Flowability Flashcards
What are 2 driving forces of flowability
Gravitation force and mechanic agitation
What are 2 restrictive forces of flowability
cohesiveness/ adhesiveness and friction
What is adhesion
Attractive forces between two chemically different substances
What is cohesion
attractive forces between 2 chemically similar substances
What is the gravity equation
Force x acceleration
What causes cohesion and adhesion
VDW forces, electrostatic interlocking and mechanical interlocking
What factors affect VDW forces
the larger a particle, the stronger the VDW and the closer the particles, the stronger the VDW
How are electrostatic forces produced between particles
friction between particles and between a surface and a particle creates static electricity thus oppositely charged particles attract
What is mechanical interlocking
when particles interlock because of their shape, sharp edges and rough surfaces.
What is friction
when with one particle moves against another or two are moving in opposing directions, stopping particle movement
Factors the affect powder flow
size, larger particles flow better
Density, denser particles flow better
Shape, rounder particles flow better
Surface texture, smoother surfaces flow better
What is the equation for specific surface area
= Total surface area/mass
The effects of a large surface area
More bonding are; more cohesion; more resistance; less flowability
Why is a spherical shape preferred to an edged shape with the same mass
has a smaller surface are and is unlikely to undergo mechanical interlocking thus reducing resistance
What is bulk density
The density of powder with air when allowed to settle properly under gravity
Bulk density equation
Bulk density = mass/bulk volume
What is tapped density
The density of particles with minus air after mechanically tapping the powder
Equation for tapped density
=mass/tapped volume
What is true volume
true volume is the density of solid particles only, without air
Equation for true volume
Bulk volume/ packing fraction
What are the 4 ways of testing powder flow
Flow rate, density ratios, angle of repose and shear cell.
What is flow rate
The amount of time taken for a specific amount of powder to empty out
What are the two methods of calculating a flow rate
1) work put how long it takes a specific amount of powder to empty out
2)measure the amount of powder in a specific amount of time
What is density ratio
Measure a change in volume after undergoing a set of parameters. E.g. tapping the container
How is density ratio measured
As a ratio or cars compressibility as %. The smaller the value, the higher its flowability
What is the angle of repose
The angle between the top of the slope downwards and horizontal
How to calculate the angle of repose
Tan-1(H/R)
H=height
R=radius, 0.5x width
What is Hausners ratio and how to calculate
A type of density ratio: tapped density/ bulk density
How to calculate cars index %
(Tapped ratio- bulk ratio/tapped ratio) x100
What is granulation
Making smaller grained larger using water
