Title:
Powder Flow
Objective:
Introduction:
Measuring the ability and the time taken for a
powder to flow through an orifice of known size is a useful method of quantifying
powder flow.
At the same time, it is important to recognize that
the ability of the powder to flow through the orifice can be affected by
factors other than the characteristics of the powder itself. Such factors
include the shape and material employed in the construction of the powder
container, the diameter and height of the powder bed and the shape of the
orifice concerned. The flow rate obtained in such a case however will depend on
the geometrical parameters of the hopper, as well as the nature and size of the
powder particles. Also, determining the flow rate through an orifice is useful
only with free-flowing materials.
Procedure:
1. 5 different diameters of hoppers are taken.
2. 4 different properties and sizes of sand are taken.
3. The orifice of the hoppers is closed and 100g of sands
are put into it.
4. The orifice of the hoppers is open and the sand flow
through it.
5. Time taken for the sand to flow through the orifice of
the hopper completely is recorded.
6. The experiment is repeated using different sizes of
hoppers and sands.
Results:
Size of Sand
(mic)
|
Diameter of
the orifice (cm)
|
Diameter of
hopper (cm)
|
Time taken for
the sand to flow (s)
|
150
|
0.8
|
4.0
|
8.99
|
1.4
|
3.55
|
||
1.6
|
2.43
|
||
0.8
|
6.0
|
7.83
|
|
1.4
|
3.63
|
||
355
|
0.8
|
4.0
|
9.35
|
1.4
|
3.61
|
||
1.6
|
2.80
|
||
0.8
|
6.0
|
11.9
|
|
1.4
|
3.71
|
||
500
|
0.8
|
4.0
|
9.14
|
1.4
|
4.44
|
||
1.6
|
3.21
|
||
0.8
|
6.0
|
8.78
|
|
1.4
|
4.57
|
||
850
|
0.8
|
4.0
|
9.35
|
1.4
|
4.37
|
||
1.6
|
4.43
|
||
0.8
|
6.0
|
11.40
|
|
1.4
|
4.84
|
||
Various
|
0.8
|
4.0
|
10.01
|
1.4
|
7.2
|
||
1.6
|
4.1
|
||
0.8
|
6.0
|
8.44
|
|
1.4
|
5.81
|
Discussion:
Powder flowability is the ability of a powder to
flow in a desired manner in specific equipment. Powders are probably the least predictable of all materials
in relation to flowability because of the large number of factors that can
change their rheological properties. Physical characteristics of the particles,
like size, shape, angularity, surface texture, porosity and hardness will all
affect flow properties. External factors such as humidity, conveying
environment, vibration and perhaps most importantly, aeration, will compound
the problem. The more common variables would include, firstly
powder or particle variables, such
as particle size, size distribution, shape and surface texture. Secondly is
external factors will influence
powder behaviour, for instances flow rate, compaction condition, vibration and
container surface effects. From the experiment, the time taken
for sand to flow is short when using large diameter of orifice and hopper. Furthermore,
the smaller the size of the sand the shorter time taken for the powders to flow
completely. However, when conducting the experiment, the time take for the sand
to flow is not consistent as in theory. This error happened due to the hopper
angle which made the sand stack there and did not flow smoothly. Other than
that, shaking the hopper also will affect the sand flow as it increase the flow
rate.
Conclusion:
I. The smaller the size
of the sand the shorter time taken for the powders to flow completely
II. The bigger the
diameter of the orifice, the shorter the time taken for the powders to flow
Question:
1.
What are the factors that affect the flow of powders?
The factors that may
affect the flow rate of powders are size of the powders, diameter of the
orifice, hopper wall angle and width of the hopper.
2.
Based on the experiments, which size of powders and diameter
of hoppers that will give the best flow rate of powders?
The smallest size of
the powders and the bigger diameters of orifice also the bigger width of the
hopper will give the best flow rate of the powders.
3.
What are the methods that can be used to increase the flow
rate of powders?
The methods used to
increase the flow rate of the powders are shaking of the containers, increasing
the hopper and orifice diameter and reduce cohesive strength of powder.
References:
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