Tauraj Ehtizazi Flashcards
What is Newtonian system?
Within a block of liquid the bottom layer is fixed, there is friction between the layers of the liquid. So when stress is applied the top layer will slide, and layers below will follow as there is friction present
What is shear rate?
Difference in velocity divided by the difference in height - s-1
What is shear stress?
Horizontal force applied per unit area - Nm-2
Pressure - vertical force
What is viscosity?
The ratio of shear stress to shear rate
Shear stress divided by shear rate
What are the units of viscosity?
Poise (P) Or centipoise (cP) 1cP = 0.01P
What is Newtonian fluid?
Viscosity depends on the temperature and not the shear rate or time
Viscosity does not change by prolonged or vigorous shaking (shear rate)
Linear graph which passes through the origin
What is a rheogram?
A plot of shear stress against shear rate for a liquid
What is pseudoplastic flow?
Fluid will flow as soon as shear stress is applied
Viscosity decreases by increasing shear rate (shaking)
Non-linear but passes through the origin
A low polymer concentration is which type of fluid?
Newtonian fluid
A high polymer concentration is which type of fluid?
Non-Newtonian fluid
What is dilatant flow?
Viscosity increases by increasing shear rate (shaking)
Non-linear but passes through the origin
How does dilatant flow occur?
At rest particles are closely packed and inter-particle voids are at a minimum which the vehicle can fill
But during flow the volume of solid material increases so now there is not enough fluid to fill the voids
What is Bingham or plastic flow?
Fluid will only flow once shear stress is above a threshold value
Viscosity usually stays constant
Linear but does not pass through the origin so there is a yield value
How can you determine the rheological properties of liquids?
Use a bob and cup viscometer
What is the usual speed of the bob in a bob and cup viscometer?
0.01-600 rpm
