Objective:
To determine the relationship between the types of powder
(different size of the sand) and diameter of the opening of hopper.
Introduction:
The widespread use of powders in the pharmaceutical industry has
generated a variety of method for characterizing powder flow. So, what is the
powder flow? Powder flow is the ability of a particle to move by flow from a
container. It is important in the process of making tablets and capsules as it
can ensure uniform particle packing to produce uniform tablet/capsule weight.
Powder flow is important to ensure efficiency, either due to process design or
intrinsic properties of the particles. For every powder of different size, the
flowability is different. In this experiment, we are able to observe and
evaluate the flowability of the sand of different diameter using different size
of hoppers.
Apparatus:
Hoppers with diameter of orifice of 8mm, 10mm, 11mm, 13mm and 16mm,
stopwatch
Materials
Sand with size of 355µm, 500µm, 850µm and a mixture of sand containing
various size.
Procedure:
1. Five hoppers with different diameter of orifice of 6mm, 8mm, 11mm,
13mm and 16mm were prepared.
2. Four types of sand with different sizes and properties in which their
particle sizes are 355µm, 500µm, 800µm and a mixture of various size of sand
were prepared, and each type of sand was weighed to be 100g.
3.The orifice of the hopper with diameter of 8mm was covered with hand
and 100g of
355µm sand was poured into it
.
4.The orifice was opened so that the sand was allowed to flow out.
5.The time taken for all the sand to flow out from the hopper was
recorded.
6.The test above (step 1 to 6) was repeated by using different sizes of
sand and hoppers.
Result and Calculation:
Time Taken (s)
|
|||||
Sand Size
Diameter of
Hopper’s Orifice
|
150um
|
355µm
|
500µm
|
850µm
|
Various
|
8mm
|
28.54
|
26.61
|
21.15
|
18.98
|
10.65
|
10mm
|
13.45
|
11.51
|
9.36
|
8.22
|
10.40
|
11mm
|
9.35
|
7.93
|
5.99
|
5.71
|
7.96
|
13mm
|
4.11
|
3.99
|
3.23
|
2.87
|
3.43
|
16mm
|
3.72
|
3.57
|
2.23
|
1.79
|
3.21
|
Questions:
1. What are the factors that affect the
powder flow?
- The factors that affect the flowability is the physical properties of the powderThe example is of the physical properties is particle size and size distribution, particle shape and texture, surface properties and handling.
2. According to the experiment, what
size of sand and hopper size have the best powder flow?
- The size of sand and hopper size have the best powder flow is the biggest size of orifice of hopper which is 16mm. This hopper have the shortest time for sand to flow so have the highest rate powder flow.
3. What are the methods that can be used
to improve the powder flow?
- The methods to improve the powder flow are to alter the particle size and size distribution through granulation. The other methods is to alter of surface forces such as electrostatic forces and moisture content. Next, another methods is adding flow activators such as glidants. The last one is can alter the process condition using vibration-assisted hoppers and force feeders and particle shape or texture to be more spherical and smooth.
Discussion:
In this experiment, the rate of powder flow was dependent on the size of
the sand and the diameter of the orifice of hopper, its rate was determined by
comparing the time taken for the sand to flow completely from the hopper
without interference such as shaking.
Flowability is the the capacity to move by
flow that characterizes fluids and loose particulate solids. It can be
determined by many ways, one of it is the by studying the rate of powder flow
from a hopper. The result above in the table shows the hopper with orifice
diameter of 16mm took the shortest time for the sand to flow out among the five
different types of orifice size. For hopper with orifice diameter of 8mm, the
sand took the longest time to flow out of the hopper. It is because when a
larger orifice size used, there is more free space to allow more sand to be
discharged from the orifice.
If no shaking is applied to the hopper, the effect is some of the sand
left in the hopper . The sand that discharges freely are said to be undergoing
mass flow while the sand that don’t discharge freely due to high adhesion or
cohesion forces and shallow hopper angles, are said to be undergoing funnel
flow. For sand with a larger particle size, they can flow freely while the
smaller ones are generally cohesive and difficult to flow freely. Based on the
result, the bigger the particle size, the shorter the time taken for the sand
to flow out indicates the higher the flow rate.
Conclusion:
As for the conclusion, the hopper
orifice diameter and the particle size of the hopper affect the flowability of
the sand to flow out of the hopper. The time required for the sand to flow out
of hopper is inversely proportional hopper flow rate. The larger the orifice
diameter (16mm) and the bigger the particle size (850µm) has higher flow rate.
References:
2. Aulton, M.E. 2002. Pharmaceutics: The Science
of Dosage form Design. Edinburgh Churchill Livingstone.
3. http://www.foamandform.com/technical-minutes/powder-flow-characteristics
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