Quantum Stirling heat engine with squeezed thermal reservoir

We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.

Recent advance on the efficiency at maximum power of heat engines

This review reports several key advances on the theoretical investigations of efficiency at maximum power of heat engines in the past five years. The analytical results of efficiency at maximum power for the Curzon-Ahlborn heat engine, the stochastic heat engine constructed from a Brownian particle, and Feynman＇s ratchet as a heat engine are presented. It is found that： the efficiency at maximum power exhibits universal behavior at small relative temperature differences; the lower and the upper bounds might exist under quite general conditions; and the problem of efficiency at maximum power comes down to seeking for the minimum irreversible entropy production in each finite-time isothermal process for a given time.

Optimization of combined endoreversible Carnot heat engines with different objectives

Taking the output power, thermal efficiency, and thermo-economic performance as the optimization objectives, we optimize the operation parameters of a thermodynamic system with combined endoreversible Carnot heat engines in this paper. The applicabilities of the entropy generation minimization and entransy theory to the optimizations are discussed. For the discussed cases, only the entransy loss coefficient is always agreeable to the optimization of thermal efficiency. The applicabilities of the other discussed concepts to the optimizations are conditional. Different concepts and principles are needed for different optimization objectives, and the optimization principles have their application preconditions. When the preconditions are not satisfied, the principles may be not applicable.

Output power analyses of an endoreversible Carnot heat engine with irreversible heat transfer processes based on generalized heat transfer law

In this paper, an endoreversible Carnot heat engine with irreversible heat transfer processes is analyzed based on generalized heat transfer law. The applicability of the entropy generation minimization, exergy analyses method, and entransy theory to the analyses is discussed. Three numerical cases are presented. It is shown that the results obtained from the entransy theory are different from those from the entropy generation minimization, which is equivalent to the exergy analyses method. For the first case in which the application preconditions of the entropy generation minimization and entransy loss maximization are satisfied, both smaller entropy generation rate and larger entransy loss rate lead to larger output power. For the second and third cases in which the preconditions are not satisfied, the entropy generation minimization does not lead to the maximum output power, while larger entransy loss rate still leads to larger output power in the third case. For the discussed cases, the concept of entransy dissipation is not applicable for the analyses of output power.The problems in the negative comments on the entransy theory are pointed out and discussed. The related researchers are advised to focus on some new specific application cases to show if the entransy theory is the same as some other theories.

The Disk-Magnet Electromagnetic Induction Applied to Thermoelectric Energy Conversions

The thermoelectric energy conversion technique by employing the Disk-Magnet Electromagnetic Induction (DM-EMI) and improved DM-EMIs is shown, and possible applications to heat engines as one of the energy harvesting technologies are also discussed. The idea is induced by integrating irreversible thermodynamical mechanism of a water drinking bird with that of a Stirling engine, resulting in thermoelectric energy generation different from conventional heat engines. The current thermoelectric energy conversion with DM-EMI can be applied to wide ranges of temperature differences. The mechanism of DM-EMI energy converter is examined in terms of axial flux magnetic lines and categorized as the axial flux generator. It is useful for practical applications to macroscopic heat engines such as wind, geothermal, thermal and nuclear power turbines and heat-dissipation lines, for supporting thermoelectric energy conversions. The technique of DM-EMI will contribute to environmental problems to maintain clean and susceptible energy as one of the energy harvesting technologies.

Two Scenarios on the Relativistic Quantum Heat Engine

We compare two different scenarios at relativistic quantum heat engine by considering three-level energy, and two non-interacting fermion in one-dimensional potential well. The difference between the scenarios is about mechanism to get into excited state by two fermions. We apply iso-energetic cycle that consists of two iso-energetic and two iso-entropic processes, and then compute and compare the efficiency at both scenarios. We also compare it with non-relativistic case. The result is that one scenario has larger efficiency than the other that does not happen at non-relativistic case.

Entangled quantum heat engine based on two-qubit Heisenberg XY model

Based on a two-qubit isotropic Heisenberg XY model under a constant external magnetic field,we construct a four-level entangled quantum heat engine（QHE）.The expressions for the heat transferred,the work,and the efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variations of the heat transferred,the work,and the efficiency with the concurrences of the thermal entanglement of two different thermal equilibrium states in zero and nonzero magnetic fields are obtained.

Influence of the coupled-dipoles on photosynthetic performance in a photosynthetic quantum heat engine

Recent evidence suggests that the multiple charge-separation pathways can contribute to photosynthetic performance.In this work,the influence of coupled-dipoles on photosynthetic performance was investigated in a two-charge separation pathways quantum heat engine(QHE) model.And the population dynamics of the two coupled sites,j-V characteristics,and power involving this photosynthetic QHE model were evaluated for the photosynthetic performance.The results illustrate that the photosynthetic performance can be greatly enhanced but quantum interference is deactivated by the coupleddipoles between the two-charge separation pathways.However,the photosynthetic performance can also be promoted by the deactivated quantum interference owing to the coupled-dipoles.It is a novel role of the coupled-dipoles in the energy transport process of biological photosynthetic,and some artificial strategies may be motivated by this photosynthetic QHE model in the future.

