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Fact sheet number: FS-2003-09-118-MSFC
Release date:

Fluid Merging Viscosity Measurement (FMVM)

Experiment Name: Fluid Merging Viscosity Measurement (FMVM)

Mission: To be delivered on Progress 13P; experiment to be conducted during International Space Station Expedition 8 and/or Expedition 9

Experiment Location: Maintenance Work Area in Destiny Laboratory Module

Investigators: Dr. Edwin Ethridge, NASA Marshall Space Flight Center, Huntsville, Ala., Dr. Basil Antar, University of Tennessee Space Institute, Tullahoma, Tenn., and Dr. William Kaukler, University of Alabama in Huntsville, Ala.

Project Manager: Jim Kennedy, NASA Marshall Space Flight Center, Huntsville, Ala.


For this experiment, scientists are mainly interested in studying viscosity - a property of fluids that causes them to resist flowing because of the internal friction created as the molecules move against each other. Viscosity can be thought of as "thickness" of the fluid. For example, honey is more viscous than water. Water molecules would flow through a small tube quicker than honey because its molecules are less viscous; the more viscous honey would move through the same tube at a slower rate.

Understanding the viscosity of molten materials is important for everything from designing laboratory experiments to industrial production of materials. It is one of the key parameters that materials scientists must measure to create accurate models predicting the best methods for materials production. Understanding and controlling viscosity can even enable researchers to make new materials or improve existing ones.

Scientists can measure the viscosity of low viscosity liquids such as molten metal in low-gravity, by measuring vibrations of liquid drops. This method cannot be used on more viscous liquids. The FMVM experiment will verify a new method for measuring the viscosity of viscous liquids by measuring the time it takes for the two spheres to coalescence into a single spherical drop.

Studying extremely viscous materials in space, such as glass, can also provide data that is difficult to obtain on Earth. When glass is processed on Earth, the molten glass crystallizes if it touches any part of the container wall, and the viscosity cannot be measured once the liquid crystallizes. This is particularly true for exotic glasses created by undercooling - cooling the glass below the temperature at which it would normally form a solid.

To obtain accurate data for precise models, it is best to measure viscosity in liquid that is free-floating and uncontained. The International Space Station's microgravity environment is an excellent test bed for this procedure because drops float freely in low gravity.

This experiment will also provide data useful for understanding the sintering of materials in low-gravity. Sintering is a method for forming powders into solid shapes. This data can be used for materials that may be fabricated and manufactured in space.

Experiment Operations

Much of the hardware used for this investigation is already available on the International Space Station. The experiment will be conducted inside the Space Station Maintenance Work Area -- a portable workbench with a tabletop that measures 36 inches by 25 inches. When not in use, it is folded and stored inside a drawer.

The Maintenance Work Area can be used throughout the Station. An astronaut unfolds and clamps it to a slotted mechanism similar to seat tracks found in cars or airplanes. The tracks are located on the sides of most of the floor-to-ceiling racks inside the Station. Gloveports on the sides and ends of the workbench's plastic cover and a front flap that unzips allow crew members to conduct the experiment but still contain the liquid.

For each test, crew members will release two drops from a syringe onto strings and record digital images of the drops as they coalesce to form one drop. One way to measure viscosity is to measure how long it takes two spheres of liquid to merge into a single spherical drop. On contact a neck will from between the two drops. This neck will increase in diameter until the two drops become one single sphere.

On Earth, gravity distorts liquid spheres and drops are too heavy to be supported by strings. Drop distortion should not occur in the Space Station's microgravity environment, and the drops can be held on strings. Without gravity's influence, the drops' movement and coalescence should be controlled by surface tension and viscosity.

To verify this technique as an accurate method for measuring viscosity, the experiment will use fluids with known viscosities: honey, corn syrup, glycerin and silicone oil. Several runs will be conducted - some with equal diameter drops and others with different size drops. The initial diameters of the drops will be measured.

The experiment will be videotaped with a digital color camera so investigators can watch the drops combine and measure the rate of shape change. They will observe how the "neck" --the place were the drops connect - is formed and how the neck grows to form the final, single drop.

Investigators may monitor the video from the Telescience Center - a work area at the Marshall Center where scientists monitor and communicate with experiments on the Space Station.

Experiments were conducted on NASA's KC-135 - an aircraft that flies in a roller coaster-like parabolic flight patterns and exposes experiments to a few seconds of low gravity. The experiment on the Space Station can be conducted over much longer periods in microgravity, allowing investigators to measure the viscosity of larger drops and more viscous fluids.


The data will provide insight to the behavior of glasses - materials that may be used to fabricate parts or equipment for long-term space missions. The viscosity measurements can be used in models that predict the viscosity of materials processed by a variety of methods. This will improve future materials processing experiments carried out in space and on Earth.

More Information

More information on this experiment and other Space Station experiments is available at:

Steve Roy
Public Affairs Office
(256) 544-0034

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