1 Granular Fluidization in Reduced Gravity University of Tulsa Supported by Research Corp. Justin Mitchell, Aaron Coyner, Rebecca Ragar, Matt Olson, Ian Zedalis, Adrienne McVey, Whitney Marshall Michael Wilson*, Shawn Jackson *Currently at National Research Council

2 Project Description  Goals Look for definitive inelastic collapse of a 3-d granular system in zero gravity. Determine parameters necessary for a granular gas, the precursor to collapse.  Methods Preliminary testing on NASA KC-135A low gravity aircraft Future flight on Space Shuttle Testing on sounding rocket * * É. Falcon et al., Phys. Rev. Lett (1999).

3 Why Investigate Granular Gases?  Large granular systems, such as planets, are not well understood.  Asteroids, planetary rings, etc. are not fully explained by gravity because sizes are too small for gravity to act alone.  Inelastic collapse models provide plausible method for formation of these smaller objects.  Small scale granular gas studies allow for lab testing of the models on reasonable time scales.

4 Experimental Description  Box set: 8 sapphire walled cubes, 1 in 3 each.  Box set mechanically shaken sinusoidally along body diagonal.  Each cube has one free wall attached to a piezoelectric sensor.  Video cameras view 3 orthogonal box set faces.

5 Box Set as Flown on KC-135A

6 System Acceleration  Shaking direction is perpendicular to mean effective gravity.  In “microgravity” the residual acceleration is ~0.03 g earth *.  Residual acceleration is usually pointed up. shaking g earth Residual acceleration * From Charles Thomas, Boston University

7 Granular Phases Solid Grains pack in one corner Fluid Grains slosh around box walls Gas ~uniform distribution of kinetic grains g residual

8 Phase Diagram o =A 2 /g residual  is the ratio of wall acceleration to g residual   diverges as g residual goes to zero. o Wall acceleration, density and g residual define the phase. cc

9 Experiment Geometries Shaking parallel to g  c 2.0 * A 2 = 19.6 m/s 2 g shaking g residual shaking Normal GeometryOur Geometry Shaking normal to g residual  c 17 A 2 = 5.00 m/s 2 *Y. Lan, A. D. Rosato, Phys. Fluids 7, 1818 (1995).

10 Conclusions  There is a  c that defines the phase transition to a granular gas.  Geometry and density affect the value of  c. o=A 2 /g residual is a convenient way to compare shaken granular experiments. oOur geometry requires a higher wall accelerations (in proportion to g residual ) to show a phase transition.

11 Future Work  Ball tracking to give speed distribution.  Analyze impact data to obtain pressure information for gas phases.  First flight was preparation for later experiments. Second KC-135A flight  Make free floating Space Shuttle

12 Experiment Parameters  0.50 mm and/or 1.00 mm grade 200 brass  Mean free path (mfp) ~Vol./(Nd 2 )  %Oc.Vl. = % of volume occupied by balls

13 Residual Acceleration  Balls above dense clusters follow parabolic path.  g Residual  g Earth Within 25% of BU Data