There are three main types of viscometers: capillary, falling, and rotational. Capillary viscometers are accurate for low viscosity newtonian fluids. They measure the time it takes a fluid to flow through a capillary tube under gravity. Rotational viscometers apply a torque to a cylinder or sphere in the fluid to determine viscosity based on shear stress. Common rotational viscometers include concentric cylinder, cone/plate, and coaxial cylinder designs which vary in whether the cup or bob rotates. Viscosity measurements depend on factors like fluid density, temperature, pressure, and rotational speed or flow time.

3.  The various viscometers used for determining
the viscosity of different systems can be broadly
divided into the following types :
 1) CAPILLARY
2) FALLING
3) ROTAIONAL

4. Capillary instruments are very accurate for the
measurement of viscosity of newtonian fluids having
low viscosity . During mesurement the time for the
fluid to flow by gravity from one mark in a capillary
column to the second marked is measured .the time
of the flow pf liquid under test is compared with the
time required for the flow of known viscosity to pass
between the two marks .
•If η1 and η2 ae viscosities of unkown and
standrad liquid . P1 and p2 are densities . T1 and t2
are time required to flow in sec then :

5. η1/η2 = realtive viscosity of liquids
•η = пr t∆P/ 8LV
R = radius of the inside capillary
t = the time of flow
∆p = the pressure head in dyne/cm²
L = length of capillary
v = volime of fluid
this eq can also be writtnen as :
η= Kt∆p

6.  The ostwalds U-tube
 THE UBBELOHDE
SUSPENDED LEVEL
FOLLWOING ARE THEIRS DETAILS 

7.  The appartaus consists
of a U tube the left
armof which has a
bulging or bulb as its a
lower part and a
marking A above the
bulb the right srm of the
tube also has bulb at the
upper part and just
below this bulb is a
capillary tub . There are
two maring B and C
above and below the
bulb of right arm .

8. Liquid is introduced into the viscometer through the left
arm untill the level reaches the mark .The visocmeter is
fixed vertically in a thermosatated bath and allowed to
attain the required temperature .
The sample volume is adjusted and the liquid is suck or
blown into the right arm untill untill its just above the mark
B . The sucktion or pressure is released and the time taken
from the bottom of the meniscus to fall from B and C .
Equation :-
η1/η2 = p1 x t1 /p2 x t2

9. Its a modified form of ostwalds
viscometer . In this
instrument there is a third
vertical arm attached to the
bulb below the capillary part
of the right arm .
Working :-
liquid is introduced into
the viscometer through
the left arm in quantity
sufficient to fill the bulb in
left arm . The viscometer
is fixed vertically in
thermostated bath and
allow to attain the temp .
Equation :-
η1/η2 = p1 x t1 /p2 x t2

10. A)Falling sphere
B) Rising sphere

11. Princilple The priciple of this instument is based on strokes law which
states that when a body falls through a viscous medium , it experience a resistance
which opposes the motion of the body .
So ,
viscous drang on body = force responsible for the downward movement
thus :
3пηdv = п/6d³g x Ps – P1
where as
D = diameter of the sphere
g = acceleration due to gravity
v = terminal velocity
Ps = density of sphere
P1= density of liquid
by reaaraning formula :
η = d²g ( Ps – p1 ) / 18v

12.  It consists of a tube having to
markings A and B on the outter
surface . The tube is fiiled by the
liquid whose viscosity is to be
determined . The tube is clamped
vertically a constant temp and
for removal ofa ir bubbles from
the liquid .
 A ball of suitable material such
as steal or glass is then allowed
to fall through the guide inside
the falling tube . The time taken
for the sphere to fall frm point
A to point B and the terminal
velocity is obtained by
divinding distance .
 By puting values in abov
formaila we can obtain
viscosity .

13. Rising sohere viscometerisa n
important instrument to study
the yield value of non –
newtonian systems .
It is 1.9 cm in diamter. Satinless
steel sphere connected to
strain guage via a platinium
rhodium wire is lifted
through the material under
test at a very slow rate by a
motor driver arm the sheering
stress caused by the strain in
the geal stucture is recorded
continously .
Stoke’s equation similar to that
used for a falling sphere
instrument is used to
determine the shear or rate of
strain .

14. These intuemnts works
on the vicous drag
exerted on a body when
its rotated in fluid
whose viscosity is to be
determined . The mai
advantage of these
instruments over rest of
viscometers is that a
wide range of shearrate
can be achieved using
these instruments
Types :-
a) concentri
cylinder or
cup shaped
and bob
b) viscometer
cone and plate

15.  Structure and
working :
this type of instrument consist
of two coaxialcylinders of
different diameters .. The
outer cylinder from the cup
into which the inner cylinder
or bob is fixed centarlly .the
sample to be anaylsed is
sheared in space between the
outter wall ov the bob and the
inner wall of cup .
 The dfferent types of
commercially available
instruments differ mainly in
wether the torque set up in th
e bob due to roatation of the
outer cup or due to rotation of
bob it self .

16. COUTTE TYPE SEARLE TYPE
In this instrument cup is
rotated
In ths intrument bob is
rotated

17. The stromer viscometers is an
instrument in which the bob
rotates and cup is stationary .
This instrument can be used to
obatin fundamental rheological
prpoerties such as yield value ,
plastic viscosity and the
thixotropic index .
Working ;-
in operation , the test system is
placed ,in space between the cup
and the bob and allowed to reach
temp equllibrium .a weight is
placed on hanger and the time for
the bob to rotate a specific number
of time is recorded . The data is
converted into rpm .

18. η = Kv ( w/v )
w = weight in grams v =
rmp generated due to w Kv = is
an instrument constant which can be determined by analysing an oil of knwn
viscosity using the instrument .
the plastic viscosity may be caculated by using
eq ;-
U = Kv ( W-W1 / V )
w1 = yield value intercept in grams
U = plastic viscosity