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The “Twin capillary” a simple device to separate shear- and slip-flow of fluids

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Abstract

When the flow behaviour of fluids is investigated with capillary-or rotational rheometers, adhesion of the fluid to the wall is normally one of the boundary conditions. For many fluids, especially for suspensions, this assumption is not valid. These fluids tend to slip at the wall. Therefore the normal evaluation of rheometer measurements leads to apparent but not compatible flow functions. The flow behaviour of these fluids can be characterized with two material functions which describe separately slipping in the boundary layer and shearing within the fluid. Only if both functions are known, correct predictions of flow processes are possible. A simple equipment to separate the shear function and the slip function is described.

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Abbreviations

Y* :

apparent shear rate

Y *w :

apparent wall shear rate

Yw :

wall shear rate corrected with Rabinowitsch and Weissenberg correction

Ys :

reduced shear rate (slip corrected)

Yws :

reduced wall shear rate (slip corrected)

ν* (r):

velocity distribution in a capillary

νG :

slip velocity (at the wall)

ν* (r):

velocity distribution in a capillary (without slip)

τ:

shear stress

τ w :

wall shear stress

VS :

total volume rate

VG :

shear volume rate

VG :

slip volume rate

p 1 :

pressure in the reservoir channel of the capillary rheometer

p 0 :

athmospheric pressure

L :

capillary length

R :

capillary radius

References

  • Mooney, M. 1931: Explicit formulas for slip and fluidity. J. Rheology 2, 210–222

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  • Rabinowitsch, B. 1929: Über die Viskosität und Elastizität von Solen. Z. Phys. Chem. 145A, 1–26

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  • Rautenbach, R.; Schlegel, D. 1969: F1ießverhalten dispers plastischer Materialien im Couette Rheometer. Chem.-Ing.-Techn. 41,369–374

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Authors and Affiliations

  1. Institut für Mechanische Verfahrenstechnik and Mechanik, Universität Karlsruhe (TH), 7500, Karlsruhe, Germany

    W. Gleißle & E. Windhab

Authors
  1. W. Gleißle
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  2. E. Windhab
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Gleißle, W., Windhab, E. The “Twin capillary” a simple device to separate shear- and slip-flow of fluids. Experiments in Fluids 3, 177–180 (1985). https://doi.org/10.1007/BF00280457

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  • DOI: https://doi.org/10.1007/BF00280457

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