Heat Engine Cycle Research Articles

Comparison with Carnot battery of an alternate thermal electricity storage charged by concentrated photovoltaic thermal system and resistance heater

In Carnot Batteries (pumped thermal electricity storage), which is known as a low-cost electricity storage method, electrical energy is stored as thermal energy and then converted back into electrical energy using a heat pump and a heat engine, respectively. In the studies carried out to date, different heat source scenarios, heat storage methods, and methods to improve heat pump and heat engine cycles have been applied to increase efficiency and reduce the cost of the Carnot Battery. This study’s novelty was using a concentrated photovoltaic thermal system and resistance heaters instead of a heat pump for the charge cycle in thermal electricity storage. This novel thermal electricity storage design aimed to reduce the levelized cost of storage of the system by eliminating the need for a heat pump and reducing the volume of the water storage tank. First, parametric analyses were performed for the specific variables of both energy storage systems. Afterward, the Carnot Battery and the proposed system were compared for the same electricity storage capacity. For charge/discharge times ranging from 4 h to 8 h and electricity storage capacities ranging from 0.5 MW to 2 MW, a 31.8 % to 58 % increase in round-trip efficiency and a 7.13 % to 20.67 % decrease in levelized cost of energy storage were achieved with the novel design.

Thermodynamic Pathways of Vertical Wind Shear Impacting Tropical Cyclone Intensity Change: Energetics and Lagrangian Analysis

Abstract This study analyzes the variations in the thermodynamic cycle and energy of a tropical cyclone (TC) under the influence of vertical wind shear (VWS), exploring the possible thermodynamic pathways through which VWS affects TC intensity. The maximum energy harnessed by the TC diminishes alongside a decrease in storm intensity in the presence of VWS. In the sheared TC, the ascending branch of the thermodynamic cycles of TC shifts toward lower entropy, which is related to the reduction in entropy in the eyewall and/or the increase in entropy and enhanced upward motion outside the eyewall. Moreover, the descending leg shifts toward higher entropy due to the increase in entropy and weakening of downward motion in both the ambient environment and the upper troposphere. These changes in the ascending and descending branches could reduce the work done by the heat engine cycle, with the former playing a primary role in the presence of VWS. Given that the ascending branch is influenced by the eyewall and the rainbands outside the eyewall under VWS, the thermodynamic pathways could be categorized into inner ventilation and outer ventilation based on the location of their roles. The pathways associated with inner ventilation primarily reduce the entropy in the eyewall. In addition to the conventional low- and midlevel ventilation, the inner ventilation also encompasses new pathways entering the midlevel eyewall after descending from the upper level and ascending from the boundary layer. Conversely, the pathways of outer ventilation are related to the increase in the entropy outside the eyewall. These include the ascent of high-entropy air to the middle and upper troposphere related to the inner and outer rainbands, the outward advection of high-entropy air from the eyewall in the midlevel and upper level, and air warming by the descending draft from the upper- to midlevel troposphere. These insights contribute to a nuanced understanding of the sophisticated interactions within TCs and their response to VWS. Significance Statement Vertical wind shear (VWS) is known to modify the thermodynamic structure of tropical cyclones (TCs), thereby affecting their development. The incorporation of multiple thermodynamic mechanisms amplifies the complexity of related studies and predictions. Within the context of a unified heat engine framework, this study aims to paint a relatively comprehensive picture of the key thermodynamic pathways through which VWS impacts the intensity of TCs. Contrary to previous studies, we emphasize the increase in entropy and the intensified upward motion outside the eyewall, which play pivotal roles in diminishing the intensity of TCs in the presence of VWS. Gaining an understanding of these critical mechanisms and structural changes offers insights and guidance that can enhance the prediction of sheared TCs.

Design and analysis of an ideal scramjet flowpath

The current work presents a novel conceptual framework for the fluid and gasdynamics that govern the design and performance of an ideal scramjet flowpath. These include a theoretical comparison between ram and scram modes, the physics of thrust loss during inlet unstart, and the design of an optimal scramjet flowpath. We present a unique explicit, closed-form relation for the wall divergence of an ideal scramjet combustor. The accompanying derivations and discussions, which leverage this formulation, seek to address uncertainties and misconceptions regarding the dominant fluid processes present in these engines. It is shown that scram and ram modes exhibit theoretical similitude for maximum thrust potential at conditions beyond the one-dimensional Rayleigh choking limit but can diverge below the global choking threshold. Additionally, it is shown that even for an ideal scramjet heat engine cycle, thermodynamic efficiencies at various flight conditions deviate from those of the classical Brayton cycle. These insights and accompanying theoretical analyses are meant to establish a foundation for the thermodynamics and gasdynamics relevant to the performance of dual-mode scramjet engines. The resulting work offers an intuitive technical perspective on supersonic combustion and the fundamentals of dual-mode scramjet operation that can be applied across a wide range of scramjet-related experimental and computational studies and design efforts in the future.

