To de-ice planes on the fly, researchers aim to control rather than
combat ice formation

Date:
July 27, 2021
Source:
Virginia Tech
Summary:
How do you control ice formation on a plane, even when it's in
flight? Engineers are developing an approach using ice itself. They
created a de- icing method that exploits how frost grows on pillar
structures to suspend ice as it forms into a layer that's easier
to remove.



FULL STORY ==========================================================================
How do you control ice formation on a plane, even when it's in
flight? Jonathan Boreyko, associate professor in the Department of
Mechanical Engineering, is leading a team working with Collins Aerospace
to develop an approach using ice itself. In a study published in Physical Review Letters, they created a de- icing method that exploits how frost
grows on pillar structures to suspend ice as it forms into a layer that's easier to remove.


==========================================================================
Ice formation on airplanes can be both an aggravation and a health hazard.

Watching an airport departure board for delays because of ice is familiar territory for winter travelers, and the National Transportation Safety
Board reports a total of 52 in-flight accidents attributed to ice
formation between 2010 and 2014, resulting in 78 fatalities.

De-icing a plane at the airport prior to takeoff is possible, but planes
also experience plummeting temperatures and rapid ice formation in
flight. Once ice forms on the wings, it can greatly inhibit a pilot's
ability to safely operate the aircraft. Equipping planes with the
ability to remove ice while flying at altitudes between 35,000 and
42,000 feet would provide a better set of tools to maintain safety,
the researchers believe.

Putting ice on a pedestal Boreyko's team worked from the knowledge that
water droplets behave in different ways, depending on the surface. They
aimed to leverage a principle known as Cassie's Law, which shows that
air can be trapped under water drops if the drops are suspended atop a structure that is bumpy and water-repellent.

With a structure that could trap air underwater in this "Cassie state,"
the researchers sought to make ice form in a layer with lower adhesion
to the surface.

Making a surface water-repellent typically requires a chemical coating
that must be periodically replenished, Boreyko explained, and the bumpy
surface also tends to wear over time. The team opted for a novel approach,
with the goal of making a water-repellent surface that doesn't require
fragile chemical coatings or ultra-fine bumps. Instead, they opted for
a simple and durable structure in the form of aluminum, millimeter-sized pillars.

Boreyko's team created an array of pillars, each one millimeter tall
by half a millimeter wide. The tiny pedestals were machined into a
pattern with a millimeter between. As the temperature dropped, frost preferentially grew on the tops of the pillars, resulting in elevated
frost tips. As more water was added, it was absorbed into this porous
frost layer. When water drops were subsequently impacted on the surface,
they were caught on the frost pedestals.

These freezing drops created tiny "ice bridges," as lead author Hyunggon
Park described, that sealed the gaps of air in the valleys between the frost-tipped pillars. "When impacting water drops froze on the surface,
we made an interesting observation: The water drops were being caught by
the frost tips and building ice bridges to trap air pockets underneath,"
Park said. Over time, a continuous and air-trapping ice canopy formed
over the frost-tipped pillars.

Whereas other de-icing methods may still allow a sheet of ice to adhere
more directly to a large surface area, these trapped air gaps cause
the sheet to be suspended, lowering the amount of adhesion ice has to
the surface.

"By using larger pillars in place of nanostructures, and frost tips in
place of a hydrophobic coating, we found we can get the same benefit of trapping air underneath the forming ice while avoiding the durability concerns," Boreyko said. "This should make our approach practical for
enhancing de-icing on aircraft or heat exchangers." With a weaker bond,
it's possible to use the air pockets to then push ice away.

This will be the next step in the researchers' process, as Boreyko's
team continues to develop their method.

========================================================================== Story Source: Materials provided by Virginia_Tech. Original written by
Alex Parrish. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Hyunggon Park, S. Farzad Ahmadi, Jonathan B. Boreyko. Using Frost to
Promote Cassie Ice on Hydrophilic Pillars. Physical Review Letters,
2021; 127 (4) DOI: 10.1103/PhysRevLett.127.044501 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210727171642.htm

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