C.
Powder
flow – hopper
OBJECTIVES
1) To study the
effect of various particle size towards the powder flow properties.
2) To study the
relationship between the diameter of the hopper with time taken for the powder
to flow through it.
INTRODUCTION
Powder flow is the ability of powders to flow in a desired manner in a specific equipment depending on few factors such as particle size, size of orifice and others. Good flowability of the powders is important in each of these industries especially in pharmaceutical industry. The uniform flow of solid mixtures is one of the most important considerations in solid dosage manufacture such as tablets and capsules. It is very useful to ensure the accuracy in dosage and weight of drugs.
Powder flow may be affected by physical properties of the powder and also the external or environment condition. The examples of physical properties are particle size, shape, density, size distribution and cohesiveness. Different particle size of powder will produce different powder flow. Besides, temperature and humidity which are categorized as environment condition which may affect the powder flow properties.
Hopper is one of the equipment used to measure the powder flow properties. Larger opening diameter of hopper will helps the powder to flow more easily downward to the hopper end opening. Powder flow may also depend on the angle of repose in the hopper surface, where the smaller the angle of repose, the particles can flow easily.
In this experiment, similar sands with different sizes are used to investigate the relationship between particle size of sand with time taken for all the sand to flow out of hopper. The flowability of the sand is determined by the time taken for sand to flow through an orifice. Hopper is used as a direct method to measure the flow rate of particles.
METHOD
MATERIALS:
100g of four different types of sand (355mic, 500 mic,850 mic and various size).
APPARATUS
Five types of hopper with different diameter. (8mm, 10mm, 11mm, 13mm and 16mm), stopwatch, weighing boat.
PROCEDURE:
1. 4 or 5 hoppers with different sizes were prepared.
2. Sand samples of varying particle sizes were prepared.
3. The hopper’s orifice was closed and 100 g of sand was placed inside the hopper.
4. The orifice was opened and the sand was allowed to flow out.
5. The time required for all the sand to flow completely out of the hopper was measured.
It was allowed to flow naturally, it was avoided to shake and tap the hopper.
6. The above steps were repeated with different sand and/or hopper sizes.
Powder flow is the ability of powders to flow in a desired manner in a specific equipment depending on few factors such as particle size, size of orifice and others. Good flowability of the powders is important in each of these industries especially in pharmaceutical industry. The uniform flow of solid mixtures is one of the most important considerations in solid dosage manufacture such as tablets and capsules. It is very useful to ensure the accuracy in dosage and weight of drugs.
Powder flow may be affected by physical properties of the powder and also the external or environment condition. The examples of physical properties are particle size, shape, density, size distribution and cohesiveness. Different particle size of powder will produce different powder flow. Besides, temperature and humidity which are categorized as environment condition which may affect the powder flow properties.
Hopper is one of the equipment used to measure the powder flow properties. Larger opening diameter of hopper will helps the powder to flow more easily downward to the hopper end opening. Powder flow may also depend on the angle of repose in the hopper surface, where the smaller the angle of repose, the particles can flow easily.
In this experiment, similar sands with different sizes are used to investigate the relationship between particle size of sand with time taken for all the sand to flow out of hopper. The flowability of the sand is determined by the time taken for sand to flow through an orifice. Hopper is used as a direct method to measure the flow rate of particles.
METHOD
MATERIALS:
100g of four different types of sand (355mic, 500 mic,850 mic and various size).
APPARATUS
Five types of hopper with different diameter. (8mm, 10mm, 11mm, 13mm and 16mm), stopwatch, weighing boat.
PROCEDURE:
1. 4 or 5 hoppers with different sizes were prepared.
2. Sand samples of varying particle sizes were prepared.
4. The orifice was opened and the sand was allowed to flow out.
5. The time required for all the sand to flow completely out of the hopper was measured.
It was allowed to flow naturally, it was avoided to shake and tap the hopper.
