Practical 8 Determination of terminal velocity.ppt

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1. APE 311 Protected Cultivation and Secondary
Agriculture (1+1)
Practical -8
Experiment on determination of terminal velocity of
different grains

2. Determination of terminal velocity of different grains
AIM:
To determine the terminal velocity of the given grain
samples.
APPARATUS:
Terminal velocity apparatus, anemometer, grain samples,
etc.
THEORY:
Aero and /or hydrodynamic properties are very important
characters in hydraulic transport and handling as well as
hydraulic sorting of agricultural products.

3. Theory
To provide basic data for the development of equipment
for sorting and sizing of agro commodities, several
properties such as: physical characteristics and terminal
velocity are needed.
The two important aerodynamic characteristics of a body
are its terminal velocity and aerodynamic drag.
Terminal velocity of the grains is the velocity at which the
grain is kept under suspension and against the gravity.

5. Theory
By defining the terminal velocity of different threshed
materials, it is possible to determine and set the
maximum possible air velocity in which material out of
grain can be removed without loss of grain or the
principle can be applied to classify grain into different size
groups.
In addition, agricultural materials and food products are
routinely conveyed using air.
For such operations, the interaction between the solid
particles and the moving fluids determine the forces
applied to the particles.

6. Theory
The interaction is affected by the density, shape, and size
of the particle along with the density, viscosity, and
velocity of the fluid.
In the handling and processing of agricultural products, air
is often used as a carrier for transport or for separating
the desirable products from unwanted materials,
therefore the aerodynamic properties, such as terminal
velocity and drag coefficient, are needed for air conveying
and pneumatic separation of materials.

7. Theory
As the air velocity, greater than terminal velocity, lifts the
particles to allow greater fall of a particle, the air velocity
could be adjusted to a point just below the terminal
velocity.
The fluidization velocity for granular material and settling
velocity are also calculated for the body immersed in
viscous fluid.
The set up usually consists of a vertical air column, which
is blown from the bottom and passes through the screen.

8. Theory
The screen uniformly distributes the air velocity.
The air column is also attached with velocity measuring
device.
The blower maintains variable speed.
When grains are allowed to drop into the column, initially
they attains acceleration, once the velocity is adjusted
they fall to the bottom with a constant velocity.
This constant velocity is termed as terminal velocity.

9. Theory
Factors affecting aerodynamic properties of biomaterials,
are frontal area and particles size orientation (In turbulent
region particles assumes position of maximum
resistance).
Terminal velocity is applied in the separation of foreign
materials from seeds, grains, etc. and conveying and
handling of grains, chopped forage, small and large fruits,
hydraulic handling of apples, cherries, mango and
potatoes, etc.

10. DESCRIPTION:
The apparatus consists of an electric blower which
discharge air blast into a transparent tapered tube used as
a cyclone which is fixed at the outlet side of the blower
through an elbow.
A screen is fitted at the bottom of the transparent tapered
tube of 8 ×4 cm cross section and a cyclone is fitted at the
top of it 15 cm square cross section.
A chock valve is built at the bottom of the cyclone to
control the air flow rate.
The chock valve is manually adjusted by the control lever.

11. Terminal velocity apparatus

12. Terminal velocity apparatus

13. DESCRIPTION:
Under steady state condition, where terminal velocity has
been achieved, if the particles density is greater than fluid
density, the particles motion will be downward.
If particles density is smaller than the fluid density, the
particle will be rise.
Using a suitable airflow measuring system, the velocity of
air is measured when the particle is under floating and
against the gravity.

14. PROCEDURE:
Check the operation of the blower and the functioning of
the choke valve.
Fit the vertical column in position and also place the mesh
/ screen.
Take the given sample of grains and open the vertical
tunnel at the place of opening provided / near the mesh.
Place about 10 seeds / grains from the given lot of the
grains/ seeds.
Close the tunnel firmly and keeping the choke valve
closed, switch on the blower.

15. PROCEDURE:
The flow of the air from the blower through the vertical
duct / tunnel may be seen and also agitating the grains
placed in the vertical tunnel.
Now slowly open the choke valve and release the air from
the blower to the vertical duct / tunnel.
Slowly increase the air flow by further opening the valve
start lifting and slowly raising.
Care should be taken to control the opening of the valve
such that the grains do not fly off from the tunnel.

16. PROCEDURE:
When the grain mass is under suspension and against the
gravity by the upward thrust of the air, place the
anemometer and note the air velocity.
This air velocity in m/s is the terminal velocity of the given
grain mass.
The determination may be repeated with different grains
and at different moisture contents.
The readings of the air velocity may be recorded in the
tables.

17. OBSERVATIONS AND CALICATIONS:
Sample–Chick pea
Grain / SeedMoisture Content
db,%
Terminal velocity,
m/s
1 12.0 13.54
2 12.0 15.96
3 12.0 14.58
Mean 14.69

18. OBSERVATIONS AND CALICATIONS:
Sample–Kidney bean
Grain / SeedMoisture Content
db,%
Terminal velocity,
m/s
1 14.0 12.48
2 14.0 12.98
3 14.0 13.55
Mean 13.67

19. OBSERVATIONS AND CALICATIONS:
Sample–Maize
Grain / SeedMoisture Content
db,%
Terminal velocity,
m/s
1 12.8 12.58
2 12.8 12.75
3 12.8 13.53
Mean 12.95

20. Results
The terminal velocity of the given grain samples at the
given moisture contents are,
Grain / SeedMoisture Content
db,%
Terminal velocity,
m/s
Chick pea 12 14.69
Kidney Bean 14 13.67
Maize 12.8 12.95