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CHAPTER 1INTRODUCTION TO BULK SOLID
1.0 Properties of Bulk Solid
1.1 Density : Particle, ρ ρρ ρ p
Particle density = total mass (kg/m3)Total volume
1.1.1 True particle density
• When volume measured excludes both open and closedpores.
• The density quoted in many reference books.
1.1.2 Apparent particle density
• When volume measured includes closed pores or bubblesof gas within the particle.
• The density is measured by gas or liquid displacementmethod like liquid or air pycnometer.
Hydrodynamicenvelope
bonding particle
volume, V p
Close Pores
Open pores
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Pycnometer(Ultrapycnometer – 1000, Quanta Chrome Co)
Powder Tester(Hosokawa Micron Powder Tester, model PT-R)
Sieve holding bar
Screen aperture
Funnel
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1.2 Density: Bulk, ρ ρρ ρ b
Bulk density, ρ ρρ ρ b = Bulk massBulk volume it occupies
• Bulk volume → includes the spaces betweenparticles and the envelope volumes of the particles.
NB: Make sure do not confuse between bulk and particledensity.
• Many people in industry measure bulk solid density in orderto get an estimate of how much volume the powder willoccupy in storage or in handling.
1.2.1 Aerated bulk density, ρ ρρ ρ abd
• The particles are separated from each other by a film ofair and are not in direct contact with each other.
• Bulk density after the powder has been aerated.
• Some of the methods in obtaining the aerated density:
1.2.2 Poured bulk density, ρρρρpbd
• Powder is poured into a container
• Height of fall is fixed
• The powder in the container must not be disturbed
• Mass of powder is determined
• Volume of powder is the volume inside the cup.
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1.2.3 Tap bulk density, ρρρρtbd
• Bulk density of a powder, which has been compacted bytapping or vibration following a specific procedure.
2.0 Voidage, εεεε or porosity
• The volume of the voids within the bed. i.e. the volumeoccupied by air divided by the total (overall) volume ofthe bed.
• Void volumes – includes the pores within the particles ifthey are porous.
Voidage,p
b1ρ
ρ−=ε
(1.1)
Where ρ b = bulk density ρ p = particle density
3.0 Powder Flowability Determination
• No flowability test is universally applicable.
• Thus series of powder flow behaviour must be testedexperimentally according to the need of industrialapplication such as powder streams in industrialstorage, transport and processing, in terms of theirrange of applicability, cost and difficulty ofmeasurement.
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• Since the state of the powder varies for different typesof applications, the test chosen has to reflect the stateof powder in the actual process.
• Below are some of the tests commonly required indetermining flow behaviour in selected process plant:
3.1 Compressibility (from bulk density)
• Compression tests are mainly used for quality control,product evaluation and to measure the tendency for caking.
• One of the way to express differences between tap densityand aerated density:
%100, ×−
=b
btbd C ilityCompressib ρ
(1.2)
Where ρtbd = tap densityρb = bulk density
3.2 Angle of Repose
• Definition: the angle of the free surface of a pile of powderto the horizontal plane.
• Whenever a heap of powder is being formed, the angle ofinclination of the free surface to the horizontal can takeany value up to a maximum.
• Any attempt to build up a heap with steeper sides resultsin its collapse.
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• Depending on the condition under which the pile has beenpoured and how the angle is measured, different values ofangle can be obtained for the same powder.
• When a mixture of uniformly sized granular particlesconsisting of components with different angle of repose ispoured on a heap, the particles having steeper angle ofrepose tend to concentrate in the center of the heap.
Measurement of Angle of repose
3.3 Hausner Ratio, HR
• The ratio of ρ tbd / ρ abd is called the Hausner ratio, HR (Greyand Beddow 1968/1979).
• If the ratio:
o HR >1.4 : Group Co 1.25 < HR < 1.4 : Transition AC
α β
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