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We have developed a computer code for the thermodynamic hierarchical equations of motion derived from a spin subsystem coupled to multiple Drude baths at different temperatures, which are connected to or disconnected from the subsystem as a function of time. The code can simulate the reduced dynamics of the subsystem under isothermal, isentropic, thermostatic, and entropic conditions. The extensive and intensive thermodynamic variables are calculated as physical observables, and Gibbs and Helmholtz energies are evaluated as intensive and extensive work. The energy contribution of the system–bath interaction is evaluated separately from the subsystem using the hierarchical elements of the hierarchical equations of motion. The accuracy of the calculated results for the equilibrium distribution and the two-body correlation functions is assessed by contrasting the results with those obtained from the time-convolution-less Redfield equation. It is shown that the Lindblad master equation is inappropriate for the thermodynamic description of a spin–boson system. Non-Markovian effects in thermostatic processes are investigated by sequentially turning on and off the baths at different temperatures with different switching times and system–bath coupling. In addition, the Carnot cycle is simulated under quasi-static conditions. To analyze the work performed for the subsystem in the cycle, thermodynamic work diagrams are plotted as functions of intensive and extensive variables. The C++ source codes are provided as supplementary material. [ABSTRACT FROM AUTHOR]

Entropy and energy had not yet been introduced to physics by the time Carnot wrote his seminal Réflexions. Scholars continue to discuss what he really had in mind and what misconceptions he might have had. Actually, his work can be read as a correct introduction to the physics of heat engines when the term calorique is replaced by entropy and entropy is used as the other fundamental thermal quantity besides temperature. Carnot's concepts of falling entropy as an analogy to the waterfall, and the separation of real thermal processes into reversible and irreversible processes are adopted. Some details of Carnot's treatise are ignored, but the principal ideas are quoted and assumed without modification. With only two thermal quantities, temperature and entropy, modern heat engines can be explained in detail. Only after the principal function of heat engines is developed is energy introduced as physical quantity in order to compare thermal engines with mechanical and electrical engines and, specifically, to calculate efficiency. [ABSTRACT FROM AUTHOR]

This study presents an innovative coal-fired power generation system that integrates a Proton Exchange Membrane Fuel Cell (PEMFC), Gas Turbine (GT), and Steam Turbine (ST) with a supercritical water gasification (SCWG) process designed to efficiently convert coal into hydrogen. A pivotal feature of this system is the first-time integration of advanced two-step SCWG technology with PEMFC, which significantly boosts hydrogen yield, thereby elevating overall efficiency. By effectively addressing the thermodynamic limitations of the Carnot cycle, the proposed system achieves an impressive coal-to-electricity conversion efficiency of 51.61%. Economic viability is demonstrated through a competitive levelized cost of energy (LCOE) of $0.052 per kWh and a rapid payback period of approximately 2.87 years. Furthermore, the study analyzes the impact of various operational parameters—such as coal feed capacity, water-to-coal ratio, operating temperatures of the PEMFC, fuel utilization rates, airflow, and hydrogen bypass flow—on system performance. The findings not only advance the efficiency of coal-to-electricity conversion but also contribute valuable insights to the evolution of sustainable coal-fueled power generation technologies. • Innovative coal fueled PEMFC-GT-RC power generation system. • Utilizes advanced two-step SCWG method for enhanced H 2 production. • Achieved 51.61% coal-to-electricity efficiency, surpassing coal plants by 3.79%. • Offers competitive LCOE at $0.052/kWh with a short payback of 2.87 years. [ABSTRACT FROM AUTHOR]

Using the Pohozaev-type arguments, we prove the nonexistence results for sub-elliptic problems with critical Sobolev-Hardy exponents and Hardy-type potentials on the Carnot group. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) has attracted wide attention because its efficiency is not limited by the efficiency of Carnot cycle. The structure of flow channel in SOFC has great effects on the internal mass distribution, which influences current density. In this paper, the height of flow channel and the position, arrangement, number and height of the fin which is placed in channel, are changed to get different structures of bi-layer interconnector, and they are applied to three layers SOFC stack. The effects of each structural parameter on the current density are studied by numerical simulation. The results show that, increasing the number of fins and bi-layer interconnector height can make more reactant gas enters the electrode. In addition, compared with the conventional structure, the current density can be increased by the bi-layer interconnector up to 31.256%, and the bi-layer interconnector structure could save n-1 layers of interconnector, which reduces the volume of SOFC stack. Among the five structural parameters, the position of fins has the least influence on temperature distribution and current density, while the arrangement of fins has the highest influence on volume current density, reaching 30%. Using a staggered arrangement and higher bi-layer interconnector can also improve the temperature distribution. • A three-dimensional SOFC stack with bi-layer interconnector was established. • Changing geometry of fins and channel height to get different structures. • Increasing number of fins and channel height improve concentration distribution. • The arrangement of fins has the greatest impact on current density. • Staggered fins and higher bi-layer interconnector reduce the highest temperature. [ABSTRACT FROM AUTHOR]

No one has yet investigated the information reach and influence of thermal analysis. Even so the heat and entropy are bound closely. The very problem of the term entropy is that it was defined specifically within the classical, equilibrium Thermodynamics like Clausius entropy, while its meaning is more general. It is usable in all areas of physics, in the communication theory and technology, and also, in social sciences, just as an universal quantitative model. The bridge to this wider world is in Boltzmann's statistical point of view used in the Shannon's information point of view. The difference is that the Shannon entropy is defined more generally, both for the uniform and for the not uniform probability distributions. But with renormalization and with the Boltzmann constant we can speak, using the Clausius entropy, about a certain thermodynamic system considered as a heat model of the area of our wider interests. So we will to deal with the heat and its entropy embodied to a wider consideration. In addition to the standard physical meaning, another thermodynamic realization in the form of a message is derived from Shannon's information theory, where the sample carries a measure of Shannon's information given by its structure or internal organization. This is also a contribution to improving the approach to thinking about the importance of observation and measurement, reflecting at the same time the costs and influence of the measurement itself and its organization on the measured object or, on its environment or, even on the environment of the measuring itself generally. Statistical sorting also carries with it the internal movement of individual elementary particles, the value of which indicates the resulting state of heat transfer and dissipation to and from the system providing a state of called equilibrium. It is statistically described by a weighted quantity called temperature, the changes of which via momentum alteration satisfy Newton's laws of inertia allowing enumeration of the related heat information processing. The terminology used is still non-institutional. [ABSTRACT FROM AUTHOR]

