Title : Practical 3 – The Flow of Powders
Objective
:
1. To study the effect of particle size and orifice diameter
on the mass flow rate.
2. To observe the powder flow with different sizes in
different sizes of hopper.
Introduction
:
Powder
flowability is the ability of a powder to flow in a desired manner in a
specific piece of equipment. Each powder of a certain material will have
different types of flow. The nature of
the powder flow affects the heat transfer and more importantly, the packing
arrangement of the particles as they deposit and melt on the mold surface.
Powder flow behaviour also can affect manufacturing efficiency and can directly
affect product quality variables such as dose uniformity. In this experiment,
the relationship between the types of powder and orifice diameter of hopper can
be determined.
MATERIAL : Sand with size of
150µm, 355µm, 500µm, 850µm and various.
Procedures
:
1.
Five hoppers with different sizes of 6mm, 8mm, 11mm, 13mm
and 16mm were prepared.
2.
Five types of sand with different sizes and properties in
which their particle sizes are 150µm, 355µm, 500µm, 800µm various kind of sand
were prepared and weighed.
3.
The orifice of the hopper was closed and 100g of the sand
was poured into the hopper.
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 For All The Sand To Flow Out From The Hopper (s)
|
|||||
Sand Size
Hopper
Orifice Diameter
|
150m
|
355m
|
500m
|
850m
|
Various
|
6mm
|
25.01
|
4.90
|
25.53
|
18.54
|
8.00
|
8mm
|
10.58
|
3.04
|
10.15
|
11.19
|
3.18
|
11mm
|
7.54
|
2.74
|
7.06
|
8.19
|
7.63
|
13mm
|
2.83
|
2.18
|
3.31
|
3.42
|
4.24
|
16mm
|
2.49
|
1.93
|
3.15
|
3.15
|
3.47
|
Discussion
:
Flowability is the result of a
combination of material physical properties that affect flow and the equipment
used for handling, storing, or processing the material. It can be defined as the capability
of a liquid or loose particulate solid to move by flow.
One of the method for
characterization of the powder flow is hopper flow rate measurement. In the
experiment, the rate of powder flow with different sizes was examined by
recording the time taken for sand to be discharged from hopper completely.
Flow behavior is multi-dimensional
and does in fact depend on many powder characteristics. Flowability is affected by the physical
properties of the powder, such as particle size and size distribution, particle
shape and texture, surface properties and handling and processing condition. As
shown on the table above, hopper with orifice diameter of 16mm took the
shortest time for the sand to flow out among the five different types of
orifice size. This shows that the rate of powder flow through orifices is
proportional to orifice diameter of the hopper. When a larger orifice size
used, there is more free space to allow more sand to be discharged from the
orifice.
Furthermore, powder that
discharges freely said to undergo mass
flow while powders that don’t discharge freely due to high adhesion or cohesion
forces and shallow hopper angles said to undergo funnel flow. Powder with larger particle size
usually flow freely while the smaller one are generally cohesive and prone to
flowability problems. Based on the result, the smaller the particle size, the
shorter the time taken for the sand to flow out indicates the higher the flow
rate. Particle size of 850µm which supposed to take the shortest time for the
sand to be discharged failed to express this property in the experiment. This
may due to moisture present inside the sand. The moisture will increase the
cohesion forces between particles, hence decreasing the flowability of powder.
Sand with larger particle sand also get stucked in the smaller hopper's orifice
sometimes result in the blockage of the sand flow in the experiment. Consolidated
powders are more resistant to flow hence ease of consolidation corresponds to
ease of flow. There
might be mistakes made when the time taken for the sand flow was recorded by
stopwatch.
There are some way to improve the
powder flowability. Those methods are through alteration of particles size and
size distribution through granulation as coarse particles are less cohesive
than fine particle and produce more spherical particles contribute to better
flow by spray drying. Moreover, alteration of process conditions to reduce
frictional contacts by the usage of vibration-assisted hoppers and force
feeders and addition of flow activators are also measures to improve power
flowability. Reduce moisture content can improve flowability too as
moisture increase bulk density and reduce porosity.
Conclusion
:
In conclusion, the sand flowability is effected by the
hopper orifice diameter and the particle size of sand to flow out of the
hopper. The larger the orifice diameter and the smaller the particle size has
higher flow rate. The time required for the sand to flow out of hopper is
inversely proportional hopper rate flow.
Reference
:
1.
Prescott, J.K., and Barnum R.A., On powder flowability,
Pharmaceutical Technology, October 2000, pp. 60-84 and 236.
2.
Barnum, Roger, Ebb and Flow: Understanding Powder Flow
Behavior, Pharmaceutical Processing, March 2009, pp. 18-21.
3.
Jenike, A.W., Storage and Flow of Solids (Bulletin 123 of
the Utah Engineering Experimental Station), 53 (26), (1964, revised 1980).
No comments:
Post a Comment