Momentum - The Magazine for Virginia Tech Mechanical Engineering Vol. 4 No. 2 Summer 2019 | Page 8

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exclusive. Now, in a paper published in the
journal Joule, Boreyko and doctoral student
Ranit Mukherjee began to consider the orien-
tation of the surface and found that by using
vertical condensers, the teaming of superhy-
drophobic surfaces and gravity produces a
condenser that is at least twice as efficient.
Jumping
drops get
boost
from
gravity
Using superhydrophobic surfaces, which
have nano-pillars and a hydrophobic coating,
water droplets can unleash the power of
surface tension whenever two or more drops
touch and merge together, to jump away from
the surface regardless of the orientation of
that surface. However, not all droplets make a
clean getaway.
A decade ago a new
idea was brought into the
general scientific com-
munity – shedding water
from condensers was more
efficient by using surface
tension to make microscopic
water droplets "jump" off
the surface. The idea took
the research community by
storm.
Ranit Mukherjee and
Assistant Professor
Jonathan Boreyko
ROSAIRE
BUSHEY
MECHANICAL
ENGINEERING
“There are some droplets that either fail to
jump, or fall back on the surface,” Boreyko
explained. “Those droplets can then join with
others and form a buildup of condensation
that coats the condenser and limits its ability
to cool. For these larger droplets, where
jumping has failed, draining them by gravity
would be a great insurance policy.”
Historically, condensers were always ori-
ented vertically to allow the water to drain
by gravity. However, researchers looking at
surface-tension-powered droplets were mostly
studying the jumping phenomenon on flat
surfaces and not talking about the importance
of orientation.
“In the last decade since
I discovered the jumping
droplets, the debate has
been using gravity versus
jumping,” said Jonathan Boreyko, assistant
professor of mechanical engineering in the
College of Engineering. “The research has been so focused on using
surface tension to shed droplets instead of
gravity, that nobody considered that this
wasn’t an ‘and/or’ situation,” Boreyko said.
“It turns out that surface tension and gravity
work far better together than either works on
its own.”
The problem was, because the jumping itself
occurs independent of gravity, what happened
after the jump wasn’t being considered. Five
years after his original paper, Boreyko went
back to the lab to discover that for efficiency,
jumping and gravity should not be mutually “What we found illustrates that there is
a single, best way to shed moisture from
condensers which increases the efficiency
of a variety of items including power plants,
or anything that requires heat exchange,”
Mukherjee said.