This ppt will help you to understand the basic concept of Viscosity and different methods to measure Viscosity.

1. Chapter 1
Measurement of Viscosity
Krunal H. Parmar
Assistant Professor
Department of Instrumentation & Control
Sardar Vallabhbhai Patel Institute of Technology, Vasad

2. Outlines
1. Introduction
- What is Viscosity?
- Why should I measure Viscosity?
2. Newtonian & Non Newtonian behavior
- Newtonian behavior
- Non Newtonian behavior
- Pseudo plastic
- Dilatants
- Plastic
- Thixotropy
- Rheopexy

3. 1. Introduction
• Viscosity is a quantitative measure of a fluid’s resistance
to flow.
• It is defined as the internal friction of fluid.
• Lack of slipperiness is called as viscosity
• Rheology: The study of the change in form and the flow
of matter, embracing elasticity, viscosity, and plasticity.
• We generally measures two types of viscosity :
1. Absolute/ Dynamic Viscosity (ƞ)
2. Kinematic Viscosity (Ʋn)

4. Viscosity
• Viscosity is the measure of the internal friction of a fluid.
• This friction becomes apparent when a layer of fluid is
made to move in relation to another layer.
• The greater the friction, the greater the amount of force
required to cause this movement, which is called shear.
• Shearing occurs whenever the fluid is physically moved
or distributed, as in pouring, spreading, spraying, mixing,
etc. Highly viscous fluids, therefore, require more force to
move than less viscous materials.

5. • Isaac Newton defined viscosity by considering the model
represented in the figure below.
• Two parallel planes of fluid of equal area A are separated
by a distance dx and are moving in the same direction at
different velocities V1 and V2.

6. • Newton assumed that the force required to maintain this
difference in speed was proportional to the difference in
speed through the liquid, or the velocity gradient. To
express this, Newton wrote:
• where Ƞ is a constant for a given material and is called its
viscosity.

7. • The velocity gradient, dv/dx , is a measure of the change
in speed at which the intermediate layers move with
respect to each other. It describes the shearing the liquid
experiences and is thus called shear rate.
• The term F/A indicates the force per unit area required to
produce the shearing action. It is referred to as shear
stress.
• So, mathematically Viscosity can be defines as

8. Why should I measure Viscosity?
• From viscosity measurement, we can obtain much useful
behavioral and predictive information for various
products.
• A frequent reason for the measurement of rheological
properties can be found in the area of quality control,
where raw materials must be consistent from batch to
batch.
• For this purpose, flow behavior is an indirect measure of
product consistency and quality.

9. Types of Viscosity

10. Newtonian fluids

11. • This type of flow behavior Newton assumed for all fluids
is called Newtonian.
• It is, however, only one of several types of flow behavior
you may encounter.
• Graph A shows that the relationship between shear
stress and shear rate is a straight line.
• Graph B shows that the fluid's viscosity remains constant
as the shear rate is varied.
• Typical Newtonian fluids include water and thin motor
oils.

12. Non Newtonian fluids
• A non-Newtonian fluid is broadly defined as one for
which the relationship is not a constant.
• It means that there is non-linear relationship between
shear rate & shear stress.
• In other words, when the shear rate is varied, the shear
stress doesn't vary in the same proportion (or even
necessarily in the same direction).
• E.g. Soap Solutions & cosmetics, Food such as butter,
jam, cheese, soup, yogurt, natural substances such as
lava, gums, etc.

13. Pseudo plastic

14. • This type of fluid will display a decreasing viscosity with
an increasing shear rate.
• Probably the most common of the non-Newtonian fluids,
pseudo-plastics include paints, emulsions, and
dispersions of many types.
• This type of flow behavior is sometimes called
"shear-thinning.

15. Dilatants

16. • Increasing viscosity with an increase in shear rate
characterizes the dilatant fluid.
• Although rarer than pseudo plasticity, dilatancy is
frequently observed in fluids containing high levels of
deflocculated solids, such as clay slurries, candy
compounds and sand/water mixtures.
• Dilatancy is also referred to as shear-thickening flow
behavior.

17. Plastic (Bingham Plastic)

18. • This type of fluid will behave as a solid under static
conditions.
• A certain amount of force must be applied to the fluid
before any flow is induced; this force is called the yield
stress (f').
• Tomato catsup is a good example of this type fluid; its
yield value will often make it refuse to pour from the
bottle until the bottle is shaken or struck, allowing the
catsup to gush freely.
• Once the yield value is exceeded and flow begins, plastic
fluids may display Newtonian, pseudoplastic, or dilatant
flow characteristics.

19. • Some fluids will display a change in viscosity with
time under conditions of constant shear rate.
• There are two categories to consider:
1) Thixotropy
2) Rheopexy

20. Thixotropy

21. Rheopexy

22. Viscosity coefficients
• Viscosity coefficients can be defined in two ways:
1) Dynamic or Absolute viscosity
2) Kinematic Viscosity
• Viscosity is a tensorial quantity that can be decomposed
in different ways into two independent components. The
most usual decomposition yields the following viscosity
coefficients:
1) Shear Viscosity
2) Extensional Viscosity

23. Dynamic Viscosity/ Absolute Viscosity
 Proportionality constant between shear stress and
velocity gradient is often called as “Dynamic Viscosity
/ Absolute Viscosity”.
 Reciprocal of Dynamic Viscosity is “Fluidity”.
 Ratio of Shear stress to the velocity gradient of the
fluid is known as Absolute Viscosity.

