Office of News and Information
212 Whitehead Hall / 3400 N. Charles Street
Baltimore, Maryland 21218-2692
Phone: (410) 516-7160 / Fax (410) 516-5251
April 10, 1996
CONTACT: Phil Sneiderman
Hopkins Scientists Hope to End Bubble Troubles
Put a pot of water on a hot stove, and you'll soon see steam
bubbles scurrying toward the surface. But if you try to boil
water aboard an orbiting space shuttle, something different will
occur: One huge bubble will form along the heated surface and
stay there, refusing to carry heat away. Soon, portions of the
heated container will dry out, and it may crack.
Bubbles can be troublesome in the gravity-free environment
of space. But by using sound waves, electric fields and forced
liquid currents, three scientists at The Johns Hopkins University
hope to make bubbles behave in more productive ways when gravity
The research is important because bubbles play a major role
in cooling and water purification, which will be crucial as space
vessels spend more time in weightless conditions. To address the
bubble problem, NASA's Microgravity Science and Applications
Division recently awarded multi-year research grants to three
faculty members in Hopkins' Whiting School of Engineering.
Aboard a space ship or an orbiting lab, rocket engines,
electronic equipment and solar radiation all generate heat, which
must be eliminated. Although commonly associated with cooking,
boiling is a highly efficient cooling process. "Boiling is the
single best way to transfer heat," said Andrea Prosperetti, a
mechanical engineering professor and grant recipient.
In normal gravity, he explained, small bubbles form when a
heated surface turns the liquid into vapor. Because gas bubbles
are lighter than the surrounding liquid, they soon detach and
float upward. As they rise, the bubbles stir the liquid, condense
and transfer some of their heat to the cooler water. In
weightless space, however, the bubbles don't rise because they
are no longer much lighter than the water around them. Instead,
one giant bubble forms and merely sticks to the hot surface.
"What I am going to look at is, what happens if you put a sound
field, an ultrasonic field, in the water?" Prosperetti said. "Can
you remove the bubbles that way?"
The Hopkins professor, collaborating with Eugene Trinh at
the California Institute of Technology, plans to send a standing
sound wave, pitched at 20 kilohertz, into the liquid, bouncing it
off the bottom. The sound is at the upper limits of the human
hearing range but well within that of a dog. "The bubbles should
pulsate, oscillate in response to the sound field," Prosperetti
said. "That should help in dislodging them from the surface."
Cila Herman, an assistant professor of mechanical
engineering, will attack the space bubble problem with another
tool. She plans to insert electrodes and apply 30 kilovolts,
forming an electric field in the liquid. "The force that is
generated by the electric field should replace the buoyancy," she
said. She plans to try various shapes of electrodes to see which
are most effective. Herman will study the heat transfer with
holographic interferometry, an innovative form of photography
that uses lasers and high-speed film.
The third Hopkins scientist, Hasan N. Oguz, an associate
research professor of mechanical engineering, will experiment
with bubbles that do not result from boiling. He will use a
hypodermic needle to push air into a liquid-filled tube in the
same way that bubbles are forced into a fish tank.
On Earth, a small bubble will form at the needle's tip, then
detach. "What happens in space is that initially it's very
similar," Oguz said. "But this process never stops. That's the
problem. You get a giant bubble, and it never detaches." To
remedy this, Oguz will pump additional liquid along the
sides of the needle, so that these currents will pull the bubble
loose. "You need very little flow to achieve this because the
tube restricts the flow around the bubbles," he said. In space,
Oguz' technique could be used in water purification systems,
which require the injection of oxygen.
Although initial work will be done in university labs, the
Hopkins bubble experiments may later be tested in drop towers,
which briefly simulate low-gravity conditions. In several years,
Herman expects to check her work aboard an astronaut-training jet
that flies a parabolic course to create a short period of
stomach-churning weightlessness. "I'm looking for graduate
students who don't get motion sickness," she said.
Johns Hopkins University news releases can be found on the
World Wide Web at
Information on automatic e-mail delivery
of science and medical news releases is available at the