scholarly journals Optimal Power and Efficiency of Multi-Stage Endoreversible Quantum Carnot Heat Engine with Harmonic Oscillators at the Classical Limit

Entropy ◽  
2020 ◽  
Vol 22 (4) ◽  
pp. 457 ◽  
Author(s):  
Zewei Meng ◽  
Lingen Chen ◽  
Feng Wu
Keyword(s):  
Classical Limit ◽  
Heat Engine ◽  
Combined Cycle ◽  
Harmonic Oscillators ◽  
Total Power ◽  
Cycle Period ◽  
Carnot Cycle ◽  
Heat Current ◽  
Operating Modes ◽  
Multi Stage

At the classical limit, a multi-stage, endoreversible Carnot cycle model of quantum heat engine (QHE) working with non-interacting harmonic oscillators systems is established in this paper. A simplified combined cycle, where all sub-cycles work at maximum power output (MPO), is analyzed under two types of combined form: constraint of cycle period or constraint of interstage heat current. The expressions of power and the corresponding efficiency under two types of combined constrains are derived. A general combined cycle, in which all sub-cycles run at arbitrary state, is further investigated under two types of combined constrains. By introducing the Lagrangian function, the MPO of two-stage combined QHE with different intermediate temperatures is obtained, utilizing numerical calculation. The results show that, for the simplified combined cycle, the total power decreases and heat exchange from hot reservoir increases under two types of constrains with the increasing number (N) of stages. The efficiency of the combined cycle decreases under the constraints of the cycle period, but keeps constant under the constraint of interstage heat current. For the general combined cycle, three operating modes, including single heat engine mode at low “temperature” (SM1), double heat engine mode (DM) and single heat engine mode at high “temperature” (SM2), appear as intermediate temperature varies. For the constraint of cycle period, the MPO is obtained at the junction of DM mode and SM2 mode. For the constraint of interstage heat current, the MPO keeps constant during DM mode, in which the two sub-cycles compensate each other.

scholarly journals Can Quantum Correlations Lead to Violation of the Second Law of Thermodynamics?

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 573
Author(s):  
Alexey V. Melkikh
Keyword(s):  
Quantum Entanglement ◽  
Local Equilibrium ◽  
Heat Engine ◽  
Thermodynamic Quantity ◽  
Second Law Of Thermodynamics ◽  
Quantum Correlations ◽  
Von Neumann Entropy ◽  
Second Law ◽  
Carnot Cycle ◽  
Technical Discussion

Quantum entanglement can cause the efficiency of a heat engine to be greater than the efficiency of the Carnot cycle. However, this does not mean a violation of the second law of thermodynamics, since there is no local equilibrium for pure quantum states, and, in the absence of local equilibrium, thermodynamics cannot be formulated correctly. Von Neumann entropy is not a thermodynamic quantity, although it can characterize the ordering of a system. In the case of the entanglement of the particles of the system with the environment, the concept of an isolated system should be refined. In any case, quantum correlations cannot lead to a violation of the second law of thermodynamics in any of its formulations. This article is devoted to a technical discussion of the expected results on the role of quantum entanglement in thermodynamics.

scholarly journals Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 536
Author(s):  
Lingen Chen ◽  
Zewei Meng ◽  
Yanlin Ge ◽  
Feng Wu
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Combined Cycle ◽  
Quantum Gases ◽  
Carnot Cycle ◽  
Leakage Loss ◽  
Optimal Power ◽  
Heat Leakage ◽  
Working Medium ◽  
Ideal Quantum

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

scholarly journals Action and Entropy in Heat Engines: An Action Revision of the Carnot Cycle

Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 860
Author(s):  
Ivan R. Kennedy ◽  
Migdat Hodzic
Keyword(s):  
Heat Engine ◽  
Working Fluid ◽  
Field Energy ◽  
Carnot Cycle ◽  
Gibbs Potential ◽  
Atmospheric Gases ◽  
Temperature Dependent ◽  
Expansion Phase ◽  
Heat Engines ◽  
The Difference

