3. Key issues for Processing in general
Temperature Pressure Flow Time
Key features of MPR
Temperature -10 to 210 Centigrade
Pressure 1 to 200 bar
Flow 1 to 100000 reciprocal seconds
Time ms to hours
Enclosed small volume
21. Model matching with experimental data
400
Best fit conditions:
350 T = 150°C, Pf = 4.0 bar, Ro = 0.1 µm,
co = 30wt%, η o= 1×105 Pa s,
300 Dw = 6×10-16 m2/s, ρ = 1500 kg/m3,
σ = 0.05 N/m, KH = 1×10-8 Pa-1
Bubble radius ( µ m)
250 B u b b le 1
B u b b le 2
200 B u b b le 3
B u b b le 4
B u b b le 5
150
M o d e l - S o = 6 0 m ic ro n s , D w = 1E - 11 m 2 / s
M o d e l - S o = 6 0 m ic ro n s , D w = 6 E - 16 m 2 / s
100 M o d e l - S o = 5 0 m ic ro n s , D w = 6 E - 16 m 2 / s
50
0
0.001 0.01 0.1 1 10 100 1000 10000
Time (s)
15
22. Starch melt rheology in the MPR
1.0E+05
Apparent viscosity (η app) of
starch melt at 70 bar pressure
Viscosity (Pa s)
1.0E+04
1.0E+03
1.0E+02
1.0E-01 1.0E+00 1.0E+01
shear rate (s-1)
Capillary: 12mm diameter, 56mm length
30% moisture content potato starch
T = 140oC 19
23. Viscoelastic behaviour of starch melt
1.0E+05
Initial pressure
maintained at 70 bar
1.0E+04
G', G'', η *
1.0E+03
Storage modulus, G’
Loss modulus, G’’
Complex viscosity, η*
1.0E+02
1.0E-01 1.0E+00 1.0E+01 1.0E+02
Frequency (Hz)
Capillary: 12mm diameter, 56mm length
25% moisture content potato starch
T = 141.9oC 20
24. Cross Slot, Kris Coventry
• The MPR action was
modified for cross-slot flow
• Pistons move out of phase
and force polymer through
a cross-slot geometry
• New inserts were
fabricated for cross-slot
flow
25. Flow Pattern
Cross-Slot flow
• The aim is to generate
a hyperbolic flow
pattern as shown.
• Near the walls the flow
deviates from ideal.
• Along the symmetry axes
we have rotation free pure extensional flow.
26. Apparatus
• Molten polymer is Servo-hydraullically
driven through a driven piston
central section by
two servo-
hydraulically driven
pistons. Slave piston
1.5 mm
0.75 mm
radius
Slave piston
• Air pressure is driven by air
pressure
driven by air
pressure
used to return it so 1.5 mm
that multiple
experiments can
be carried out on
the same
Servo-hydraullically
driven piston
apparatus
Exptl: No of bubbles = 150 Test surface area: 12 mm X 12 mm Therefore cell density: 150 bubbles/cm2 ~ 20,000 cells/cm3 From model: Sfinal ~ Rfinal Sfinal from expt: 0.5 mm Model SO = 0.15 mm; which is less than Sfinal_expt.. Void fraction: ~90%.