Fingering patterns during droplet impact on heated surfaces

Area of Science:

• Fluid dynamics
• Thermodynamics
• Heat transfer

Background:

• The Leidenfrost effect describes a liquid droplet levitating on a hot surface due to vapor.
• Previous studies qualitatively described the transition to the Leidenfrost regime as abrupt.
• The "contact-boiling" regime is characterized by intense boiling before the Leidenfrost state.

Purpose of the Study:

• To quantitatively characterize the transition to the Leidenfrost regime.
• To investigate the role of vapor flow in the Leidenfrost transition.
• To identify a measurable parameter for describing the transition dynamics.

Main Methods:

• Experimental observation of droplet impingement on heated surfaces.
• Analysis of the wetted area as a function of surface temperature.
• Visualization of vapor flow patterns beneath the droplet.

Main Results:

• The wetted area serves as a continuous quantitative measure of the transition to the Leidenfrost regime.
• Wetted area is a continuous function of surface temperature up to the Leidenfrost point.
• Fingering patterns in the wetted area indicate significant vapor flow under the liquid.

Conclusions:

• Vapor transport plays a critical role in the Leidenfrost transition.
• The study reveals the physical mechanism driving the transition to the Leidenfrost regime.
• The wetted area provides a novel, quantitative method for studying this phenomenon.