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Inhibition of Condensation Frosting by Arrays of Hygroscopic Antifreeze Drops
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posted on 2015-12-29, 00:00 authored by Xiaoda Sun, Viraj G. Damle, Aastha Uppal, Rubin Linder, Sriram Chandrashekar, Ajay R. Mohan, Konrad RykaczewskiThe formation of frost and ice can
have negative impacts on travel
and a variety of industrial processes and is typically addressed by
dispensing antifreeze substances such as salts and glycols. Despite
the popularity of this anti-icing approach, some of the intricate
underlying physical mechanisms are just being unraveled. For example,
recent studies have shown that in addition to suppressing ice formation
within its own volume, an individual salt saturated water microdroplet
forms a region of inhibited condensation and condensation frosting
(RIC) in its surrounding area. This occurs because salt saturated
water, like most antifreeze substances, is hygroscopic and has water
vapor pressure at its surface lower than water saturation pressure
at the substrate. Here, we demonstrate that for macroscopic drops
of propylene glycol and salt saturated water, the absolute RIC size
can remain essentially unchanged for several hours. Utilizing this
observation, we demonstrate that frost formation can be completely
inhibited in-between microscopic and macroscopic arrays of propylene
glycol and salt saturated water drops with spacing (S) smaller than twice the radius of the RIC (δ). Furthermore,
by characterizing condensation frosting dynamics around various hygroscopic
drop arrays, we demonstrate that they can delay complete frosting
over of the samples 1.6 to 10 times longer than films of the liquids
with equivalent volume. The significant delay in onset of ice nucleation
achieved by dispensing propylene glycol in drops rather than in films
is likely due to uniform dilution of the drops driven by thermocapillary
flow. This transport mode is absent in the films, leading to faster
dilution, and with that facilitated homogeneous nucleation, near the
liquid–air interface.