Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Viscosity is a measure of a fluid's resistance to flow, and it is a useful parameter in the design of efficient product processing and quality control in a wide range of industries. A variety of viscometers are used to obtain the most accurate readings of experimental materials. The standard method of measuring viscosity is through a glass tube viscometer, which estimates viscosity by measuring the amount of time it takes fluid to flow through a capillary tube made of glass¹.

Rotational viscometers operate by applying shearing forces and measuring the time it takes a flowing¹. These viscometers make use of the flowing force of the fluid, and they can use either a spring system or a digital encoder system¹. Different measuring systems exist as well, with the standard being a cone and plate system, where fluid flows under the cone shape and over the plate, in order to minimize shear stress¹. Parallel plate systems use two parallel plates and is ideal for measuring across temperature gradients, allowing a smooth transition¹. Couette systems use a cup and filling material, and the fluid flows in between the two¹. These systems are best for materials with low viscosity, since this system minimizes shear stress, but the system is also harder to operate routinely due to issues with cleaning and needing larger volumes of fluid¹.

In this experiment, a Cannon-Fenske viscometer will be used to measure the viscosities of several propylene glycol solutions to determine the relationship between viscosity and composition.