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Related Concept Videos

The Carnot Cycle01:30

The Carnot Cycle

Converting work to heat is an irreversible process, and the purpose of a heat engine is to reverse the effect partially. Heat engines aim to increase the efficiency of the reversal, that is, maximize the work retrieved from heat. If the efficiency of a heat engine were 100%, it would imply reversing the process completely without introducing any other effect. Thus, it would violate the second law of thermodynamics.
What could be the theoretical limit to the efficiency of a heat engine? The...
Statements of the Second Law of Thermodynamics01:15

Statements of the Second Law of Thermodynamics

The second law of thermodynamics can be stated in several different ways, and all of them can be shown to imply the others. The Clausius’ statement of the second law of thermodynamics is based on the irreversibility of spontaneous heat flow. It states that heat will not flow from the colder body to the hotter body unless some other process is involved. Additionally, as per the Kelvin’s statement, it is impossible to convert the heat from a single source into work without any other effect. This...
Entropy01:18

Entropy

The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...
Entropy02:39

Entropy

Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
The Carnot Cycle and the Second Law of Thermodynamics01:20

The Carnot Cycle and the Second Law of Thermodynamics

The Carnot engine works between two heat reservoirs of fixed temperatures. The Carnot cycle begs the following question: Is it possible to devise a heat engine that is more efficient than a Carnot engine between two fixed temperatures? The answer lies in designing a Carnot refrigerator.
Since the individual steps in a Carnot cycle can be reversed, the entire cycle is, thus, reversible. If a Carnot cycle is reversed, it becomes a Carnot refrigerator. It extracts heat Qc from a cold reservoir at...
Heat Engines01:10

Heat Engines

A heat engine is a device used to extract heat from a source and then convert it into mechanical work used for various applications. For example, a steam engine on an old-style train can produce the work needed for driving the train.
Whenever we consider heat engines (and associated devices such as refrigerators and heat pumps), we do not use the standard sign convention for heat and work. For convenience, we assume that the symbols Qh, Qc, and W represent only the amounts of heat transferred...

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Related Experiment Video

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Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation
09:09

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Published on: February 5, 2020

Quantum heat engines and nonequilibrium temperature.

Ramandeep S Johal1

  • 1Department of Physics, Indian Institute of Science Education and Research Mohali, Transit Campus, MGSIPA Complex, Sector 26, Chandigarh 160019, India.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|November 13, 2009
PubMed
Summary

Two quantum systems in different thermal states do not reach a common temperature after work extraction. Researchers defined an effective temperature for the final nonequilibrium state, analyzing its unique properties.

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Area of Science:

  • Quantum thermodynamics
  • Statistical mechanics
  • Quantum information theory

Background:

  • Quantum systems can be prepared in various thermal states.
  • Work extraction processes in quantum mechanics are fundamental.
  • Understanding thermalization and equilibrium in quantum systems is crucial.

Purpose of the Study:

  • To investigate the final thermal state of two-level quantum systems after unitary work extraction.
  • To determine if systems reach a common temperature post-process.
  • To define and analyze an effective temperature for the resulting nonequilibrium state.

Main Methods:

  • Utilizing a theoretical model of two coupled two-level quantum systems.
  • Simulating a reversible work extraction process via a work source.
  • Defining and calculating an effective temperature for the final passive, nonequilibrium state.

Main Results:

  • The two-level systems do not generally reach a common temperature after work extraction.
  • A method for defining an effective temperature for the final state was established.
  • Properties of this effective temperature in the nonequilibrium state were analyzed.

Conclusions:

  • Unitary work extraction from systems in different initial thermal states does not guarantee thermal equilibrium.
  • The concept of an effective temperature is useful for characterizing final nonequilibrium quantum states.
  • Further analysis of effective temperature properties can provide insights into quantum thermalization dynamics.