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The Carnot Cycle

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...

The Carnot Cycle and the Second Law of Thermodynamics

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...

Efficiency of The Carnot Cycle

Efficiency of The Carnot Cycle

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...

Limits of the First Law of Thermodynamics

Limits of the First Law of Thermodynamics

Spontaneous processes, like a rock falling to the ground or sodium reacting with chlorine, occur without external work and often involve a decrease in the system‘s energy. However, certain endothermic processes, such as the dissolution of sodium chloride in water, occur spontaneously even though they increase the energy of the system. This limitation suggests that the First Law of Thermodynamics, which states that the total energy of a system is constant in an isolated system, cannot...

Otto and Diesel Cycle

Otto and Diesel Cycle

An Otto engine is a four-stroke engine that uses a mixture of gasoline and air as the working fuel. The fuel is injected into the cylinder, and the piston is moved completely down so that the cylinder is at maximum volume. By moving the piston up, adiabatic compression takes place. The spark plug ignites the gasoline-air mixture, and the burning fuel adds heat to the system at a constant volume. The heated mixture expands adiabatically and gets further cooled by exhausting heat, and this cyclic...

Entropy Change in Reversible Processes

Entropy Change in Reversible Processes

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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Rapid PCR Thermocycling using Microscale Thermal Convection

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Otto engine beyond its standard quantum limit.

Bruno Leggio¹, Mauro Antezza^1,2

¹Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier, F-34095 Montpellier, France.

Physical Review. E

|March 18, 2016

Summary

This summary is machine-generated.

We introduce a quantum Otto cycle using a two-level system and a realistic electromagnetic field. This novel cycle significantly outperforms the ideal Otto cycle, achieving high efficiency even with finite power.

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Area of Science:

Quantum thermodynamics
Statistical mechanics
Quantum information science

Background:

Quantum Otto cycle is a fundamental thermodynamic cycle.
Real-world reservoirs often deviate from ideal thermal equilibrium.
Controlling quantum environments is challenging.

Purpose of the Study:

To propose a quantum Otto cycle utilizing a realistic, out-of-equilibrium electromagnetic field as a reservoir.
To investigate the performance of this cycle under non-ideal conditions.
To explore the potential for high efficiency in quantum heat engines.

Main Methods:

Modeling a two-level system interacting with a noncoherent thermal radiation field.
Analyzing the quantum Otto cycle under finite-time transformations.
Calculating thermodynamic performance metrics like efficiency and power.

Main Results:

The proposed quantum Otto cycle operates effectively with a realistic electromagnetic reservoir.
The cycle demonstrates superior performance compared to the ideal Otto cycle, even in finite-time processes.
Unit efficiency is asymptotically achieved at finite power output.

Conclusions:

A practical quantum Otto cycle can be realized using readily available electromagnetic fields.
This approach offers a pathway to highly efficient quantum heat engines without complex environmental control.
The findings have implications for the development of quantum technologies and energy conversion.