Practical 3 : Powder Flow

Purpose

To determine the relationship between the types of powder (different size of the sand) and diameter of the opening of hopper.

Introduction

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 and to have more consistent physicomechanical properties (tablet). 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	355µm	500µm	850µm	Various
8mm	26.61	21.15	18.98	10.65
10mm	11.51	9.36	8.22	10.40
11mm	7.93	5.99	5.71	7.96
13mm	3.99	3.23	2.87	3.43
16mm	3.57	2.23	1.79	3.21

Questions

1. What are the factors that affect the powder flow?

            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.

2. According to the experiment, what size of sand and hopper size have the best powder flow?

            The biggest size of sand which is 850µm and the biggest size of orifice of hopper which is 16mm gives the shortest time and have the highest rate powder flow.

3. What are the methods that can be used to improve the powder flow?

           Methods to improve the powder flow are to alter the particle size and size distribution though granulation, alter of particle shape or texture to be more spherical and smooth,alter of surface forces such as electrostatic forces and moisture content, adding flow activators such as glidants and lter the process condition using vibration-assisted hoppers and force feeders.

Discussion

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. 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.

It is actually a direct method to measure the powder flow rate using 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.

There is some of the sand left in the hopper if no shaking is applied to 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. For the various size of sand, some of it is very big and stuck at the orifice.

Conclusion :

In conclusion, flowability of the sand to flow out of the hopper is effected by the hopper orifice diameter and the particle size of it. The larger the orifice diameter (16mm) and the bigger the particle size (850µm) has higher flow rate. The time required for the sand to flow out of hopper is inversely proportional hopper flow rate.

References

1. Aulton, M.E. 2002. Pharmaceutics: The Science of Dosage form Design. Edinburgh Churchill

         Livingstone.

2. http://www.merriam-webster.com/dictionary/flowability