Fluid Merging Viscosity Measurement (FMVM) - 07.14.16
This experiment is designed to test a new method for measuring the viscosity of high viscosity materials by measuring the time it takes two nearly free-floating drops of a liquid to merge. The materials used are of known viscosities (corn syrup, glycerin and silicone oil) so that the accuracy of the fluid merging test can be compared to the methods used on Earth. The FMVM experiment can lead to a greater understanding of glass formation from melted lunar soil. It will also lead to a better understanding of liquid phase sintering processes for in-space fabrication methods that can be used for constructing surface habitat structures. Science Results for Everyone
Just a drop will do it. This experiment tested a method for determining a material’s fluid thickness, or viscosity, by measuring how long it takes two nearly free-floating drops of liquid to merge. Researchers used four materials with known viscosity – honey, corn syrup, glycerin, and silicone oil – in seven different conditions. Preliminary data demonstrate that a numerical model can calculate viscosity based on the surface tension of a liquid and the time it takes for drops to merge. This model will provide insight into behavior of glasses, useful for potential fabrication of structures in space and in the casting industry. Experiment Details
Edwin C. Ethridge, Ph.D., Marshall Space Flight Center, Huntsville, AL, United States
Basil N. Antar, Ph.D., University of Tennessee Space Institute, Tullahoma, TN, United States
William F. Kaukler, Ph.D., University of Alabama at Huntsville, Huntsville, AL, United States
NASA Marshall Space Flight Center, Huntsville, AL, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
April 2004 - October 2004; April 2005 - October 2005
Viscosity measurements of molten metals have been conducted previously in space but this droplet merging test has not yet been conducted aboard the Station.
- This experiment is designed to test a new method for measuring the viscosity (fluid thickness) of high viscosity materials by measuring the time it takes two nearly free-floating drops of a liquid to merge.
- It will measure the time for coalescence of drops from four materials of known viscosities: honey, corn syrup, glycerin and silicone oil to determine the accuracy of the fluid merging test and determine its future applications.
- This information will provide valuable insight into the behavior of glasses for potential fabrication in space and will also be useful for liquid phase sintering processes used in the casting industry.
The Fluid Merging Viscosity Measurement (FMVM) experiment was developed rapidly after the Columbia accident to provide a low-mass experiment using hardware already on board ISS. The purpose of FMVM is to measure the rate of coalescence of two highly viscous liquid drops and correlate the results with liquid viscosity and surface tension. The FMVM experiment will verify a new method for measuring the viscosity of highly viscous liquids by measuring the time it takes for two spheres of liquid to coalescence into a single spherical drop, where the time constant is proportional to the viscosity. The results are applied to calculating crystallization parameters of a liquid above and below the glass melting point, including an extremely broad range of viscosities of the liquid.
If this new method of measuring viscosity is validated, it could provide a method by which to measure viscosities of materials that cannot currently be measured. An example of this is liquid (molten) glass that crystallizes while cooling from liquid to solid. The viscosity in most of the crystallization range cannot be measured using current, Earth-based technology in spite of the fact that this is the most interesting range for the study of crystallization.
To obtain accurate data for precise models, it is best to measure viscosity in liquid that is free-floating and uncontained. The station's microgravity environment is an excellent testbed for this procedure because drops float freely in low gravity. The simple test apparatus was constructed of materials already on board ISS, and sample liquids, representing a range of viscosities, were deployed to station on a Russian Progress vehicle. These liquids consisted of glycerin, silicone oil (high and low viscosities), honey, honey mixed with water, corn syrup, and corn syrup mixed with water.
Understanding the viscosity of molten materials and coalescence of liquid drops is important for everything from glass formation laboratory experiments to industrial materials processes such as sintering (a method of fusing together particles of material at lower temperatures and without melting). Viscosity 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. Micro-gravity advantageously eliminates the gravitational distortion of liquid drops, permitting liquids to be suspended in a free-floating condition. Scientists can measure the viscosity of low viscosity liquids such as molten metal in low-gravity levitators, by measuring vibrations of liquid drops. However, the oscillation method cannot be used on more viscous liquids like molten glass, since they will not oscillate. The FMVM experiment can ultimately lead to a greater understanding of glass formation from melted lunar soil. It will also lead to a better understanding of liquid phase sintering processes for in-space fabrication methods that can be used for constructing surface habitat structures from sintered lunar soil and vehicle components for longer-term space missions.