Exact simulation of classical heat engine cycles using single-ion phonon laser

Heat engines are essential devices in modern industry, converting heat energy into useful mechanical work via their working substances. Here we experimentally simulate the conventional heat engine by employing the vibrational mode of a single trapped ion as the working substance. In contrast to simply employing the ion in thermal motion, we consider coherently stimulating the ion’s vibrational motion as the phonon laser, which helps acquire clearer results by effectively suppressing the thermal fluctuation. As such, we demonstrate in an exact and high signal-to-noise way the standard steps of both the Otto and Carnot cycles in a single ion, and compare their maximum efficiencies by monitoring the amplitude and frequency of the vibration. Our work witnesses an interesting single-atom thermal engine using coherently controlled phonons. It would be the smallest platform for simulating or demonstrating classical thermodynamic laws and phenomena at a single ion scale via optical manipulation techniques for phonon lasers.

Multi-objective optimization of an endoreversible closed Atkinson cycle

Abstract Based on finite-time-thermodynamic theory and the model established in previous literature, the multi-objective optimization analysis for an endoreversible closed Atkinson cycle is conducted through using the NSGA-II algorithm. With the final state point temperature (T 2) of cycle compression process as the optimization variable and the thermal efficiency (η), the dimensionless efficient power ( E ̄ P ${\bar{E}}_{P}$ ), the dimensionless ecological function ( E ̄ $\bar{E}$ ) and the dimensionless power ( P ̄ $\bar{P}$ ) as the optimization objectives, the influences of T 2 on the four optimization objectives are analyzed, multi-objective optimization analyses of single-, two-, three- and four-objective are conducted, and the optimal cycle optimization objective combination is chosen by using three decision-making methods which include LINMAP, TOPSIS, and Shannon Entropy. The result shows that when four-objective optimization is conducted, with the ascent of T 2, P ̄ $\bar{P}$ descends, η ascends, both E ̄ $\bar{E}$ and E ̄ P ${\bar{E}}_{P}$ firstly ascend and then descend. In this situation, the deviation index is the smallest and equals to 0.2657 under the decision-making method of Shannon Entropy, so its optimization result is the optimal. The multi-objective optimization results are able to provide certain guidelines for the design of practical closed Atkinson cycle heat engine.

An Adsorption-Desorption Heat Engine for Power Generation from Waste Heat

According to the United States Department of Energy, waste heat recovery would allow up to a 20% reduction in greenhouse gases (GHG) emission. Most of the waste energy is discharged as a low-grade heat at temperatures less than 250°C. Therefore, the development of new technologies and the enhancement of existing ones to convert low-grade heat into electrical or mechanical energy are of great importance. The working principle of adsorption-desorption heat pumps with cyclic switching between adsorption and desorption is adapted in the proposed heat engine to generate electrical power from low-temperature heat. Thermodynamic analysis of the heat engine cycle is carried out for the pair adsorbant-adsorbent: CO<sub>2</sub>-activated carbon. Its efficiencies are calculated accepting the ideal gas law and an adsorption-desorption equilibrium at the key points of the cycle. The cycle consists of two isochores and two isotherms like the Stirling engine, but at the same temperature range and without heat regeneration, its thermal efficiency (work per heat supplied) can reach 11.3% vs. 5.0% and specific work 50.7 vs. 3.55 in the latter. The proposed unit has thermal efficiency in the range of Organic Rankine Cycle units and can be utilized in small-scale applications up to 40kWe, where manufacturing cost of turbines or expanders for ORCs increases dramatically. Accounting for quality (temperature) of utilized heat, the proposed cycle’s exergy efficiency, <em>ζ<sub>ex</sub></em> = 34.5% approaches that of water-steam Rankine cycles utilizing natural gas or coal combustion.

