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CHAPTER V

Concentric Cylinder Vlscometers. The Elastic Pro. perties of Sols. Flow-elastidty. Relaxation. Maxwell’s Equation and its Modifications. Technical Viscometers (Redwood, Saybolt and Engler Types). The Bingham. Murray Viscometer and its Modifications. Its Application to Starches, Paints, Nitrocellulose and Honey.

Having dealt in some detail with flow through capillary tubes, attentiori must now be given to other methods of measuring viscosity. Imagine two concentric cylinders, the inner one of radius a, being rotated with a uniform angular velócity (fli the outer cylinder, radius b, being fixed, as iii Fig. 9^ Imagine the space between the cylinders tp,.be. fiUed with viscous liquid to which the Nevrton hypothesis can be applied, at any ratę at Iow spieeds. The liquid will rotate in layers concentric with the cylinders, the yelocity varying regularly from^ ai the śurface of the inner cylinder to zero afetne" surface of the outer cylinder. As in the case capillary tubę, consider an intermediate layer^ąt a distance r from the centre, the angular velócity at this point being <0. The angular yelocity ^gtadient is dujdr, and the linear velocity across the Mail element will be r. doi/dr. The yiscous force exerted on this hypothetical cylinder, radius r and łseight h, by the fluid layer next to it and extending to the outer wali, will be

T)f{duildr) x 2itrh,

2 nrh being the area.

Fig. 9.