6. The above steps were repeated with different sand and/or hopper sizes.
DISCUSSIONS
In this experiment, the powder flow is measured by time taken for the sand powders to move out from the hopper orifice with different diameters. Four different size particles of sands are used which are 355 mic, 500 mic, 850 mic and various size particles of sand. Their ability to flow is tested by allowing them to flow through different diameter of hoppers, time taken for all the sands to flow out is measured. The different hoppers with different diameter used are 8mm, 10mm, 11mm, and 16mm of diameter. The flow properties of powders depend on their physical properties such as size, shape, density and size distribution of particles.
Theoretically, when we test with the smaller size of sand (355 mic), it will take a longer time (25.00s) for all the sands to move out from hopper. When the size of sand is larger (850mic), it takes a shorter time(7.21s) to flow out from the hopper. It is because the smaller size of sands ( 355 mic) has greater cohesive force, lower flowability and thus it takes longer time to flow out of the hopper. Bigger sand size will have lesser cohesive flow and greater flowability and it takes shorter time to flow out from hopper. For various size of sands, it take longer time(18.05s) than sands with 850mic (7.21s) to flow out from the hopper, it is because sands with various size will have be closely packed (small sand particle fill space in between large sand particle). The closely packed sands has greater cohesive force and lower flowability, so it need longer time to flow out from hopper.
In term of diameter of hopper orifice, sands with size of 355mic which flow through 8mm of orifice in 25.00s, while it flows through 16mm of hopper orifice in 5.08s. It is due to larger diameter of orifice which allows more sands to flow out per unit of time, thus shorter time taken for all sands to move out from hopper. Moreover the angle of hopper opening also plays a major role in determining the powder flow. The greater the hopper angle, it will be more difficult for the sands to flow out, hence it will take longer time. The greater angle of hopper angle might cause the funnel flow, while small hopper angle causes the mass flow of sands.
In addition, force of gravity is one of the reasons that increase the flowability of sands from hopper. The larger the force of gravity on the sands, the faster it flows out from hopper and takes shorter time. The larger the size of sand, there is the greater gravitational forces on it. Thus, larger size of sands will be pull downward and increase its flowability.
There are few precautions step to be taken while handling this experiment. Firstly, the end opening of the hopper should be closed before started the stopwatch, so that there is no change in the weight of sand due to leakage that will affect the accurate calculation of flowability. Next, the stopwatch must be started at the same time when the sand starts to flow out, so that the time taken recorded for the sand to flow completely is accurate. We can repeat the experiment twice to get the average time which is more accurate. Thirdly, the sand must be weighed in a close system which avoid air movement, thus enable us to obtain the accurate weight of the sand. Lastly, we should let the sand to flow out from the hopper naturally and not affected by any external factors, thus we avoid tapping and shaking the hopper. As we shake and tap the hopper, it will cause the sands to flow out easily.
QUESTIONS
1. What are the factors that influence the flow of a powder?
Powder flow is influenced by physical characteristics of the particles and also external factors. Physical characteristics include size of particles, shape, diameter and shape of instrument used, and density will affect flow properties of the powder. The external factors or environmental conditions during processing, handling, or transport are temperature and humidity. Surface properties of powder (presence of surface charges) and usage of glidants also affect the powder flow.
2. Based on the above experiment, which sand and hopper size resulted in the best powder flow?
Based on the experiment above, the sand with 850 mic sizes which pass through 16mm diameter of hopper orifice takes the shortest time for powder flow, that is 4.75 seconds. The larger sizes of sand have smaller cohesive force, it flows out of the hopper size at shorter time (best flowability). Next, the larger size of hopper orifice enables more sand to pass through per unit of time, thus it takes a shorter time (best flowability).
3. What other methods can you use to determine the flow of a powder?
There are some indirect and direct methods in determining the powder flow. Examples of indirect method are angle of repose, bulk density and critical orifice diameter. Next, direct method like recording flowmeter also used in measuring flow of powder.
In this experiment, the powder flow is measured by time taken for the sand powders to move out from the hopper orifice with different diameters. Four different size particles of sands are used which are 355 mic, 500 mic, 850 mic and various size particles of sand. Their ability to flow is tested by allowing them to flow through different diameter of hoppers, time taken for all the sands to flow out is measured. The different hoppers with different diameter used are 8mm, 10mm, 11mm, and 16mm of diameter. The flow properties of powders depend on their physical properties such as size, shape, density and size distribution of particles.
