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The Physics of Orange Juice

Shuttle experiments target the behavior of fluid mixtures in microgravity

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

strawberry and grape juice try to mix in space 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.

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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Experiment test samples will contain plastic spheres that are about one-tenth of the thickness of a human hair in diameter. In orbit, the samples will sit for several days while the spheres organize themselves. The spheres, like atoms, will settle into an arrangement that gives each sphere the most space. A sample with a low concentration of spheres is expected to maintain fluid movement, like atoms in a liquid. In samples with a very high concentration of spheres, no crystals will form. This last behavior is similar to the solidification of liquids into glass materials in which the atoms move so slowly that it takes millions of years for them to organize into crystalline structures.
For CDOT and another ongoing experiment, Structural Studies of Colloidal Suspensions (CGEL), researchers will shine laser light through the colloidal samples to study the arrangements of suspended particles. The laser light will be scattered from the surface of the structures, similar to the way sunlight "sparkles" on snow flakes.
While these investigations are being conducted inside the glovebox, three video cameras will record the action. These data are transmitted to scientists on Earth, allowing them to instruct the crew to make experimental adjustments if necessary.

Right: Shuttle video from STS-94. Deformation of a drop of water using ultrasound.

Web Links

 NASA Space Shuttle home page

ShuttlePressKit.com -- background information about STS-95

www.Microgravity.com -- learn more about low-gravity science at microgravity.com

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Author: Dr. Tony Phillips
Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Responsible NASA official: John M. Horack