Dissipation in thermodynamics refers to an irreversible process within a thermodynamic system where energy (such as kinetic, potential, or internal energy) transforms into a less useful form, reducing its capacity to do work. For example, heat transfer disperses concentrated energy, increasing entropy according to the second law of thermodynamics. In mechanical engineering, dissipation converts mechanical energy into thermal energy, raising entropy. Irreversible processes producing dissipation include heat flow, fluid flow, chemical reactions, and electric current through electrical resistance with Joule heating.
Definition
Dissipative thermodynamic processes are essentially irreversible because they produce entropy. Planck regarded friction as the prime example of an irreversible thermodynamic process.2 In a process in which the temperature is locally continuously defined, the local density of rate of entropy production times local temperature gives the local density of dissipated power.
A particular occurrence of a dissipative process cannot be described by a single individual Hamiltonian formalism. A dissipative process requires a collection of admissible individual Hamiltonian descriptions, exactly which one describes the actual particular occurrence of the process of interest being unknown. This includes friction and hammering, and all similar forces that result in decoherence of energy—that is, conversion of coherent or directed energy flow into an indirected or more isotropic distribution of energy.
Energy
"The conversion of mechanical energy into heat is called energy dissipation." – François Roddier3 The term is also applied to the loss of energy due to generation of unwanted heat in electric and electronic circuits.
Computational physics
In computational physics, numerical dissipation (also known as "Numerical diffusion") refers to certain side-effects that may occur as a result of a numerical solution to a differential equation. When the pure advection equation, which is free of dissipation, is solved by a numerical approximation method, the energy of the initial wave may be reduced in a way analogous to a diffusional process. Such a method is said to contain 'dissipation'. In some cases, "artificial dissipation" is intentionally added to improve the numerical stability characteristics of the solution.4
Mathematics
A formal, mathematical definition of dissipation, as commonly used in the mathematical study of measure-preserving dynamical systems, is given in the article wandering set.
Examples
In hydraulic engineering
Dissipation is the process of converting mechanical energy of downward-flowing water into thermal and acoustical energy. Various devices are designed in stream beds to reduce the kinetic energy of flowing waters to reduce their erosive potential on banks and river bottoms. Very often, these devices look like small waterfalls or cascades, where water flows vertically or over riprap to lose some of its kinetic energy.
Irreversible processes
Important examples of irreversible processes are:
- Heat flow through a thermal resistance
- Fluid flow through a flow resistance
- Diffusion (mixing)
- Chemical reactions56
- Electrical current flow through an electrical resistance (Joule heating).
Waves or oscillations
Waves or oscillations, lose energy over time, typically from friction or turbulence. In many cases, the "lost" energy raises the temperature of the system. For example, a wave that loses amplitude is said to dissipate. The precise nature of the effects depends on the nature of the wave: an atmospheric wave, for instance, may dissipate close to the surface due to friction with the land mass, and at higher levels due to radiative cooling.
History
See also: Timeline of thermodynamics
The concept of dissipation was introduced in the field of thermodynamics by William Thomson (Lord Kelvin) in 1852.7 Lord Kelvin deduced that a subset of the above-mentioned irreversible dissipative processes will occur unless a process is governed by a "perfect thermodynamic engine". The processes that Lord Kelvin identified were friction, diffusion, conduction of heat and the absorption of light.
See also
General References
- "Dissipative system, a system that loses energy in the course of its time evolution." Benenson, W.; Harris, J. W.; Stocker, H.; Lutz, H. (2002). "6.1.3". Handbook of Physics. New York, NY: Springer-Verlag. p. 219. ISBN 978-0-387-21632-4.
References
Escudier, Marcel; Atkins, Tony (2019). A Dictionary of Mechanical Engineering (2 ed.). Oxford University Press. doi:10.1093/acref/9780198832102.001.0001. ISBN 978-0-19-883210-2. 978-0-19-883210-2 ↩
Planck, M. (1926). "Über die Begründung des zweiten Hauptsatzes der Thermodynamik", Sitzungsber. Preuss. Akad. Wiss., Phys. Math. Kl., 453—463. /wiki/Max_Planck ↩
Roddier F., Thermodynamique de l'évolution (The Thermodynamics of Evolution), parole éditions, 2012 http://www.editions-parole.net/?product=thermodynamique-de-levolution-un-essai-de-thermo-bio-sociologie ↩
Thomas, J.W. Numerical Partial Differential Equation: Finite Difference Methods. Springer-Verlag. New York. (1995) ↩
Glansdorff, P., Prigogine, I. (1971). Thermodynamic Theory of Structure, Stability, and Fluctuations, Wiley-Interscience, London, 1971, ISBN 0-471-30280-5, p. 61. /wiki/Ilya_Prigogine ↩
Eu, B.C. (1998). Nonequilibrium Thermodynamics: Ensemble Method, Kluwer Academic Publications, Dordrecht, ISBN 0-7923-4980-6, p. 49, /wiki/ISBN_(identifier) ↩
W. Thomson On the universal tendency in nature to the dissipation of mechanical energy Philosophical Magazine, Ser. 4, p. 304 (1852). ↩