Inertia in a cone-and-plate geometry

When a low-viscosity viscoelastic liquid is tested at high rotational speed in a cone-and-plate geometry, there is an inertial force acting outwards that tends to pull the plates together, thus counteracting the normal-force effects which tend to push the plates apart. When this effect is just measurable, the overall force is then given by 

This can be used to correct the normal-force results. However, when the correction becomes large, secondary flows are present in the cone-and-plate gap, and this means that the results are then unreliable. 

7 Postscript - flow of a viscoelastic liquid into a contraction. 

All else being equal, an increase in flow-rate for an elastic liquid, or an increase in the level of elasticity (measured as, say, the first normal-stress difference) produces the effect on the flow pattern in a contraction shown in figure 30. The complex flow pattern shown on the right of the figure is very susceptible to flow instabilities. The onset of these instabilities dictates the maximum flow-rate possible for an extrudate emerging from the end of the die having a smooth, acceptable surface. (See chapter 17 for a discussion of the role of extensional viscosity in this kind of flow.) 

Many of the structured liquids that we come across in everyday life are suspensions/ dispersions of particles in a liquid, with examples ranging from mud to blood, and custard to mustard. Other examples of the kind of suspensions we are dealing with here, and the places you might find them are 

---