Compression Characteristics of Liquid Ring Compressors With Fixed and Freely Rotating Casings

Abstract Liquid ring compressors (LRC) are used for a wide range of compression and vacuum applications, including corrosive or flammable gases for which other compression technologies may not be feasible. The presence of a surrounding liquid ring may offer the possibility of polytropic compression due to incremental heat loss to the liquid. This aspect may play a critical role in compression (and expansion) processes of heat engine cycles toward approaching the targeted Carnot efficiencies. To date, published research addressing the physical phenomena behind LRC is highly limited. Experimentally studying these machines will result in a demonstration of aggregate performance. In order to improve our understanding of LRC with and without freely rotating casings and to be able to analyze the complex inner workings, a numerical approach using computational fluid dynamics (CFD) tools, supported by available experimental data for validation purposes, has been established. Physical parameters such as water–air interface, temperature, pressure, entropy production, vorticity, and shear strain rate are presented for a baseline geometry taken from the open literature. Finally, temperature-entropy paths and isothermal and isentropic efficiencies are presented. The significant performance gain from the freely rotating casing is highlighted. Detailed results present insights into work addition processes of such machines.

Construction of a quantum Stirling engine cycle tuned by dynamic-angle spinning

In this contribution, we investigate two coupled spins as a working substance of the quantum Stirling heat engine cycle. We propose an experimentally implementable scheme in which the cycle is driven by tuning the dipole-dipole interaction angle via a dynamic-angle spinning technique under a magnetic field. Realistic parameters are chosen for the proposed heat engine cycle. In addition, our goal is to calculate the power of the engine. To this end, we focus on the microdynamics of the quantum isothermal process to predict the required-time per engine cycle. The obtained results show that the engine has high efficiency. Furthermore, the engine attains maximum power at the same point where the maximum efficiency is satisfied.

Magnetocaloric and electrocaloric heat engine and refrigeration cycles in the open Fermi-Hubbard optical dimer with attractive interactions

Quantum heat engines and refrigerators can be realized in a Fermi-Hubbard optical dimer through immersion in a mean-field Fermi gas bath using the magnetocaloric and electrocaloric effects. It is demonstrated that in the presence of onsite and heat bath-induced attractive interactions, singlet-to-triplet transitions are achieved with a finite external magnetic field. Similarly, triplet-to-singlet transitions occur in the presence of an applied finite electric field. Results show that to lift the degeneracies, considerable electric potential magnitudes are needed. These magnitudes are greater than the magnetic potential strengths where the degeneracies occur. Furthermore, in the attractive regime, combinations of direct and inverse caloric effects can be combined to operate quantum heat engines and refrigerators, like what happens in the repulsive regime.

Applying the Action Principle of Classical Mechanics to the Thermodynamics of the Troposphere

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.

Finite-time thermodynamic and economic analysis of Rankine Carnot battery based on life-cycle method

Rankine Carnot battery (R-CB) has a great potential in renewable energy-to-grid integration, and the theoretical thermodynamic performance is inaccurate because of the dynamic heat transfer processes and system performance. In this paper, an R-CB system consisting of a heat pump, a heat engine cycle, and a sensible heat storage tank was established. The finite-time thermodynamic model considering the irreversible loss of energy transfer and conversion processes was proposed. Based on the combination of finite-time thermodynamic model and life-cycle method, the levelized cost of energy storage model was established for the combination of economic and energy performance. Furthermore, evaporation temperature, heat storage temperature, temperature difference of shared heat exchanger, and shared heat transfer area were adopted as main variables to conduct the global optimization and parametric analysis of the system. The simulation is based on an R-CB system with a storage capacity of 10 MW/6h, and the results showed the optimized system roundtrip efficiency was 78.1%, and the levelized cost of storage (LCOS) was 0.329 $/kWh with an evaporation temperature of 100 ℃. The roundtrip efficiency increased from 25.6% to 78.1% with the evaporation temperature rising from 60 to 100 ℃, while LCOS decreased by 45.8 %. Reducing the highest heat storage temperature effectively increased the roundtrip efficiency and reduced the heat storage cost, while decreasing the LCOS. The increase in roundtrip efficiency, which was obtained by reducing the shared heat exchange temperature difference and increasing the shared heat transfer area, was the primary factor in reducing the LCOS. The combination of finite-time thermodynamics and the life-cycle method in this paper may provide a more realistic evaluation approach for measuring the technical and economic potential of R-CB systems.

