Determination of viscosity

Whole detail about various method to determine viscosity

1. Determination of Viscosity
Prepared by.... Sushmita RANA
Assistant Professor
(Specialised in Pharmaceutics)

2. Determination of viscosity:
In case of Newtonian systems the rate of shear is directly
proportional to the shearing stress.
Therefore, single point viscometer i.e. the equipment that works
at a single rate of shear, is sufficient.
For evaluation of Non-Newtonian fluids multipoint viscometers
are required, because the apparent viscosity is to be determined at
a several of rates of shear to get entire consistency curve.

3. Viscometer
Single point
Multipoint
At a single rate of
shear one point on
the curve
Several rates of shear
many points on the
curve
Equipment:
Ostwald viscometer,
Falling sphere
viscometer
Equipment:
Cup and bob
Cone and plate
Application:
Newtonian Fluids
Application:
Non Newtonian fluids &
Newtonian Fluids

4. •CAPILLARY VISCOMETER
•Also known as U-tube viscometers, capillary
viscometers include the Ostwald and
Ubbelohdevariations.
•They’re straight-forward and simple to use,
consisting of a U-shaped glass tube with two
bulbs (one higher and one lower).
•Fluid passes from the higher bulb to the lower
bulb through a capillary, and viscosity is
measured by timing how long it takes the
fluid to pass through the tube

5. Introduction:
These viscometers are suitable for only Newtonian systems.
Principle:
Capillary Viscometer based on Poiseuille’s law. This method of
measurement,Measures timetaken for defined quantity of fluid to flow
through a capillary with known diameter and length. It is then
compared with time required to flow by a liquid of known viscosity
(usually water) .
The viscosity of unknown liquid can be determined by using equation:
η1/η2= ρ1t1/ ρ2t2

6. η1/ η2= RELATIVE VISCOSITY OF LIQ.
The above eq. is based on POISEUILLE’S LAW for liq.
flowing through capillary tube
η= π r⁴tΔP/ 8lV
Where, r = radius of inside capillary t= time flow
ΔP=Pressureunder which liq. Flow
L= length of capillary
V= Volume of fluid flowing
This e.qcan also be written as
η= KtΔP

7. Capillary Viscometer
Ostwald viscometer
Suspended level
viscometer
Couette type Or revolving
cup type or Mac Michael
viscometer
Searle type or revolving
bob type or stormer
viscometer

8. •OSTWALD’S VISCOMETER:
•Ostwald’s viscometer also known as U-tube viscometer
•A device which is used to measure the viscosity of the
liquid with a known density. This device is named after
“Wilhelm Ostwald
Working & Principle:
The viscometer is filled with liq. Uptobulk Athrough 1 starm.
Then suck the liq. Through 2 nd arm to upper point C of the bulk B .
Now allow the liq. To pass from upper marked C to lower marked D.
And note the time of flow from upper marked C to lower marked D.
Now the viscosity of liq. Can be calculated by using formula;
η1/η2= ρ1t1/ ρ2t2

9. •SUSPENDED LEVEL VISCOMETER:
It is a modified form of Ostwald’s viscometer.
In it ,there is third vertical arm attached to the bulb below the capillary part of
the right arm. Liquid is introduced into the viscometer through the left arm In
quantity sufficient to fill the bulb in the left arm.
FALLING SPHERE VISCOMETER
INTRODUCTION:
Falling sphere viscometer is suitable for Newtonian systems.
PRINCIPLE:
Stoke’slaw is the basis of the falling sphere viscometer, in which the fluid is stationary.
Stoke’slaw:
“It states that when a body falls in viscous media, it
experiences a resistance which oppose the motion of the fluid.”
WORKING
The sample &ball are placed in the inner glass tube & allowed to reach temperature
equilibrium with the water in the surrounding constant temperature jacket.
The tube and jacket are then inverted. Which effectively placed the ball at the top of inner
glass tube. The time for the ball to fall between two marks is accurately measured and
repeated several time.

10. FORMULA:
Viscous drag on body = force responsible for the
downward movement, thus :
3пηdv = п/6d³g x Ps–P1
where,
D = diameter of the sphere
g = acceleration due to gravity v = terminal velocity
Ps = density of sphere P1= density of liquid by
rearranging formula :
η = d²g ( Ps –p1 ) / 18v

11. •CUP AND BOB VISCOMETER:
•This is a multipoint viscometer and belongs to the category of rational viscometer.
•It is consist of two coaxial cylinders of different diameters.
•The outer cylinder forms the cup into which the inner cylinder or bob is fixed
centrally.
•The torque set up in the bob is measured in terms of angular deflection Q of a
pointer that exhibit on the scale.
Principle: The sample is placed in the cup and the bob is placed in the cup uptoan
appropriate height. The sample is accommodation between the gap of cup and bob.
Now wither the cup or bob is made to rotate and the torque resulting from the
viscous drag is measured by a spring or sensor in the drive of the bob.

12. Couette type Or
revolving cup type or
Mac Michaelviscometer
Searle type or
revolving bob type or
stormer viscometer
TYPES

13. COUETTE TYPE VISCOMETER
•In this the cup is rotated and the viscous drag on the
bob produced by the liquid results in a torque which
is proportional to the viscosity of the liquid.
•Example:
MacMichaelviscometer

14. SEARLE TYPE VISCOMETER
•In searle type viscometer, the bob is rotated while the cup is
held stationary. Examples: Stormer viscometer &Brookfield
viscometer
•FORMULA
η=kv w/v
Where
Kv =instrument constant
W=weight in gram
V=rpm generated due to w

15. •CONE AND PLATE VISCOMETER
•A cone-plate is precise torque meter which driven as discrete
rotational speed.
•The torque measuring system which consist of a calibrated
beryllium copper spring connecting the driven mechanism to rotating
cone, sense of resistance to rotation caused by
presence of sample fluid between the cone and stationary flat plate

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