Objectives :
1. To determine the angle of repose of the various sizes of the sand with/without the addition of glidant.
2. To study the factor that affect the angle of repose of the sand.
Date of Experiment : 30 September 2014
Introduction :
The
angle of repose for a particular powder can be used to determine the flow
characteristics of a powder. Various methods are available to measure this
value. In this practical, students are given sand of various sizes and
with/without the addition of glidant. This test is conducted to determine the
angle of repose and the factors that may influence it.
Material/apparatus:
Different
types of dry sand, beaker, electronic balance, cylinder, rubber base, ruler,
glidant/water, spatula, newspaper
Procedure:
1. 100g
(or any suitable weight) of sand is prepared.
2. The
sand is placed in the cylinder with the rubber base at the bottom.
3. The
cylinder is removed and the sand is allowed to flow out and a heap is formed.
4. The
height, slope and diameter of the heap are measured.
5. The
angle of repose is calculated.
6. The
experiment is repeated using other sand or with the addition of glidant/water.
Result:
Beaker:
36.0056 g
Water:
10 ml
Size of sand
|
Height
|
Slope
|
Diameter
|
Angle of repose
|
Various sizes
|
3.90
|
4.00
|
4.60
|
77.16
|
850 mc
|
2.15
|
2.80
|
4.70
|
50.16
|
500 mc
|
2.50
|
3.00
|
4.70
|
56.44
|
355 mc
|
2.00
|
3.00
|
4.40
|
41.81
|
150 mc
|
2.18
|
3.50
|
4.50
|
38.53
|
Various sizes of sand: sin ø = height/ slope
Ø = sin-1 3.90/4.00 = 77.16°
850 mc = sin ø = height/ slope
Ø = sin-1
2.15/2.80 = 50.16°
500 mc =sin ø = height/ slope
Ø = sin-1 2.50/3.00 = 56.44°
355 mc =sin ø = height/ slope
Ø = sin-1
2.00/3.00 = 41.81°
150 mc = sin ø = height/ slope
Ø = sin-12.18/3.50
= 38.53°
Discussion:
The
angle of repose can be used to test the powder flow. Angle of repose is the
steepest angle of the descent or dip relative to the horizontal plane to which
a material (sand) can be piled without slumping. The angle of repose can range
from 0° to 90°. In this experiment, the various sizes of the sand are used to
determine the angle of repose of the sand.
For
the various sizes of sand, the angle of repose is 77.16°. It is the highest
angle of repose among the five different sizes. The angle is high because the
size of the sand is not uniform and it was a combination of the small and big size
of the sand. So it forms the higher piles on the rubber base. The sand with
high angle of repose has poor flow property.
The
smallest angle of repose is for fine sand, the smallest size, 150 mc. The angle
of repose is 38.53° and it shows that the fine powder has a good flow property.Sand
with low angle of repose forms flatters piles than sand with a high angle of
repose. The addition of the glidant is to increase the flow properties.
There
is an error occurs during carry out the experiment. Two persons take part in
releasing the powder on the rubber base. So the force or energy used to release
the powder is not consistent and it affected the result of the experiment.
Therefore, it is suggested that the releasing of the powder is done by the same
person to minimize the error.
Conclusion:
In
general, powder with angle of repose more than 50° have poor flow property. The
various size of sand has the angle of repose is 77.16° and it indicates that
the flow property of the powder is poor. Besides the fine size of sand, 150 mc
has angle of repose is 38.53° and it has a good flow property.
Question:
1. What
are the angles of repose for the sands that you use?
Size of sand
|
Height
|
Slope
|
Diameter
|
Angle of repose
|
Various sizes
|
3.90
|
4.00
|
4.60
|
77.16
|
850
mc
|
2.15
|
2.80
|
4.70
|
50.16
|
500
mc
|
2.50
|
3.00
|
4.70
|
56.44
|
355
mc
|
2.00
|
3.00
|
4.40
|
41.81
|
150
mc
|
2.18
|
3.50
|
4.50
|
38.53
|
2. What
are the factors that influence the angle of repose of a powder?
i.
Particle size-the big
particle sizes has the big angle of repose.
ii.
The addition of glidant
increase the flow properties
iii.
Particle shape- the
spherical particles have the smaller angle of repose.
3. What
other methods can you use to measure the angle of repose?
i. Tilting
box method- this method is appropriate for
fine-grained, non-cohesive materials, with individual particle size less than
10mm. The material is placed within a box with a transparent side to observe
the granular test material. It should initially be level and parallel to the
base of the box. The box is slowly tilted at a rate of approximately 0.3
degrees/second. Tilting is stopped when the material begins to slide in bulk,
and the angle of the tilt is measured.
ii.
Fixed
funnel method- the material is poured through a
funnel to form a cone. The tip of the funnel should be held close to the
growing cone and slowly raised as the pile grows, to minimize the impact of
falling particles. Stop pouring the materials when the pile reaches a
predetermined height or the base a predetermined width. Rather than attempt to
measure the angle of the resulting cone directly, divide the height by half the
width of the base of the cone. The inverse tangent of this ratio is the angle
of repose.
References:
Aulton, M.E. 2002. Pharmaceutics: The Science of Dosage form Design. Edinburgh Churchill Livingstone.
Martin, A.N. 2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences. Ed. Ke-5. Philadelphia: Lea & Febiger.
Michael E. Aulton. 2007. 3rd Edition Aulton’s Pharmaceutics : The Design And Manufacture of Medicines. Churchill Livingstone Elsevier.
www.pharmacopeia.cn/v29240/usp29nf24s0_c1174.html
www.slideshare.net/mobile/visualbeeNetwork/angle-of-repose-seamanship
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