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November 3, 1998: Imagine trying to pour a glass of
orange juice in zero gravity. It may not be as easy as it sounds.
Without gravity to pull the fluid into the cup, you might end
up with a room full of orange mist -- tiny drops of OJ held together
by surface tension. How to control drops of fluid in low gravity,
and what happens inside a "colloidal mixture" like
orange juice (pulp suspended in a thinner fluid), are the subjects
of three fluid physics experiments on shuttle Discovery.
The first experiment, called Internal Flows in Free Drops, will
use sound waves to remotely control the position of free-floating
drops in the Microgravity Science Glovebox (see right).
Investigators want to measure the internal fluid flows induced
by the acoustic field as well as the surface tension on the drops.
Surface tension is the property of a liquid's surface that, like
a skin, holds it together. The results could improve manufacturing
processes here on Earth and in space by providing new ways to
monitor and control liquids.
The Physics of Orange Juice
Colloidal mixtures are systems of fine particles suspended in
fluid. Milk, orange juice, and paint are some common examples.
On Earth, gravity causes the denser particles in a colloidal
suspension to settle to the bottom, which is why some colloids,
like orange juice and paint, must be stirred before use. Microgravity
enables scientists to study colloids because the effects of density
differences between particles and their surrounding fluids are
decreased. "Settling" is less of a problem, and it's
possible to maintain an even distribution of particles in the
fluid. That's a big improvement over fluid experiments conducted
on Earth.
The Colloidal Disorder-Order Transition (CDOT) experiment will
use colloidal fluids in zero gravity to gain some insight into
atomic physics. Colloidal hard spheres will be suspended in liquid
in varying concentrations to model the behavior of atoms as they
form into orderly solid structures. In solutions with a certain
concentration of hard spheres, crystal-like structures form.
The behavior is similar to the changes in atomic structure that
take place in the transition from liquid to solid, such as when
water freezes and becomes ice. Initially, atoms in the water
are randomly distributed but, as the water freezes, atoms organize
themselves into crystalline patterns.
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Microgravity
Science Glovebox
A drop of fluid held in place by acoustic
waves in the Microgravity Science Glovebox
To many people, gloveboxes
are what medical researchers use to separate themselves from
deadly viruses. But gloveboxes come in many shapes and sizes.
The Microgravity Science Glovebox, developed at the NASA Marshall
Space Flight Center, is designed for hands-on work inside the
shuttle in the microgravity environment of space.
Don Thomas does some "hands-on"
science using the glovebox on a previous shuttle mission.
"It's a useful
device, to have a work station where you can run many different
kinds of experiments, where the crew can do hands-on work, where
you can make changes on the fly," said project scientist
Don Reiss of NASA Marshall's Space Sciences Laboratory. This
week the crew of Shuttle Discovery will use the glovebox for
experiments with fluids in space. more
information |
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