Experimental test of power-efficiency trade-off in a finite-time Carnot cycle.

The Carnot cycle is a prototype of an ideal heat engine cycle to draw mechanical energy from the heat flux between two thermal baths with the maximum efficiency, dubbed as the Carnot efficiency η_{C}. Such efficiency is reached by thermodynamical equilibrium processes with infinite time, accompanied unavoidably with vanishing power-energy output per unit time. The quest to acquire high power leads to an open question of whether a fundamental maximum efficiency exists for finite-time heat engines with given power. We experimentally implement a finite-time Carnot cycle with sealed dry air as a working substance and verify the existence of a trade-off relation between power and efficiency. Efficiency up to (0.524±0.034)η_{C} is reached for the engine to generate the maximum power, consistent with the theoretical prediction η_{C}/2. Our experimental setup shall provide a platform for studying finite-time thermodynamics consisting of nonequilibrium processes.

Enhancement of Quantum Heat Engine by Encircling a Liouvillian Exceptional Point.

Quantum heat engines are expected to outperform the classical counterparts due to quantum coherences involved. Here we experimentally execute a single-ion quantum heat engine and demonstrate, for the first time, the dynamics and the enhanced performance of the heat engine originating from the Liouvillian exceptional points (LEPs). In addition to the topological effects related to LEPs, we focus on thermodynamic effects, which can be understood by the Landau-Zener-Stückelberg process under decoherence. We witness a positive net work from the quantum heat engine if the heat engine cycle dynamically encircles a LEP. Further investigation reveals that a larger net work is done when the system is operated closer to the LEP. We attribute the enhanced performance of the quantum heat engine to the Landau-Zener-Stückelberg process, enabled by the eigenenergy landscape in the vicinity of the LEP, and the exceptional point-induced topological transition. Therefore, our results open new possibilities toward LEP-enabled control of quantum heat engines and of thermodynamic processes in open quantum systems.

Dynamic performance for discharging process of pumped thermal electricity storage with reversible Brayton cycle

Pumped thermal electricity storage (PTES) is suitable for large-scale energy storage applications because of its low cost and no geographical constraints. In this study, the performance of PTES system for adjusting the net power output of the heat engine cycle to meet the load demand variation, is investigated. Based on the off-design condition models of turbomachinery and heat exchangers, the heat engine cycle dynamic model of a 5 MW PTES system is established. The disturbance simulation of the user-side load is carried out, and the dynamic response results are obtained. The inventory control strategy of working fluid is proposed to control the net power output to follow the variations of the load demand. The traditional PI controller is used in the two control processes of 50% ramp-down in load demand and a typical day load demand in Zhangbei District of north China. The results indicate that the net power output of the heat engine cycle can follow the variation of load demand in time. With the inventory control strategy, the heat engine cycle mode of PTES system can adjust the net power output to meet changes in load demand.

Heat Transfer Enhancement in Stirling Engines Using Fins with Different Configurations and Air Flow

The Stirling engine, in comparison to other classical engines, is an external enclosed heat engine cycle with extraordinary theoretical efficiency and minimal emissions. However, when combined with a minor heat source, the productivity of the Stirling engine suffers. Thus, this study emphasizes research on improving engine performance using heat transfer. A simulation was done using CFD analysis in ANSYS Fluent to enhance heat transfer using different types of fins, air blowers, and roughness. κ-ω SST model was used as the turbulence model to capture the heat transfer behavior near and away from the surface. All runs showed a higher heat transfer rate per unit area than the no finned case. Increasing the number of fins reduces the heat transfer by 10 %, Applying this solution would cost more since more material is needed to decrease the gap between fins. When doubling the length of the fin, the heat transfer of the circular design was reduced by 1%, the pinned design by 5%, and the squared design by 30%. The addition of fins reduced the flow of heat to the cold end and kept the temperature near the cold end below 100°C. Increasing the roughness resulted in a small increase in heat flow. Comparing the laminar flow to the transitional flow, the transitional flow increases the heat transfer by 1000%.

Four-Objective Optimization of an Irreversible Stirling Heat Engine with Linear Phenomenological Heat-Transfer Law.

