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Powder property influence on the local force profile in a
granular column
Agnès Duri-Bechemilh, Sandra Mandato, Bernard Cuq, Thierry Ruiz
To cite this version:
Agnès Duri-Bechemilh, Sandra Mandato, Bernard Cuq, Thierry Ruiz. Powder property influence on
the local force profile in a granular column. Colloque STPMF - Science et Technologie des Poudres et
Matériaux Frittés, Apr 2015, Nancy, France. 2015. �hal-01606453�
0 1 2 3 4 5 140 120 100 80 60 40 20 0 Vertival force (N) Local profile Janssen's profile Hydrostatic profile
ISSUES
SampleName SEM Image d50(mm) d(mm)90-d10 compactnessBed repose (°)Angle of
Fine semolina 0.210 0.321 0.416 32.2 Semolina 0.298 0.434 0.446 31.4 Fine couscous 0.676 0.645 0.578 12.1 Medium couscous 0.953 0.517 0.573 9.8 Large couscous 1.095 0.406 0.578 7.6
Agnès DURI, Sandra MANDATO, Bernard CUQ, Thierry RUIZ
Short-term: characterization of the mechanical static state in ensiled granular media of different physical properties(particle size, restitution coefficient, coefficient of friction, cohesion, angle of repose, compactness, history of the bed formation…).
Long-term: better understanding the contribution of the intial mechanical
static state of the powder bed on the mobility of the particles.
The mechanical static state is achieved by measuring the local vertical force (in
triplicate) perceived by the blade (immobile) in different z positions in the powder bed. LOCAL profile
¹
GLOBAL profiles Janssen’s profile Hydrostatic profile PSEUDO-HYDROSTATIC behaviourIsotropic contact network
BOTTOM effect
Redirection of the force to the wall
DEVIATION from the PSEUDO-HYDROSTATIC behaviour
Polarization of the contact network
Pseudo-hydro > coucous Pseudo-hydro < semolinas Depth z (mm)
• PIV analysis will be performed to
characterize theparticle motionunder the action of the blade motion in the three zones of the bed.
• Define sizing criteria of powder mixers from thecharacteristic lengths.
3differentlayersin the bed
OBJECTIVES
In a mixer equipment, the external mechanical stress induces the mobility of the particles that allows their mixing, segregation or association.
The mobility of the particles are greatly affected by the initial mechanical static
state of the powder bed.
• How to evaluate the mechanical static state of the powder bed before mixing? • How the physical properties of the particles influence this mechanical static
state?
MATERIALS
METHOD
cell (5.1 x 10 x 16 cm) blade sensor (4.5 x 2 cm) x 14 cm 0 z blade powder bed texture analyzer (force acquisition) force measurement positionFront view Side view
RESULTS
Approach – Transposition from an industrial mixing device (with a 3D
blade motion) to a anunidirectional mixing device.
Depth
z
(mm)
Powders-5 wheat-based powdersof identical origin but with a different
structure.
Local – Global profiles Local profiles – Physical properties of the particles
lS~ 50 mm
lbott~ 120 mm
lbott~ 120 mm
CONCLUSIONS
PERSPECTIVES
The study of the mechanical static state indicates:
• Aninhomogeneous lateral repartitionof the mechanical static state of the powder bed.
• Asuperficial layerof about50 mmwith low shear level and independent from the physical properties of the particles.
• Amedian layerof about70 mmwith higher friction level for semolina than for couscous.
• Abottom layerof about20 mmfor which the bottom wall effect is independent from the physical
properties of the particles.
Agnès Duri – 2, place Pierre Viala – 34000 Montpellier – FRANCE - [email protected] Fhydro= F rs g z
PJ= Psat(1-e-z/lJ)
withlJ the Janssen’s length
Powder property influence on the
local force profile in a granular column
140 120 100 80 60 40 20 0 0 20 40 60 80 100 120 140 160 Pseudo-hydrostatic profile Fine couscous Medium couscous Large couscous
Vertical force normalised by the slope of the pseudo-hydrostatic profile (mm)
Fine Semolina Semolina