Theoretically, when we test with the smaller size of sand (355 mic), it will take a longer time (25.00s) for all the sands to move out from hopper. When the size of sand is larger (850mic), it takes a shorter time(7.21s) to flow out from the hopper. It is because the smaller size of sands ( 355 mic) has greater cohesive force, lower flowability and thus it takes longer time to flow out of the hopper. Bigger sand size will have lesser cohesive flow and greater flowability and it takes shorter time to flow out from hopper. For various size of sands, it take longer time(18.05s) than sands with 850mic (7.21s) to flow out from the hopper, it is because sands with various size will have be closely packed (small sand particle fill space in between large sand particle). The closely packed sands has greater cohesive force and lower flowability, so it need longer time to flow out from hopper.
In term of diameter of hopper orifice, sands with size of 355mic which flow through 8mm of orifice in 25.00s, while it flows through 16mm of hopper orifice in 5.08s. It is due to larger diameter of orifice which allows more sands to flow out per unit of time, thus shorter time taken for all sands to move out from hopper. Moreover the angle of hopper opening also plays a major role in determining the powder flow. The greater the hopper angle, it will be more difficult for the sands to flow out, hence it will take longer time. The greater angle of hopper angle might cause the funnel flow, while small hopper angle causes the mass flow of sands.
In addition, force of gravity is one of the reasons that increase the flowability of sands from hopper. The larger the force of gravity on the sands, the faster it flows out from hopper and takes shorter time. The larger the size of sand, there is the greater gravitational forces on it. Thus, larger size of sands will be pull downward and increase its flowability.
There are few precautions step to be taken while handling this experiment. Firstly, the end opening of the hopper should be closed before started the stopwatch, so that there is no change in the weight of sand due to leakage that will affect the accurate calculation of flowability. Next, the stopwatch must be started at the same time when the sand starts to flow out, so that the time taken recorded for the sand to flow completely is accurate. We can repeat the experiment twice to get the average time which is more accurate. Thirdly, the sand must be weighed in a close system which avoid air movement, thus enable us to obtain the accurate weight of the sand. Lastly, we should let the sand to flow out from the hopper naturally and not affected by any external factors, thus we avoid tapping and shaking the hopper. As we shake and tap the hopper, it will cause the sands to flow out easily.
QUESTIONS
1. What are the factors that influence the flow of a powder?
Powder flow is influenced by physical characteristics of the particles and also external factors. Physical characteristics include size of particles, shape, diameter and shape of instrument used, and density will affect flow properties of the powder. The external factors or environmental conditions during processing, handling, or transport are temperature and humidity. Surface properties of powder (presence of surface charges) and usage of glidants also affect the powder flow.
2. Based on the above experiment, which sand and hopper size resulted in the best powder flow?
Based on the experiment above, the sand with 850 mic sizes which pass through 16mm diameter of hopper orifice takes the shortest time for powder flow, that is 4.75 seconds. The larger sizes of sand have smaller cohesive force, it flows out of the hopper size at shorter time (best flowability). Next, the larger size of hopper orifice enables more sand to pass through per unit of time, thus it takes a shorter time (best flowability).
3. What other methods can you use to determine the flow of a powder?
There are some indirect and direct methods in determining the powder flow. Examples of indirect method are angle of repose, bulk density and critical orifice diameter. Next, direct method like recording flowmeter also used in measuring flow of powder.
CONCLUSION
The smaller the particle size, the poorer the flowability of particles due to greater cohesive force.
The larger the diameter of hopper orifice, the shorter the time taken for powder to flow out of hopper.
REFERENCES
1. http://regentsprep.org/regents/earthsci/units/weathering/deposition.cfm
2. Aulton, M.E. 2007. Pharmaceutics: The Design and Manufacture of Medicines. Ed. Ke-3. Churchill Livingstone Elsevier.
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