Dynamic Defrosting on Scalable Superhydrophobic Surfaces

Area of Science:

• Materials Science
• Surface Science
• Thermal Engineering

Background:

• Frost formation on superhydrophobic surfaces can occur in a suspended Cassie state.
• Melting Cassie frost can spontaneously form mobile, quasi-spherical slush droplets.
• The defrosting efficiency of Cassie frost versus conventional surfaces is not well-established.

Purpose of the Study:

• To systematically compare the defrosting efficiency of superhydrophobic and conventional hydrophobic surfaces.
• To investigate the influence of frost thickness on meltwater mobilization.
• To explore novel defrosting strategies using surface properties.

Main Methods:

• Characterization of frost defrosting on a dual-surface aluminum plate (superhydrophobic and hydrophobic).
• Evaluation of meltwater shedding at various tilt angles for different frost thicknesses.
• Demonstration of a dynamic defrosting method using inverted surface orientation.

Main Results:

• Superhydrophobic surfaces effectively shed meltwater from thick frost (>1 mm) even at low tilt angles.
• Hydrophobic surfaces showed minimal meltwater shedding, even at a 90° tilt.
• Thin frost layers (≲1 mm) did not mobilize on superhydrophobic surfaces due to high apparent contact angles preventing droplet coalescence.
• A novel upside-down defrosting method demonstrated uniform frost detachment and self-propagation.

Conclusions:

• Treating surfaces to promote Cassie frost is highly desirable for rapid, low-energy defrosting of sufficiently thick frost layers.
• Superhydrophobic surfaces enhance meltwater drainage, but are less effective for thin frost layers.
• Surface nanostructuring and orientation are critical factors for efficient frost removal.