Freezing in a drop impacting a cold substrate: Where dendrites can't penetrate?

Area of Science:

• Physics of Fluids
• Materials Science
• Aerospace Engineering

Background:

• Ice accretion on cold surfaces from supercooled water drops (SLD) presents significant challenges in aviation and infrastructure.
• The freezing behavior of SLD, specifically the formation of dendritic ice structures and subsequent runback ice, is not fully understood.
• Existing hypotheses suggest the relative thicknesses of ice and liquid layers influence freezing patterns.

Purpose of the Study:

• To investigate the freezing dynamics of supercooled water drops impacting cold surfaces.
• To determine the critical factors governing the formation of dendritic ice structures versus non-dendritic ice layers.
• To develop a predictive model for ice accretion phenomena.

Main Methods:

• High-speed imaging was used to observe the freezing of room-temperature and supercooled water drops on cold substrates.
• Experiments were conducted at substrate temperatures as low as -35°C and -10°C for supercooled drops.
• A wind tunnel was utilized to control impact velocity for supercooled drops in a cold chamber.

Main Results:

• Three distinct freezing regimes were identified: dendrite propagation, thin ice layer expansion, and reverse freezing.
• A one-dimensional heat conduction model was developed, incorporating temperature-dependent thermal properties.
• A critical threshold was established: dendritic ice formation occurs when the supercooled liquid layer is thicker than the propagating ice layer.

Conclusions:

• The study successfully explains the observed freezing regimes based on the relative thicknesses of ice and liquid layers.
• Theoretical predictions from the heat conduction model align well with experimental data.
• Findings provide crucial insights into freezing dynamics, with direct implications for improving ice prediction models in aerospace applications.