Frost halos from supercooled water droplets

Area of Science:

• Physics
• Materials Science
• Chemistry

Background:

• Icing and frost formation on surfaces are common phenomena with significant impacts on safety and performance.
• The underlying mechanisms of water freezing, influenced by atmospheric conditions and surface properties, are complex and not fully understood.
• Developing ice-free (icephobic) surfaces requires a deep understanding of the initial ice formation processes.

Purpose of the Study:

• To investigate the intricate mechanisms of water freezing on solid surfaces, focusing on the role of evaporation and condensation.
• To elucidate how initial freezing events trigger subsequent frost propagation and affect surface behavior.
• To identify the key factors governing the extent of ice formation and spread.

Main Methods:

• Studied the freezing of supercooled sessile water droplets under controlled humidity conditions.
• Utilized substrates with a wide range of thermal conductivities (spanning three orders of magnitude).
• Observed the explosive evaporation and subsequent condensation halo formation during recalescent freezing.

Main Results:

• Explosive evaporation from a freezing droplet generates a condensation halo, leading to crystallization and altered surface behavior.
• The process involves simultaneous multiple phase transitions and can initiate sequential freezing, causing domino-effect icing and frost propagation.
• The final size of the frozen condensate halo is determined by the interplay between heat diffusion and vapor transport, controlling frost spread.

Conclusions:

• The study reveals a novel mechanism of ice formation initiated by droplet freezing and subsequent condensation halo crystallization.
• The balance between heat and vapor transport critically influences the extent of frost formation and propagation.
• Findings provide crucial insights for designing advanced icephobic surfaces and managing icing phenomena.