It is shown that the droplet generator is capable of producing droplets in a wide size range for a given nozzle (e.g., about 0.7–2.2 mm for a 1.0 mm diameter nozzle). A single droplet is stably generated at Z = 268.1, obviously higher than the published data and the Weber number of a fluid jet (Wej) ranging from 2.1 to 5.6. The droplet generator presented here will be useful for research related to large droplets, such as freezing rain in atmospheric science and supercooled large drops in aircraft icing.