Bulk Solids Characterization

Question 1

What is a bulk solid?

Answer 1

An assembly of solid particles that should consist of sufficiently large enough particles to be statistically representative.

Question 2

What are the three types of density?

Answer 2

Solid, bulk and tapped density

Question 3

What is solid density?

Answer 3

Ratio of mass to the volume of the solid particles (excluding the volume of open and closed voids)

Ros = m / Vs

Question 4

What 2 methods are used to find solid volume?

Answer 4

The liquid displacement method or gas pycnometry

Question 5

What is the liquid displacement method?

Answer 5

Choose a solvent that won’t dissolve your powder. Pour the liquid into a measuring cylinder and make a note of it’s volume. Pour the powder into the measuring cylinder and note the new volume. Calculate the change in volume, this is the solid volume of the powder.

Question 6

What is gas pycnometry?

Answer 6

You have two chambers attached to each other by a pipe with a valve on it. One chamber is larger (measuring chamber) and the other smaller (expansion chamber). You fill the chambers with a gas (normally helium) and shut the valve. Then you put the powder into the measuring chamber. Take the pressure in the measuring chamber, then open the valve and take the pressure in the measuring chamber again. The pressure difference can then be used to calculate the solid volume.

Vs = Vm - [Pm1 Ve / (Pm0 - Pm1)]

Vm = measuring cylinder volume
Ve = Expansion chamber volume
Pm0 = Initial measuring chamber pressure
Pm0 = Measuring chamber pressure after valve is opened

Question 7

How do you work out the effective density of a mixture?

Answer 7

RoM = mM / Vsm = (RoA VsA + RoB VsB) / VsM = RoA EpsilonA + RoB EpsilonB

Question 8

What is Bulk density?

Answer 8

Mass of the bulk solid divided by the total volume it occupies including voids. It is dependent on how the particles are handled.

Question 9

What is tapped density?

Answer 9

The mass of the bulk solid divided by the volume that is occupied after tapping. Is dependent on how many taps and how hard the taps are.

Question 10

What is voidage?

Answer 10

The volume of space between particles in relation to the bulk powders volume

Question 11

What is porosity?

Answer 11

The space within the particles.

Question 12

How is the surface area of a powder measured?

Answer 12

Adsorption

Question 13

What is degassing?

Answer 13

A pre treatment of a bulk powder before adsorption. Used to remove gases and contaminates from the surface of a bulk powder so that an adsorptive gas can cover the entirety of its surface.

Question 14

How does adsorption work?

Answer 14

A pre-treated bulk solid is cooled to cryogenic temperature (0 degrees Celsius) in a vacuum. It is then dosed with an adsorptive gas under incrementally increasing pressure. The volume of gas adsorbed to create a monolayer of the surface area is then measured.

Question 15

What is flowability?

Answer 15

Quantifies the flow of bulk solids. Dependent on the physical properties of the solid.

Question 16

What is the angle of repose?

Answer 16

Slope angle of the free surface of a bulk solid settled under gravity.

Question 17

What are the three ways of measuring the angle of repose?

Answer 17

-Poured -Drained -Dynamic

Question 18

What is the poured angle of repose?

Answer 18

Slope angle of a heap of the bulk solid poured from a specific height. Useful for storage design.

Question 19

What is the drained angle of repose?

Answer 19

The slope of the free surface once the bulk solid is discharged from a silo. Indicates the best hopper angle to promote mass flow.

Question 20

What is the dynamic angle of repose?

Answer 20

When spinning a solid around in a drum, the angle of repose is the steepest slope formed before the surface collapses. Useful for predicting behaviour in kilns and drums.

Question 21

What is segregation in a bulk powder?

Answer 21

When a well mixed mixture of bulk solids separates due to differing physical properties.

Question 22

When is angle of repose useful?

Answer 22

For bulk solids with low to medium cohesion.

Question 23

What is the Hausner ratio?

Answer 23

H = Bulk density / Tapped density

Higher = more cohesive

Question 24

What is the Carr index?

Answer 24

Carr index = (tapped density - bulk density) / tapped density

Higher = more cohesive

Question 25

What is the Jenike index?

Answer 25

If you were to apply a stress onto a bulk solid in a container, it will attempt to expand laterally.

ffc = vertical stress / lateral stress

Question 26

ffc for a hardened flowability?

Answer 26

ffc<1

Question 27

ffc for a very cohesive flowability?

Answer 27

1 <= ffc < 2

Question 28

ffc for a cohesive flowability?

Answer 28

2 <= ffc < 4

Question 29

ffc for a easy flowing flowability?

Answer 29

4 <= ffc < 10

Question 30

ffc for a free flowing flowability?

Answer 30

ffc > 10