Theory

The viscosity of a fluid is the fluid's innate resistance to flow. Maple syrup has a high viscosity, while air has a low viscosity. Measuring a fluid's viscosity is important for many engineering applications, including the oil industry. With knowledge of a particular oil reservoir's viscosity, artificial lift systems can be properly designed to maximize crude oil recovery. The purpose of this particular viscometer is the measure the viscosity of a wide range of crude oil samples. 

The basic idea behind this measurement device employs the assumption of flow between two parallel plates. The lower plate is stationary and the upper plate has a constant velocity, V. The shear rate, γ, is the ratio between the velocity of the upper plate and the distance, h, between the two plates.²

Furthermore, the shear force on the plate, τ, is directly proportional to the dynamic viscosity, η, times the shear rate, γ.²

For this specific mechanism, the velocity will have to be calculated from the following equation:

For this torsional spring viscometer, the shear force, τ, is equal to the spring force times the area of the plate. In this case, the area of the plate is the label area of the cylinder that is immersed in the fluid.³

Finally, the following equation incorporates all the known values of our mechanism, and can calculate the fluid's viscosity, η: