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Transport phenomena
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Viscosity, conduction and diffusion in gases.
Diffusion (mass), viscosity (momentum) and heat conduction (energy) all arise from molecules carrying properties across layers. In gases η ≈ ⅓ρv̄λ, independent of pressure.
Gas viscosity increases with temperature, unlike liquids.
All three share the same underlying mechanism.
In more detail
Transport phenomena include diffusion, viscosity and thermal conduction, all arising from molecular motion and collisions. They share a common mathematical structure.
Real-world uses
- Chemical engineers design reactors using transport theory.
- Biomedical engineers model drug transport in tissues.
- Engineers designing vacuum systems and gas pipelines use the transport properties of gases such as viscosity and diffusion.
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Frequently asked questions
How are they related?
Each involves transfer of a quantity, such as mass, momentum or energy, by molecular motion.
Which is largest in gases?
It depends on the property and gas; kinetic theory gives estimates for each.
Do all three transport properties come from the same origin?
Yes. Each comes from molecules carrying momentum, energy or particles across the mean free path.
Related topics in Kinetic Theory & Statistical Physics
Random walks · Equation of state of ideal gas in statistical terms · Heat conduction at microscopic level · Phase transitions · Ising model · Critical phenomena