Identifying the transition region between splashing and spreading of fuel drops

In many industrial processes, droplet splashing on heated surfaces can lead to uneven distribution, hotspots and temperature gradients that are both difficult to predict and control. By studying the effects of various parameters on the dynamics of a fuel drop impacting a heated surface, Akshay Sreenivasan and Sivakumar Deivandren sought to identify transition regions between droplet splashing and spreading.

The researchers found increasing the temperature of the surface suppresses splashing since it reduces the local gas density, which encourages spreading. In contrast, at lower temperatures, the initially spreading droplet forms a thin liquid sheet that splashes outward from its edges.

“It is the liquid sheet that destabilizes to eject secondary droplets that characterize splashing,” Deivandren said.

Before shifting from splashing behavior into pure spreading, the droplet enters a transition region. This transition is temperature dependent due to its effects on the droplet’s viscosity and Weber number. In this region, the liquid sheet merges back into the droplet rather than breaking up. The droplet then continues to spread without generating splash.

To observe this phenomenon, Sreenivasan and Deivandren used high-speed video imaging of the impact of a fuel drop onto a smooth test surface. They used a drop dispenser to make nearly identical droplets and varied the impact height and surface temperature.

The current experimental setting is an idealization, and additional parameters must be considered for real-world applications, such as fuel spray impingement and spray cooling.

“Previous studies point toward the role of surface roughness and wettability in altering the splash dynamics,” Deivandren said. “Hence, understanding the splashing of fuel drops on rough surfaces models these applications better.”

Source: “Splashing of fuel drops impacting on heated solid surfaces,” by Akshay Sreenivasan and Sivakumar Deivandren, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5139589 .