Efficiency Of Heat Engine Research Articles

The heat engine of magnetic black holes in AdS space with rational nonlinear electrodynamics

The heat engine of magnetic black holes in Einstein-AdS gravity coupled to rational nonlinear electrodynamics, as the working substance, is studied. The dynamical negative cosmological constant is considered as a thermodynamic pressure. We investigate the efficiency of black hole heat engines in extended space thermodynamics for rectangle closed path in the P−V plane and the maximally efficient Carnot cycles. The exact efficiency formula which is written in terms of the mass of the black hole is obtained. It was demonstrated that the black hole efficiency decreases when the nonlinear electrodynamics coupling increases and the black hole efficiency increases if the magnetic charge increases. The relation between the efficiency, event horizon radiuses (entropy) and pressure is obtained. We study an efficiency of the holographic heat engine of a cycle in the vicinity of a critical point. Thus, the heat engine of our model can produce work.

Heat engine efficiency for four-dimensional charged AdS black holes in Rastall gravity

In this paper, we analyze the [Formula: see text] criticality and the heat engine efficiency of two black holes, one is the four-dimensional charged AdS black hole in Rastall gravity and the other is the four-dimensional charged AdS black hole surrounded by quintessence in Rastall gravity. For the four-dimensional charged AdS black hole in Rastall gravity, the ratio [Formula: see text] is related to the Rastall parameter [Formula: see text]. When [Formula: see text] the ratio becomes [Formula: see text], which is same as the van der Waals liquid-gas system. Additionally, as the Rastall parameter [Formula: see text] increases, the heat engine efficiency [Formula: see text] of the black hole will increase. Moreover, the efficiency [Formula: see text] decreases rapidly at first and then increases with the entropy [Formula: see text]. But the efficiency ratio [Formula: see text] decreases with the Rastall parameter [Formula: see text]. For the four-dimensional charged AdS black hole surrounded by quintessence in Rastall gravity, as the charge q increases, the critical specific volume [Formula: see text] and the efficiency ratio [Formula: see text] also increase, however, the critical temperature [Formula: see text] and the critical pressure [Formula: see text] gradually decrease. Moreover, the heat engine efficiency [Formula: see text] and the efficiency ratio [Formula: see text] of the black hole are similar to the four-dimensional charged AdS black hole in Rastall gravity.

A quantum otto heat engine driven by three quantum dots

A quantum heat engine composed of three coupled quantum dots as a working substance is proposed. Since quantum dots naturally obey the Fermi Hubbard Hamiltonian, the strong coupling interaction regime allows the working substance to be evaluated under an effective Heisenberg Hamiltonian. Indeed, the influence of the strength coupling, between the three dots, on quantum machine efficiency and work in the presence of a homogeneous magnetic field is also examined. Furthermore, the influence of entanglement on the efficiency & work of the quantum dot Otto heat engine is well analyzed. As a tripartite working substance, we are interested in analyzing the local work and efficiency associated with each single and pair of quantum dots. The results show that the local efficiency associated with a pair of quantum dots achieves a maximum value, unlike the global efficiency. Indeed, the entanglement impact on Global/local work is studied.

Improving performance of quantum heat engines using modified Otto cycle

The efficiency of a quantum heat engine is maximum when the unitary strokes of the quantum Otto cycle are adiabatic. On the other hand, this may not be always possible due to small energy gaps in the system, especially at the critical point (CP) where the gap between the ground state and the first excited state vanishes and the system gets excited. With the aim to regain this lost adiabaticity, we modify one of the unitary strokes of the Otto cycle by allowing the system to first evolve with a time dependent Hamiltonian as in the case of a usual Otto cycle, followed by an additional evolution with a different time independent Hamiltonian so that the system reaches a less excited state. This will help in increasing the magnitude of the heat absorbed from the hot bath so that the work output and efficiency of the engine can be increased. We demonstrate this method using an integrable model and a non-integrable model as the working medium and discuss the generality and limitations of this method. In the case of a two spin system, the optimal value for the time till which the system needs to be freely evolved is calculated analytically in the adiabatic limit. The results show that implementing this modified unitary stroke significantly improves the work output and efficiency of the engine, especially when it crosses the CP.

Reverse osmosis-based water treatment for green hydrogen production

We analyze the use of excess natural gas (currently flared/vented) to instead treat oilfield-produced water via reverse osmosis (RO) to generate ultrapure electrolysis-grade water (Total Dissolved Solids (TDS): 0.028‐0.5 ppm) for green hydrogen production. We combine an analytical ε-MTU model and CPavg model to predict average permeate concentration, to obtain improved estimates of electrolysis-grade water production from RO systems. The theoretical upper limit of the recovery of a RO system (similar to Carnot efficiency of heat engines) is established. Analysis is conducted for conditions corresponding to Niobrara Shale field (TDS: 29.1 g/L), as well as for brackish water (TDS: 5-15 g/kg) and seawater (TDS: 35–45 g/kg) feeds. Results show that electrolysis-grade water production can be as high as 0.75 m3 per cubic meter of water treated, with 1.38 m3 of natural gas providing the required energy. This translates to hydrogen production of 74.6 kg per cubic meter of produced water treated. Relatively low volumes of gas can treat large water volumes (<4 % of excess gas in Niobrara Shale can treat the entire quantity of produced water). These numbers highlight the benefits of our approach of utilizing two waste streams to create a high-value commodity, critical for decarbonization.

