CBE 30355 - Lecture Notes - Aug. 23, 2022

Announcements

Class notes

• What are Fluid Mechanics?
• What is a fluid?

Goals:

• Identify properties of fluids.
• Know how to classify simple fluid mechanics problems.

Reading

• The class notes.
• BS&L, chapter 1

Additional Readings:

In class today we discussed fluid properties such as viscosity and density. It's a good idea to have a 'gut' knowledge of the magnitude of these quantities so you have a better chance of knowing when your calculations are off - a sort of "Wait a minute, that doesn't make any sense" ability. For a classic example of what can happen if you - don't - I offer you the Gimli Glider, described here.

Demonstration:

In class today we demonstrated one difference between Newtonian and non- Newtonian fluids, in this case the difference between a pure Newtonian fluid and a suspension of sand (glass spheres). As the suspension is squeezed out between the plates particles accumulate at the advancing meniscus, causing a classic viscous fingering instability. The migration occurred because the particles "push" each other apart as a suspension is sheared between the plates. These sorts of phenomena are important in multiphase flows used in such disparate areas as oil recovery and medical diagnostic chips. Papers describing this and related phenomena may be found here. Many materials exhibit non-Newtonian behavior ranging from simple yield stresses (mayo) to the non-zero normal stresses of the concentrated suspension in this example. We'll mainly focus on Newtonian fluids this term due to their simplicity and importance (e.g., water is all around us!) but you should also be aware that it is a special (albeit pretty common) case of a larger range of observed behaviors.