This paper was focused on the solvability of a class of doubly critical sub-Laplacian problems on the Carnot group : Here, , , , , and . By means of variational techniques, we extended the arguments developed in [1]. In addition, we also established the existence result for the subelliptic system which involved sub-Laplacian and critical homogeneous terms. [ABSTRACT FROM AUTHOR]

The issue of marketing efficiency, or how to better transform inputs into outputs within a marketing system, has always occupied a special place in the macromarketing literature. The concept of marketing efficiency has not been studied in closed and isolated systems that exhibit distinctive behavioral patterns compared to conventional open systems and can explain important and understudied marketing phenomena, including autarky. This study challenges some of the conventional premises of marketing systems by defining autarky as a closed marketing system that 1) operates with the specific purpose of propaganda in a relatively predictable and efficient manner; 2) has minimal, though not entirely absent, interaction with the international environment; and 3) involves participants (actors) who do not engage in voluntary exchanges with one another but rather collectively, as well as individually, adhere consistently to the self-reliance ideology. We demonstrate how a classical thermodynamic model (i.e., the Carnot cycle for maximum energy efficiency) can be metaphorically associated with the behavior of the North Korean autarkic system to better understand the long-term efficiency of its propaganda machine. To the best of our knowledge, this is the first attempt to develop a holistic metaphorical framework for exploring the efficiency of an autarkic system and to establish common criteria for measuring relationships between autarkic properties and autarkic processes. [ABSTRACT FROM AUTHOR]

The problem of using a steam generator plant, operating on the Rankine cycle, to utilize some of the thermal energy as part of the system for ensuring the thermal regime of a spacecraft is considered. The thermal energy released by the instrumentation equipment is removed to external radiators using loop heat pipes, after which it is radiated into outer space. Part of the heat is converted into electricity to maintain the functioning of on-board radio-electronic equipment. The work assessed the influence of a steam generator plant on thermal systems (with a preliminary solution of a system of thermohydraulic equations with characteristic initial-boundary conditions of loop heat pipes), its design parameters, such as the area of external radiators and the mass of the system, and conclusions are made about the feasibility of its use. This system for ensuring thermal conditions using loop heat pipes can be useful for energy-consuming unmanned spacecraft with low restrictions on the mass and size characteristics of the device. [ABSTRACT FROM AUTHOR]

We investigate the efficiency of a quantum Carnot engine based on open quantum dynamics theory. The model includes time-dependent external fields for the subsystems controlling the isothermal and isentropic processes and for the system–bath (SB) interactions controlling the transition between these processes. Numerical simulations are conducted in a nonperturbative and non-Markovian SB coupling regime by using the hierarchical equations of motion under these fields at different cycle frequencies. The work applied to the total system and the heat exchanged with the baths are rigorously evaluated. In addition, by regarding quasi-static work as free energy, we compute the quantum thermodynamic variables and analyze the simulation results by using thermodynamic work diagrams for the first time. Analysis of these diagrams indicates that, in the strong SB coupling region, the fields for the SB interactions are major sources of work, while in other regions, the field for the subsystem is a source of work. We find that the maximum efficiency is achieved in the quasi-static case and is determined solely by the bath temperatures, regardless of the SB coupling strength, which is a numerical manifestation of Carnot's theorem. [ABSTRACT FROM AUTHOR]

Direct ethanol fuel cell can convert chemical energy into electric energy directly, and has the advantages of being free from Carnot cycle and being friendly to environment, so it has a broad application prospect. However, the insufficient activity and toxicity resistance of anodic catalysts limit their commercial application, mainly due to the limited adsorption sites and the toxic inactivation of catalysts resulting from the production of toxic intermediates (CO ads) during the ethanol oxidation reaction (EOR) process. In this study, the Au@PdAg porous hemispherical catalyst assembled by nanotubes was successfully prepared by soft template method and co-reduction method using dioctadecyl dimethyl ammonium chloride (DODAC) as surfactant, and its EOR performance was tested. Au@Pd 1.0 Ag 1.0 has the highest mass current density with a peak value of 4048.8 mA mg Pd − 1 , which is 7.8 times of Pd/C (JM). After 5000 s stability test, the residual current density value is still 863.4 mA mg Pd − 1 . The results showed that the introduction of the oxygenophilic metal Ag was conducive to the formation of OH ads and the oxidation of CO ads. The porous structure of the nanotube assembly facilitates electron transfer and provides more adsorption sites, which makes the catalyst show good electrocatalytic activity and anti-CO poisoning ability. [Display omitted] • Anisotropic hemispherical nanostructure was formed by BO 2 − inhomogeneous adsorption. • Porous hemispherical Au@PdAg catalyst enhancing ethanol electrooxidation was prepared. • The catalyst exhibited excellent activity and regenerative for ethanol oxidation. [ABSTRACT FROM AUTHOR]

