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Capillary Channel Flow (CCF)

CCF Status

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Liquid Flow
Liquid flow through an open capillary channel consisting of two parallel plates.
Inside the MSG
The experimental setup insde the Microgravity Science Glovebox (MSG) onboard the ISS.

CCF On-Board Sounding rocket
A capillary channel flow experiment onboard the TEXUS-37 sounding rocket with a parallel plates geometry.

internal design & fluid loop

internal design & fluid loop
    internal design & fluid loop
internal design & fluid loop

October 2013 – The CCF Experiment Unit #2 completed operations on July 26, 2013. The CCF EU #2 Co-I Mark Weislogel and his team are starting on the data analysis. The CCF Experiment Unit #1 is scheduled to be installed in the Microgravity Science Glovebox in February 2014 to start operations.

July 16, 2013 – The CCF EU #2 experiment hardware was installed into the MSG on June 15, 2013. The CCF team performed a four day commissioning checkout of the hardware. The CCF EU #2 operations started on June 20, 2013 and are scheduled to continue to July 26, 2013. The CCF team is collecting approximately 60-70 test points per shift and sending over 1,000 commands to the CCF experiment per day.

June 10, 2013 – The CCF fluid physics experiment is scheduled to be installed in the Microgravity Science Glovebox (MSG) on June 15, 2013. This second session of CCF operations will use Experiment Unit #2 (EU # 2) with the MSG cameras instead of the Optical Diagnostic Unit.

June 13, 2012 – The CCF experiment team is planning to re-install the CCF experiment in the Microgravity Science Glovebox after several MSG experiments are completed.  CCF operations are anticipated in mid-December 2012.  The Principal Investigator for Experiment Unit #1 (EU#1), Michael Dryer and his team have developed a test matrix to fill in the gaps in the data points for subcritical and supercritical steady flow for the groove geometry and the parallel plate geometry, not obtained in the first run of CCF in 2011.  The Principal Investigator for Experiment Unit #2 (EU#2), Mark Weislogel and his team have developed a test matrix to test EU#2 to fill in data points for steady, subcritical two-phase re-stabilization, and transient positive acceleration flows in the wedge geometry.  CCF will utilize an on-board MSG camera as the primary science image camera.

April 30, 2012 – The Microgravity Science Glovebox team and the CCF experiment team are working the ability to substitute an on-board MSG camera in place of the CCF high-speed camera.

January 16, 2012 – The Microgravity Science Glovebox team worked with the CCF experiment team to schedule additional CCF operations to expand the CCF test points for both experiment units EU#1 and EU#2. October 5, 2011 –
The EU#2 critical flow and subcritical flow tests were completed.  In addition, a preliminary 2-phase flow regime map for the wedge-shaped capillary geometry was generated from  over 270 separate bubble generation test points.

September 19, 2011 Mike Fossum performed additional procedures on CCF to re-align the MSG camera and remove a stray optical surface cover.  CCF completed commissioning and Experiment Unit #2 operations commenced.

September 13, 2011, CCF was re-installed in the Microgravity Science Glovebox (MSG) by Increment 29 commander Mike Fossum.


On March 17, 2011, CCF Experiment Unit #1 completed its test operations with 900 test points.  The CCF Experiment Unit #1 Principal Investigator Michael Dryer and his team are starting the data analysis.

As of February 9, 2011, CCF has collected 547 test points for Experiment Unit #1 out of the planned 900 test point test matrix.

On January 4, 2011, CCF began remote controlled experiment operations at ZARM in Bremen, Germany.

On January 2, 2011, CCF completed full commissioning (a series of checkout tests) at MSFC.

On December 27, 2010, CCF was installed in the Microgravity Science Glovebox (MSG) by Increment 26 commander, Scott Kelly.

On April 5, 2010, CCF was launched to the ISS on STS-131 (flight 19A).

The test matrix has been completed for the Experimental Unit #1 (EU#1), i.e. the parallel plate/groove channel geometry, and the CCF hardware was removed from the MSG on March 17. Plans are to re-install CCF with the EU#2 (wedge geometry) in MSG in August 2011 to complete the second half of CCF science.

