Discussion:: Discussion The powder flow in this experiment is mass flow. Mass flow which is also known as mass transfer and bulk flow is the movement of material matter. Mass flow involves powder that discharged freely when first in first out. Mass flow also reduces the extent to which some types of segregation affect the powder. Although all of the material is moving, velocity profiles may still exist within the hopper. From this experiment, we can see that mass flow is influenced by both diameter of hopper orifice and also the particle sie !diameter of sand". From the result obtained, the sands of different particle sies flow through hopper with #$ mm orifice diameter with an average of %.$# s, which is relatively fast compared to hopper with orifice diameter #% mm !&.'( s", ## mm !$.&& s", #) mm !(. s" and * mm !##.)% s". +and flows through the hopper with the smallest hopper orifice in this experiment !* mm" with the highest average duration that is ##.)% s. This shows that hopper with larger orifice gives a better particle flow, in this case, sand flow while hopper with small orifice causes a slower flow. This can be explained as the larger the hopper orifice, the less the contact surface area of the particle !sand" to the wall of hopper. This causes reduction in friction and therefore the particle !sand" can move smoothly and faster. Another factor affecting powder flow in this experiment is sie of particle, in this case, diameter of the sand. From the result obtained, sand of various diameters has a better flow than that of diameters % -m, )) -m and *) -m. This can be explained by strong cohesion between sand of different sies as the sand with smaller sie filling up the spaces in between sand with larger sie, indicating larger contact surface area of and particle. This is followed by sand of diameter *) -m, )) -m and then %-m. This shows that the larger the particle sie, the faster the particle flow. This is due to larger particle has larger gravitational force which will pull down the particle faster towards the ground. There is some inconsist inconsistency ency of data obtained from the experiment where the duration of sand flow fluctuated. This might be caused by external forces accidentally applied by person holding the hopper, different shallow hopper angle and also hopper with different diameter. To overcome these problems, a distort stand can be used instead of using bare hand to hold the hopper when sand flow out from it. This can also ensure a constant height where the sand flows out of the hopper. oppers with same shallow hopper angles and also diameter should be used although the orifice diameter is difference. This can ensure more accurate results and prevent other factors affecting the experiment. There are many other factors that will influence flow property of powder such as shaking, presence of water and moisture, cohesion and adhesion force of particle, particle shape, particle density and particle packing geometry.
Conclusion:: Conclusion /owder flow depends on the orifice diameter of the hopper and also particles sie of powder a. /owder flow better and faster with larger hopper orifice diameter and larger particle sie of powder while powder flows slower with smaller hopper orifice diameter and smaller particle sie.
Questions: 1. What are the factors that affect powder flow? Factors that influence the flow property of powder including shaking, presence of water and moisture, cohesion and adhesion force of particle, particle shape, particle density and particle packing geometry. 2. Based on the experiment above, what is the sie of powder and hopper !ive the best powder flow? +ie of powder that gives the best powder flow is sand of various sies. opper with orifice diameter #$ mm gives the best powder flow. ". What are the methods that can be used to help the flow of certain powder? Firstly, alteration of particle sie and sie distribution can be carried out by manipulating proportion of coarser and finer particles for example granulation. Alteration of particle shape or texture also can be carried out by making more spherical particles using spray drying. +urface forces also can be altered by reducing electrostatic forces through earthing and also reducing moisture content. Flow activators such as colloidal silicon dioxide and magnesium oxide help to reduce adhesion and cohesion thus improve powder flow. /rocess condition also can be altered for example using vibration0assisted hoppers and force feeders.
D#$C%$$#&' Angle of repose is one of the methods used to characterie the flow of a material. 1n this experiment, angle of repose for different sies of sand and with the presence of a glidant is determined. The factors that affect the angle of repose are also studied. From the result obtained, in the absence of glidant, the angle of repose decreases as the sie of particles increases. This is because smaller particles have dominant cohesive and adhesive forces as compared to particle weight, whereas in bigger particles gravity plays a dominant role thus giving a smaller angle of repose. +tudies have shown that angle of repose is also gravity0dependant. 2ohesiveness of finer particles due to electrostatic forces causes difficulties in flowing thus forming a steeper pile which shown by the % micron sand having the highest angle !%$.%3" compared to )) and *) micron sand. 4n the other hand we can see that mixture of various sies of sand give a high angle of repose also !%(.53". 6hen particles of different sies and irregular shape is mixed together, the mechanical interlocking of particles increases and thereby increase the rolling friction. As a result a steeper pile with bigger angle of repose is formed. 7enerally, a value of 8 9%)3 indicates excellent; flow whereas 8 concentration of magnesium stearate is added, the angle of repose increases. Magnesium stearate is used as a glidant. 1t may also act as a lubricant in reducing friction. 7lidant functions in improving the flow of a material. From the result, )),*) micron sand and various sies sand have a passable which may hang up; flow. 4n the other hand, %% micron sand have a poor flow. The addition of a glidant should decreases the angle of repose and enhances the flow of the materials. ?ut however the addition of %> magnesium stearate in this experiment produces a product of viceversa. This is because the rate of flow is improved by the addition of magnesium stearate up to a limiting concentration of glidant. Above a certain concentration !in this case %>", the glidant will in fact function to inhibit flowability. Thus, a glidant will only work at a certain range of concentrations. From the result of other groups, it is shown that addition of magnesium stearate is only effective at concentration of ).> and #> where the angle of repose decreasing with the presence of a glidant. This proved it function in improving the flow of the material. For a better result, it is adviced to use a protractor instead of ruler as it reduces parallax error and it measures an accurate angle. The glidant and the sand should be mixed until an even distribution of mixture is obtained. This is to ensure that the glidant function effectively. ?esides, the lifting velocity of the cylinder should @ust be moderate to avoid distraction to the material flow. For a clean and tidy working environment, a paper should be placed before starting the experiment so that the sand did not cluttered elsewhere. xperimenter must also wear goggle, mask and lab coat all the time to protect the eyes and nose from coming in contact with the sand.
C&'C(%$#&' From the experiment, the angle of repose for different materials is measured to describe the flow of each material. +maller angle indicates a good flow property compared to bigger angle. +everal factors that influence the angle of repose is also determined which are the particle sie, particle shape, cohesiveness and the method by which the angle is measured. +maller particles have a bigger angle of repose due to the cohesiveness. This cohesivity causes a poor flow. Mixture of particles with various sies also gives a bigger angle of repose owing to the friction. ?esides the angle of repose is also gravity0dependant. The flow of the materials is improved with the addition of a glidant at low concentration. The glidant only work at a certain range of concentration.
#. Biu, Chichao !5)##" Measuring The Angle 4f Depose 4f 7ranular +ystems Esing ollow 2ylinders http:GGd0scholarship.pitt.eduG$&)#G 5. Dakhi ?. +hah, Mobin A. Tawakkul, Mansoor A. Hhan !5))* February #" 2omparative valuation of Flow for /harmaceutical /owders and 7ranules http:GGwww.ncbi.nlm.nih.govGpmcGarticlesG/M25('$(##G %. T. M. I4J+ !#($(" The effect of glidant addition on the flowability of bulk particulate solids http:[email protected]
Aug ), 5)## Angle of Depose http:GGwww.slideshare.netGvisualbeeJetworkGangle0of0repose