Efficiency of a microscopic heat engine subjected to stochastic resetting.

We explore the thermodynamics of stochastic heat engines in the presence of stochastic resetting. The setup comprises an engine whose working substance is a Brownian particle undergoing overdamped Langevin dynamics in a harmonic potential with a time-dependent stiffness, with the dynamics interrupted at random times with a resetting to a fixed location. The effect of resetting to the potential minimum is shown to enhance the efficiency of the engine, while the output work is shown to have a nonmonotonic dependence on the rate of resetting. The resetting events are found to drive the system out of the linear response regime, even for small differences in the bath temperatures. Shifting the reset point from the potential minimum is observed to reduce the engine efficiency. The experimental setup for the realization of such an engine is briefly discussed.

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

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

Research on the application of heat engine efficiency in reducing energy consumption

In recent years, the problem of global warming and environmental pollution has become increasingly serious, so improving the efficiency of heat engines is of great significance to reduce energy consumption. This paper uses the method of literature review to study the current situation and prospects of heat engine efficiency in reducing energy consumption in three aspects. Firstly, the heat engine and its efficiency are summarized from the theoretical derivation. Secondly, the working principles of the Carnot heat engine and the Stirling heat engine are explained in detail through formula derivation and comparative analysis. Finally, taking the air-source heat pump as an example, we explain the basic principle, operation mechanism, and technical ways to improve efficiency in detail.

Особливості застосування альтернативних палив у теплових двигунах

The subject of the study is the use of alternative fuels and hydrogen in heat engines in different concentrations at different operating modes. The purpose of this study is to decarbonize various types of transport, especially aviation, to increase the energy efficiency and environmental performance of heat engines. Task: to investigate the use of such alternative fuels as biofuels, synthetic fuels, hydrogen and hydrogen mixtures. The use of aviation fuels shows that they must satisfy the relevant requirements, so the choice of alternative fuels must satisfy these requirements with the improvement of their characteristics, first in terms of energy efficiency and environmental indicators. To do this, starting with the ground test of a modern aircraft engine, Rolls-Royce conducted tests on an early conceptual demonstrator using green hydrogen. Green hydrogen was created by wind and tidal energy to prove that hydrogen could be the zero carbon aviation fuel of the future with zero carbon emissions. After analyzing the early ground test concept, the developers are planning a series of further bench tests leading to a full-scale ground test of a green hydrogen jet engine with the goal of achieving zero net carbon emissions from the engine Research Methods. According to the recommendations of the IPCC on the use of scarce fuel, the coefficients of harmful emissions (EI) are calculated for some types of aircraft for the Landing Take Off (LTO) cycle (landing / takeoff). Harmful emissions are calculated using the same method when alternative fuels are used in engines Since jet fuel emissions play an important role in the greenhouse effect, new technologies are being introduced to reduce emissions, among which one of the most effective and environmentally friendly is the use of biofuels, as biofuels are produced using modern biological processes. In this study, an experimental study of the influence of hydrogen addition on a traditional internal combustion diesel engine was conducted. The results. It was determined that the supply of small additions of gaseous hydrogen to the diesel manifold increases the efficiency of the engine at nominal and, largely, at partial modes of operation. The environmental parameters of the diesel engine are improved: the concentration of nitrogen oxides in the exhaust gases decreases, the soot content decreases by 30-40% and by 35%. A calculation method for the quantitative assessment of harmful emissions when using alternative fuels in aircraft engines is defined. Conclusions. The practical significance of the obtained results is that the obtained dependencies can be used when choosing the type of fuel for heat engines and determining the optimal concentration of an alternative fuel such as hydrogen to increase energy efficiency and improve the environmental performance of heat engines.

