Impinging micro jets – IJET

The massive use of inkjet printing and the recent democratization of 3D printers have led to a large number of studies on the dynamics of liquid impinging a substrate surface. Unlike the impact of a drop on a solid substrate, which is now well documented both theoretically and experimentally, an impinging submillimeter continuous liquid jet (typically 10-100 microns in diameter) raises inspiring questions about experimental realization and film morphogenesis (e.g., the appearance of strong variations in the film thickness, like in hydraulic jumps), as well as its potential applications. In the engineering literature, jets seem to be a key feature for surface cooling (especially in microelectronics) and cleaning, as well as for 3D printing optimization: increasing the printing speed through a larger jet velocity should bring a breakthrough in the printing technologies if undesired hydrodynamic instabilities are avoided. In the same vein, the use of multiple jets to crank up the total flow and cooling rates could be thought of as a smart solution to improve processes efficiency.
This project aims at shedding light on the dynamics of jets impinging a surface. IJET is divided into two work packages:
- first, we will study the physics of impinging microjets. New techniques will be developed to probe the multiple behaviors of these jets, which may be very sensitive to the boundary conditions. We mainly expect three free surface structures: the puddle, the rebound, and hydraulic jumps. We will uncover a global flow diagram that depends on the physical parameters (viscosity, flow rate, incidence angle, wettability, …). In this package, we will carefully characterize the features of micro hydraulic jumps, alone or in interaction with another, where new physical mechanisms will be at play, like the surface tension, or the surface properties. The interaction of two hydraulic jumps, with diameter around 1 cm, has been studied and gives rise to strong modifications of the flow pattern. The nature of the interaction will be modified with hydraulic jumps generated by microjets and we expect new flow patterns to appear.
- second, we will study heat transfers due to a difference in temperature between the liquid and the substrate. We will also question how phase transitions influence the behavior of the jet. Our approach will rely on experiments, in parallel to theoretical modeling. The mutual enrichment of these complementary approaches makes us confident in obtaining outstanding results in the hot topics investigated in this project.

Our new experiments will challenge the knowledge on these subjects, and they should result in striking results. Dissemination to the scientific community will be promoted through participation in numerous conferences in our different disciplines.

Among the intense research conducted on these topics internationally, this proposal will offer a wonderful opportunity to showcase the French activity in this domain.