JW Lecture 1 - Intro & Dispersed Systems

Question 1

Different classes of unit operations

Answer 1

1. Size reduction
2. Size enlargement
3. Mixing
4. Separating
5. Storage, transport and dosage

Question 2

What are dispersed systems

Answer 2

Particle technology deals with particulate materials, bulk solids or powders, and particles or droplets that are contained within a gas or a liquid. Such particle collectives are named “Dispersed systems”. They usually consist of many single particles, the dispersed phase, and the surrounding medium, the continuous phase.Both dispersed phase and the continuous phase can be solid, liquid or gaseous. Dispersed phases can be two-phase or three-phase systems. A three phase system for example are solid particles and droplets within a liquid.

Question 3

What are particles?

Answer 3

Any dispersed material within a fluid. Particles are normally solids, but could be also oil droplets in water, water droplets in air, etc.

Question 4

Size dependent properties of dispersed systems

Answer 4

Decreasing particle size:

specific surface area increases: SV ≈ 1/x

• adhesive forces increase vs mass forces
• increased tendency to agglomerate and stick to surfaces - pellets and agglomerates become more stable
• free-flowing properties (flowablity) decreases
• bulk-density decreases and porosity increases
• mixing becomes more difficult but less self-segregation - reactivity increases
• solubility, vapour-pressure and reaction rate increase
• drag force increases vs mass force under flow conditions - electrostatic interactions increase

optical properties change (scattering, diffraction, reflection, absorption)

homogeneity of single particles increases: rigidity increases and grindablity
decreases