Despite the remarkable success of Carnot’s heat engine cycle in founding the discipline of thermodynamics two centuries ago, false viewpoints of his use of the caloric theory in the cycle linger, limiting his legacy. An action revision of the Carnot cycle can correct this, showing that the heat flow powering external mechanical work is compensated internally with configurational changes in the thermodynamic or Gibbs potential of the working fluid, differing in each stage of the cycle quantified by Carnot as caloric. Action (@) is a property of state having the same physical dimensions as angular momentum (mrv = mr2ω). However, this property is scalar rather than vectorial, including a dimensionless phase angle (@ = mr2ωδφ). We have recently confirmed with atmospheric gases that their entropy is a logarithmic function of the relative vibrational, rotational, and translational action ratios with Planck’s quantum of action ħ. The Carnot principle shows that the maximum rate of work (puissance motrice) possible from the reversible cycle is controlled by the difference in temperature of the hot source and the cold sink: the colder the better. This temperature difference between the source and the sink also controls the isothermal variations of the Gibbs potential of the working fluid, which Carnot identified as reversible temperature-dependent but unequal caloric exchanges. Importantly, the engine’s inertia ensures that heat from work performed adiabatically in the expansion phase is all restored to the working fluid during the adiabatic recompression, less the net work performed. This allows both the energy and the thermodynamic potential to return to the same values at the beginning of each cycle, which is a point strongly emphasized by Carnot. Our action revision equates Carnot’s calorique, or the non-sensible heat later described by Clausius as ‘work-heat’, exclusively to negative Gibbs energy (−G) or quantum field energy. This action field complements the sensible energy or vis-viva heat as molecular kinetic motion, and its recognition should have significance for designing more efficient heat engines or better understanding of the heat engine powering the Earth’s climates.

scholarly journals Quantum control of excitons for reversible heat transfer

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Conor N. Murphy ◽  
Paul R. Eastham
Keyword(s):  
Heat Transfer ◽  
Quantum Dot ◽  
Quantum Control ◽  
Heat Engine ◽  
Laser Pulses ◽  
Heat Current ◽  
Light Emitting ◽  
Laser Dressing ◽  
Working Medium ◽  
Heat Transfers

Abstract Lasers, photovoltaics, and thermoelectrically-pumped light emitting diodes are thermodynamic machines which use excitons (electron-hole pairs) as the working medium. The heat transfers in such devices are highly irreversible, leading to low efficiencies. Here we predict that reversible heat transfers between a quantum-dot exciton and its phonon environment can be induced by laser pulses. We calculate the heat transfer when a quantum-dot exciton is driven by a chirped laser pulse. The reversibility of this heat transfer is quantified by the efficiency of a heat engine in which it forms the hot stroke, which we predict to reach 95% of the Carnot limit. This performance is achieved by using the time-dependent laser-dressing of the exciton to control the heat current and exciton temperature. We conclude that reversible heat transfers can be achieved in excitonic thermal machines, allowing substantial improvements in their efficiency.

The Role of Internal Irreversibilities in the Performance and Stability of Power Plant Models Working at Maximum ϵ-Ecological Function

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Gabriel Valencia-Ortega ◽  
Sergio Levario-Medina ◽  
Marco Antonio Barranco-Jiménez
Keyword(s):  
Power Plants ◽  
Heat Engine ◽  
Combined Cycle ◽  
Ecological Function ◽  
Operating Conditions ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Engine Model ◽  
Improved Stability ◽  
The Stability

Abstract The proposal of models that account for the irreversibilities within the core engine has been the topic of interest to quantify the useful energy available during its conversion. In this work, we analyze the energetic optimization and stability (local and global) of three power plants, nuclear, combined-cycle, and simple-cycle ones, by means of the Curzon–Ahlborn heat engine model which considers a linear heat transfer law. The internal irreversibilities of the working fluid measured through the r-parameter are associated with the so-called “uncompensated Clausius heat.” In addition, the generalization of the ecological function is used to find operating conditions in three different zones, which allows to carry out a numerical analysis focused on the stability of power plants in each operation zone. We noted that not all power plants reveal stability in all the operation zones when irreversibilities are considered through the r-parameter on real-world power plants. However, an improved stability is shown in the zone limited by the maximum power output and maximum efficiency regimes.

Thermodynamic Processes

2019 ◽  
pp. 132-147
Author(s):  
Robert H. Swendsen
Keyword(s):  
Real World ◽  
Heat Engine ◽  
Second Law Of Thermodynamics ◽  
Heat Pumps ◽  
Second Law ◽  
Carnot Cycle ◽  
Heat Engines ◽  
Negative Temperatures ◽  
Special Case ◽  
Thermodynamic Processes

This chapter begins by defining terms critical to understanding thermodynamics: reversible, irreversible, and quasi-static. Because heat engines are central to thermodynamic principles, they are described in detail, along with their operation as refrigerators and heat pumps. Various expressions of efficiency for such engines lead to alternative expressions of the second law of thermodynamics. A Carnot cycle is discussed in detail as an example of an idealized heat engine with optimum efficiency. A special case, called negative temperatures, where temperatures actually exceed infinity, provides further insights. In this chapter we will discuss thermodynamic processes, which concern the consequences of thermodynamics for things that happen in the real world.