CCF is a versatile experiment for studying a critical variety of inertial-capillary dominated flows key to spacecraft systems that cannot be studied on the ground. The results of CCF will help innovate existing and inspire new applications in the portion of the aerospace community that is challenged by the containment, storage, and handling of large liquid inventories (fuels, cryogens, and water) aboard spacecraft. The results will be immediately useful for the design, testing, and instrumentation for verification and validation of liquid management systems of current orbiting, design stage, and advanced spacecraft envisioned for future lunar and Mars missions. The results will also be used to improve life support system design, phase separation, and enhance current system reliability.

Since hydrostatic pressure is absent in microgravity, technologies for liquid management in space use capillary forces to position and transport liquids. On earth, the effect of capillary forces is limited to a few millimeters. In space, these forces still affect free surfaces that extend over meters. For the application of open channels in propellant tanks of spacecraft, design knowledge of the limitations of open capillary channel flow is a requirement. These limitations are based on the restriction that the liquid fuel must be free of bubbles prior to entering the thrusters.

Video clip of a capillary channel flow experiment onboard the TEXUS-37 sounding rocket with a parallel plates geometry.

Currently, spacecraft fuel tanks rely on an additional reservoir to prevent the ingestion of gas into the engines during firing. Research is required to update current models, which do not adequately predict the maximum flow rate achievable through the capillary vanes.

CCF will test the theoretical predictions for the free surface shapes and the critical flow velocities for open capillary channel (vane) flows in microgravity. CCF is designed to validate the assumptions used to develop the governing equations. The experiments will provide the verifications for the flow rate limits and corresponding critical flow velocities.

Of the myriad of geometries envisioned for the capillary control of fluids in low-g environments, CCF will examine flows in parallel plate channels, grooves, and interior corner capillary conduits. These geometries represent a class of practical capillary geometries that are implemented in designs of the fuels and tank community of the aerospace industry. Current spacecraft fluid processing equipment is replete with such constructs. Validation of theoretical models developed for such geometries is expected to lend confidence to the application of theory to other geometries pertinent to advanced microgravity fluid systems development.

The highlights of the CCF experiments may be described as follows:

• Provide performance limits for capillary dominated systems such as passive fluids management (i.e. capillary collection, pumping, and containment) and processes such as passive phase separation and transport. This is a current and pressing requirement for a wide range of spacecraft fluid systems.

• CCF will use multiple test cell geometries and variable parameter ranges to investigate the ability of capillary systems to passively change multiphase flow regimes. It will also be used to study capillary dominated multiphase flow that may be exploited to assist other active or passive systems.

• CCF will provide critical data for the uniquely low-g inertial-capillary flow regime important to liquid fuels and cryogen storage and management.


Forced liquid flows through open capillary channels with free liquid surfaces will be investigated in the Microgravity Science Glovebox (MSG) onboard ISS. In open capillary channels, if a certain critical flow rate is exceeded, the flow becomes unsteady, the surfaces collapse, and gas ingestion occurs at the outlet. From a fluid mechanical point of view, a characteristic critical velocity must exist at which the steady subcritical flow turns into an unsteady supercritical flow, which involves the collapse of the free surfaces. To find this velocity and the location of collapse of the free surface, the surface profile must be measured with great accuracy. Furthermore, the local flow velocity must be known at dedicated points of the channel.

In order to achieve a high degree of flexibility, the experiment was designed as a modular system consisting of the Fluid Management System (FMS), the Board Computer (BC), and two Experiment Units (EU), which include the Test Units (TU). For the investigation of the selected channel geometries (parallel plates channel, groove channel, and a wedge-shaped channel) and different channel dimensions, the TUs are exchangeable. This also enables the use of the setup for other projects with similar technology driven research objectives. Furthermore, TU2 includes a gas bubble generator to test two-phase flow stability.

The FMS is equipped with the required components to establish the flow (pumps, plungers, valves), while the EU contains the TU, a phase separation chamber, (PSC), a compensation tube (CT), cameras for the video observation as well as the required illumination. The experiment control, the sampling of the housekeeping data, and the communication with both the MSG interfaces and the ground station (PI site) is performed by the BC.

The experiments are scheduled to take place on the ISS in 2010 and will be monitored from the ground station in Bremen, Germany.

Project Management:


Contacts at NASA Glenn Research Center

Project Manager: Robert W. Hawersaat

Project Scientist: Robert D. Green, NASA GRC

DLR Principal Investigator: Prof. Dr. Michael Dreyer, ZARM

Co-Investigator: Prof. Mark Weislogel, Portland State University

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