This video demonstrates the Cone-and-Plate method of measuring absolute viscosity of liquids. What are viscosity, viscometry and rheometry? Find out answer to these in this video.
Viscosity is the property of a fluid by which it resists motion/deformation in shear. High viscous fluid will require higher force to shear it. The shearing stress (N/mm^2 or Newton per meter square) also depends upon the speed with which we are deforming (in shear) the fluid and the thickness of the fluid within which shearing is taking place. Shear rate is given as the velocity of shearing (v) divided by the fluid thickness (h), that is, v/h and it has the unit of s^-1 (per second). Viscosity is given as the ratio of the shear stress to shear rate. This is also known as the Newton's Law of viscosity. The viscosity measured by this principle is known as the dynamic or absolute viscosity. The units of this viscosity is Pascal second. Viscosity of a fluid is highly dependent on the prevailing temperature and pressure. There are relationships that can be used to find viscosity at different temperatures and pressures if viscosity at normal temperature pressure is known along with some constants of the equations.
The method that I have used in this video is known as the Cone-and-Plate viscometry. The machine was built by Anton Paar company. In the method, the torque (N-m) to rotate the cone at a fixed speed is measured and then we can use a formula to obtain viscosity at that shear rate. If the liquid is non-Newtonian then this viscosity will be the apparent viscosity because it will change if you change the shear rate.
Rheology is the study of flow properties of complex fluids which are mostly non-Newtonian in nature. Rheometers are basically viscometers for these complex fluids.
In this video you will find data and plot of viscosity as a function of the shear rate for two liquids, the synthetic engine oil and olive oil.