Rheology Flashcards
What is Rheology?
The study of deformation and the flow of matter
Define Viscosity of a liquid?
It is resistance to flow or move Due to intermolecular interactions
Can be considered as ‘inner fraction’.
What is the equation for shear rate?
Dv / Dr
r = the thickness of the layer (cm)
v = velcoity (s-1)
What is the units for shear rate?
s-1
Explain the relationship between rate and stress?
The rate of flow is directly proportionate to the applied stress
What is the equation for Shear stress?
F / A
F = Force A = Area (m2)
What is the equation for Dynamic viscosity?
The shear stress / the shear rate
What are the units for Dynamic Viscosity?
Nm-2 or Pa S
What is Dynamic Viscosity?
The measure of the internal resistance (or friction) involved in the relative motion of one layer of molecules
What is Kinematic Viscosity (v) equation?
v = n/p
p = density
n = dynamic viscosity
What are the units for Kinematic Viscosity?
m2s-1 or S cm2s-1
Explain the Characteristics of Newtonian Flow?
It is the linear relationship between shear stress and shear rate (they are directly proportional)
Is Viscosity affected by shear rate?
No, so you can measure viscosity at any shear rate.
Is Viscosity affected by shear stress?
No, so you can measure viscosity at any shear stress.
What are Colloidal dispersions?
One phase dispersed in another immiscible phase in the form of particles.
What is the Viscosity of a pure solution and a colloid?
Pure = ηo Colloids = η
What is equation for relative viscosity and specific viscosity?
What is Einstein Equation?
When you re-arrange the equation, you get:
Specific viscosity (Ns) = 2.5
So Ns is only depedent on the volume fraction on the colloid
What is the dispersed phase and how do you calculate the volume of the dispersed phase?
The particles are the dispersed phase.
If you add the number of the particles up, you get the volume of the dispersed phase
Explain what Laminar flow is?
The liquid in a pipe, flows through in a laminar way.
Flows out horizontally along the line, not going to any other part of the pipe.
Explain The Boundary Layer?
In a pipe, the majority of the liquid is flowing at velocity, v.
But the region next to it is different.
The liquid touching the pipe (the inside wall of the pipe), has a velocity of 0.
So as you move towards the centre of the pipe, the velocity increases.
Within the boundary layer the velocity will increase from 0, as you move to the centre of the pipe.
Explain Turbulent Flow?
Liquid from any point within the pipe, may flow to any other part.
So random.
Explain Transitional Flow?
When you have a laminar flow and you increase the speed little by little, the liquid starts to become wavy.
Starts to move to different places
When you get to certain speeds, you reach turbulent flow
What is equation for Reynolds number?
Re = pvd / n
P = density
V – velocity
D = characteristic length (diameter in the case of a pipe)
N = dynamic viscosity
Explain how Reynolds number can predict the kind of flow occuring?
If Re <2000, laminar flow
If Re >4000, turbulent flow
If Re 2000< Re < 4000, depending on the surface.
If smooth, laminar
If rough, turbulent
So larger speed = large Re value
