In thermodynamics, a reversible process (or reversible cycle if the process is cyclic) is a process that can be "reversed" by means of infinitesimal changes in some property of the system.^[1] Due to these infinitesimal changes, throughout a reversible process, the system is at equilibrium. Since it would take an infinite amount of time for the process to finish, reversible processes are impossible to carry out. In a reversible cycle, the system and its surroundings will be exactly the same after each cycle. ^[2] Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of temperature, pressure, and volume changes on physical systems at the macroscopic scale. ...

A process that is not reversible is termed irreversible. In an irreversible process, finite changes are made; therefore the system is not at equilibrium throughout the process. At the same point in an irreversible cycle, the system will be in the same state, but the surroundings are permanently changed after each cycle. ^[2]

Boundaries and states

A reversible process changes the state of a system in such a way that the net change in the combined entropy of the system and its surroundings is zero. Reversible processes define the boundaries of how efficient heat engines can be in thermodynamics and engineering: a reversible process is one where no heat is lost from the system as "waste", and the machine is thus as efficient as it can possibly be (see Carnot cycle). For other senses of the term entropy, see entropy (disambiguation). ... In physics, mechanical efficiency is the effectiveness of a simple machine. ... A heat engine performs the conversion of heat energy to work by exploiting the temperature gradient between a hot source and a cold sink. Heat is transferred to the sink from the source, and in this process some of the heat is converted into work. ... A heat engine is an engine that uses heat to produce mechanical work by carrying a working substance through a cyclic process. ...

In some cases, it is important to distinguish between reversible and quasistatic processes. Reversible processes are always quasistatic, but the converse is not always true.^[1] For example, an infinitesimal compression of a gas in a cylinder where there exists friction between the piston and the cylinder is a quasistatic, but not reversible process.^[3] Although the system has been driven from its equilibrium state by only an infinitesimal amount, heat has been irreversibly lost due to friction, and cannot be recovered by simply moving the piston infinitesimally in the opposite direction. In thermodynamics a quasistatic process is a process that happens infinitely slowly. ... In physics, friction is the non-conservative resistive force that occurs when two surfaces travel along each other when forced together. ...

Engineering archaisms

Historically, the Tesla principle was the term used for reversible processes. ^[4] However, this phrase is no longer in conventional use. The principle was for systems that can be reversed and operate in a complimentary manner. This principle was developed during his Nikola Tesla's research in alternating currents where the current's magnitude and direction varies cyclically. During a demonstration of the Tesla turbine, the disks revolve and machinery fastened to the shaft is operated by the engine. If the turbine's operation is reversed, the disks act as a pump. ^[5] In language, an archaism is the deliberate use of an older form that has fallen out of current use. ... Nikola Tesla (July 10, 1856 – c. ... city lights viewed in a motion blurred exposure. ... The Tesla turbine is a bladeless turbine design patented by Nikola Tesla in 1913. ... Manual pump used to obtain water A pump is a mechanical device used to move liquids or gases. ...

References

1. ^  Sears, F.W. and Salinger, G.L. (1986), Thermodynamics, Kinetic Theory, and Statistical Thermodynamics, 3rd edition (Addison-Wesley.)

2. ^  Zumdahl, Steven S. (2005) “10.2 The Isothermal Expansion and Compression of an Ideal Gas.” Chemical Principles. 5th Edition. (Houghton Mifflin Company)

3. ^  Giancoli, D.C. (2000), Physics for Scientists and Engineers (with Modern Physics), 3rd edition (Prentice-Hall.)

4. ^  Electrical Experimenter, Janaury 1919. p. 615. [1]

5. ^  "Tesla’s New Monarch of Machines". New York Herald Tribune, Oct. 15, 1911. (Available online. Tesla Engine Builders Association. [2])

See also

• Carnot cycle
• Toffoli gate
• Time evolution
• quantum circuit
• reversible computing

A heat engine is an engine that uses heat to produce mechanical work by carrying a working substance through a cyclic process. ... The Toffoli Gate is computational circuit suitable for reversible computing, invented by Tommaso Toffoli. ... For a system with internal state, (also called stateful system) time evolution means the change of state brought about by the passage of time. ... A quantum circuit is a specific form for a quantum computational device. ... The term reversible computing refers to any computational process that is (at least to some close approximation) reversible, i. ...

External links

• Reversible Logic
• Reversible Computing