scholarly journals Extrusion rheometry of collagen dough

2021 ◽  
Vol 39 (No. 5) ◽  
pp. 384-392
Author(s):  
Jan Štípek ◽  
Jan Skočilas ◽  
Jaromír Štancl ◽  
Rudolf Žitný
Keyword(s):  
Rheological Properties ◽  
Stress Measurement ◽  
Wall Slip ◽  
Extrusion Process ◽  
Shear Rates ◽  
High Shear Rates ◽  
Rectangular Slit ◽  
High Concentrations ◽  
Gap Width ◽  
Very High

Although collagen is widely used (for example, in the food industry, in the pharmaceutical industry and in biomedicine), the rheological properties of the material are not well known for high concentrations (8% collagen, 90% water). Rheological properties were measured using a capillary-slit rheometer (an extrusion process), where the tested sample of collagen matter was pushed by a hydraulically driven piston through a narrow rectangular slit at very high shear rates of 50–6 000 s<sup>–1</sup>. The Herschel-Bulkley (HB) constitutive equation and a new correlation taking into account the finite gap width was used to evaluate the rheological properties (n = 0.2, K = 879 Pa s<sup>n</sup>, τ<sub>0</sub> = 2 380 Pa). Use was made of a new yield stress measurement method evaluating τ<sub>0</sub> 'post mortem' after extrusion stops. The effects of wall slip and of air bubbles, which caused apparent compressibility of the 'silly putty' collagen material, were also studied. Corrections of the wall slip effect were implemented using sliding layer thickness δ.

Rheology of Nanofluids in Microchannels

2008 ◽  
Author(s):  
Fre´de´ric Ayela ◽  
Olivier Tillement ◽  
Julien Chevalier
Keyword(s):  
Rheological Properties ◽  
Peclet Number ◽  
High Shear ◽  
Shear Rheology ◽  
Péclet Number ◽  
Shear Rates ◽  
High Shear Rates ◽  
On Chip ◽  
Very High ◽  
High Shear Rheology

Microfluidics is often presented for applications where only microliters sample volumes are available. But the benefits of microchannels do not reduce to a low consumption of fluids. From a physical and mechanical point of view, microfluidics can offer high shear rates combined with low Reynolds number and low viscous heating. It becomes possible to explore high shear rheology on a lab-on-chip. We have micromachined microviscometers to study the rheological properties of nanofluids under very high shear rates conditions. Nanofluids are fluid suspensions of solid nanoparticles. Recent experiments have indicated an anomalous increase in thermal conductivity of these suspensions. But less attention has been payed to the rheological properties of nanofluids. The few results concerning the viscosity of nanofluids exhibit scattered values higher than those of fluid suspensions of microparticles, because of a higher rate of collisions due to Brownian motion and shearing motion which enhance aggregation. These experiments were performed with commercially available rheometers over a limited range of shear rates. Our viscometers on chip are silicon — Pyrex microchannels (H ≈ 10 – 20 μm) equipped with local pressure drop sensors. Nanofluids under test were ethanol-based SiO2 nanoparticles. For particle sizes from 20 nm to 190 nm, and solid volume fractions from 1.4% to 7%, a newtonian behaviour has been observed up to 5.104 s−1. High shear rheology is the only way to reach high Peclet number values with nanoparticles in a laminar flow. It was possible to cover a wide range of Peclet number and to have Pe > 1 with diameter in the tens of nanometers range. Our results have demonstrated that an apparent solid volume fraction φa > φ, due to aggregation, was responsible of the increment of viscosity. More important was the demonstration that the shape of the clusters could be modified and that the ratio φa/φ could be lowered by a very high shear rate. Very high shearing rates in microchannels appear to be a way for nanofluids to converge to a well-defined value of viscosities.

