Mooney/Ewart system

The Mooney/Ewart system (Fig. 3.7) is a combined cylinder/cone and plate geometry, wherein the same shear rate or shear stress can be set up over the whole measuring slit (cylinder and cone and plate). 

Since the surface for the power transmission is big compared to that of the plain cone/plate system, the Mooney/Ewart system is suitable for low viscous liquids. The advantage in comparison to normal cylinder geometries is the avoidance of edge effects at the lower cylinder wall for the smaller sample volume. The Mooney/Ewart system requires a high precision setting of the vertical distance, and is therefore as the cone and plate system mostly used in rheometer systems. 

Several designs have been described which overcome end-effects due to the shear flow at the bottom of the concentric cylinder geometry. These include the recessed bottom system which usually entails trapping a bubble of air (or a low viscosity liquid such as merciuy) beneath the inner cylinder of the geometry. Alternatively the Mooney-Ewart design, which features a conical bottom may, with suitable choice of cone angle, cause the shear rate in the bottom to match that in the narrow gap between the sides of the cylinders, see Figme 2.4. 

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