Other Eccentric Geometries

Eccentric rotating cylinders can give accurate and G data but only at rather small strains (Broadbent and Walters, 1971). At larger deformation, cavitation or extrusion of the sample from the gap can occur. This also seems to be the problem for such other eccentric geometries as the tilted rotating disks or cone and plate (Davis and Macosko, 1973 Walters, 1975). 

Armstrong, R. C. Hassager, 0., Dynamics of Polymeric Liquids, Vol. 1 Fluid Mechanics, 2nded. Wiley New York, 1987. 

Chandrasekhar, S., Hydrodynamic and Hydromagnetic Stability, Oxford University Press London, 1961. 

Cokelet, G. R., in The Rheology of Human Blood, Symposium on Biomechanics , Fung, Y. C. Perrone, N, Anliker, M. Eds. Prentice-Hall Englewood Cliffs, NJ, 1972. 

Giesekus, H., Proceedings of the Fourth International Congress on Rheology Wiley- Interscience New York, 1963 p. 249. 

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The other eccentric geometries described in Sections 5.7.1-5.7.3 all accomplish an oscillatory motion in a similar way by rotating the sample through a deformation fixed in laboratory space. These oscillations are not identical to sinusoidal oscillations, but in the region of linear viscoelastic response, the dynamic moduli can readily be obtained from the solution for an ideal elastic or ideal viscous material (Abbot et al., 1971 Pipkin, 1972). 

Several other eccentric geometries have been described. Three of them are shown in Figure 5.7.5. Kepes (1968) and Kaelble (1969) developed tilted rotating hemispheres also known as the Kepes balance rheometer. Figure 5.7,3 shows that this rheometer can measure li and G data accurately. ... 

Other eccentric rotating geometries (a) tilted rotating hemispheres (also called balance rheometer), (b) eccentric rotating cylinders, and (c) tilted rotating cone and plate. 

Figure 5.7.2a illustrates the eccentric rotating disk (ERD) geometry (recall Exercise 1.10.7 and Example 2.3.1). A sample is placed between two disks that rotate at the same angular velocity but about offset or eccentric axes. Surface tension holds the sample between the disks. The flow between these eccentric rotating disks results in a shearing motion, with material elements moving in circular paths with respect to each other. A coordinate system r, j, z that rotates with the lower disk (Figure 5.7.2b) can describe the relative motion between particles (Figure 5.7.2c). The deformation is seen to be of constant magnitude, but continually changing direction.

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