Non-Newtonian fluids v frictional resistance of discs and cones rotating in power-law non-Newtonian fluids

Mitschka, P.; Ulbrecht, J.

doi:10.1007/bf00411568

Cited by 28 publications

(10 citation statements)

References 5 publications

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“…For a rheometrical exploiration of eq. (2), it is advantageous to use finite discs in a. sufficiently large ("infinite") vessel, since reliable values of the function b (n) are well known for such configurations [3][4][5]. Moreover, for systems with .rapidly rotating discs, the laminar boundary regime extends to relatively high values of the Reynolds number, Rek=O(105).…”

Section: M=4xb(n) R(3+sn)/(l+n)q3n/(l+n)~n/(l+n)k A/(l+n) (2)mentioning

confidence: 99%

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A novel approach to high shear rate rheometry

Wichterle

Mitschka

1986

Rheol Acta

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A procedure is presented for converting torque-speed plots obtained from experiments using discs rotating rapidly in shear thinning materials into information on the viscosity function. The method is based on an exact boundary-layer solution for the power-law model and on the concept of pseudo-similarity of nonNewtonian flows. It enables the rheological behaviour to be evaluated at very high shear rates. Experimental data for concentrated shear-thinning kaolin suspensions at shear rates from 400 to 2-10Ss -1 are compared with values of the viscosity function obtained from customary viscometers of the Brookfield and Couette type.Key words: Viscosity function, rotating disc rheometry, high shear rate, kaolin suspension I. IntroduetionCommercially available rheometers usually allow measurements to be made in the range of shear rates from 1 to 1000s-l; with special instruments and for certain types of fluids it is possible to obtain data outside this interval.A special part of rheodynamics concerns flows at high shear rates and, in particular, under extreme loads such as in lubricated bearings. However, it is often overlooked that during rapid flow past solid bodies or during their motion through fluids considerable velocity changes take place in relatively thin boundary layers, where the velocity gradient may achieve values up to the order of 106s -1. Such conditions are met even in common engineering practice, for example on the blades of high-speed agitators. The rheological data necessary for describing the flow in these regions are usually not available, especially when the fluids are non-Newtonian.The realization of viscometric flows at high shear rates is not easy; end devices are usually used in which the fluid sample is placed into an extremely narrow gap between a stationary and a rapidly moving wall. It taust be taken into consideration that in order to obtain a shear rate of 10Ss -1 within a 0.1 mm gap a relative velocity of 10 m's -1 is required. Thus, the geometric precision of the apparatus taust be extremely high. Moreover, such measurements can be influenced by various side effects, such as nonisothermicity due to high dissipation rates of mechanical energy, or inertial forces which may lead, for example, to the formation of Taylor vortices; in microheterogeneous fluids phase separation 120 may occur. Such devices are certainly unsuitable for the rheometrical characterization of dispersions containing coarse particles.For investigating the rheological properties at high shear rates we therefore propose to employ flow situations in which such shear rates occur naturally. In this context flows past solid walls under laminar conditions can be considered. For these, an efficient (boundary-layer) theory of flow is known to be valid and the corresponding equations of motion can in many cases be solved for a power-law model for the purely viscous behaviour:(1)The purpose of such a solution is usually to determine relations between kinematic and dynamic quantities of practical interest (such as the...

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Section: M=4xb(n) R(3+sn)/(l+n)q3n/(l+n)~n/(l+n)k A/(l+n) (2)mentioning

confidence: 99%

“…For rheometrical purposes the three-dimensional laminar boundary layer flows generated by rotating axisymmetrical bodies [1][2][3] are much more suitable as the experiments can be performed relatively easily, for example, using a modified rotational viscometer or a common device for testing agitator power inputs.…”

Section: Introduetionmentioning

confidence: 99%

A novel approach to high shear rate rheometry

Wichterle

Mitschka

1986

Rheol Acta

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“…Kale et al! chose to relate the stress tensor to the Rivlin-Ericksen kinematic tensors by (10) where Al is the Rivlin-Ericksen tensor of first order, and A z is the Rivlin-Ericksen tensor of (; second order.…”

Section: The Work Of Kale Et Allmentioning

confidence: 99%

Reduction of Drag Experienced by a Disk Rotating in Viscoelastic Polymer Solutions under Laminar Flow Conditions

Ulbrecht¹,

Gasparetto²

1980

Journal of Rheology

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A disk slowly rotating in a pool of viseoelastie polymer solution experienees a torque lower than it does in an inelastie liquid of the same viseosity. It is suggested that this reduetion of frietional drag under laminar flow eonditions is due to the reversal of the seeondary (radial) flow and a simple model is proposed. Laser Doppler anemometry was used to measure the primary and seeondary velocity profiles around a disk rotating in solutions of polyvinylpyrrolidone and polyacrylamid and the experimentally obtained values of radial and tangential velocity gradients were used to predict the reduetion of frictional resistanee. These predietions are eompatible with the experimental data of D. D.

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“…und s~2 die Reynolds-Zahl ftir die Rotation yon festen K6rpern in ruhenden nieht-Newtonschen Fltissigkeiten [4], die ftir die Scheibe die Form…”

Section: Mit 2 Abbildungenunclassified

Bestimmung der Parameter des Potenzansatzes nach Ostwald-de Waele aus rheometrischen Messungen an einem Viskosimeter mit schnellrotierender Scheibe

Wichterle

Ulbrecht

1967

Rheol Acta

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Non-Newtonian fluids v frictional resistance of discs and cones rotating in power-law non-Newtonian fluids

Cited by 28 publications

References 5 publications

A novel approach to high shear rate rheometry

A novel approach to high shear rate rheometry

Reduction of Drag Experienced by a Disk Rotating in Viscoelastic Polymer Solutions under Laminar Flow Conditions

Bestimmung der Parameter des Potenzansatzes nach Ostwald-de Waele aus rheometrischen Messungen an einem Viskosimeter mit schnellrotierender Scheibe

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