The vane geometry

It offers the possibility of inserting the thin vanes into an existing rested or stored sample with the minimum of disturbance. 

Theoretical analyses of this geometry has been carried out by several workers who all essentially concluded that for yield-stress/very-shear-thinning liquids, the vane geometry acted as a circumscribing cylinder defined by the tips of the vane blades, with the material inside the virtual cylinder essentially acting as a solid body, and the material outside being sheared in the normal way [1]. This ensures that slip is completely overcome at the rotating member. 

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Commonly, the thickening of liquids by hydrophilic silica is explained by the formation of H-bonds between the silanol groups of silica particles [6]. According to this model, the stability of silica gels in styrene and toluene, two fluids with comparable dielectrical properties, should be more or less identical. Figure 2 depicts the shear yield-stress experiments using the vane geometry of HDK N20 in styrene and toluene. 

The vane viscometer is yet another form of the concentric cylinder instrument, in which the bob is replaced by a rotor with four blades or vanes each attached by one edge to a vertical shaft, at 90° intervals around the shaft (Figure 22.7). This geometry, which can be used either with a cup or in the infinite sample mode, is particularly useful for measuring yield stress, and can also be used to measure the rheological properties of non-Newtonian liquids. Its advantages are described by Gunasekaran and Ak (2002). 

Barnes, H. A. and Camali, J. O. 1990. The vane-in-cup as a novel rheometer geometry for shear thinning and thixotropic materials. J. Rheol. 34 841-865. 

The analysis of flow pattern models occurring inside the radial distribution of the velocity vector components and the pressure at swirl generator exit are nonuniform the same burner equipped with an annular vane swirl generator in the same furnace can produce different velocity vector components, when the quarl geometry is changed (dQ/di, = 2-3.5) the shape and size of CRZ are primarily a function of quarl geometry and not of vane swirler diameter. 

Fig. 10.5 High-pressure attachment for the rheometer, consisting of a magnetic coupiing, a pressure head, a rotating vane geometry, and a cup. (Reprinted with permission from industriai and Engineering Chemistry Research, Voi. 42(25), N.M.B. Fiichy,...

The geometry of the vane-moderator system means that the energy spread and the width of the extracted slow positron beam will be considerably larger than what can be obtained with a -decay positron beam. For example, the apparatus shown in fig. 3.6 produces a beam which, after the beam transport system, is 20 mm wide with an energy spread of S-30 eV depending on the beam energy (Ebel et al. [3.17]). 

In contrast, a vaned wheel directs the flow of the liquid feed across the surface of an inner liquid distributor in which liquid slippage over the surface of the distributor occurs until there is contact with the vane or channel. The feed then flows outward due to centrifugal force and forms a thin film across the surface of the vane. As the liquid film leaves the edge of the vane, droplet formation occurs as a result of the radial and tangential velocities experienced. Atomizer wheel characteristics that influence droplet size include speed of rotation, wheel diameter, and wheel design, e.g., the number and geometry of the vanes. 

The flow of liquids down grooved geometries is well documented in the literature see Mann et al. (1995), for example. The relationship between the driving pressure due to surface tension forces and the radii of curvature along the vane is expressed as ... 

Figure 3 The vane and the vane-and-basket geometries 7.2.4 Evaporation...

Rather than characterising slip, we might want to eliminate it. This can often be done by sandblasting or otherwise roughening or profiling (with ribs etc.) the surfaces where the test liquid comes in contact with the viscometer. In fact, any regular surface undulations of the order of 10 /an should elirninate slip effects in most cases. See chapter 7 for a further discussion of the elimination of slip, especially by the use of the vane and basket geometry. 

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