The Rheology of Entangled Polymers at Very High Shear Rates

1993 ◽  
Vol 21 (4) ◽  
pp. 451-456 ◽  
Author(s):  
M. E Cates ◽  
T. C. B McLeish ◽  
G Marrucci
Keyword(s):  
High Shear ◽  
Shear Rates ◽  
Entangled Polymers ◽  
High Shear Rates ◽  
Very High

Rheology of Commercial and Model Ice Creams

2008 ◽  
Vol 18 (1) ◽  
pp. 12913-1-12913-11 ◽  
Author(s):  
P.J. Martin ◽  
K.N. Odic ◽  
A.B. Russell ◽  
I.W. Burns ◽  
D.I. Wilson
Keyword(s):  
Milk Fat ◽  
Sucrose Solution ◽  
Shear Thickening ◽  
Wall Slip ◽  
Ice Cream ◽  
Viscous Effects ◽  
Capillary Rheometry ◽  
Shear Rates ◽  
High Shear Rates ◽  
Slip Effects

Abstract The rheologies of a shear-frozen commercial ice cream and of a model ice cream foam have been studied at − 5ºC and other temperatures by capillary rheometry on a commercial manufacturing line and in a Multi-Pass Rheometer, respectively. Both were 50 vol% aerated emulsions of milk fat in an aqueous sucrose solution, but the model ice cream foam was without ice crystals. The data indicate significant wall slip effects which have been analysed using the classical Mooney method, the Jastrzebski variant and one based on Tikhonov regularization. The latter approach yields ‘most convincing results’, including a previously unreported region of shear thickening at very high shear rates of ~ 3000 s-1 for the model ice cream foam, when the capillary number indicates a possible transition in the flow around bubbles from domination by interfacial effects to viscous effects. Viscous heating effects were observed at relatively low shear rates for the commercial ice cream, but not the model ice cream foam. This was attributed to the melting of the ice crystal phase in the commercial ice cream, and, hence, absent from the model ice cream foam.

Measurement of the viscosity of supercooled liquids at high shear rates with a Hopkinson torsion bar

1982 ◽  
Vol 381 (1780) ◽  
pp. 195-214 ◽  
Keyword(s):  
Shear Stress ◽  
High Pressures ◽  
Rolling Contact ◽  
Shear Strain Rate ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Short Time ◽  
Torsion Bar ◽  
Very High

The Eyring theory of viscous flow suggests that lubricating oils should exhibit shear thinning when the shear stress exceeds about 5 MPa. The results of friction experiments in rolling-contact disc machines where very high pressures are generated in the lubricant film support this prediction, but are open to the criticism that the fluid is subjected to a high pressure for such a short time ( ca . 10 -4 s) that an equilibrium state may not be reached. In the present investigation the appropriate condition of the lubricant is achieved, not by subjecting it to very high pressures but by maintaining it in the supercooled state. The lubricant is thus in a condition of equili­brium and the shear experiments are carried out at atmospheric pressure. The lubricant specimen is retained in a suitably adapted split Hopkinson torsion bar, and at the high rates of shear applied ( ca . 10 4 s -1 ) the shear stress at sufficiently low temperatures can exceed 5 MPa. By this tech­nique the shear pulse is applied for a sufficiently short time ( ca . 10 -3 s) to avoid viscous heating of the sample, which bedevils normal viscometry at high shear rates. Two fluids were tested: polyphenyl ether 5P4E and a mineral oil Shell HVI 650. Nonlinearity in the shear-stress-shear-strain-rate relation was found when the stress exceeded about 3 MPa. The elastic shear modulus G ∞ was also measured, yielding ca . 500 MPa for 5P4E and ca . 50 MPa for HVI 650.These values compare with ca . 1100 MPa and 300 MPa as found by the high-frequency oscillating shear technique at small strains.

Effect of Aggregation on the Rheological Properties of Carbon Nanotube Dispersions

2006 ◽  
Vol 953 ◽  
Author(s):  
Sameer Sharad Rahatekar ◽  
Jeffrey W Gilman ◽  
K K Koziol ◽  
Simon Butler ◽  
James A Elliott ◽  
...  
Keyword(s):  
Shear Rate ◽  
Rheological Properties ◽  
Optical Observations ◽  
Interconnected Network ◽  
Shear Rates ◽  
High Shear Rates ◽  
Suspension Viscosity ◽  
The Matrix ◽  
Viscosity Enhancement ◽  
Low Shear

ABSTRACTIn this pape effect of nanotube aggrates on the rheological properties of multiwall carbonanntube abd epoxy suspension in epoxy resin.The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected network between aggregates of nanotubes, and not by nanotube alignment.

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