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Capillary Flow Experiments-2 (CFE-2)

A Lab Aloft: The Advantage of Laboratory Time in Space

Guest blogger Dr. Mark Weislogel shares his thoughts on the advantages of working long-duration investigations on the International Space Station.

By engaging in long-duration investigations, there is time to think things over and, when unexpected events occur, there is time to respond in a creative and curious way.

 Time, resources and astronaut involvement factor into the success of long-duration investigations on the station.

The full text for this blog is available here.

The entry for the A Lab Aloft blog can be found at:

Upcoming Events

  • June 2013 – The second set of Interior Corner Flow (ICF) vessels (ICF3, ICF5, ICF6, ICF7, and ICF8) were launched on board the ATV-4 on June 5, 2013. Operations on board the ISS are continuing for the first set on CFE-2 vessels ICF4 and ICF9.

  • November 2012 – The first set of ICF vessels (ICF4 and ICF9) were launched on SpaceX-1 on October 7, 2012, then transferred to the ISS.  The next set of five ICF vessels (ICF3, ICF5, ICF6, ICF7 and ICF8) are currently going through environmental testing on the ground in preparation for flight and are scheduled to launch on ATV-4 in April 2013.
  • October 2012 The next set of ICF vessels (ICF4 and ICF9) are tentatively scheduled to launch on SpaceX-1.  Five additional ICF vessels (ICF3, ICF5, ICF6, ICF7, and ICF8) are tentatively scheduled to launch on SpaceX-2 at the end of 2012.  Each ICF vessel is uniquely designed to explore the effect of the vessel geometry on interior corner wetting in microgravity.

  • May to June 2012 – The final two scheduled Vane Gap 2 (VG2) unfilled perforations tests were completed.   Don Pettit completed a test on May 10, 2012, and Joe Acaba completed the second test on June 13, 2012.  Both Don and Joe were able to find all four critical wetting angles.  All scheduled unfilled perforation tests have been completed for VG2.

  • May 2012 – Astronaut crew training was held for Capillary Flow Experiments 2 (CFE-2) flight experiments on April 30 and May 1 at NASA JSC.  Astronauts Chris Cassidy (Increments 35-36) and Karen Nyberg (Increments 36-37) were trained with the CFE-2 ICF4 and ICF9 trainer units, including installation on a Maintenance Work Area (MWA) in a mockup of the ISS LAB module.  CFE-2 training was performed by Chuck Bunnell (ZIN).  The CFE-2 PI, Mark Weislogel attended and provided a science overview for the CFE-2 experiment.

  • March 29, 2012 – A Systems Acceptance Review (SAR-1) was held for ICF4 and ICF9 to verify the hardware is ready for flight.  The ICF4 and ICF9 hardware passed the SAR-1 review and are being prepared for flight on SpaceX-1.

  • January to March 2012 – Increment 30 commander, Dan Burbank, and flight engineer, Don Pettit, completed a series of vane gap tests with filled (VG1) and unfilled (VG2) vane perforations to determine critical wetting angles.  An extra science test was also completed using the ICF1 vessel.  All test matrices and extra science runs have been completed for VG1 and ICF1.

  • January 26, 2012 – Astronauts Sunita Williams, Tom Marshburn, and Kevin Ford were trained on installation of CFE-2 units on the Maintenance Work Area (MWA) and CFE-2 science operations. Oct. 7, 2011 – Increment 29 commander, Mike Fossum performed a Filled Perforations test of VG1 investigating the critical angles in quadrants 3 and 4.  Observed the same bulk shift phenomena initially observed during the Sept. 15 test.

  • Sept. 30, 2011 – Increment 29 commander, Mike Fossum performed the VG2 initial “Dry Chamber” test and found the expected critical angles within 3-4 deg of predictions.

  • Sept 15, 2011 – Increment 28 flight engineer, Mike Fossum performed the first Filled Perforations test of VG1 investigating the critical angles in quadrants 1 and 2.  Observed a bulk shift phenomena, i.e. movement of fluid from one side of vane to the other at base of test chamber.

  • May 3, 2011 – The ISS flight engineer Ron Garan operated the CFE-2 Interior Corner Flow2 (ICF2) vessel in the US Lab on the Maintenance Work Area (MWA).  The test operation consisted of two compressed bubble tests in the transport tube of the ICF2 vessel. The Principal Investigator, Mark Weislogel was at the NASA Glenn Research Center to observe and direct operations from the Telescience Support Center.

  • January 18, 2011 – Cady Coleman completed 3 test runs on the CFE-2 Interior Corner Flow2 (ICF2).  This series of tests were performed with ICF2 to test capillary flow with bubbles in the test fluid.

  • December 2010 - Capillary Flow Experiment-2 (CFE) Vane Gap-1 operated on ISS.  The CFE Van Gap-1 (VG-1) module was operated for a fourth time by Increment 25 astronaut Scott Kelly on Wednesday, December 8, 2010. 

