Capillary Flow Experiment (CFE)
Research Area: Fluid Physics
Expedition(s): 9, 12-16
Principal Investigator(s): ● Mark Milton Weislogel, PhD, Portland State University,
Portland, Oregon
RESEARCH OBJECTIVES
Capillary Flow Experiment (CFE) is a suite of fluid physics experiments that investigate capillary
flows and phenomena in low gravity and consists of 3 investigations: Vane Gap (VG), Interior
Corner Flow (ICF), and Contact Line (CL). Results will improve current computer models that are
used by designers of low-gravity fluid systems and may improve fluid transfer systems on future
spacecraft.
EARTH BENEFITS
The results of the flight experiments are also expected to provide insights into terrestrial
interfacial phenomena and may lead to models predicting fluid flows in porous media (i.e.,
ground water transport), complex capillary structures (i.e., high-performance wicks for heat
pipes employed in electronics cooling), and Lab-On-Chip technologies (i.e., microscale biofluids
processing).
SPACE BENEFITS
The knowledge gained from this payload has the potential to be instrumental in the design of
future fluid systems for spacecraft-impacting fluid-bearing containers such as propellant and
cryogenic fluids tanks, thermal control system coolant reservoirs, water storage and
management systems, liquid state low-gravity materials processing equipment, and biofluids
handling instruments for inflight, human health systems. By performing this experiment,
researchers will gain information that will lead to improvements in system reliability with
reductions in system mass and complexity. These applications of CFE are in direct support of
NASA's mission to develop safe, reliable, and affordable spacecraft to pursue the greater
exploration of our solar system and universe.
RESULTS
Vanes are structures built along propellant tank walls or inside the tanks that liquid clings to
and is “wicked” away from its source. They are used as a form of passive fluid control in very
low gravity to transfer wetting (ability of a liquid to maintain contact with a solid surface) fuels
to resupply rocket engines. In space, acceleration forces can pool liquid propellant anywhere in
the tank so the vanes, by having corners (such as the corner formed by the side vanes and the
tank wall), serve to create a flow path to the outlet.
The CFE Vane Gap (VG) experiments identified the angles, known as critical wetting angles
where a perfectly or partially wetting fluid is drawn up large or small corner gaps between the
vane and cylinder wall and “wets” the entire length of the vane. Results showed critical angles
were in close agreement with predictions for the perfectly wetting fluid, whereas these angles
deviate substantially from predictions for a partially wetting fluid. Also, a bulk shifting