Size Reduction Flashcards
Grinding
Reduction of size by fracturing
Pressure exerted along the weakness causes a fracture where heat is released
Only minimum energy should be exerted to see the rupture
First crushing
At beginning size of granule is varied considerably but a dominant size appears
Very large surface area which can cause instability explosive oxidation
Specific surface
Surface area per mass unit
Hammer mills
2 hammers rotating at high speeds
Used for croaste brittle materials
Rotor mills
2 rollers at different speeds milling flour
Plate mills
One fixed one rotating
Material enters the axis of rotation and is crushed
Often horizontal
Edge runner mill
Trough round a circular barrel
Used to grind cocoa and chocolate
Ball mill
Milled with steel balls
Cutting
Knives in a particular direction that chop up material
Knives are hard to ensure they are sharp to make sure they are cutting not tearing
Bowl cutter
A vertical knife with material spinning underneath
Emulsification
Stable suspension of one liquid in another
Continuous and dispersed phases
Stability dependent on
Surface area
Size of dispersed phase
Emulsifying agents added
High pressure for nozzle
7x10^3kPa
Atomisation
Increase surface to mass ratio in which evaporation will take place
Pressure nozzles
Milk is pushed through a small gap at very high pressure to ensure emulsion
Must overcome surface tension
Centrifugal nozzles
Droplets are centrifuged at 100-200m/s
Quickly breaks into droplets
Colloid mill
Used for medium and high velocity liquids
Coarse emulsion is fed into colloid mill
More efficient
Secondary homogenisation
Ultrasonication
Ultrasonic waves transmitted through a liquid
Acoustic cavitation
Nuclear ion and gas bubbles collapse
High energy event
Energy efficient
Reduced droplet size
Pros of ultrasonication
Help in development of new flavoured milk with nutritional contents
Pasteurisation and emulsifying dairy technique with minimal processing and heat treatment