24. Units of Absolute Viscosity

25. Kinematic Viscosity

26. Shear Viscosity
• The most important one, often referred to as simply
viscosity, describing the reaction to applied shear
stress; simply put, it is the ratio between the
pressure exerted on the surface of a fluid, in the
lateral or horizontal direction, to the change in
velocity of the fluid as you move down in the fluid
(this is what is referred to as a velocity gradient).

27. Volume Viscosity or Bulk Viscosity
• Bulk viscosity becomes important only for such
effects where fluid compressibility is essential.
Examples would include shock waves and sound
propagation.
• It appears in the Stokes' law (sound attenuation) that
describes propagation of sound in Newtonian liquid.

28. Extensional Viscosity
• A linear combination of shear and bulk viscosity,
describes the reaction to elongation, widely used for
characterizing polymers.
• For example, at room temperature, water has a
dynamic shear viscosity of about 1.0 * 10−3 Pa·s and
motor oil of about 250 * 10−3 Pa·s.

29. Instruments for Measuring Viscosity

30. Measurement of Shear viscosity
 Depends upon dynamics of shear force acting upon fluid
either Newtonian / non- Newtonian.
 Instruments which measures the viscosity are called as
Viscometers. Viscometers only measures under one flow
condition.
 Most popular viscometers to measure shear viscosity are
1. Capillary flow viscometer
2. Circular couette flow viscometer
3. Cone & plate flow viscometer
4. Parallel plate flow viscometer

31. Principle of Viscosity Measurement

32. Capillary Flow Viscometer
• Capillary flow viscometers are based on pressure
drop

36. • With this as a starting point we can derive the
Hagen-Poiseuille Equation:
Q 
(P)R4
8L
 
(P)R4
8LQ

37. Couette Viscometer

40. Cone & Plate Viscometer

42. Parallel Plate Viscometer

43. Shop Floor Viscometers
• Mainly used in Industrial applications to measure
viscosity of mostly Newtonian types of fluid.
• These viscometers consisting simple & convenient
method for viscosity measurement.
• Most popular shop-floor viscometers :
1. Rotational Viscometer
2. Flow through restriction type Viscometer
3. Flow around type Viscometer

44. Rotational Viscometer (Brook field
Viscometer)
• Determine viscosity by measuring the
resistance on a shaft rotating in the
fluid .
• They are designed to make a direct
measurement of the absolute
Viscosity.
• The theory of operation of a rotational
viscometer is based on the Couette
flow model for fully developed,
steady and laminar flow between two
surfaces, one of which is moving.
• Pointer displacement is directly
proportional to fluid viscosity.

46. Flow through restriction type

47. Flow around obstruction type

48. Viscometer standard table

49. Most popular flow around type
Viscometer

51. Measurement of Extensional Viscosity

52. Operating Principle

53. Effect of Temperature
• The viscosity of liquids decreases with increase the
temperature.
• The viscosity of gases increases with the increase the
temperature.
• The lubricant oil viscosity at a specific temperature
can be either calculated from the viscosity -
temperature equation or obtained from the
viscosity-temperature chart.

54. Viscosity Temperature equations

56. Viscosity Index
• An entirely empirical parameter which would accurately
describe the viscosity- temperature characteristics of the
oils.
• The viscosity index is calculated by the following
formula:
VI = (L - U)/ (L - H) * 10
where ,
VI is viscosity index
U is the kinematic viscosity
of oil of interest
L and H are the kinematic
viscosity of the reference oils

57. Effect of Pressure
• Lubricants viscosity increases with pressure.
• For most lubricants this effect is considerably largest
than the other effects when the pressure is
significantly above atmospheric.
• The Barus equation :

59. Online Viscosity Measurement

60. Applications
• Selection of lubricants for various purpose.
- we can choose an optimum range of viscosity for
engine oil.
- for high load and also for speed operation high
viscous lubricants is required.
• In pumping operation
- for high viscous fluid high power will require.
- for low viscous fluid low power will require.
• In making of blend fuel
- less viscous fuels easy to mix.
• In the operation of coating and printing.

61. Important Questions
1. Explain Coutte Viscometer in detail.
2. Define Viscosity. What are the different methods of Viscosity
measurement? Explain any one method with basic Principle, working &
suitable application.
3. Explain the measurement of viscosity under extremes of temperature
and pressure.
4. Explain in detail construction and working of cone and plate viscometer
and parallel plate viscometer.
5. Define the viscosity with necessary equation and discuss Newtonian
and non-Newtonian behavior of various fluids
6. Explain the measurement of shear viscosity using capillary viscometer
with necessary equation
7. Give explanation about following terms: Viscosity, Bingham Plastic,
Pseudoplastic, Shear Thinning, Shear Thickening, Thixotropy &
Rheopexy