PRACTICAL 1 : (C) POWDER FLOW - HOPPER

Title : Evaluating of powder flow with various sand with different particles sizes using hoppers with different dimension and orifice size.

Objective : To evaluating the powder flow with various sand with different particles sizes using hoppers with different dimension and orifice size.

Date of Experiment : 30 September 2014

Introduction :

                The flowability of the powder is defined as the capability of a liquid or loose particulate solid to move by flow. This is important to ensure uniform feeding from the container/hopper to equipment to make sure uniform particle packing, constant volume-to-mass ratio, thus produce uniform tablet/capsule weight.

                Uneven flow will result from the excess fine particles causes lubrication problems therefore enhancing the risk of dust contamination. Particle size, particle shape, and also particle density , hopper with different dimension and orifice size are the factors that may affect the flow rate of powder but in this experiment is the flow of sand.

Procedure :

    1. 4 hoppers with different sizes are prepared.

    2. Sand sample with different particles sizes are prepared.

    3. The hopper’s orifice is closed and 100g of sand is placed inside the hopper.

    4. The orifice then is opened to allow the sand to flow out.

    5. The time required for the sand to stop flow is recorded by stopwatch. The flow is allowed to   

         happen naturally.

    6. The step above is repeated with different sand and with different hopper size.

Result :

Discussion :

                Powder flow is an important factor in the production of tablets and capsules. The uneven flow is resulting when the particles tend to stick to themselves (cohesion) and other surfaces (adhesion) due to presence of molecular forces. The cohesion forces mainly as result of short-range non-specific Van der Waals forces.

                There are many factors that may effect the flow of the sand for this experiment. The particles size of the sand need to be considered in order to determine the flowability. Generally, the fine the particles, the greater the cohesion forces. The greater the cohesion force, the shorter the time taken for the sand to stop flow as the resistance to flow is higher. As the size of the particles increase, the density is higher, thus lead to less problematic flow, less resistance, therefore the time taken for the sand to stop flow is longer.

                Next, there other factors which may influence the flow of the sand in this experiment is the diameter of the hopper’s orifice. The larger the diameter of the orifice, the shorter the time taken for the sand to stop flow. This is because of the less resistance created by the less adhesion/cohesion forces between the sand particles.

                Particles sand shape also may affect the flowability of the sand. The various the shape of the sand, the shorter the time taken for the sand to stop flow. This is because the various shapes of the particles cause the more tightly pack and this require higher driving force to produce flow. The less tightly packed particles flow easily as the bulk density is lower other than have more porous.

                Particles/sands that discharged freely said to undergo mass flow. It flow layer by layer without forming ‘pipe’ inside the hopper. Particles/sands that don’t discharged freely undergo funnel flow. It cause the formation of ‘pipe’, ‘rat hole’, ‘funnel’ and this contribute to rapid discharged of the flow.

               

Questions :

1. What are the factors that influence the flow of a powder?

The factors that may influence the flow of a powder are the particle size, particles shape and also particle density.

2. Based on this experiment, which sand and hopper size resulted in the best powder flow?

Sand with bigger size with bigger diameter of hopper’s orifice.

3. What are the other methods can be used to determine the flow of a powder?

For indirect method of determining the flow of powder, we can calculate the angle of repose, bulk density measurement and also critical orifice diameters. For direct method of determining the powder flow, we can measure the hopper flow rate, which is the rate at which the powder discharge from hopper and also by recording the flowmeter.

Conclusion :

This experiment is depend on the sand’s size and the diameter of the hopper’s orifice. The bigger the sand’s size with the greater diameter of the hopper’s orifice, may increase the flowability of the sand from the hopper.

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.