The JETC Conference held in Salerno (June 12–17, 2023) was the opportunity to honor the two centuries anniversary of the booklet publication of Sadi Carnot. The paper reports on a selective review summarizing the evolution of the ideas and concepts proposed by Carnot. We consider mainly: a. The Carnot cycle relative to thermomechanical engine, b. The concept of efficiency (Carnot efficiency), c. The forms of energy (thermal energy or heat, Q, and mechanical energy or work, W), d. The concept of entropy, rediscovered and completed by Clausius. We show the importance of the energy conversion irreversibilities that started to be considered more recently by two methods, namely, the ratio method and the entropy production method. The second approach provides more significant results from a global point of view, also with more local modeling (cycle process modeling). Some examples are given that illustrate the proposal: Carnot cycle in endo-irreversible or exo-reversible configuration, Chambadal modeling, Curzon–Ahlborn modeling. More generally, the modeling is done in the frame of FTT (Finite Time Thermodynamics), FST (Finite Speed Thermodynamics), or FDOT (Finite physical Dimensions Optimal Thermodynamics). Preliminary conclusions and perspectives are proposed. [ABSTRACT FROM AUTHOR]

This article discusses the existence and multiplicity of positive solutions for subelliptic systems on Carnot groups. The authors use variational methods and the Nehari manifold to prove the existence of at least two positive solutions for certain parameter pairs. The article also explores the sub-Laplacian Hardy-Sobolev inequality and the difficulties in applying known techniques to the problem. The article presents several theorems proving the existence of positive solutions for different cases of nonlinearity. The article also provides preliminary results and definitions related to the Carnot group functional setting. [Extracted from the article]

In this paper, using variational methods and critical point theory we establish the existence of multiple solutions for a class of elliptic equations on Carnot groups depending on one real positive parameter and involving a subcritical nonlinearity. Some recent results are extended and improved. [ABSTRACT FROM AUTHOR]

This paper presents a continuation of the Chambadal model optimization of the irreversible Carnot engine. We retrieved the results presented in the Special Issue "Carnot Cycle and Heat Engine Fundamentals and Applications II" and enriched them with new contributions that allowed comparing two points of view: (1) the now classical one, centered on entropy production in the four processes of the cycle, which introduces the action of entropy production, with several sequential optimizations; (2) the new one that is relative to an energy degradation approach. The same démarche of sequential optimization was used, but the results were slightly different. We estimate that the second approach is more representative of physics by emphasizing the energy conservation and the existence on an upper and a lower bound in the mechanical energy and power output of the engine. [ABSTRACT FROM AUTHOR]

Periodically driven quantum dots can act as counterparts of cyclic thermal machines at the nanoscale. In the slow-driving regime of geometric pumping, such machines have been shown to operate in analogy to a Carnot cycle. For larger driving frequencies, which are required to increase the cooling power, the efficiency of the operation decreases. Up to which frequency a close-to-optimal performance is still possible depends on the magnitude and sign of on-site electron–electron interaction. Extending our previous detailed study on cyclic quantum-dot refrigerators [Phys. Rev. B 106, 035405 (2022)], we here find that the optimal cooling power remains constant up to weak interaction strength compared to the cold-bath temperature. By contrast, the work cost depends on the interaction via the dot's charge relaxation rate, as the latter sets the typical driving frequency for the onset of non-geometric pumping contributions. [ABSTRACT FROM AUTHOR]

We explain that a full description of how the non-equilibrium state of the system evolves in time requires the consideration and solution of its general equation of motion. In the case of the Carnot medium, as a general equation of motion, there must be taken two balances of: nonequilibrium specific volume and non-equilibrium specific entropy. Instead of taking the classical approach where the balance of entropy is postponed to more advanced and theoretical treatments, we focus on the analysis of two, most general, volume and entropy fluxes. These fluxes of motion are universal features of thermodynamics. It has been shown that the Carnot working continuum mathematical model is captured by the two general nonmathematical statements valid for all systems that we call the first law and the second law of thermodynamics. [ABSTRACT FROM AUTHOR]

Power plants constitute the main sources of electricity production, and the calculation of their efficiency is a critical factor that is needed in energy studies. The efficiency improvement of power plants through the optimization of the cycle is a critical means of reducing fuel consumption and leading to more sustainable designs. The goal of the present work is the development of semi-empirical models for estimating the thermodynamic efficiency of power cycles. The developed model uses only the lower and the high operating temperature levels, which makes it flexible and easily applicable. The final expression is found by using the literature data for different power cycles, named as: organic Rankine cycles, water-steam Rankine cycles, gas turbines, combined cycles and Stirling engines. According to the results, the real operation of the different cases was found to be a bit lower compared to the respective endoreversible cycle. Specifically, the present global model indicates that the thermodynamic efficiency is a function of the temperature ratio (low cycle temperature to high cycle temperature). The suggested equation can be exploited as a quick and accurate tool for calculating the thermodynamic efficiency of power plants by using the operating temperature levels. Moreover, separate equations are provided for all of the examined thermodynamic cycles. [ABSTRACT FROM AUTHOR]

Increasing interest has been shown in the subject of non-additive entropic forms during recent years, which has essentially been due to their potential applications in the area of complex systems. Based on the fact that a given entropic form should depend only on a set of probabilities, its time evolution is directly related to the evolution of these probabilities. In the present work, we discuss some basic aspects related to non-additive entropies considering their time evolution in the cases of continuous and discrete probabilities, for which nonlinear forms of Fokker–Planck and master equations are considered, respectively. For continuous probabilities, we discuss an H-theorem, which is proven by connecting functionals that appear in a nonlinear Fokker–Planck equation with a general entropic form. This theorem ensures that the stationary-state solution of the Fokker–Planck equation coincides with the equilibrium solution that emerges from the extremization of the entropic form. At equilibrium, we show that a Carnot cycle holds for a general entropic form under standard thermodynamic requirements. In the case of discrete probabilities, we also prove an H-theorem considering the time evolution of probabilities described by a master equation. The stationary-state solution that comes from the master equation is shown to coincide with the equilibrium solution that emerges from the extremization of the entropic form. For this case, we also discuss how the third law of thermodynamics applies to equilibrium non-additive entropic forms in general. The physical consequences related to the fact that the equilibrium-state distributions, which are obtained from the corresponding evolution equations (for both continuous and discrete probabilities), coincide with those obtained from the extremization of the entropic form, the restrictions for the validity of a Carnot cycle, and an appropriate formulation of the third law of thermodynamics for general entropic forms are discussed. [ABSTRACT FROM AUTHOR]

