Measurement of rheological properties of ultrathin lubricant films at very high shear rates and near‐ambient pressure

1995 ◽  
Vol 78 (5) ◽  
pp. 3107-3114 ◽  
Author(s):  
Ulf Jonsson ◽  
Bharat Bhushan
Keyword(s):  
Rheological Properties ◽  
Ambient Pressure ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Lubricant Films ◽  
Very High

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.

Shear Thinning of Nanometer-Thick Liquid Lubricant Films Measured at High Shear Rates

2014 ◽  
Vol 53 (3) ◽  
pp. 555-567 ◽  
Author(s):  
Shintaro Itoh ◽  
Koki Ishii ◽  
Kenji Fukuzawa ◽  
Hedong Zhang
Keyword(s):  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Liquid Lubricant ◽  
High Shear Rates ◽  
Lubricant Films

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

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.

Rheological properties of wood polymer composites at high shear rates

2016 ◽  
Vol 51 ◽  
pp. 58-62 ◽  
Author(s):  
Krzysztof Lewandowski ◽  
Kazimierz Piszczek ◽  
Stanisław Zajchowski ◽  
Jacek Mirowski
Keyword(s):  
Rheological Properties ◽  
Polymer Composites ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Wood Polymer ◽  
Wood Polymer Composites
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