PRACTICAL 3
Powder Flow
Aim
To study the relationship of hopper’s
diameter and size of sand with the rate of powder flow.
Introduction
Powder flow is essential in tablet
and capsule production. Each powder of any material has different flow.
In this experiment, a powder flow
of various sizes of sand is tested using hopper with different size and its
orifice.
Material and apparatus
1.
Narrow
hopper with different diameter of orifice:
i.
8mm.
ii.
13mm.
iii.
16mm.
2.
Wide
hopper with different diameter of orifice:
i.
10mm.
ii.
16mm.
3.
Different
size of sand:
i.
355 micron.
ii.
500
micron.
iii.
850
micron.
iv.
Mixture of
various sizes of sand.
4.
Stopwatch.
Method
1.
5 hoppers
with different sizes are prepared.
2.
5
different sizes and nature of sand are prepared.
3.
The
hopper’s orifice is closed and 100g of sand are poured into the hopper.
4.
The
orifice is let open to allow sand flow.
5.
The time
taken for all sand to flow out is recorded.
6.
Steps 1 to
5 are repeated using different size of sand and hopper.
Result
Tabulation of data
1.
Time taken
for powder to flow out of hopper.
|
Sand
sizes (micron)
Hopper diameter (mm)
|
350
|
500
|
850
|
Various
Sizes
|
|
Narrow hopper
8
|
13.92s
|
13.82s
|
16.60s
|
15.93s
|
|
13
|
4.10s
|
4.21s
|
4.81s
|
4.51s
|
|
16
|
2.71s
|
2.11s
|
2.80s
|
3.61s
|
|
Wide hopper
10
|
8.40s
|
7.51s
|
8.82s
|
6.23s
|
|
16
|
2.81s
|
4.11s
|
3.81s
|
4.31s
|
2.
Amount of
sand left in the hopper.
|
Sand
sizes (micron)
Hopper diameter (mm)
|
350
|
500
|
850
|
Various Sizes
|
|
Narrow hopper
8
|
A little
|
A little
|
A little
|
A little
|
|
13
|
A quarter of sand
|
A little
|
A little
|
A little
|
|
16
|
A little
|
A little
|
A little
|
A little
|
|
Wide hopper
10
|
A quarter of sand
|
A quarter of sand
|
A quarter of sand
|
A quarter of sand
|
|
16
|
Very little
|
A little
|
Very little
|
A little
|
Graph
1.
Graph of diameter
of orifice of narrow hopper against time taken for powder to fall down.
2.
Graph of Diameter
of orifice of wide hopper against time taken for powder to fall down.
Discussion
In
this experiment we chose 5 hoppers (3 narrow cylinder hopper and 2 wide
cylinder hopper) with different size of orifice. The size of orifice is
measured by its diameter. The size of sand used is also varied; 350 microns,
500 microns, 850 microns and various sizes (mix sand). The sand is let to flow
with the effect of the gravity (no shaking/force applied to the hopper to force
the sand out). The time is taken when there is no more powder flow out. The
leftover of sand in the hopper is observed by its quantity.
Based
on the result obtained, the sand leftover is high when wide hopper with small
orifice is used. Based on the graph, the flow of sand took shorter time if the
orifice of the hopper used is bigger and vice versa. The width of hopper also
affects the time taken for a complete flow. For example, with the same diameter
of orifice i.e. 16 mm, the wider hopper recorded slower flow of sand than sand
in the narrow hopper maybe due to less adhesion between the wall of hopper and
sand particles and the potential energy created by higher sand as sand in
narrow hopper is deeper than sand in wide hopper.
On the other hand, when we compare between the
sizes of sand with the time taken for it to flow completely, the relationship
is not clear. For example, for 350 microns sand to flow from a wide hopper with
10 mm diameter of orifice takes 8.4 seconds which is longer compared to 500
microns sand (7.51 seconds) but when using 16 mm diameter of hopper, the 350
microns sand flow faster compared to 500 microns sand which is 2.81 seconds
compared to 4.11 seconds. This finding maybe affected by other factors such as
the angle of the hopper, the cohesion and adhesion between sand particles and
the shape of the sand particle.
The accuracy of
the reading may not be accurate because this experiment depends on the hand-eye
coordination of the tester, therefore, the reading should be taken at least 3
times to get the average result.
Question
1.
What are
the factors affecting powder flow?
The factors affecting powder flow are:
a.
Orifice
diameter of a hopper.
b.
Hopper
width.
c.
Hopper
wall angle.
d.
Head
size/powder depth.
2.
Based on
the test conducted on the powder and which size of hopper that gives the best
flow?
The best flow is the fastest and least residue which 500 microns sand
flowed through 16 mm of narrow hopper with a little residue in 2.11 seconds.
3.
What
method can be used to aid in powder flow?
The methods can be used to aid in powder flow are:
a.
Alteration
of particle size & size distribution
b.
Alteration
of particle shape/texture.
c.
Alteration
of surface forces.
d.
Formulation
additives; flow activators.
e.
Alteration
of process condition.
i.
Vibration
assisted hopper.
ii.
Force
feeder.
Conclusion
Powder
flow is affected by several factor, one of it is the size of hopper orifice.
The bigger the size of an orifice, the shorter the duration for powder to flow
whereas the smaller the orifice, the longer the powder flow duration.
References
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