Effect of convergent-shaped vessel on the velocity of impact-induced focused liquid jets

The impact-induced focused liquid jet technology can eject high-viscosity liquids (up to about 8,000 mPa・s) with a simple mechanism. The generation of faster jets is expected to make it possible to use this technology in various fields, including industrial and medical fields. In this study, impact-induced liquid jet ejection experiments were conducted with two vessels to investigate the effect of vessel geometry on the jet velocity. We used a Kjeldahl flask, in which the two-dimensional pressure distribution is not negligible, and a test tube used in previous studies, which has a simple cylindrical shape and is considered to have a one-dimensional, linear pressure distribution. Remarkably, as a result, by using a Kjeldahl flask, we successfully generate jets with velocity about twice that of a test tube. To understand the results, the Laplace equation on the pressure impulse inside the vessel is solved numerically and analytically. The distribution of the pressure impulse showed consistent results with the jet velocity measured in experiments. Importantly, unlike the test tube with no cross-sectional area change, a convergent-shaped vessel has a stronger nonlinearity in the pressure impulse distribution, resulting in an increase in the liquid velocity at the gas-liquid interface.