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Related Concept Videos

The Carnot Cycle01:30

The Carnot Cycle

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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...
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The Carnot Cycle and the Second Law of Thermodynamics01:20

The Carnot Cycle and the Second Law of Thermodynamics

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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...
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Efficiency of The Carnot Cycle01:16

Efficiency of The Carnot Cycle

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The hypothetical Carnot cycle consists of an ideal gas subjected to two isothermal and two adiabatic processes. Since the internal energy of an ideal gas depends only on its temperature, which is the same before and after the completion of the Carnot cycle, there is no change in its internal energy. Hence, using the first law of thermodynamics, the total heat exchanged by the ideal gas equals the total work done. Thus, we can quantify the efficiency of the Carnot cycle via the heat exchanged...
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Heat Engines01:10

Heat Engines

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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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Entropy Change in Reversible Processes01:10

Entropy Change in Reversible Processes

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In the Carnot engine, which achieves the maximum efficiency between two reservoirs of fixed temperatures, the total change in entropy is zero. The observation can be generalized by considering any reversible cyclic process consisting of many Carnot cycles. Thus, it can be stated that the total entropy change of any ideal reversible cycle is zero.
The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
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Energy Conservation and Bernoulli's Equation01:16

Energy Conservation and Bernoulli's Equation

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Applying the conservation of energy principle or the work-energy theorem to an incompressible, inviscid fluid in laminar, steady, irrotational flow leads to Bernoulli's equation. It states that the sum of the fluid pressure, potential, and kinetic energy per unit volume is constant along a streamline.
All the terms in the equation have the dimension of energy per unit volume. The kinetic energy per unit volume is called the kinetic energy density, and the potential energy per unit volume is...
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Related Experiment Video

Updated: Sep 8, 2025

A Rapid Method for Modeling a Variable Cycle Engine
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Optimal finite-time Brownian Carnot engine.

Adam G Frim1, Michael R DeWeese1,2,3

  • 1Department of Physics, University of California, Berkeley, Berkeley, California 94720, USA.

Physical Review. E
|June 16, 2022
PubMed
Summary
This summary is machine-generated.

Researchers optimized mesoscale heat engines using thermodynamic geometry. New Brownian Carnot cycles show improved energy dissipation and efficiency for practical applications.

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Area of Science:

  • Thermodynamics
  • Mesoscale physics
  • Statistical mechanics

Background:

  • Recent advances in colloidal systems enable the creation of mesoscale thermodynamic devices.
  • Theoretical and experimental progress has been made in designing and analyzing these devices, including textbook engines operating far from equilibrium.

Purpose of the Study:

  • To characterize the optimal finite-time nonequilibrium cyclic operation of a parametric harmonic oscillator using thermodynamic geometry.
  • To derive and analyze new Brownian Carnot cycles and compare their performance against existing protocols.

Main Methods:

  • Application of thermodynamic geometry methods.
  • Analysis of a parametric harmonic oscillator coupled to a time-varying heat bath.
  • Derivation and comparison of optimally parametrized Carnot cycles.

Main Results:

  • Derivation of an optimally parametrized Carnot cycle and two novel cycles.
  • Demonstration of up to 20% improvement in dissipated energy compared to previous experimental protocols.
  • Achieved approximately 50% improvement in dissipated energy under certain conditions.
  • Identified an engine with superior efficiency and power output.

Conclusions:

  • The study provides a theoretical framework for optimizing mesoscale heat engines.
  • The derived cycles offer enhanced performance in terms of energy dissipation, efficiency, and power.
  • Results pave the way for the experimental realization of optimal mesoscale heat engines.