  • September 29, 2010 – The CFE-2 experiment launched 4 test vessels on STS-131/Flight 19A in April 2010. On September 7, 2010 the CFE-2 experiment was set up in the Japanese Experiment Module and operated by crewmember Shannon Walker. To date CFE-2 has completed 11 of 16 Interior Corner Flow 1 (ICF1) test points.

Capillary Flow Experiment (CFE) Vane Gap-1 experiment
Capillary Flow Experiment - NASA astronaut Scott Kelly, Expedition 26 commander, works on the hardware setup for a Capillary Flow Experiment (CFE) Vane Gap-1 experiment. The CFE is positioned on the Maintenance Work Area in the Destiny laboratory of the International Space Station. CFE observes the flow of fluid, in particular capillary phenomena, in microgravity.

Download Video: MP4, WebM, Ogg

Astronaut Don Petit demonstrates how to use a cup he made from a piece of transparency paper. The unique shape allows him to drink his coffee in zero gravity without having to suck it from a bag.

• Capillary Flow Experiments (CFE-2) consists of eleven approximately 1 to 2 kg test vessels designed to probe certain capillary phenomena of fundamental and applied importance, such as: capillary flow in complex containers, critical wetting in discontinuous structures and surfaces, and passive gas-liquid phase separations. Quantitative video images from the simply-performed flight experiment crew procedures will provide immediate confirmation of the usefulness of current analytical design tools, as well as provide guidance to the development of new ones.

• Vane Gap experiments investigate a fundamental, geometric critical wetting condition that occurs in complex systems where one or more substrates are porous (i.e. screens or perforated plates). The experiments determine both dynamic wetting and equilibrium interface behavior.

• Interior Corner Flow experiment quantifies the nature of large length scale capillary flows and bubbly capillary flows throughout 3-dimensional polygonal containers for the purpose of theory development, verification, a demonstration of passive phase separation.

Capillary Flow Experiments (CFE)


The CFE experiment was completed in November 2007 and all 6 CFE units were returned. CFE was operated 19 times over Increments 9-16 (August 2004 thru November 2007), exceeding the original test matrix of 6 planned operations. The experiment utilized 55+ crew hours and 7 different astronauts have operated CFE (M. Fincke, W. McArthur, J. Williams, M. Lopez-Alegria, S. Williams, C. Anderson, P. Whitson). Approximately 39 hours of video data were recorded and downlinked, and included over 700 individual test points. Over fifteen invited, published and other technical presentations on the CFE status and results have been made to date. Two journal articles have been published and a third is in preparation.


The Capillary Flow Experiments (CFE) are a suite of fluid physics flight experiments designed to investigate large length scale capillary flows and phenomena in low gravity. The CFE data to be obtained will be crucial to the Space Exploration Initiative, particularly as it pertains to fluids management systems such as fuels and cryogen storage systems, water collection and recycling, thermal control systems, and materials processing in the liquid state.  NASA’s current plans for exploration missions assume the use of larger liquid propellant masses than have ever flown on interplanetary missions. Under low-gravity conditions, capillary forces can be exploited to control fluid orientation so that such large mission-critical systems perform more reliably.

CFE Experiment Video

Download Video: MP4, WebM, Ogg

CFE is a simple fundamental scientific study that can yield quantitative results from safe, low-cost, short time-to-flight, handheld fluids experiments. The experiments aim to provide results of critical interest to the capillary flow community that cannot be achieved in ground-based tests such as tests to probe dynamic effects associated with a movingcontact boundary condition, capillary-driven flows in interior corner networks, and critical wetting phenomena in complex geometries. Specific applications of the results center on particular fluids challenges concerning propellant tanks. The knowledge gained will help spacecraft fluid systems designers increase system reliability, decrease system mass, and reduce overall system complexity.

CFE encompasses three experiments with two unique experimental units per experiment. There are multiple tests per experiment. Each of the experiments employs parametric ranges and test cell dimensions that cannot be achieved in groundbased experiments. All units use similar fluid injection hardware, have simple and similarly sized test chambers, and rely solely on video for highly quantitative data. Silicone oil will be used for these tests. Differences between units are primarily fluid properties, wetting conditions, and test cell geometry. The experiment procedures are simple and intuitive.

CFE Interior –ICF

Spontaneous capillary flows in containers of increasing complexity have been designed to determine important transients for low-g propellant management. Significant progress has been made for complex containers that are cylindrical, but many practical systems involve containers with geometries that are tapered.

The taper of the irregular polygonal cross section of the test cells provides particular design advantages in preferentially locating the liquid where desired. Passive capillary flow in such containers is called imbibition and cannot be tested on the ground for large three-dimensional geometries with “underdamped fluids”—a most common characteristic of low-g fluids systems. The equations governing the process are known but have not been solved analytically to date because of a lack of experimental data identifying the appropriate boundary conditions for the flow problem. Experimental results will guide the analysis by providing the necessary boundary condition(s) as a function of container cross section and fill fraction. The benchmarked theory can then be used to design and analyze capillary devices such as three-dimensional vane networks and tapered screen galleries for bubble-free collection and positioning of fuels for satellites, an important and outstanding problem for propellant management aboard spacecraft.

