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In physics, transport phenomena are all irreversible processes of statistical nature stemming from the random continuous motion of molecules mostly observed in fluids. They involve a net macroscopic transfer of matter, energy or momentum in thermodynamic systems that are not in statistical equilibrium.^[1] They are usually described by equations that connect flux with a "motive force". Examples include heat conduction and convection (energy transfer), viscosity, radiation, molecular diffusion (mass transfer), momentum transfer in Newtonian fluids and electric charge transfer in semiconductors which gives rise to drift and diffusion currents.

In solid state physics, the motion and interaction of electrons, holes and phonons are studied under "transport phenomena" ^[2]. The science of transport phenomena is an important complement to rheological study of Newtonian fluids.

In biomedical engineering, some transport phenomena are thermoregulation, perfusion, and microfluidics.

Contents 1 Analogy between phenomena 2 External influence 3 Equations 4 See also 5 Resources 6 External links 7 References

[edit] Analogy between phenomena

An important principle in the study of transport phenomena is analogy between phenomena. For example, mass, energy, and momentum can all be transported by diffusion:

• The spreading and dissipation of odours in air is an example of mass diffusion.
• The conduction of heat in a solid material is an example of heat diffusion.
• The drag (physics) experienced by a rain drop as it falls in the atmosphere is an example of momentum diffusion (the rain drop loses momentum to the surrounding air through viscous stresses and decelerates).

[edit] External influence

The transport of mass, energy, and momentum can also be affected by the presence of external sources:

• An odour dissipates more slowly when the source of the odor remains present.
• The rate of cooling of a solid that is conducting heat depends on whether a heat source is applied.
• The gravitational force acting on a rain drop counteracts the drag imparted by the surrounding air.

All these effects are described by the generic scalar transport equation.

[edit] Equations

The generalized method adopted for solving transport phenomena problems start with quantity analysis for any given system as:

(Rate of quantity IN) + (Rate of Production of the quantity) = (Rate of quantity OUT) + (Rate of Accumulation of the Quantity)     ^[3]

The transferring quantity here can be momentum, energy or mass. For example, during momentum transport analysis for a freely falling film of a Newtonian liquid, gravitational force is counted as a factor increasing momentum in the system; and the momentum dissipation will be in the form of fluid moving out of the system, and work losses. ^[4]

The same equations governing convection in heat transfer can be applied to convection in mass transfer. When studying complex transport phenomena problems, one must use tools from continuum mechanics and tensor calculus and often problems can be expressed as partial differential equations.

[edit] See also

• Constitutive equation
• Continuity equation
• Wave propagation
• Pulse
• Action potential

[edit] Resources

• "Some Classical Transport Phenomena Problems with Solutions - Fluid Mechanics". http://www.syvum.com/eng/fluid/. 
• "Some Classical Transport Phenomena Problems with Solutions - Heat Transfer". http://www.syvum.com/eng/heat/. 
• "Some Classical Transport Phenomena Problems with Solutions - Mass Transfer". http://www.syvum.com/eng/mass/. 

[edit] External links

• Transport Phenomena Archive in the Teaching Archives of the Materials Digital Library Pathway

[edit] References

1. ^ "Physics", Alonso & Finn, Addison Wesley 1992, chapter 18
2. ^ J. M. Ziman, Electrons and Phonons: The Theory of Transport Phenomena in Solids (Oxford Classic Texts in the Physical Sciences)
3. ^ "Initial Quantity" + "Sum of Increments" = "Sum of Decrements" + "Final Quantity"
4. ^ R. Byron Bird, Warren E. Stewart, Edwin N. Lightfoot, Transport Phenomena (1960) John Wiley & Sons, New York, ISBN 0-471-07392-X, pp.42-48