Emulsions: Principles and preparation - Making emulsions using flow fields - Equipment

9 important questions on Emulsions: Principles and preparation - Making emulsions using flow fields - Equipment

How does making emulsions using flow fields work?

Flow around a droplet induces a shear force onto the droplet. When this force is sufficiently large, the droplet can break up into smaller droplets. The more intense a flow field is, the smaller the droplets become.

Mention 3 different types of machines used to make emulsions using flow fields

  1. Rotor-stator machines
  2. High-pressure homogenisers
  3. Ultrasound systems

Mention 3 different types of rotor-stator machines and their differences?

  1. Stirred tank --> not very intense, droplets stay relatively large (> 10 um). Wide droplet size distribution, smaller when longer treated --> turbulent flow
  2. Colloid mill --> High rotation rate and small size --> smaller droplet sizes
    1. Viscosity high --> laminar flow Re < 370
    2. Re > 370 --> turbulent flow
  3. Toothed mill --> small droplet sizes, turbulent flow
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What is the mechanism in a high-pressure homogeniser?

Mixture is pumped through a very small hole or gap. Cavitation causes a strong and very local turbulence that can break up the droplets further.

What is the difference between small, lab-scale homogenisers and industrial-scale homogenisers?

Lab-scale homogenisers --> laminar
Industrial-scale homogenisers --> turbulent

Mention 2 types of high-pressure homogenisers

  1. Valve systems --> dairy industry
  2. Nozzle systems --> openings in series

What is the mechanism in ultrasound systems?

Sound is a pattern of propagating pressure fluctuations. When the sound is sufficiently intense, the pressure fluctuations will become so large, that in small regions the pressure becomes lower than the pressure of water --> cavitation.

Why is using ultrasound systems to make emulsions not very applicable for large scale production?

The treatment chamber has to be relatively small, as the intensity of the ultrasound quickly declines away from the actuator (speaker).

Which molecules cannot handle cavitation?

Chemically labile molecules, such as unsaturated fatty acids.

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