Holographic heat engine efficiency of hyperbolic charged black holes

We consider a four-dimensional charged hyperbolic black hole as working matter to establish a black hole holographic heat engine,and use the rectangular cycle to obtain the heat engine efficiency.We find that when the increasing of entropy is zero,the heat engine efficiency of the hyperbolic black hole becomes the well-known Carnot efficiency.We also find that less charge corresponds to higher efficiency in the case of˜q>0.Furthermore,we study the efficiency of the flat case and spherical case and compare the efficiency with that of the hyperbolic charged black holes.Finally,we use numerical simulation to study the efficiency in benchmark scheme.

Predicting the Curvature of the Cosmos, and Point of Volume Contraction in a Big Bounce Scenario

Based on the latest Planck surveys, the universe is close to being remarkably flat, and yet, within observational error, there is still room for a slight curvature. If the curvature is positive, then this would lead to a closed universe, as well as allow for a big bounce scenario. Working within these assumptions, and using a simple model, we predict that the cosmos may have a positive curvature in the amount, Ω0=1.001802, a value within current observational bounds. For the scaling laws associated with the density parameters in Friedmann’s equations, we will assume a susceptibility model for space, where, , equals the smeared cosmic susceptibility. If we allow the to decrease with increasing cosmic scale parameter, “a”, then we can predict a maximum Hubble volume, with minimum CMB temperature for the voids, before contraction begins, as well as a minimum volume, with maximum CMB temperature, when expansion starts. A specific heat engine model for the cosmos is also entertained for this model of a closed universe.

Thermodynamics of Hurricanes Revisited

Hurricanes and tropical storms are heat engines operating between warm tropical oceans and the cold upper troposphere. The purpose of this article is to examine the existing theories for hurricanes and tropical storms, and to discuss their validity. It is argued that contrary to previous claims that hurricanes are Carnot engines, these systems operate at efficiencies considerably below their maximum thermodynamic efficiency. As such, the validity of the current theories of thermodynamics of hurricanes remains questionable, and the phenomenon continues to be a geophysical enigma.

Study on the atmospheric heat engine efficiency and heat source characteristics of the Qinghai-Tibet Plateau in summer

There are many types of atmospheric heat engines in land-air systems.The accurate definition,calculation and interpretation of the efficiency of atmospheric heat engines are key to understanding energy transfer and transformation of landair systems.The atmosphere over the Qinghai-Tibet Plateau(QTP)in summer can be regarded as a positive heat engine.The study of the heat engine efficiency is helpful to better understand land-air interaction and thermal-dynamic processes on the QTP.It also provides a new perspective to explain the impact of the QTP on the climate of China,East Asia and even the world.In this paper,we used MOD08 and ERA5 reanalysis data to calculate the atmospheric heat engine efficiency,surface heat source and atmospheric heat source on the QTP in summer(May to September)from 2000 to 2020.The average atmospheric heat engine efficiency on the QTP in summer from 2000 to 2020 varies between 1.2%and 1.5%,which is less than 1.6%;the heat engine efficiency in summer is higher than that in June,July and August;the Qaidam Basin is the region with the highest atmospheric heat engine efficiency,followed by the western QTP.The mean surface heat source on the QTP in summer from 2000 to 2020 is 96.0 W m^(−2),the atmospheric heat source is 90.7 W m^(−2),and the release of precipitation condensation latent heat is the most important component of the atmospheric heat source on the QTP in summer.There is a strong and significant positive correlation between the atmospheric heat engine efficiency and the surface heat source on the QTP in summer.The precipitation condensation latent heat is the most important component of the atmospheric heat source in summer and can reflect the precipitation process.There is a strong and significant negative correlation between the atmospheric heat engine efficiency and the atmospheric heat source on the QTP in summer.

Nonequilibrium thermodynamics in cavity optomechanics

Classical thermodynamics has been a great achievement in dealing with systems that are in equilibrium or near equilibrium.As an emerging field,nonequilibrium thermodynamics provides a general framework for understanding the nonequilibrium processes,particularly in small systems that are typically far-from-equilibrium and are dominated by thermal or quantum fluctuations.Cavity optomechanical systems hold great promise among the various experimental platforms for studying nonequilibrium thermodynamics owing to their high controllability,excellent mechanical performance,and ability to operate deep in the quantum regime.Here,we present an overview of the recent advances in nonequilibrium thermodynamics with cavity optomechanical systems.The experimental results in entropy production assessment,fluctuation theorems,heat transfer,and heat engines are highlighted.

