Rheology

Question 1

What is Rheology?

Answer 1

The study of deformation and the flow of matter

Question 2

Define Viscosity of a liquid?

Answer 2

It is resistance to flow or move Due to intermolecular interactions

Can be considered as ‘inner fraction’.

Question 3

What is the equation for shear rate?

Answer 3

Dv / Dr

r = the thickness of the layer (cm)

v = velcoity (s-1)

Question 4

What is the units for shear rate?

Answer 4

s-1

Question 5

Explain the relationship between rate and stress?

Answer 5

The rate of flow is directly proportionate to the applied stress

Question 6

What is the equation for Shear stress?

Answer 6

F / A

F = Force A = Area (m2)

Question 7

What is the equation for Dynamic viscosity?

Answer 7

The shear stress / the shear rate

Question 8

What are the units for Dynamic Viscosity?

Answer 8

Nm-2 or Pa S

Question 9

What is Dynamic Viscosity?

Answer 9

The measure of the internal resistance (or friction) involved in the relative motion of one layer of molecules

Question 10

What is Kinematic Viscosity (v) equation?

Answer 10

v = n/p

p = density

n = dynamic viscosity

Question 11

What are the units for Kinematic Viscosity?

Answer 11

m2s-1 or S cm2s-1

Question 12

Explain the Characteristics of Newtonian Flow?

Answer 12

It is the linear relationship between shear stress and shear rate (they are directly proportional)

Question 13

Is Viscosity affected by shear rate?

Answer 13

No, so you can measure viscosity at any shear rate.

Question 14

Is Viscosity affected by shear stress?

Answer 14

No, so you can measure viscosity at any shear stress.

Question 15

What are Colloidal dispersions?

Answer 15

One phase dispersed in another immiscible phase in the form of particles.

Question 16

What is the Viscosity of a pure solution and a colloid?

Answer 16

Pure = ηo Colloids = η

Question 17

What is equation for relative viscosity and specific viscosity?

Answer 17

Question 18

What is Einstein Equation?

Answer 18

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

Question 19

What is the dispersed phase and how do you calculate the volume of the dispersed phase?

Answer 19

The particles are the dispersed phase.

If you add the number of the particles up, you get the volume of the dispersed phase

Question 20

Explain what Laminar flow is?

Answer 20

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.

Question 21

Explain The Boundary Layer?

Answer 21

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.

Question 22

Explain Turbulent Flow?

Answer 22

Liquid from any point within the pipe, may flow to any other part.

So random.

Question 23

Explain Transitional Flow?

Answer 23

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

Question 24

What is equation for Reynolds number?

Answer 24

Re = pvd / n

P = density

V – velocity

D = characteristic length (diameter in the case of a pipe)

N = dynamic viscosity

Question 25

Explain how Reynolds number can predict the kind of flow occuring?

Answer 25

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