Loading the lesson
Loading the lesson
Search AllRounder.ai
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Learn it your way
A short class with Sarah and her students. The other ways are under More.
Sign up free to listen. Transcripts are free to read.
Let’s start with shear stress and shear strain rate. Can anyone tell me how these two concepts are related in fluid mechanics?
Shear stress is the force per unit area acting parallel to the surface.
Exactly! And shear strain rate describes how quickly layers of fluid slide past each other. Now, according to Newton’s law of viscosity, what do we know about the relationship between them?
Shear stress is proportional to the shear strain rate.
Correct! We can summarize that with the equation: shear stress (τ) = dynamic viscosity (μ) times the shear strain rate (du/dy). Remember the acronym VSS - 'Viscosity is Shear Stress proportional'.
Now, how does temperature affect viscosity in liquids versus gases?
In liquids, increasing temperature decreases viscosity.
But in gases, increasing temperature increases viscosity!
Exactly! As temperature rises, the intermolecular forces weaken in liquids, leading to lower viscosity. For gases, the increased kinetic energy leads to more random movement, increasing viscosity. Use the phrase TCL - 'Temperature Changes Liquids'.
Let’s differentiate between Newtonian and non-Newtonian fluids. Who can define them?
Newtonian fluids have a constant viscosity irrespective of the shear rate.
Non-Newtonian fluids have variable viscosity depending on the rate of deformation.
Great job! Remember the acronym NTT - 'Newtonian is Time-independent, Non-Newtonian is Time-dependent'. Can anyone give an example of a non-Newtonian fluid?
Toothpaste is a good example—it thickens under shear.
Very good! We can categorize non-Newtonian fluids further like pseudoplastic and dilatant.
Shear stress is directly proportional to the shear strain rate, emphasizing the difference between fluid and solid mechanics.
An increase in temperature typically decreases viscosity in liquids due to weaker intermolecular forces, while gases exhibit an increase in viscosity with temperature rise.
A specific equation that correlates dynamic viscosity with temperature for gases, encompassing specific constant values for different fluids.
Newtonian fluids maintain a constant viscosity regardless of shear rates, while non-Newtonian fluids exhibit variable viscosity based on shear forces, categorized further into pseudoplastics, dilatants, and Bingham plastics.
In summary, the section thoroughly examines viscosity's behavior under varying conditions, establishing fundamental principles necessary for understanding fluid dynamics.
Term
What is dynamic viscosity?
Click to flip
Term
How does temperature affect viscosity?
Click to flip
Term
What characterizes Newtonian fluids?
Click to flip
A measure of a fluid's resistance to flow or deformation.
The force acting parallel to a surface per unit area.
The rate at which adjacent layers of fluid slide past one another.
Fluids whose viscosity does not change with the rate of shear strain.
Fluids that have a viscosity that changes with the rate of shear strain.
This section discusses the relationships between shear stress, shear strain rate, and dynamic viscosity, emphasizing their implications in fluid mechanics.
The section delves into how dynamic viscosity varies with temperature and pressure, the differentiation between Newtonian and non-Newtonian fluids, and the relevance of shear stress and strain rate. It introduces key concepts like the Sutherland correlation and explores how viscosity behaves across different types of fluids.
This section focuses on dynamic viscosity in fluid mechanics, especially through the analysis of shear stress and shear strain rates. In a scenario where fluid flows between two parallel plates, with one stationary and the other moving at a velocity V, the fluid experiences linear velocity variations. This linear relationship leads to angular deformations in the fluid element over time, highlighting how velocity gradients relate to shear strains.
In summary, the section thoroughly examines viscosity's behavior under varying conditions, establishing fundamental principles necessary for understanding fluid dynamics.