FIG. 7.

Droplet volume dependence on impulse time and applied pressure for two nozzle heights. The images show one characteristic time point in the simulation for different impulse times: top row 5 μm, middle row 25 μm nozzle heights. Impulse times for images (A)–(D) are 20, 25, 30, and 40 ms and (E)–(H) are 20, 30, 40, and 50 ms, while keeping the applied pressure fixed to 9 and 7.5 kPa, respectively. The simulation was performed using open source software (see Sec. II G), with appropriate lateral channel dimensions for the real devices: 100 μm (Length) by 40 μm (width). Stable simulations could be performed with increasing numbers of finite elements and run times down to 5 μm nozzle height. Plots left: droplet volume as function of injection impulse time. Right: droplet volume as function of applied pressure with fixed injection impulse time (20 ms).