This comprehensive treatise is written for the special occasion of the author's 70th birthday. It presents his lifelong endeavors and reflections with original reasoning and re-interpretations of the most critical and sometimes misleading issues in thermodynamics—since now, we have the advantage to look at the historical developments more comprehensively and objectively than the pioneers. Starting from Carnot (grand-father of thermodynamics to become) to Kelvin and Clausius (fathers of thermodynamics), and other followers, the most relevant issues are critically examined and put in historical and contemporary perspective. From the original reasoning of generalized "energy forcing and displacement" to the logical proofs of several fundamental laws, to the ubiquity of thermal motion and heat, and the indestructibility of entropy, including the new concept of "thermal roughness" and "inevitability of dissipative irreversibility," to dissecting "Carnot true reversible-equivalency" and the critical concept of "thermal-transformer," limited by the newly generalized "Carnot-Clausius heat-work reversible-equivalency (CCHWRE)," regarding the inter-complementarity of heat and work, and to demonstrating "No Hope" for the "Challengers" of the Second Law of thermodynamics, among others, are offered. It is hoped that the novel contributions presented here will enlighten better comprehension and resolve some of the fundamental issues, as well as promote collaboration and future progress. [ABSTRACT FROM AUTHOR]

• Four refrigeration cycle architectures for two-door refrigerators are compared. • Analyses were carried out by means of quasi-steady cycle simulation models. • Several layers of internal and external irreversibilities were considered. • Two independent single-evaporator cycles performed the best. • The single-evaporator fan-and-damper solution performed the worst. In this study, four different refrigeration cycle architectures for two-door applications were evaluated and compared: (i) fan-and-damper single-evaporator cycle, (ii) serial/parallel (hybrid) dual-evaporator architecture, (iii) parallel dual-evaporator architecture, and (iv) two independent single-evaporator cycles. The performance analysis was carried out by means of quasi-steady mathematical models that combine steady-state submodels for the refrigeration loop with transient submodels for the refrigerated compartments. The numerical calculations were conducted in such a way that layers of internal and external irreversibility could be introduced into the analysis, from a fully-reversible Carnot cycle to the cycling behavior imposed by the control logic. The dual-evaporator cycles, which are far more complex than single-evaporator ones, were prototyped and tested in a climate chamber to gather data used to calibrate and validate the mathematical models. A methodology was devised on thermodynamic grounds to allow a fair comparison between the architectures. The system with two independent single-evaporator cycles performed the best, followed by parallel and hybrid dual-evaporator loops, and the single-evaporator fan-and-damper solution. Also, the replacement of isobutane with n-butane in the fresh-food branch of the two independent cycles led to an extra 5% energy consumption reduction under the same conditions, providing better matching of the compressor capacity to the thermal loads. [ABSTRACT FROM AUTHOR]

This study revisits the issue of why tropical cyclones (TCs) develop more rapidly at lower latitudes, using ensemble axisymmetric numerical simulations and energy diagnostics based on the isentropic analysis, with the focus on the relative importance of the outflow-layer and boundary layer inertial stabilities to TC intensification and energy cycle. Results show that although lowering the outflow-layer Coriolis parameter and thus inertial stability can slightly strengthen the outflow, it does not affect the simulated TC development, whereas lowering the boundary layer Coriolis parameter largely enhances the secondary circulation and TC intensification as in the experiment with a reduced Coriolis parameter throughout the model atmosphere. This suggests that TC outflow is more likely a passive result of the convergent inflow in the boundary layer and convective updraft in the eyewall. The boundary layer inertial stability is found to control the convergent inflow in the boundary layer and depth of convection in the eyewall and thus the temperature of the energy sink in the TC heat engine, which determines the efficiency and overall mechanical output of the heat engine and thus TC intensification. It is also shown that the hypothesized isothermal and adiabatic compression legs at the downstream end of the outflow in the classical Carnot cycle are not supported in the thermodynamic cycle of the simulated TCs, implying that the hypothesized classical TC Carnot cycle is not closed. It is the theoretical maximum work of the heat engine, not the energy expenditure following the outflow downstream, that determines the mechanical work used to intensify a TC. [ABSTRACT FROM AUTHOR]

Advances in applied mechanics have facilitated a better understanding of the recycling of heat and work in the troposphere. This goal is important to meet practical needs for better management of climate science. Achieving this objective may require the application of quantum principles in action mechanics, recently employed to analyze the reversible thermodynamics of Carnot's heat engine cycle. The testable proposals suggested here seek to solve several problems including (i) the phenomena of decreasing temperature and molecular entropy but increasing Gibbs energy with altitude in the troposphere; (ii) a reversible system storing thermal energy to drive vortical wind flow in anticyclones while frictionally warming the Earth's surface by heat release from turbulence; (iii) vortical generation of electrical power from translational momentum in airflow in wind farms; and (iv) vortical energy in the destructive power of tropical cyclones. The scalar property of molecular action (@t ≡ ∫mvds, J-sec) is used to show how equilibrium temperatures are achieved from statistical equality of mechanical torques (mv2 or mr2ω2); these are exerted by Gibbs field quanta for each kind of gas phase molecule as rates of translational action (d@t/dt ≡ ∫mr2ωdϕ/dt ≡ mv2). These torques result from the impulsive density of resonant quantum or Gibbs fields with molecules, configuring the trajectories of gas molecules while balancing molecular pressure against the density of field energy (J/m3). Gibbs energy fields contain no resonant quanta at zero Kelvin, with this chemical potential diminishing in magnitude as the translational action of vapor molecules and quantum field energy content increases with temperature. These cases distinguish symmetrically between causal fields of impulsive quanta (Σhν) that energize the action of matter and the resultant kinetic torques of molecular mechanics (mv2). The quanta of these different fields display mean wavelengths from 10−4 m to 1012 m, with radial mechanical advantages many orders of magnitude greater than the corresponding translational actions, though with mean quantum frequencies (v) similar to those of radial Brownian movement for independent particles (ω). Widespread neglect of the Gibbs field energy component of natural systems may be preventing advances in tropospheric mechanics. A better understanding of these vortical Gibbs energy fields as thermodynamically reversible reservoirs for heat can help optimize work processes on Earth, delaying the achievement of maximum entropy production from short-wave solar radiation being converted to outgoing long-wave radiation to space. This understanding may improve strategies for management of global changes in climate. [ABSTRACT FROM AUTHOR]

