Mass transfer

Mass transfer is the net movement of mass from one location (usually meaning stream, phase, fraction, or component) to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration, and distillation. Mass transfer is used by different scientific disciplines for different processes and mechanisms. The phrase is commonly used in engineering for physical processes that involve diffusive and convective transport of chemical species within physical systems.

Some common examples of mass transfer processes are the

liquid-liquid extraction. Mass transfer is often coupled to additional transport processes, for instance in industrial cooling towers

. These towers couple heat transfer to mass transfer by allowing hot water to flow in contact with air. The water is cooled by expelling some of its content in the form of water vapour.

Astrophysics

In

gravitationally bound to a body, usually a star, fills its Roche lobe and becomes gravitationally bound to a second body, usually a compact object (white dwarf, neutron star or black hole), and is eventually accreted onto it. It is a common phenomenon in binary systems, and may play an important role in some types of supernovae and pulsars

.

Chemical engineering

Mass transfer finds extensive application in chemical engineering problems. It is used in reaction engineering, separations engineering, heat transfer engineering, and many other sub-disciplines of chemical engineering like electrochemical engineering.^[1]

The driving force for mass transfer is usually a difference in

liquid-liquid extraction

.

While thermodynamic equilibrium determines the theoretical extent of a given mass transfer operation, the actual rate of mass transfer will depend on additional factors including the flow patterns within the system and the

dimensionless numbers, often including Péclet numbers, Reynolds numbers, Sherwood numbers, and Schmidt numbers, among others.^[2]^[3]^[4]

Analogies between heat, mass, and momentum transfer

There are notable similarities in the commonly used approximate differential equations for momentum, heat, and mass transfer.

Fourier's law for heat, and Fick's law for mass are very similar, since they are all linear approximations

to transport of conserved quantities in a flow field. At higher Reynolds number, the analogy between mass and heat transfer and momentum transfer becomes less useful due to the

Navier-Stokes equation (or more fundamentally, the general momentum conservation equation

), but the analogy between heat and mass transfer remains good. A great deal of effort has been devoted to developing analogies among these three transport processes so as to allow prediction of one from any of the others.

References

^ Electrochimica Acta 100 (2013) 78-84. https://doi.org/10.1016/j.electacta.2013.03.134
^
ISBN 9780471022497
.

^ Bird, R.B.; Stewart, W.E.; Lightfoot, E.N. (2007). Transport Phenomena (2 ed.). Wiley.
^ Taylor, R.; Krishna, R. (1993). Multicomponent Mass Transfer. Wiley.

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Astrophysics

Chemical engineering

Analogies between heat, mass, and momentum transfer

References

See also