Heat engines of the Kerr-AdS black hole

In this paper,we investigate three types of heat engines for the rotating Kerr-Anti de Sitter(Kerr-AdS)black hole.We first briefly review the thermodynamics and phase structure of the Kerr-AdS black hole and obtain the phase structure in the T-S chart.The thermal stability of Kerr-AdS black holes,along with their dependence on various parameters,is thoroughly examined.Then,by utilizing the phase diagram,we consider three types of heat engines:the maximal Carnot engine,Stirling engine,and Rankine engine.We calculate both the work and efficiency for these engines.The results indicate that angular momentum has a significant influence on these heat engines.

Maximum power and corresponding efficiency of an irreversible blue heat engine for harnessing waste heat and salinity gradient energy

In this study,a novel irreversible cyclic model of a capacitive mixing blue heat engine mainly consisting of super capacitors,charging and discharging circuits,a heat source,as well as two water sources with given salt concentrations is established for harvesting salinity gradient energy and waste heat.Additionally,the effects of the charging voltage and ratio of the minimum to maximum surface electric charge density on the thermodynamic efficiency and power output of the cycle are discussed.The maximum power output of the cycle is calculated.The optimized ranges of efficiency and power output as well as the temperatures of two isothermal processes are determined.It is established that during the isoelectric quantity process,there is not only an increase in thermal voltage owing to the temperature difference,but also an increase in concentration voltage owing to the salinity gradient.Consequently,the blue heat engine can obtain higher energy conversion efficiency than a conventional heat engine.When the temperature ratio of the heat source to the heat sink is 1.233,the maximum efficiency can reach approximately36%.The results obtained can promote the application of capacitive mixing technology in real life,reducing the consumption of fossil fuels.

Abstract models for heat engines

We retrospect three abstract models for heat engines which include a classic abstract model in textbook of thermal physics,a primary abstract model for finite-time heat engines,and a refined abstract model for finite-time heat engines.The detailed models of heat engines in literature of finite-time thermodynamics may be mapped into the refined abstract model.The future developments based on the refined abstract model are also surveyed.

Consistency of optimizing finite-time Carnot engines with the low-dissipation model in the two-level atomic heat engine

The efficiency at the maximum power(EMP)for finite-time Carnot engines established with the low-dissipation model,relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generationΔS^(ir)on the operation timeτ,i.e.ΔS^(ir)∝1/τ.The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling.Yet,such consistency was not tested due to the unknown coefficient of the 1/τ-scaling.In this paper,we reveal that the optimization of the finite-time two-level atomic Carnot engines with the low-dissipation model is consistent only in the regime ofη_(C)<<2(1-δ)/(1+δ),whereη_(C)is the Carnot efficiency,andδis the compression ratio in energy level difference of the heat engine cycle.In the large-η_(C)regime,the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the 1/τ-scaling,and the exact EMP of the engine is found to surpass the well-known boundη_(C)=η_(C)/(2-η_(C)).

Thermal-structural analysis of regeneratively-cooled thrust chamber wall in reusable LOX/Methane rocket engines

To predict the thermal and structural responses of the thrust chamber wall under cyclic work,a 3-D fluid-structural coupling computational methodology is developed.The thermal and mechanical loads are determined by a validated 3-D finite volume fluid-thermal coupling computational method.With the specified loads,the nonlinear thermal-structural finite element analysis is applied to obtaining the 3-D thermal and structural responses.The Chaboche nonlinear kinematic hardening model calibrated by experimental data is adopted to predict the cyclic plastic behavior of the inner wall.The methodology is further applied to the thrust chamber of LOX/Methane rocket engines.The results show that both the maximum temperature at hot run phase and the maximum circumferential residual strain of the inner wall appear at the convergent part of the chamber.Structural analysis for multiple work cycles reveals that the failure of the inner wall may be controlled by the low-cycle fatigue when the Chaboche model parameter c3= 0,and the damage caused by the thermal-mechanical ratcheting of the inner wall cannot be ignored when c3〉 0.The results of sensitivity analysis indicate that mechanical loads have a strong influence on the strains in the inner wall.

Charged torus-like black holes as heat engines

We investigate the thermodynamical properties of charged torus-like black holes and take it as the working substance to study the heat engines.In the extended phase space,by interpreting the cosmological constant as the thermodynamic pressure,we derive the thermodynamical quantities by the first law of black hole thermodynamics and obtain the equation of state.Then,we calculate the efficiency of the heat engine in the Carnot cycle as well as the rectangular cycle,and investigate how the efficiency changes with respect to volume.In addition,to avoid a negative temperature,we emphasize that the charge of this black hole cannot be arbitrary.Last,we check the calculation accuracy of a benchmark scheme and discuss the upper bound and lower bound for charged torus-like black hole in the scheme.