Understanding Rotational Rheometers-2 — Lesson 2

This lesson covers the principles of rotational viscometers, specifically focusing on the transport phenomena of non-Newtonian fluids. It delves into the working principles of concentric cylinder rheometers, explaining how to calculate shear stress and shear rate. The lesson also discusses the importance of the gap between the inner and outer cylinder in determining the curvature effect. It further explains how to measure normal stresses in Couette flow or concentric cylinder geometry. The lesson concludes with an example problem demonstrating how to obtain shear stress and shear rate data for a food product using a cone and plate geometry.

Video Highlights

01:11 - Explanation of how to measure the rheology of a fluid using concentric cylinder rheometers and the equations for shear stress and shear rate.
10:37 - Introduction to the concept of normal stresses in Couette flow and how to measure them using concentric cylinders.
18:20 - Explanation of how to obtain the rheological behavior of a fluid using a concentric cylinder viscometer through an example problem.
22:59 - Introduction to the cone and plate rheometer, its advantages, and how to measure normal stresses, shear stress, and shear rate using this geometry.
50:18 - Explanation of how to obtain the rheological behavior of an unknown fluid using a cone and plate geometry through an example problem.

Key Takeaways

• The shear stress in concentric cylinder rheometers can be measured using the torque.
• The gap between the inner and outer cylinder plays a crucial role in determining the curvature effect.
• Normal stresses in Couette flow can be measured using the concentric cylinders.
• The cone and plate geometry is useful for studying the rheological behavior of unknown fluids, especially those with non-Newtonian behavior.
• The shear stress and shear rate can be obtained from the rotational velocity and torque data.