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.

1. Preparing the Viscometer

1. Prepare seven solutions with varying concentrations of propylene glycol in water (between 0 - 100 mole % polypropylene glycol). Label all solutions. These will be used for calibration. Obtain a sample of the unknown concentration and set it aside
2. Check the samples for lint, dust, or other solid material. If needed, filter the sample through a sintered glass filter or fine mesh screen.
3. Clean the appropriate viscometer using water, and dry with filtered air to rem

In this experiment, the viscosity of several concentrations of propylene glycol were measured. As expected, the viscosity was found to increase with propylene glycol concentration. The time for the sample solutions to traverse the viscometer were measured and used to determine the kinematic viscosity. Numerous measurements were collected to minimize random error.

The kinematic viscosity was determined using the time as measured

The goal of this experiment was to test the relationship of viscosity and composition by using the viscosity of the unknown substance to find its composition. A number of known concentration solutions of propylene glycol and one unknown concentration solution were tested. Relationships between density, dynamic viscosity, and kinematic viscosity were used to compare the solutions. Since solutions become more viscous as they became more concentrated, we were able to narrow the concentration of the unknown solution to a sma