This paper combines the mechanical efficiency theory and finite time thermodynamic theory to perform optimization on an irreversible Stirling heat-engine cycle, in which heat transfer between working fluid and heat reservoir obeys linear phenomenological heat-transfer law. There are mechanical losses, as well as heat leakage, thermal resistance, and regeneration loss. We treated temperature ratio of working fluid and volume compression ratio as optimization variables, and used the NSGA-II algorithm to carry out multi-objective optimization on four optimization objectives, namely, dimensionless shaft power output , braking thermal efficiency , dimensionless efficient power and dimensionless power density . The optimal solutions of four-, three-, two-, and single-objective optimizations are reached by selecting the minimum deviation indexes with the three decision-making strategies, namely, TOPSIS, LINMAP, and Shannon Entropy. The optimization results show that the reached by TOPSIS and LINMAP strategies are both 0.1683 and better than the Shannon Entropy strategy for four-objective optimization, while the s reached for single-objective optimizations at maximum , , , and conditions are 0.1978, 0.8624, 0.3319, and 0.3032, which are all bigger than 0.1683. This indicates that multi-objective optimization results are better when choosing appropriate decision-making strategies.

Heat Engine Cycle Configurations for Maximum Work Output with Generalized Models of Reservoir Thermal Capacity and Heat Resistance

Abstract A class of two finite-heat-reservoir endoreversible heat engine with the generalized models of both the reservoir thermal capacities and heat resistances is investigated. The optimality condition for cycle maximum work output is derived by applying optimal control theory, and impacts of both thermal capacity characteristics of heat reservoirs and heat transfer laws on the optimal configurations are discussed. The results obtained in some previous researches are special cases of those obtained herein, which can provide some guidelines for optimal design of actual heat engines.

Second Law for Active Heat Engines

Macroscopic cyclic heat engines have been a major motivation for the emergence of thermodynamics. In the last decade, cyclic heat engines that have large fluctuations and operate at finite time were studied within the more modern framework of stochastic thermodynamics. The second law for such heat engines states that the efficiency cannot be larger than the Carnot efficiency. The concept of cyclic active heat engines for a system in the presence of hidden dissipative degrees of freedom, also known as a nonequilibrium or active reservoir, has also been studied in theory and experiment. Such active engines show rather interesting behavior such as an ``efficiency'' larger than the Carnot bound. They are also likely to play an important role in future developments, given the ubiquitous presence of active media. However, a general second law for cyclic active heat engines has been lacking so far. Here, upon using a known inequality in stochastic stochastic thermodynamics for the excess entropy, we obtain a general second law for active heat engines, which does not involve the energy dissipation of the hidden degrees of freedom and is expressed in terms of quantities that can be measured directly from the observable degrees of freedom. Besides heat and work, our second law contains an information-theoretic term, which allows an active heat engine to extract work beyond the limits valid for a passive heat engine. To obtain a second law expressed in terms of observable variables in the presence of hidden degrees of freedom we introduce a coarse-grained excess entropy and prove a fluctuation theorem for this quantity.

Optimal linear cyclic quantum heat engines cannot benefit from strong coupling.

Uncovering whether strong system-bath coupling can be an advantageous operation resource for energy conversion can facilitate the development of efficient quantum heat engines (QHEs). Yet, a consensus on this ongoing debate is still lacking owing to challenges arising from treating strong couplings. Here, we conclude the debate for optimal linear cyclic QHEs operated under a small temperature difference by revealing the detrimental role of strong system-bath coupling in their optimal operations. We analytically demonstrate that both the efficiency at maximum power and maximum efficiency of strong-coupling linear cyclic QHEs are upper bounded by their weak-coupling counterparts with the same degree of time-reversal symmetry breaking. Under strong time-reversal symmetry breaking, we further reveal a quadratic suppression of the optimal efficiencies relative to the Carnot limit when away from the weak-coupling regime, along with a quadratic enhancement of the mean entropy production rate.

Optimization of asymmetric quantum Otto engine cycles

We consider the optimization of the work output and fluctuations of a finite-time quantum Otto heat engine cycle consisting of compression and expansion work strokes of unequal duration. The asymmetry of the cycle is characterized by a parameter r_{u} giving the ratio of the times for the compression and expansion work strokes. For such an asymmetric quantum Otto engine cycle, with working substance chosen as a harmonic oscillator or a two-level system, we find that the optimal values of r_{u} maximizing the work output and the reliability (defined as the ratio of average work output to its standard deviation) shows discontinuities as a function of the total time taken for the cycle. Moreover we identify cycles of some specific duration where both the work output and the reliability take their largest values for the same value of the asymmetry parameter r_{u}.