A Novel Hybrid CSP-PV Power Plant Based on Brayton Supercritical CO2 Thermal Machines

A novel hybrid CSP-PV power plant is presented. Instead of the integration used in current hybrid power plants, where part of the PV production is charged into the thermal energy storage system through electrical resistors, the proposed system integrates both PV and thermal solar fields using a high-temperature heat pump. Both the heat pump and the heat engine are based on Brayton supercritical CO2 thermodynamic cycles. Such integration allows for charging the molten salt storage as if a central tower receiver field supplied the thermal energy, whereas parabolic trough collectors are employed. Unlike conventional hybrid plants, where the storage of PV production leads to a decrease in power injected into the grid throughout the day, the power injected by the proposed system remains constant. The heat engine efficiency is 44.4%, and the COP is 2.32. The LCOE for a 50 MWe plant with up to 12 h of storage capacity is USD 171/MWh, which is lower than that of existing CSP power plants with comparable performance. Although the cost is higher compared with a PV plant with batteries, this hybrid system offers two significant advantages: it eliminates the consumption of critical raw materials in batteries, and all the electricity produced comes from a synchronous machine.

Experimental study and prospect analysis of LiBr-H2O reverse electrodialysis heat engine

Reverse electrodialysis heat engines are a theoretically efficient technique to harvest <100 °C low-grade heat and convert it into electric power. However, the feasibility, technical bottleneck, and application potential of such a concept are unclear because of the experimental study lack. This work experimentally investigates its performance and indicates current technical bottlenecks. After that, a prospect analysis is conducted based on sensitivity analyses to exhibit its potential assuming those bottlenecks are solved. Results show that the regeneration sub-unit performance is close to the theoretical values. The low permselectivities of ion exchange membranes in the reverse electrodialysis sub-unit constrain the performance of the heat engine. Developing high permselectivities of ion exchange membranes under high concentration conditions should be the priority. The prospect analysis indicates that energy and exergy efficiencies of reverse electrodialysis heat engines can reach 2.6% and 19%, respectively, when generation temperatures are 70 °C. It is hoped that this work clarifies that low permselectivities are current technical bottlenecks and provides a guideline for the following research.

Relativistic quantum heat engine with the presence of minimal length

The presence of a minimal length has a significant effect on relativistic physical systems. This paper discusses how minimal length affects the efficiency of a relativistic quantum heat engine. The working substance chosen is a Dirac particle trapped in a one-dimensional infinite potential well. In this paper, we calculate the efficiency of a quantum heat engine in three thermodynamic cycles, namely the Carnot, Otto, and Brayton cycles. The engine efficiency is calculated analytically and numerically. In this research, the minimal length is a correction factor for the relativistic energy. The result is that the minimal length could increase or decrease the efficiency of the relativistic quantum heat engine on the small potential width according to the particle mass, the expansion parameter, and the thermodynamic cycle.

Efficiency and thermodynamic uncertainty relations of a dynamical quantum heat engine

In the quest for high-performance quantum thermal machines, looking for an optimal thermodynamic efficiency is only part of the issue. Indeed, at the level of quantum devices, fluctuations become extremely relevant and need to be taken into account. In this paper we study the thermodynamic uncertainty relations for a quantum thermal machine with a quantum harmonic oscillator as a working medium, connected to two thermal baths, one of which is dynamically coupled. We show that parameters can be found such that the machine operates both as a quantum engine or refrigerator, with both sizeable efficiency and small fluctuations.

Effects of the self-propulsion parity on the efficiency of a fuel-consuming active heat engine.

We propose a thermodynamically consistent, analytically tractable model of steady-state active heat engines driven by both temperature difference and a constant chemical driving. While the engine follows the dynamics of the active Ornstein-Uhlenbeck particle, its self-propulsion stems from the mechanochemical coupling with the fuel consumption dynamics, allowing for both even- and odd-parity self-propulsion forces. Using the standard methods of stochastic thermodynamics, we show that the entropy production of the engine satisfies the conventional Clausius relation, based on which we define the efficiency of the model that is bounded from above by the second law of thermodynamics. Using this framework, we obtain exact expressions for the efficiency at maximum power. The results show that the engine performance has a nonmonotonic dependence on the magnitude of the chemical driving and that the even-parity (odd-parity) engines perform better when the size of the engine is smaller (larger) than the persistence length of the active particle. We also discuss the existence of a tighter upper bound on the efficiency of the odd-parity engines stemming from the detailed structure of the entropy production.

Model-free optimization of power/efficiency tradeoffs in quantum thermal machines using reinforcement learning.

A quantum thermal machine is an open quantum system that enables the conversion between heat and work at the micro or nano-scale. Optimally controlling such out-of-equilibrium systems is a crucial yet challenging task with applications to quantum technologies and devices. We introduce a general model-free framework based on reinforcement learning to identify out-of-equilibrium thermodynamic cycles that are Pareto optimal tradeoffs between power and efficiency for quantum heat engines and refrigerators. The method does not require any knowledge of the quantum thermal machine, nor of the system model, nor of the quantum state. Instead, it only observes the heat fluxes, so it is both applicable to simulations and experimental devices. We test our method on a model of an experimentally realistic refrigerator based on a superconducting qubit, and on a heat engine based on a quantum harmonic oscillator. In both cases, we identify the Pareto-front representing optimal power-efficiency tradeoffs, and the corresponding cycles. Such solutions outperform previous proposals made in the literature, such as optimized Otto cycles, reducing quantum friction.

