During our
discussion on previous post “Hydraulic Fluid”, I have promised to create one
post for understanding the concept of viscosity measurement with the help of
viscometer technology.
Let us understand how we can measure viscosity of a fluid, i have decided to produce one live experiment report for better understanding the concept of measurement of viscosity .
Let’s start!!!
Let us understand how we can measure viscosity of a fluid, i have decided to produce one live experiment report for better understanding the concept of measurement of viscosity .
Let’s start!!!
Let us think we
have to measure the viscosity of glycerin with the help of falling
viscometer technology. We will start to
understand the viscosity measurement with following basic points.
 Concept & Theory
 Apparatus
 Experimental procedure
 Result and Analysis
 Conclusion
Sphere

D
(m)

W
(N)

T
(s)

U
(m/s)

Re

C

µ1
( Pa. S)

1

0.0043688

0.00341

4.06

0.0750

0.444

54

0.9292

2

0.0043688

0.00341

4.19

0.0727

0.417

57.53

0.9590

3

0.0043688

0.00341

3.88

0.07855

0.487

49.31

0.8881

4

0.0043688

0.00341

4.00

0.0762

0.46

52.40

0.91552

5

0.0043688

0.00341

4.07

0.07488

0.44

54.26

0.93154

6

0.0043688

0.00341

4.00

0.0762

0.46

52.40

0.91552

7

0.0043688

0.00341

4.13

0.0738

0.429

55.86

0.94527

8

0.0043688

0.00341

3.87

0.078759

0.489

49

0.88576

9

0.0043688

0.00341

3.94

0.07736

0.472

50.84

0.90178

10

0.0043688

0.00341

4.00

0.0762

0.46

52.40

0.91552

11

0.0043688

0.00341

4.03

0.0756

0.92239


12

0.0043688

0.00341

3.97

0.07677

0.90865


13

0.0043688

0.00341

3.90

0.07815

0.89263


14

0.0043688

0.00341

4.09

0.07452

0.93612


15

0.0043688

0.00341

4.06

0.07507

0.92925


16

0.0043688

0.00341

4.09

0.07452

0.93612


17

0.0043688

0.00341

3.75

0.08128

0.8583


18

0.0043688

0.00341

3.87

0.78759

0.88576


19

0.0043688

0.00341

3.84

0.079375

0.87899


20

0.0043688

0.00341

3.97

0.07677

0.90865

Concept & Theory
When a body falls in a liquid due to
gravity,' it accelerates until the weight of the body is equivalent to the
drag force and buoyancy and the velocity of the body at this point is known as
terminal velocity. We may determine the viscosity of the liquid by determining
the terminal velocity of object or sphere in that liquid.
Let us understand, with the help of
free body diagram, drag force, buoyancy force and weight of object or sphere
during falling in liquid.
When this sphere will achieve its terminal velocity, we will have following force balanced equation
∑ F = 0
W= F_{D} + F_{B}
Where,
W= weight of sphere = Ƴ_{S}.
V
F_{D} = drag force
F_{B}= Buoyancy force
Drag force:
F_{D}= (Cρ_{1}U^{2} A) / 2
Where,
C = drag coefficient
ρ_{1}= density of liquid
(kg/m^{3})
U= terminal velocity of sphere (m/s)
A = (πD^{2}/4)
In case of creeping flow
Drag coefficient, C = 24/ Re
Where, Re= Reynolds
number = ρ_{1}UD/µ_{1}
Where, D = Sphere
diameter
µ_{1}=
Liquid Dynamic viscosity
ρ_{1}= density of liquid
But we must be aware that for creep
flow, Re<1
As per the Archimedes principle,
The force of buoyancy of a submerged
body will be equivalent to the weight of the liquid which is displaced by the
body.
Let us consider
about the buoyancy force
F_{B}= Ƴ_{1}.
V
Ƴ_{1}= Liquid specific weight
V= Volume of sphere
After solving above
equation, we will have the final result as mentioned below for dynamic
viscosity.
µ_{1}= (Ƴ_{S} Ƴ_{1}). D^{2}/ (18 U)
Apparatus
We have used
following mentioned apparatus
 Stop watch
 Thermometer
 Glycerol
 Needlenose pliers or tweezers
 Scale of 1 Foot
 1000 ml graduated cylinder
 Micrometer or vernier caliper
 Electronic scale
 Copper plated steel spheres (BB s)
 Masking tape
 Ring stand
Experimental procedure
We may briefly
describe the procedure as mentioned below
 Measure the diameter with micrometer or vernier of 20 sphere and consider the average value for each sphere.
 Measure the weight of those 20 spheres of steel and consider the average value of weight of each sphere.
 Filling of graduate cylinder with glycerol and must assure that there will not be any entry of air bubbles.
 Now we will locate one masking tape piece on the cylinder approximate 100 mm below the glycerol surface and must be noted that the other piece i. e second piece should be about 305 mm lower than the first piece.
 Saturate the thermometer in the glycerol and must assure that temperature might be measured any time during experiment.
 Hold one sphere, with the help of pillers, approximate 25 mm lower the glycerol surface in the center of the cylinder. Now release the sphere.
 Measure the time with the help of stop watch that sphere takes to fall 305 mm as marked by the pieces of masking tape.
 Repeating the last two steps.
 Use the equation and determine the viscosity.
Result & Discussion
Some important point
1.
1 Pa. s = 1000 CP
2. Possible
source of experimental error.There will be some
error in measuring the time.There is also
possibility in measuring the diameter of sphere
3. Wall
effect will have a retarding effect over the terminal velocity due to Presence of wall
Wall effect is
normally indicated in terms of wall factor.
4.
Accuracy of the experiment could be improved by correct measurement of
diameter of sphere and measurement of duration of time to fall the sphere by a
distance as specified in experiment.
5. Glycerol
is Newtonian fluid
Conclusion
We have concluded
the following points after studying this blog
 let us consider about the result that we have secured from our experiment. We have secured dynamic viscosity 912.20 Centipoise (it's average value)
 Objective of this blog is to secure the value of dynamic viscosity by falling ball viscometer technique.
 Glycerol is Newtonian fluid Wall effect will have a retarding effect over the terminal velocity due to presence of wall
 Wall effect is normally indicated in terms of wall factor
 Possible source of experimental error
 There will be some error in measuring the time
 There is also possibility in measuring the diameter of sphere
Accuracy of this report could be improved by correct measurement of diameter of
sphere and measurement of duration of time to fall the sphere by a distance as
specified in experiment.
Let us move towards new post.
Keep reading...