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INTRODUCTION TO BULK SOLID

Properties of Bulk Solid

A. Density : Particle, (pParticle density = total mass

Total volume

(i) True particle density

When volume measured excludes both open and closed pores.

The density quoted in many reference books.

(ii) Apparent particle density

When volume measured includes closed pores or bubbles of gas within the particle.

The density is measured by gas or liquid displacement method like liquid or air pyknometer.

Pycnometer (Ultrapycnometer -1000, Quanta Chrome Co)

Hosakawa Mikron Model PT-R

B. Density: Bulk, (bBulk density, (b = Bulk mass

Bulk volume it occupies

Bulk volume ( includes the spaces between particles and the envelope volumes of the particles.

NB: Make sure do not confuse between bulk and particle density.

Many people in industry measure bulk solid density in order to get an estimate of how much volume the powder will occupy in storage or in handling.

(i) Aerated bulk density, (abd The particles are separated from each other by a film of air 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:

(ii) Poured bulk density, (pbd Powder is pored 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.

(iii) Tap bulk density, (tbd Bulk density of a powder, which has been compacted by tapping or vibration following a specific procedure.C. Voidage, ( or porosity

The volume of the voids within the bed. i.e. the volume occupied by air divided by the total (overall) volume of the bed. Void volumes includes the pores within the particles if they are porous.

Voidage,

(1.1)

Where (b = bulk density

(p = particle density

Powder Flowability Determination

No flowability test is universally applicable.

Thus series of powder flow behaviour must be tested experimentally according to the need of industrial application such as powder streams in industrial storage, transport and processing, in terms of their range of applicability, cost and difficulty of measurement.

Since the state of the powder varies for different types of applications, the test chosen has to reflect the state of powder in the actual process.

Below are some of the tests commonly required in determining flow behaviour in selected process plant: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 density and aerated density:

(1.2)

Where (tbd = tap density

(b = bulk density

Angle of Repose

Definition: the angle of the free surface of a pile of powder to the horizontal plane.

Whenever a heap of powder is being formed, the angle of inclination of the free surface to the horizontal can take any value up to a maximum.

Any attempt to build up a heap with steeper sides results in its collapse.

Depending on the condition under which the pile has been poured and how the angle is measured, different values of angle can be obtained for the same powder.

When a mixture of uniformly sized granular particles consisting of components with different angle of repose is poured on a heap, the particles having steeper angle of repose tend to concentrate in the center of the heap.

Hausner Ratio, HR The ratio of (tbd/(abd is called the Hausner ratio, HR (Grey and Beddow 1968/1979). If the ratio:

HR >1.4 : Group C

1.25 < HR < 1.4 : Transition AC

HR < 1.25 : Group A, B or D Other available types of test such as:

Funnel/discharge est

Fluidization index, deaeration, permeability

Floodibility test

Dispersibility

Pick up velocity

Pseudoviscosity and suspension-flow behaviour index etc.

Hydrodynamic envelope bonding particle volume, Vp

Close Pores

Open pores

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