We develop an endoreversible scheme for thermoradiative cells where the thermodynamic variables are functionals of the Carnot efficiency of the reversible part of the model. The new description enlarges previous embodiments since it includes new thermodynamic properties (total entropy and ecological function) that depend on the temperatures of the hot and cold reservoirs assisting the conversion. The new model is used to find optimal working conditions of spatial thermoradiative cells where the converter gets the heat from the radiative emission of Earth and rejects energy to colder space. Our calculations show that optimal working points can be found using the total entropy or the ecological function. In the last part of the paper, we compare our results with those found in previous works using models that do not consider the entropy losses. [ABSTRACT FROM AUTHOR]

We investigate the finite-time performance of a quantum endoreversible Carnot engine cycle and its inverse operation — Carnot refrigeration cycle, employing a spin-1/2 system as the working substance. The thermal machine is alternatively driven by a hot boson bath of inverse temperature β h and a cold boson bath at inverse temperature β c (> β h). While for the engine model the hot bath is constructed to be squeezed, in the refrigeration cycle the cold bath is established to be squeezed, with squeezing parameter r. We obtain the analytical expressions for both efficiency and power in heat engines and for coefficient of performance and cooling rate in refrigerators. We find that, in the high-temperature limit, the efficiency at maximum power is bounded by the analytical value η + = 1 − sech (2 r) (1 − η C) , and the coefficient of performance at the maximum figure of merit is limited by ε + = sech (2 r) (1 + ε C ) sech (2 r) (1 + ε C) − ε C − 1 , where η C = 1 – β h/ β c and ε C = β h/(β c – β h) are the respective Carnot values of the engines and refrigerators. These analytical results are identical to those obtained from the Carnot engines based on harmonic systems, indicating that the efficiency at maximum power and coefficient at maximum figure of merit are independent of the working substance. [ABSTRACT FROM AUTHOR]

Carnot cycles of samples of harmonically confined ultracold 87 Rb fluids, near and across Bose–Einstein condensation (BEC), are analyzed. This is achieved through the experimental determination of the corresponding equation of state in terms of the appropriate global thermodynamics for non-uniform confined fluids. We focus our attention on the efficiency of the Carnot engine when the cycle occurs for temperatures either above or below the critical temperature and when BEC is crossed during the cycle. The measurement of the cycle efficiency reveals a perfect agreement with the theoretical prediction (1 − T L / T H) , with T H and T L serving as the temperatures of the hot and cold heat exchange reservoirs. Other cycles are also considered for comparison. [ABSTRACT FROM AUTHOR]

An ejector refrigeration system is a promising heat-driven refrigeration technology for energy consumption. The ideal cycle of an ejector refrigeration cycle (ERC) is a compound cycle with an inverse Carnot cycle driven by a Carnot cycle. The coefficient of performance (COP) of this ideal cycle represents the theoretical upper bound of ERC, and it does not contain any information about the properties of working fluids, which is a key cause of the large energy efficiency gap between the actual cycle and the ideal cycle. In this paper, the limiting COP and thermodynamics perfection of subcritical ERC is derived to evaluate the ERC efficiency limit under the constraint of pure working fluids. 15 pure fluids are employed to demonstrate the effects of working fluids on limiting COP and limiting thermodynamics perfection. The limiting COP is expressed as the function of the working fluid thermophysical parameters and the operating temperatures. The thermophysical parameters are the specific entropy increase in the generating process and the slope of the saturated liquid, and the limiting COP increases with these two parameters. The result shows R152a, R141b, and R123 have the best performance, and the limiting thermodynamic perfections at the referenced state are 86.8%, 84.90%, and 83.67%, respectively. [ABSTRACT FROM AUTHOR]

Rankine-based Carnot battery is promising system with outstanding performances in addressing the challenges of local consumption of renewable energy generation and utilization of low-grade waste heat. A suitable working fluid is fundamental to the Rankine-based Carnot battery cycle and profoundly influences system performance. However, studies on working fluid selection for the Rankine-based Carnot battery are limited to a predefined database. This approach fails to study or design novel working fluids. Therefore, the nine molecular groups used as a set of molecular groups in this paper can cover most organic working fluids in Rankine-based thermodynamic cycle systems. Developing an accurate cross-scale model based on the group contribution method is used in working fluid selection for Rankine-based Carnot battery. Meanwhile, for the sake of testing the accuracy of the proposed model, twenty-one promising organic working fluids were selected to be compared and analyzed with the results calculated by the REFPROP under the typical working conditions of the Rankine-based Carnot battery. The results show that the absolute average relative deviation of the boiling temperature prediction using the multiple linear regression model proposed in this study is only 3.9 %, while the absolute average relative deviation of the critical temperature based on the proposed boiling temperature model is 5 %. Finally, the present work demonstrates excellent accuracy in predicting the thermodynamic performance of this system. The absolute average relative deviation of the coefficient of performance, generation efficiency and power-to-power-efficiency is 4.6 %, 2.0 %, and 6.4 %, respectively. [ABSTRACT FROM AUTHOR]