Power and efficiency optimization of an irreversible quantum Carnot heat engine working with harmonic oscillators

2020 ◽  
Vol 550 ◽  
pp. 124140 ◽  
Author(s):  
Lingen Chen ◽  
Xiaowei Liu ◽  
Yanlin Ge ◽  
Feng Wu ◽  
Huijun Feng ◽  
...  
Keyword(s):  
Heat Engine ◽  
Harmonic Oscillators ◽  
Efficiency Optimization

Hybrid Heat Engines: The Power Generation Systems of the Future

2000 ◽  
Author(s):  
Abbie Layne ◽  
Scott Samuelsen ◽  
Mark Williams ◽  
Patricia Hoffman
Keyword(s):  
Fuel Cell ◽  
Gas Turbine ◽  
Power Plants ◽  
Technology Development ◽  
Heat Engine ◽  
Combined Cycle ◽  
Heat Engines ◽  
Hybrid Concept ◽  
Hybrid Program ◽  
Power Generation Systems

A hybrid heat engine results from the fusion of a heat engine with a non-heat-engine based cycle (unlike systems). The term combined cycle, which refers to similar arrangements, is reserved for the combination of two or more heat engines (like systems). The resulting product of the integration of a gas turbine and a fuel cell is referred to here as a hybrid heat engine or “Hybrid” for short. The intent of this paper is to provide, to the gas turbine community, a review of the present status of hybrid heat engine technologies. Current and projected activities associated with this emerging concept are also presented. The National Energy Technology Laboratory (NETL) is collaborating with other sponsors and the private sector to develop a Hybrid Program. This program will address the issues of technology development, integration, and ultimately the demonstration of what may be the most efficient of power plants in the world — the Hybrid System. Analyses of several Hybrid concepts have indicated the potential of ultra-high efficiencies (approaching 80%). In the Hybrid, the synergism between the gas turbine and fuel cell provides higher efficiencies and lower costs than either system can alone. Testing of the first Hybrid concept has been initiated at the National Fuel Cell Research Center (NFCRC).

CO2 Emission and Energy Assessments of a Novel Pre-Purification Unit for Cryogenic Air Separation Using Supersonic Separator

2019 ◽  
Vol 965 ◽  
pp. 59-67
Author(s):  
George Victor Brigagão ◽  
Lara de Oliveira Arinelli ◽  
José Luiz de Medeiros ◽  
Ofélia de Queiroz Fernandes Araújo
Keyword(s):  
Molecular Sieve ◽  
Low Pressure ◽  
Combined Cycle ◽  
Air Separation ◽  
Total Power ◽  
Trace Species ◽  
Pressure Steam ◽  
Purification Unit ◽  
Air Compression ◽  
Supersonic Separator

Thermal power plants with oxy-combustion CO2 capture are featured by large scale oxygen demand, where cryogenic air separation is most suitable. In such context, a Pre-Purification Unit (PPU) is required, prior to air fractionation, to remove hazardous air contaminants – H2O, CO2 and several trace-species – preventing ingress into the Cold Box. The conventional PPU – named FULL-TSA – remove those contaminants by means of Temperature Swing Adsorption (TSA), ordinarily using double-layered bed with activated alumina for adsorbing H2O and zeolitic molecular sieve for adsorbing CO2 and further trace-species, which implicates in relatively high demand of low-pressure steam for impurities desorption. A novel pre-purification concept (SS-TSA) embraces a Supersonic Separator (SS) performing the bulk of separation service, abating nearly 98.5% of H2O, followed by a finishing single-bed molecular sieve (MS) TSA step, which is featured by its relatively small size, for removing CO2 and remaining impurities. This work presents the energy analysis, as well as the related indirect CO2 emissions, of such a novel concept (SS-TSA) comprising air compression, cooling, SS dehydration and finishing MS-TSA against the conventional method fully based in TSA purification (FULL-TSA). Process simulation in HYSYS 8.8 assisted technical evaluation and comparison of alternatives, which included the use of two Hysys Unit Operation Extensions – SS-UOE and PEC-UOE – for rigorous thermodynamic SS modeling with phase equilibrium sound speed. SS was designed to impose only 1.4% of head loss, while shrinking TSA service to about 10% of FULL-TSA counterpart, also recovering super-cooled aqueous condensate that reduces water make-up and N2 consumption for cooling. Changing from FULL-TSA to SS-TSA the average demand of low-pressure steam reduced from 1.37 to 0.16 MW. In terms of electricity demand the difference was quite small, referring to a tiny increase of 0.07 MW in SS-TSA comparatively to total power demand of 14.97 MW in FULL-TSA. Assuming a natural gas combined cycle cogeneration plant matching requirements to air compression and pre-purification process, equivalent reduction in CO2 indirect emission was 20 kg/h for SS-TSA. These results point superiority of SS-TSA.

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