CFE Vane –VG

A complicated critical wetting condition arises between interior corners that do not actually contact; such as in the gap formed by a vane and tank wall of a large propellant storage tank (a commonality in practice), or near the intersection of vanes in a tank with complex vane network. Two CFE units will be employed to investigate this phenomenon using a right cylinder with elliptic cross section with a single central vane that does not contact the container walls.

The vane can be pivoted varying the angle between the vane and the wall and also varying the size of the vane-wall gap. The vane is slightly asymmetric so that two gaps can be tested for each container. All static interface shapes recorded by video will be compared quantitatively with shapes computed using a computer algorithm. A major goal of this experiment is to carefully observe all interface configurations during the rotation of the vane and to test the repeatability and reversibility of the critical wetting phenomena.

CFE Contact –CL

Two CFE units will be used to study a fundamental and practical concern for low-g fluid phenomena—the impact of the dynamic contact line. The contact line controls the interface shape, stability, and dynamics of capillary systems in low g. The CFE–CL experiments will provide a direct measure of the extremes in behavior expected from an assumption of either the free or pinned contact line condition. The two units are identical except for their respective wetting characteristics.


The CL–1, the ICF, and VG units are complete and awaiting launch. CFE–CL unit 2 (CL–2) was launched to the International Space Station (ISS) on Progress 13 in January 2004. ISS Science Officer Michael Fincke, operated the CL–2 unit on August 28 and again on September 18, 2004. CL–2 operations were also performed on December 20, 2005 and on April 18, 2006 by ISS Science Officers, William McArthur and Jeff Williams, respectively. Video data was taken and is currently being analyzed. Tests include a variety of fluid disturbances, such as tap, slide, multiple slide, push, swirl, and axial perturbations.

Preliminary results were recently reported1 where it has been observed that the correct contact line boundary condition is pivotal to accurate modeling of large length scale capillary surface dynamics. In addition, it was observed how large amplitude multiple slide disturbances act to form ‘hourglass’ configurations in the smooth cylinder while the surface remains pinned in the pinning cylinder. Axial mode drop ejection tests were performed and obvious differences in settling time and natural frequency as a function of contact line condition and  disturbance type were observed. Publication of the quantified data awaits further analysis of the data.

CFE ISS Gallery
Astronaut Cady Coleman.
Increment 26 flight engineer Cady Coleman operates the CFE-2 Interior Corner Flow 2 unit.
Astronaut Peggy A. Whitson, Expedition 16 commander
Astronaut Peggy A. Whitson, Expedition 16 commander
ISS Science Officer, Mike Fincke
ISS Science Officer, Mike Fincke in the U.S. Lab aboard the International Space Station.
Astronaut Sunita Williams performing ICF2 ops during Increment 15
Sunita Williams performing ICF2 ops during Increment 15 on the International Space Station.
Astronaut Jeffrey N. Williams, Expedition 13 NASA space station science officer and flight engineer
Astronaut Jeffrey N. Williams, Expedition 13 NASA space station science officer and flight engineer, performs one of multiple tests of the Capillary Flow Experiment (CFE) investigation on the ISS.



Contacts at NASA Glenn Research Center
Project Manager:Robert W. Hawersaat

Project Scientist: Dr. Robert Green, NASA GRC

Principal Investigator: Prof. Mark Weislogel, Portland State University


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ISS Research Project Links
Space Station Research & Technology  
Space Station Project Links
  Capillary Flow Experiments (CFE)  
Space Flight Systems Links
  Space Flight Systems @ GRC
  Human Research Program  
This Month in Exploration  
GRC Microgravity and Technology Flight Experiments
CFE Related Documents
small acrobat icon   NASA Tech Briefs October 2011
small acrobat icon   CFE-2 Overview Chart
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CFE Short Overview Presentation
small acrobat icon   CFE SRD  
small acrobat icon   CFE-2 SRD  
small acrobat icon   Publications & Presentations
CFE Related Links
  Fascinating Fluid Physics
  Prof. Mark Weislogel's Web Site

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Capillary Flow Experiments
CFE-ICF flight units / tapered isosceles vessel
CFE-ICF flight units / tapered rectangular vessel
CFE–ICF flight units: tapered isosceles vessel (top) and tapered rectangular vessel (bottom).
CFE-VG flight unit
CFE–VG flight unit.
CFE-CL flight unit
A CFE–CL flight unit with smooth cylinder on left and pinning
cylinder on right.
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Tim Reckart
NASA Official: Thomas St. Onge
Last Updated: June 11, 2013
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