The electro-thermal conversion working mode implies that Carnot batteries have the potential to transform into multi-energy management systems by scheduling and converting different energy vectors according to energy demands. In this paper, a thermodynamic model of Joule-Brayton cycle Carnot battery multi-energy systems is established, based on which two methods of conversion and utilisation of external multi-grade heat and cold are proposed to respond to changes in energy demand. The effects of key parameters such as heat and cold source temperatures, the amount of absorbed heat and cold energy, working fluid mass flow rate and discharge duration on the performance of electricity efficiency, exergy efficiency and coefficient of performance are discussed. The results show that the electricity efficiency of the Carnot battery multi-energy system can be increased to 68.8%–78.0% when the system integrates heat sources only, and to 113.9%–115.2% when the system integrates both heat and cold sources. Additionally, the methods of increasing the working fluid mass flow rate and extending discharge duration allow such systems to integrate with multiple heat and cold sources in combined cooling, heating and power mode. Furthermore, the technical feasibility of such systems is also evaluated for a large energy hub in China, with the coefficient of performance, exergy efficiency and reduced CO 2 emissions rate reaching 119.3%, 85.1% and 94.3 t/h, respectively. The Carnot battery multi-energy system possesses sufficient flexibility in the domain of multi-energy utilisation, demonstrating its potential to evolve into smart energy hubs for cities or districts. • Carnot batteries integrated with multi-grade heat and cold sources are proposed. • Effective approaches to utilise external multi-grade heat and cold are explored. • COP of 128.4% is achieved by integrating with external heat and cold in CCHP mode. • Technical feasibility evaluated for a large energy hub, with COP reaching 119.3%. • Feasibility of developing into future smart energy management systems is discussed. [ABSTRACT FROM AUTHOR]

Recently, pursuing a strategic alternative to traditional fossil fuels has become an important method to meet the increasing energy demands and environmental improvement needs. Polymer electrolyte membrane fuel cells (PEMFCs) can directly convert the chemical energy of fuels into electricity without contamination and the restriction of the Carnot cycle effect. The flow field plate (FFP) is a critical part of a PEMFC that provides mechanical support, conductive medium, the channel of reaction gases, and water and thermal management. However, the complicated mechanisms of the FFP are not very clearly understood since the materials and structures are associated closely with cost, performance, and lifetime. In this paper, different materials and structures are analyzed and their characteristics are summarized. Meanwhile, an opinion was proposed that the porous metal foam flow field will be the most promising development direction in the future, mainly focusing on surface treatment, pattern, and manifold design. [ABSTRACT FROM AUTHOR]

The climate change assessment of the Intergovernmental Panel on Climate change is based on a radiative forcing methodology, and thermodynamic analysis of the climate does not appear to be utilized. Although equivalent to the radiative model, the thermodynamic model captures details of thermodynamic interactions among the earth's subsystems. Carbon dioxide emission returns the net chemical energy exchanged with the climate system to the surface of the earth as heat. The heat is equal to the sum of the heat produced by fossil fuels and deforestation minus the heat of surface greening. Accordingly, trends of climate parameters are calculated. Nearly 51.40% of carbon dioxide production has been sequestered by green matter, and surface greening is approximately 3.0% per decade. Through 2020, the heat removed by surface greening has approached 12.84% of the total heat. Deforestation on the other hand has contributed nearly 22.85% of the total heat of carbon conversion to carbon dioxide. The increase in sea and average land surface air temperatures are 0.80 °C and 1.39 °C, respectively. Present annual sea level rise is nearly 3.35 mm, and the calculated reductions in the temperature and geopotential height of the lower stratosphere are about −0.66 °C and −67.24 m per decade, respectively. Unlike natural sequestration of carbon dioxide, artificial sequestration is not a photosynthetic heat sink process and does not appear to be a viable methodology for mitigating climate change. [ABSTRACT FROM AUTHOR]

In this paper, we have assumed that the thermodynamic pressure may be generated by the negative cosmological constant and the thermodynamic parameters of the n-dimensional asymptotically Anti-de Sitter (AdS)-Tangherlini black holes are identical with the polytropic gas and modified Chaplygin gas separately. The black hole mass, volume, entropy, and temperature have been written due to the assigned gases' thermodynamic system. We found the solutions of Einstein's field equations of n-dimensional black hole for polytropic gas and modified Chaplygin gas. The null energy condition, weak energy condition, strong energy condition, and dominant energy condition have been examined for the fluid sources in n-dimensional black hole system due to both the gases. We found that the four energy conditions completely depend on the model parameters and the dimensions of the spacetime. We have studied the heat engine phenomena for both the black holes and analyzed the work done with the efficiencies due to the Carnot and other cycles. [ABSTRACT FROM AUTHOR]

This paper focuses on the thermodynamic comparison between pure supercritical Carbon Dioxide and blended transcritical Carbon Dioxide power cycles by means of a thorough exergy analysis, considering exergy efficiency, exergy destruction and efficiency losses from Carnot cycle as main figures of merit. A reference power plant based on a steam Rankine cycle and representative of the state-of-the-art (SoA) of Concentrated Solar Power (CSP) plants is selected as base-case. Two different temperatures of the energy (heat) source are considered: 575 °C (SoA) and 725 °C (next generation CSP). Compared to SoA Rankine cycles, CO 2 blends enable cycle exergy efficiency gains up to 2.7 percentage points at 575 °C. At 725 °C, they outperform both SoA and pure CO 2 cycles with exergy efficiencies up to 75.3%. This performance is brought by a significant reduction in the exergy destruction across the compression and heat rejection process rounding 50%. Additionally, it has been found that the internal condensation occurring inside the heat recuperator for those mixtures with a large temperature glide improves recuperator exergy efficiency, supporting the use of simpler layouts without split-compression. Finally, CO 2 blends exhibit lower cycle exergy efficiency degradation than pure sCO 2 in the event of an increase in the design ambient temperature. • CO 2 mixtures enable exergy efficiencies up to 75% at high ambient temperatures. • CO 2 mixtures outperform both SoA steam-Rankine and pure sCO 2 technologies. • Exergy efficiency is significantly enhanced by WF condensation in the recuperator. • Maximum cycle pressure level beyond 250 bar are found to be of scarce interest. [ABSTRACT FROM AUTHOR]

