Simulation of the spreading of a gas-propelled micro-droplet upon impact on a dry surface using a lattice-Boltzmann approach

Abstract

Spray cooling is one of the most promising methods of cooling high heat flux electronics. Depending on the type of the nozzle, spray cooling can be categorized as single phase or two phase.In the latter, which is known to be more effective, a secondary gas is used to further pressurize the liquid and form smaller droplets at higher velocities. The gas is also assumed to assist the spreading phase by imposing normal and tangential forces on the droplet free surface which adds to the complicated hydrodynamics of the droplet impact. Moreover, the order of magnitude of droplet size in spray cooling is 10 −6 m thereby introducing a low Weber and Reynolds numbers impact regime which heretofore has not been well understood. A 3D lattice Boltzmann method was implemented to simulate the impact of a single micro-droplet on a dry surface in both ambient air and under a stagnation gas flow. Two cases were closely compared and correlations were proposed for the instantaneous spreading diameter. Contrary to recent findings at higher impact We and Re, it was found that stagnation flow only significantly affects the spreading phase for Ca * ≥ 0.35 but has little influence on the receding physics.

Airflow-Assisted Impact of Drops of Various Viscosities: The Role of Viscous Dissipation, Normal Imposed Pressure, and Shear Flow of Air

“…When the Weber number is high, the incident airflow does not affect the spreading significantly but affects the receding and suppresses the splashing. 2,4 Both the retraction rate and the rise of the drop on the surface decline with the Reynolds number of air. 23 However, the spreading does not always increase with the Reynolds number of air; the combination of the rise in the impact Weber number and the Reynolds number of air increases the deceleration rate and restricts the radial movement of the drop.…”

“…The impact of drops is essential because of its broader application, e.g., spray cooling, − metal forming, plasma spraying, inkjet printing, , and soil erosion by rain . The study of enhancing a drop spreading on a given surface is mostly targeted because of obvious reasons, e.g., to enhance cooling.…”