Mechanical Technology April 2015

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40 Mechanical Technology — April 2015
⎪ Nota bene ⎪
Index to advertisers
Afrox........................................32
Axiom Hydraulics. .......................2
BMG............................. OFC, OBC
Bonfiglioli.................................12
EMS. ...................................... IFC
Festo........................................35
Hansen Industrial Gearboxes......IBC
Hytec Holdings..........................20
Lincoln Electric. ........................26
SASSDA...................................15
SEW Eurodrive..........................16
Voith........................................23
Industry diary
May 2015
SME Pressure Vessels Section VIII
Div 1
4-6 May
Johannesburg, Cedar Park Hotel
Phindi Mbedzi:+27 11 325 0686
Securex and A-OSH Expo
12-14 May
Gallagher Convention Centre
Marlene Bosch and Sven Riddle
+27 11 835 1565
African Utility Week and Clean
Power Africa
12-14 May
Cape Town International Convention
Centre
Spintelligent:+27 21 700 3500
Researchers at Drexel University
have developed a metallic nano
coating derived from a virus of
the tobacco plant that could lead to more
efficient steam production, improving the
performance of steam turbines, air condi-
tioning and electronics cooling systems.
Water’s transition from liquid to gas
has plenty of applications beyond the
kitchen: water treatment plants; heating
and air conditioning systems; and the
steam turbines that we use to produce
electricity are all heavily dependent on
this process. Making this transition even
slightly more efficient could have a big
impact on energy efficiency.
The breakthrough comes from an
unexpected source – a virus common to
tobacco plants. The tobacco mosaic virus
was the very first virus to be identified,
back in 1930, and has been studied in
detail since then. It’s a simple organ-
ism that consists of a single strand of
RNA surrounded by a dense network of
coating proteins. Today, scientists think
that this layout is ideal for building self-
assembling nanostructures.
Matthew McCarthy and his team at
Drexel University are using the virus to
create a special coating that uses capil-
lary forces to distribute water evenly
across a surface. When used to coat
the surface that separates a heat source
from the liquid being heated, the scien-
tists found that this coating helps boil
the liquid more than three times more
effectively.
As water (or any other liquid) starts to
boil, there comes a point where bubbles
of vapour form and stick to the surface
that separates the liquid from the heat
source. This point, known as the ‘critical
heat flux’, is problematic because these
air bubbles prevent local heating of the
liquid, overheating the surface instead.
To work around the issue, McCarthy’s
team used a mutation of the tobacco mo-
saic virus that features molecular ‘hooks’.
These hooks let the virus attach to nearly
any surface, be it stainless steel, alumin-
ium, copper, gold, silicon or a polymer.
The virus is then coated with a thin layer
of metal to form a solid structure that the
researchers called ‘metallic grass’.
When liquid comes in contact with
this surface, it quickly sticks and spreads
due to capillary forces, making it harder
for the surface to dry out even while
boiling. When air bubbles do form on the
surface, they also tend to leave faster, for
a much greater heating efficiency.
In the team’s preliminary results, ap-
plying the metallic grass coating to the
boiling surface showed a 240% increase
in critical heat flux, meaning that much
more heat can be transferred from the
heat source to the liquid before bubbles
start sticking to the boiling surface.
“Phase-change heat transfer plays an
important role in everything from power
generation to water purification, HVAC
and electronics cooling,” says McCarthy.
“Increasing performance of these systems
would translate into significant improve-
ments in the way we produce, consume
and conserve our energy and water
resources.”
McCarthy’s team will now look at
the performance of dozens of different
surface configurations, changing both
the spacing of the nanostructures and
the shape and the coating metal, so as to
find ways of improving the performance
of the coating even further. q
Inaugural Metals and Engineering Indaba 2015
The Southern African Metals and Engineer-
ing Indaba (MEIndaba 2015), hosted by the
Steel and Engineering Industries Federation
of Southern Africa (SEIFSA), will be held at
Emperors Palace, Ekurhuleni, Gauteng from
May 28-29, 2015. The event, the first of
its kind in the sector and will be graced by
high profile business, government and civil
society leaders.
Setting the tone is the first plenary ses-
sion, entitled: ‘Does Manufacturing Have a
Future in Southern Africa?’ with contribu-
tions from Trade and Industry minister, Rob
Davies; ArcelorMittal CEO, Paul O’Flaherty;
deputy chairman of the South African
Institute of International Affairs (SAIIA),
Moeletsi Mbeki; the Democratic Alliance’s
Geordin Hill-Lewis; and Bobby Godsell,
chairman of Business Leadership South
Africa. meindaba.co.za
Metallic grass coating for efficient steam production
A ‘metallic grass’ nano coating derived from a virus of
the tobacco plant has been found to significantly improve
heat transfer at the phase-change point, where gas
bubbles start to from on the heating surface.
The virus used is a simple organism that
consists of a single strand of RNA sur-
rounded by a dense network of coating
proteins.