A model for tropical cyclone (TC) potential size (PS), which is capable of predicting the equilibrium outer radius of a TC solely from environmental parameters, is proposed. The model combines an updated Carnot cycle model with a physical model for the wind profile, which serve as energetic and dynamic constraints, respectively, on the minimum pressure. Physically, the Carnot cycle model defines how much the surface pressure can be dropped energetically, and the wind profile model defines how large the steady-state storm needs to be to yield that pressure drop for a given maximum wind speed. The model yields an intrinsic length scale VCarnot/f, with f the Coriolis parameter, VCarnot similar to the potential intensity Vp, but without a dependence on the surface exchange coefficients of enthalpy Ck and momentum Cd. Analytic tests with the theory varying outflow temperature, sea surface temperature (SST), and f demonstrate that the model predictions are qualitatively consistent with the Vp/f scaling for outer size found in past work. The model also predicts a weak dependence of outer size on Cd, Ck, and horizontal mixing length lh of turbulence, consistent with numerical simulation results. Idealized numerical simulation experiments with varied tropopause temperature, SST, f, Cd, Ck, and lh show that the model performs well in predicting the simulated outer radius. The VCarnot/f scaling also better captures the dependence of simulated TC size on SST than Vp/f. Overall, the model appears to capture the essential physics that determine equilibrium TC size on the f plane. [ABSTRACT FROM AUTHOR]

Power plants constitute the main sources of electricity production, and the calculation of their efficiency is a critical factor that is needed in energy studies. The efficiency improvement of power plants through the optimization of the cycle is a critical means of reducing fuel consumption and leading to more sustainable designs. The goal of the present work is the development of semi-empirical models for estimating the thermodynamic efficiency of power cycles. The developed model uses only the lower and the high operating temperature levels, which makes it flexible and easily applicable. The final expression is found by using the literature data for different power cycles, named as: organic Rankine cycles, water-steam Rankine cycles, gas turbines, combined cycles and Stirling engines. According to the results, the real operation of the different cases was found to be a bit lower compared to the respective endoreversible cycle. Specifically, the present global model indicates that the thermodynamic efficiency is a function of the temperature ratio (low cycle temperature to high cycle temperature). The suggested equation can be exploited as a quick and accurate tool for calculating the thermodynamic efficiency of power plants by using the operating temperature levels. Moreover, separate equations are provided for all of the examined thermodynamic cycles.

The neural systems' electric activities are fundamental for the phenomenology of consciousness. Sensory perception triggers an information/energy exchange with the environment, but the brain's recurrent activations maintain a resting state with constant parameters. Therefore, perception forms a closed thermodynamic cycle. In physics, the Carnot engine is an ideal thermodynamic cycle that converts heat from a hot reservoir into work, or inversely, requires work to transfer heat from a low- to a high-temperature reservoir (the reversed Carnot cycle). We analyze the high entropy brain by the endothermic reversed Carnot cycle. Its irreversible activations provide temporal directionality for future orientation. A flexible transfer between neural states inspires openness and creativity. In contrast, the low entropy resting state parallels reversible activations, which impose past focus via repetitive thinking, remorse, and regret. The exothermic Carnot cycle degrades mental energy. Therefore, the brain's energy/information balance formulates motivation, sensed as position or negative emotions. Our work provides an analytical perspective of positive and negative emotions and spontaneous behavior from the free energy principle. Furthermore, electrical activities, thoughts, and beliefs lend themselves to a temporal organization, an orthogonal condition to physical systems. Here, we suggest that an experimental validation of the thermodynamic origin of emotions might inspire better treatment options for mental diseases. [ABSTRACT FROM AUTHOR]

We consider the charged d-dimensional black holes in the cavity in extended phase space and investigate the heat engine and the Joule-Thomson (JT) expansion. Since the phase structure of black holes in the cavity is similar to anti-de-sitter (AdS) cases, we take black holes in a cavity as the working substance in the heat engine and calculate their efficiency in Carnot cycle and rectangular cycle. Also, we discuss whether the JT expansion of charged black holes in the cavity is consistent with AdS cases and find the charged black hole in a cavity always cools down during the isenthalpic process with the decreasing pressure. [ABSTRACT FROM AUTHOR]

This comprehensive treatise is written for the special occasion of the author’s 70th birthday. It presents his lifelong endeavors and reflections with original reasoning and re-interpretations of the most critical and sometimes misleading issues in thermodynamics—since now, we have the advantage to look at the historical developments more comprehensively and objectively than the pioneers. Starting from Carnot (grand-father of thermodynamics to become) to Kelvin and Clausius (fathers of thermodynamics), and other followers, the most relevant issues are critically examined and put in historical and contemporary perspective. From the original reasoning of generalized “energy forcing and displacement” to the logical proofs of several fundamental laws, to the ubiquity of thermal motion and heat, and the indestructibility of entropy, including the new concept of “thermal roughness” and “inevitability of dissipative irreversibility,” to dissecting “Carnot true reversible-equivalency” and the critical concept of “thermal-transformer,” limited by the newly generalized “Carnot-Clausius heat-work reversible-equivalency (CCHWRE),” regarding the inter-complementarity of heat and work, and to demonstrating “No Hope” for the “Challengers” of the Second Law of thermodynamics, among others, are offered. It is hoped that the novel contributions presented here will enlighten better comprehension and resolve some of the fundamental issues, as well as promote collaboration and future progress.

