How Thick Can You Get? A Low-Cost Concentric Cylindrical Couette Flow Viscometer Lab

Every student of fluid dynamics must learn the meaning of fluid viscosity. Some fluids are intuitive to compare (like honey vs. water). Fluid categories, such as Newtonian, dilatant, and pseudoplastics are simple concepts, but require experiments to fully comprehend. While many viscometers are available on the market, their cost is prohibitive for many undergraduate fluid dynamics courses. Many undergraduate students of fluid dynamics never observe this kind of experiment, and conclude that viscosity of something you just look up in a property table. In this work, a simplified, cost-effective means to accurately measure the viscosity of fluids of a range of strain rates was developed. The viscometer created for this research was based on concentric cylinder Couette flow. This viscometer contains a variable speed rotating cylinder within a larger, stationary cylinder with a uniform gap distance. The shear forces are measured by a torque transducer attached to the stationary cylinder. Details of this simplified device are provided, enabling more professors to include a viscosity measurement experience in any introductory fluid dynamics course. The experience results in an increased intuitive understanding of the viscosity, shear stress, and shear strain relationship.