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%.
MPR portugal 2007
“The Cambridge Multipass Rheometer” By Malcolm Mackley Department of Chemical Engineering University of Cambridge
Key issues for Processing in generalTemperature Pressure Flow Time Key features of MPRTemperature -10 to 210 CentigradePressure 1 to 200 barFlow 1 to 100000 reciprocal secondsTime ms to hoursEnclosed small volume
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
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
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
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
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.
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