A solar hybrid CCHP (combination of cooling, heating and power) system was proposed to organically integrate the Brayton and reverse Carnot cycle by trans -critical CO 2 working medium. The transient thermal storage in a solar hybrid CCHP system (SCCHP) was designed to overcome the energy coupling challenges in regions rich in solar and gas resources. Moreover, the incorporation of an optimally efficient throttling expander in cooling cycle was designed to enhance energy utilization efficiency. The thermodynamic performance of the SCCHP system was systematically evaluated by comparing with the ejector hybrid CCHP system from energetic, exergetic, and economic perspectives. The results suggest that elevating the intake pressure of both the high-pressure compressor from 5.2 kW to 6.4 kW and turbine from 7.3 kW to 7.8 kW, led to an enhancement in the COP of the SCCHP system. Moreover, raising the turbine intake temperatures from 483.15 K to 503.15 K yielded a significant improvement in system energy efficiency from 0.66 to 0.71 and COP from 1.58 to 1.72. Furthermore, in contrast to the ECHP system, the components in the SCCHP system demonstrated not only less exergy efficiency variation to the influence of ambient temperature but also lower hourly economic costs. The SCCHP has an average hourly investment cost that is 5.70 USD (kgh)−1 lower than ECHP, and its economic efficiency improves with higher ambient temperatures. [ABSTRACT FROM AUTHOR]

• Thermodynamic cycle with isothermal expansion. • Isothermal nozzles: theory and design. • Simulation and experimental studies on nozzles with isothermal expansion. • Innovative gas isothermal turbine: design, simulation calculations and experimental studies. The efficiency of power plants with steam or gas turbines depends on the efficiencies of a thermodynamic cycle and devices implementing this cycle. In the case of high power outputs, we cannot expect a significant increase in the efficiency of individual devices. Therefore, what remains is to increase the efficiency of the implemented thermodynamic cycle − the complex Rankine cycle in the case of steam turbines or the extended Brayton cycle in gas turbine units. The efficiencies of these cycles depend on the hot reservoir temperatures, limited by the materials used. The solution seems to be the thermodynamic cycles with the highest efficiency within given temperature limits, the „generalized Carnot cycles". About gas turbines, such a cycle is the Ericsson cycle. The most difficult element of this cycle is carrying out high-temperature expansion. So far, there is no literature data on a technical device implementing this process. In this article, we present a method for designing turbine nozzles for isothermal expansion and the results of experimental tests of the first isothermal turbine. In the case of gas microturbines with a regenerator, isothermal expansion can increase efficiency from 24% to 28% up to 36%. An increase in efficiency of several to a dozen percentage points is expected for Organic Rankine Cycle (ORC) turbines. Due to such significant increases in energy generation efficiency, an isothermal turbine may become a future solution for energy systems. [ABSTRACT FROM AUTHOR]

Efficient engine technologies to convert low-grade heat to electricity are urgently desired. In this work, a conceptual structure of engine for a novel cycle or one-way oscillating flow cycle (OOFC), which consists of two isochoric and two adiabatic processes, is described for low-grade heat utilization. Characteristics of OOFC allows for the working fluid temperature glide to be matched to the decrease in temperature of low-grade heat. Then, thermodynamic model is developed for evaluating the performance. Theoretical simulation results show that maximum specific output works are in the range of 12.2 kJ kg−1 – 79.7 kJ kg−1. Compared to Stirling cycle system, maximum specific output work in OOFC system could be improved by 16.2 %–24.8 %. Compared to ideal Carnot cycle engine system, maximum specific output works in OOFC system is nearly the same and 1.8 %–2.6 % lower. As Carnot cycle engine is ideal while thermodynamic cycle loss and heat transfer loss in cold heat exchangers are considered in OOFC engine, the ratios of maximum specific output work demonstrate that OOFC system could be very promising for low-grade heat utilization as a result of well-matched temperature profile in hot heat exchanger. • Structure of OOFC engine with temperature glide heat addition is described. • Large temperature glide heat rejection is achieved in OOFC engine. • Maximum specific output work of OOFC system is 116 %–125 % of Stirling cycle system. • Maximum specific output work in OOFC system are equivalent to ideal Carnot cycle system. • OOFC engine has well-matched temperature profile for low-grade heat utilization. [ABSTRACT FROM AUTHOR]

In the proposed work, the MATLAB program was used to model and simulate the performance of the investigated two-stage adsorption chiller with and without heat recovery using an activated carbon/methanol pair. The simulated model results were then validated by the experimental results conducted by Millennium Industries. The model was based on 10th order differential equations; six of them were used to predict bed, evaporator and condenser temperatures while the other four equations were used to calculate the adsorption isotherm and adsorption kinetics. The detailed validation is stated in the next paragraphs; for example, it clearly notes that the simulation model results for the two-stage air cooled chiller are well compared with the experimental data in terms of cooling capacity (6.7 kW for the model compared with 6.14 kW from the experimental results at the same conditions). The Coefficient of Performance (COP) predicted by this simulation was 0.4, which is very close to that given by the Carnot cycle working at the same operating conditions. The model optimized the switching time, adsorption/desorption time and heat recovery time to maximize both cooling capacity and COP. The model optimized the adsorption/desorption cycle time (300 to 400 s), switching cycle time (50 s) and heat recovery cycle time (30 s). The temporal history of bed, evaporator and condenser temperatures is provided by this model for both heat recovery and without heat recovery chiller operation modes. The importance of this study is that it will be used as a basis for future series production. [ABSTRACT FROM AUTHOR]