Fluid Mechanics LAB:
Measuring-Viscosity & Specific gravity
ENTC - 303
ENTC-303
PROF. ALVARADO
1
Objective
To learn how to measure two important fluid
properties:
• The fluid viscosity
• The fluid specific gravity
Viscosity
• Viscosity is a measure of the resistance of a fluid which is being
deformed by either shear stress or tensile stress.
• The absolute viscosity of a substance can be represented by
u
 
y
• τ is the shear stress and Δu/Δy is the rate of change of the velocity with
respect to the distance from the surface
Reference:1. http://en.wikipedia.org/wiki/Viscosity
2. http://en.wikipedia.org/wiki/File:Laminar_shear.svg
Types of Fluids
• Newtonian fluids
- Viscosity of the fluid is a function mainly of
u
the temperature of the fluid.    y
• Non-Newtonian fluids
- Viscosity of the fluid is a function mainly of
the temperature of the fluid and the velocity
gradient.
u n
  (
)
y
The comparison between Newtonian
and Non Newtonian Fluid
u n
  (
)
y
 
u
y
Devices
• Brookfield DV-I+ digital viscometer
Falling Ball Viscometer
The ball inside the viscometer is
made of stainless steel
hydrometer –
Specific gravity measuring
apparatus
Brookfield Viscometer
Steps:
1. Turn on the viscometer switch at the back.
2. There are different kinds of spindles depending on the viscosity of fluid
measured. The spindle used for this experiment is a 'zero-zero' spindle.
Spindle is connected to the motor.
3. Pour the fluid in the container.
4. Insert and center spindle in the fluid until the fluid’s level is at or above the
immersion groove shown in the spindle’s shaft. Make sure the spindle is
set at '00'.
5. Select the desired speed setting. Set the initial speed to 1.5 RPM.
If the % range is not within 10% - 99%, adjust the speed so that the % falls
within the limit.
6. Use the thermometer to measure the temperature of the fluid in container.
7. Allow time for the indicated reading to stabilize.
8. Run the experiment for the same temperature at 3 different speeds1.5RPM, 3RPM and 6RPM
9. Take the average of the viscosity at the three different speeds for one single
temperature.
10. wait for TA to change the temperatures on the chiller .
Data
• 1. Plot Viscosity vs. Temperature (at 20°C, 22°C,
24°C).
• 2. Plot Viscosity vs. Rotational Velocity 1.5
RPM 3 RPM, 6 RPM (at 22°C).
• Determine if the fluid is Newtonian or nonNewtonian.
Falling ball Viscometer
1. Initially let the ball travel drop in the opposite direction
until it crosses the red marks.
2. Invert the viscometer and note down the time taken by
the ball to travel between any two red marks.
3. Take three trials of time for oil. Convert the time into
minutes and take the average of the trials.
Hydrometer
• Make sure the Hydrometer is clean and dry.
• Immerse the Hydrometer slowly in the liquid to a point below
which it naturally sinks (not over 1/8").
• Do not make reading until the hydrometer and liquid are at rest
and free from air bubbles.
• Wait one minute until the hydrometer stabilizes.
• The temperatures of the hydrometer and liquid tested should
be equal.
• When fluid is transparent, observe a point below the plane of
the liquid surface and then raise the line of vision until this
surface, seen as an ellipse, becomes a straight line. The point
where this line cuts the hydrometer is the reading of the
instrument.
Density of fluid = SG(specific gravity) x Density of water (1 gms/ml)
Temperature
Speed
Reading 1 Reading 2
(cP)
(cP)
Reading 3
(cP)
Average
(cP)
1.5 rpm
20 °C
3 rpm
6 rpm
1.5 rpm
22 °C
3 rpm
6 rpm
1.5 rpm
24 °C
3 rpm
6 rpm
1 (s)
Falling Ball
Viscometer
(Viscosity)
2 (s)
3 (s)
Average (s)
1
Hydrometer
(Specific
Gravity)
2
3
Average
Average
(cP)