Thermodynamic stability and holographic heat engine efficiency of a Kerr–Newmann-NUT-Kiselev-AdS black hole in Rastall gravity

Einstein’s general relativity was modified to the Rastall gravity by generalizing the energy–momentum conservation law to T;μμν=λRν and for this change in the covariant conservation of Tμν the thermodynamic characteristics also show some interesting properties. Here we discuss the thermodynamics, phase transition, stability and heat engine construction of a Kerr–Newman-NUT-Kiselev-AdS black hole in 4D Rastall gravity. We consider the space to be surrounded by dark energy, a specific perfect fluid matter. The dark energy has significant effects on the thermodynamic variables of the black hole. Here, the energy condition constraints the Rastall parameter (λ). We finally find that the equation-of-state is related to the Rastall parameter (λ) even when it is reduced to the critical point. The cosmological constant leads us to consider the black hole as a heat engine and determine the efficiency of the Carnot cycle for the black hole. In conclusion, we discuss possible methodologies for constraining the black hole parameters from astrophysical observations.

Quantum Otto heat engine with Pöschl–Teller potential in contact with coherent thermal bath

Work and efficiency of quantum Otto heat engines (QOHEs) can increase by using non-thermal baths or by inhomogeneous scaling of energy levels of the working substance. Given these points, at first, we construct the coherent thermal state for a trigonometric Pöschl–Teller (PT) potential. Then using a particle in this potential, which has unequally spaced energy levels, as a working substance, we investigate the work extraction and the efficiency of QOHEs that operates between cold and hot coherent thermal baths. The results show that changing the PT potential parameters in the adiabatic processes of QOHE, which causes an inhomogeneous shift in energy levels or/and make use of the hot coherent thermal bath, improve work extraction and efficiency of QOHE relative to the classical counterpart.

Efficiency at optimal performance of Brownian heat engines under double tangent constraint

The efficiency of a steady-state thermochemical Brownian heat engine is considered, where the heat flux from the hot to the cold reservoir drives particles from the lower chemical potential of the hot reservoir to the higher chemical potential of the cold reservoir, converting heat into chemical or potential energy. This model system is used to investigate the optimal performance of a Brownian heat engine under a new constraint based on a double tangent construction between the occupation number distributions of the particles in the two heat reservoirs with temperatures and chemical potentials . This constraint allows an operation mode that forces the heat engine to attain Carnot efficiency at nonvanishing power output when approaching thermal equilibrium. For classical particles, the efficiency at maximum power under double tangent constraint results to with the asymptotic series expansion , which shows Carnot behavior for toward zero. This efficiency is significantly higher than the corresponding efficiency at unconstrained maximum power derived by Tu (2008 J. Phys. A Math. Theor. 41 312003) for the classical Feynman ratchet and by van den Broeck and Lindenberg (2012 Phys. Rev. E 86 041144) for classical particle transport, which has the expansion showing the Curzon–Ahlborn behavior for toward zero. The applicability of the double tangent constraint to other optimization criteria is demonstrated using the ecological criterion as an example. The method can also be applied to quantum distributions, for which, however, only a numerical solution is possible.

Carnot Battery Based on Brayton Supercritical CO2 Thermal Machines Using Concentrated Solar Thermal Energy as a Low-Temperature Source

Carnot batteries store surplus power as heat. They consist of a heat pump, which upgrades a low-temperature thermal energy storage, a high-temperature storage system for the upgraded thermal energy, and a heat engine that converts the stored high-temperature thermal energy into power. A Carnot battery is proposed based on supercritical CO2 Brayton thermodynamic cycles. The low-temperature storage is a two-tank molten salt system at 380 °C/290 °C fed by a field of parabolic trough collectors. The high-temperature storage consists of another two-tank molten salt system at 589 °C/405 °C. Printed circuit heat exchangers would be required to withstand the high pressure of the cycles, but shell and tube heat exchangers are proposed instead to avoid clogging issues with molten salts. The conventional allocation of high-temperature molten salt heat exchangers is then modified. Using solar energy to enhance the low-temperature thermal source allowed a round-trip efficiency of 1.15 (COP of 2.46 and heat engine efficiency of 46.5%), thus increasing the stored power. The basic configuration has a levelised cost of storage of USD 376/MWh while replacing the shell and tube heat exchangers with hybrid printed circuit heat exchangers is expected to lower the cost to USD 188/MWh.

Time-dependent solutions for efficiency and velocity of a Brownian heat engine that operates in a two-dimensional lattice coupled with a nonuniform thermal background

Time-dependent solutions for efficiency and velocity of a Brownian heat engine that operates in a two-dimensional lattice coupled with a nonuniform thermal background