The Capillary Flow Experiment-2 (CFE-2) consists of eleven fluid modules with unique geometries designed to test capillary flow in the microgravity environment. The first type of CFE-2 fluid module is the Interior Corner Flow (ICF) module, there are nine modules each with a different interior corner angle and geometry. The second type of CFE-2 fluid module is the Vane Gap (VG) module, there are two of these modules, each with a different cross section profile. The CFE-2 fluid modules are set up in the Maintenance Work Area (MWA) on board the International Space Station (ISS) and operated by an ISS crew member. The capillary flow data is in the format of video, and is recorded by the MWA camera and downlinked to the ground for data analysis.
July 2014 – The International Space Station commander Steve Swanson performed several bubble-free drain tests using the Interior Corner Flow 5 (ICF5) vessel on July 3, 2014. The ICF5 vessel has a square cross-section, and the top half of the test section is divided into 4 smaller square channels. There are 4 valves at the top of the test section corresponding to each of the 4 channels. During the runs, silicone oil was deployed into the test section to commence the top drain tests through one open valve. The silicone oil was drained from the test chamber through the open valve without ingesting gas into the reservoir. A top drain test with all the top valves open was then run. The Principal Investigator and his team at Portland State University are reviewing the test results.
CAPILLARY FLOW EXPERIMENTS (CFE)
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 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.
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.
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.
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.
April 2014 – The ISS Increment 39 flight Engineer Rick Mastracchio preformed the third operation of the Interior Corner Flow-7 (ICF7) vessel for CFE-2 on April 3, 2014. The test chamber of the ICF7 vessel has a circular right cylinder bisected by a tapered vain running the entire length. There are two valves that connect the test chamber with the fluid reservoir. The fluid reservoir contains a piston to transport the fluid into and out of the test chamber. The first set of Tip Drain tests involved deploying liquid of a known volume – determined by the location of the piston in the reservoir – into the test chamber. Then the liquid was drained through one valve (with the other closed), while keeping the meniscus of the gas in the test chamber as close to the drain port as possible without ingesting gas. The Tip Drain test was repeated. Then the Tip Drain tests were repeated with opposite valve configuration. This configuration resulted in a long drain time so only a partial drain was conducted to allow time for a repeat run. The Bubbly Tip Drain tests followed the same procedure with the addition of a Bubble Generation step. After the last drain test was complete, air was intentionally drawn into the reservoir, compressed, and broken up using the whipper plate. The resulting froth was dispensed into the test chamber through one of the valves and a Tip Drain test was conducted through the opposite valve. During the operations Rick introduced Steve Swanson to the CFE test procedures and test vessel. Applications to science conducted include drain limits of spacecraft fuel tanks in orbit and medical devises on earth.
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.