A viscometer is an instrument used to measure the viscosity of fluids. There are several types of viscometers, including rotational viscometers, vibrational viscometers, oscillation viscometers, falling piston viscometers, and falling sphere viscometers. Rotational viscometers can measure viscosity for both Newtonian and non-Newtonian fluids under varying conditions. Vibrational viscometers are suited to measuring non-Newtonian liquids in pipes and tanks. Falling sphere viscometers use Stokes' law to calculate viscosity based on the terminal velocity of spheres falling through a fluid.

1. BITS EDU CAMPUS
FLUID MECHANICS
Subject: Viscometer

2. Prepared By:

3. Topics
• Introduction
• Types of viscometer

4. Viscometer
What Is Viscometer?
• A Viscometer is an instrument used to measure the
viscosity of a fluid.
• It is also known as Viscosimeter.
• For liquids with viscosities which vary with flow
conditions, an instrument called a rheometer is used.
Viscometers only measure under one flow condition.

5. Types of Viscometer
• Rotational Viscometer
• Vibrational Viscometer
• Oscillation Viscometer
• Falling Piston Viscometers
• Falling Sphere Viscometer

6. Rotational Viscometer
• Rotational viscometer gathers data
on a material’s viscosity behavior
under different conditions.
• Rotational viscometers can be
used for the accurate
measurement of viscosity for both
Newtonian and non-Newtonian
fluids.

7. Fig: Rotational Viscometer

8. Vibrational Viscometer
• A Vibrational Viscometer is used for
continuous direct measurement of
viscosity in pipes and/or tanks.
• Vibratory Viscometers are better suited
to measure non-newtonian liquids

9. Fig: Vibrational Viscometer

10. Oscillation Viscometer
• The oscillating piston viscometer
technology has been adapted for small
sample viscosity and micro-sample
viscosity testing in laboratory
applications.
• It has also been adapted to measure high
pressure viscosity and high temperature
viscosity measurements in both
laboratory and process environments

11. Fig: Oscillation Viscometer

12. Falling Piston Viscometers
• The principle of viscosity measurement in
this rugged and sensitive industrial device
is based on a piston and cylinder assembly.
• The piston is periodically raised by an air
lifting mechanism, drawing the material
being measured down through the
clearance (gap) between the piston and
the wall of the cylinder into the space
which is formed below the piston as it is
raised.

13. Fig: Falling Piston Viscometer

14. Falling Sphere Viscometer
• The falling ball viscometer is based on Stokes’ Law.
• This type of viscometer consists of a circular cylinder
filled by the liquid under investigation.
• A standard ball is allowed to fall down this tube over a
calibrated distance of 100 mm.
• Stokes' law can be used to calculate the viscosity of the fluid.
A series of steel ball bearings of different diameter are
normally used in the classic experiment to improve the
accuracy of the calculation.

15. • George Gabriel Stokes derived an expression for the frictional force
exerted on spherical objects with very small Reynolds numbers in a
continuous viscous fluid by changing the small fluid-mass limit of
the generally unsolvable Navier-Stokes equations:
where:
F is the frictional force,
r is the radius of the spherical object,
is the fluid viscosity, and
is the particle's velocity.

16. Fig:Falling Sphere Viscometer

17. • If the particles are falling in the viscous fluid by their own
weight, then a terminal velocity, also known as the
settling velocity, is reached when this frictional force
combined with the buoyant force exactly balance the
gravitational force. The resulting settling velocity is given
by:
where:
Vs is the particles' settling velocity (m/s)
r is the Stokes radius of the particle (m),
g is the gravitational acceleration (m/s2),
ρp is the density of the particles (kg/m3),
ρf is the density of the fluid (kg/m3), and
𝜇 is the (dynamic) fluid viscosity (Pa s).

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