This new viscosity measuring process is ideally suited for use with difficult glass forming liquids. It can be used to make measurements that are impossible by other methods. The droplet merging method of viscosity measurement might be applied to small glass samples melted in terrestrial containerless levitation processing facilities.
It will also be possible to measure the viscosity of undercooled liquids much more rapidly than with other viscosity methods. Methods being developed by the FMVM experiment will make it possible to determine the viscosity of highly undercooled viscous glassy liquids at temperatures impossible with current methods. New methods to measure viscosity at very low shear rates also has technological significance. This method should permit the investigation of the non-Newtonian viscosity behavior of glasses at very low shear rates. Such viscosity data will be very useful for the modeling of crystallization behavior of materials of scientific interest.
Examination of the droplet shape changes with time can also lead to a better understanding of terrestrial industrial and in-space processes. The coalescence of drops has direct application to the science of liquid phase sintering. It should be possible to test models for liquid drop coalescence used to understand liquid phase sintering. Insight into the materials deposition processes is also important to the industrial process of rapid prototyping.
Operational Requirements and Protocols
Conducted inside the ISS Maintenance Work Area. Crew will release a liquid drop from a syringe onto 2 separate strings and record digital video of the drops as they merge together after being brought into contact by the crewman. Several fluids with different viscosities (glycerin, honey, corn syrup and silicone oil) will be used. Each will be evaluated several times with different drop diameters for each sample.
For each test, crew members will release a drop from a syringe onto separate strings and record digital video 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.
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FMVM tests a new method for measuring the viscosity of high viscosity materials by measuring the time it takes two nearly free-floating drops of a liquid to merge. Preliminary results from data analysis indicate agreement with the predicted coalescence time (Antar 2006). The experiments demonstrate that when the surface tension of a liquid is known, the coefficient of viscosity for that liquid can be determined by the contact radius speed. These data can be fit to numerical results to calculate the viscosity, thus validating the model for this new viscosity measurement method (Antar 2007).
The original data tapes for the FMVM investigation were returned to Earth on Space Shuttle flight STS-114/LF-1 in August 2005; later experiments were carried out onboard ISS in July of 2004 and May of 2005. The behavior of two coalescing drops in microgravity was examined; calculations were run on seven different conditions to determine the theoretical coalescence half time (time at which the neck diameter of the converging drops was half the original drop diameter) for each condition. These results were then compared with the observed times from experiments conducted on board ISS and were found to be in close agreement, with the exception of the high viscosity silicone oil condition (which may have been due to invalid initial conditions input to the analytical model). The results of this experiment validate this numeric model used to calculate a liquid’s viscosity from measured half time coalescence and known surface tension (Ethridge 2009).
Ethridge EC, Antar BN, Lehman D. Fluid Merging Viscosity Measurement (FMVM) Experiment on the International Space Station. 45th Aerospace Sciences Meeting and Exhibit, Reno, NV; 2007
Ethridge EC, Kaukler WF, Antar BN. Modeling of the Fluid Merging Viscosity Measurement (FMVM) International Space Station experiment with Comsol MultiPhysics. 47th Aerospace Sciences Meeting and Exhibit, Orlando, FL; 2009 January 7 pp.
Ground Based Results Publications
Antar BN, Ethridge EC, Maxwell D. Utilization of Low Gravity Environment for Measuring the Viscosity of Highly Viscous Liquids. Advances in Space Research. 1999; 24(10): 1289-1292. DOI: 10.1016/S0273-1177(99)00735-8.
Antar BN, Ethridge EC, Maxwell D. Viscosity Measurement Using Drop Coalescence in Microgravity. Microgravity Science and Technology. 2003; 14: 9-19.
Antar BN, Ethridge EC, Maxwell D. Viscosity Measurement of Highly Viscous Liquids Using Drop Coalescence in Low Gravity. 37th AIAA Aerospace Sciences Meeting, Reno, NV; 1999 Jan 11-14
NASA Fact Sheet
NASA Image: ISS009E14557 - This image shows Mike Fincke in front of the MWA with a syringe of corn syrup liquid.
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NASA Image: ISS009E14560 - This image shows Mike Fincke deploying one of the liquid drops onto the Nomex thread.
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This image shows two 4 ml silicone oil viscosity standard liquid drops in the process of coalescing to a single spherical drop. Image courtesy of Marshall Space Center.
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This image shows two 0.5 ml drops of corn syrup in the process of coalescing to a single spherical drop. Image courtesy of Marshall Space Center.
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Image of two honey drops before merging on ISS Expedition 11. Image courtesy of Marshall Space Center.
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