Efficiency Of Heat Engine Research Articles

Cooperative efficiency boost for quantum heat engines

The power and efficiency of many-body heat engines can be boosted by performing cooperative non-adiabatic operations in contrast to the commonly used adiabatic implementations. Here, the key property relies on the fact that non-adiabaticity is required in order to allow for cooperative effects, that can use the thermodynamic resources only present in the collective non-passive state of a many-body system. In particular, we consider the efficiency of an Otto cycle, which increases with the number of copies used and reaches a many-body bound, which we discuss analytically.

Measurements and modeling of piston temperature in a research compression ignition engine during transient conditions

Abstract The knowledge of piston temperature during internal combustion engine operation represents a precious information to evaluate heat losses and engine efficiency. Experimental measurements of piston temperature during engine functioning is very challenging; hence, modeling this process can be very helpful. In the present work, temperature measurements have been collected using a research compression ignition engine, both in motored and fired mode. They have been used to set-up a 1d model of heat transfer through the piston optical window. A good agreement has been obtained. Moreover, the model can provide information not available from experiments.

Thermodynamics of charged accelerating AdS black holes and holographic heat engines

Using a reasonable choice in normalizing the timelike Killing vector, we investigate the thermodynamic properties of charged accelerating Anti-de Sitter (AdS) black holes. We find that the expression of the thermodynamic mass in the first law of thermodynamics displays an inextricably intertwining behavior with the charge due to the unusual asymptotic structure of the accelerating black holes. Meanwhile, the thermodynamic length as a potential conjugate to the varying cosmic string tension is introduced and analyzed in detail, and the possible phase behavior of the charged accelerating black holes is also discussed in a standard thermodynamic analysis. Furthermore, we also investigate the properties of holographic heat engines with charged accelerating AdS black holes as the working substance in a benchmarking scheme. We find that the efficiencies of the black hole heat engines can be influenced by both the size of the benchmark circular cycle and the cosmic string tension. More interestingly, the existence of charge may significantly increase the efficiencies of the black hole heat engines and make them be more sensitive to a varying cosmic string tension. A cross-comparison of the efficiencies of different black hole heat engines suggests that the acceleration also increases the efficiency and renders it more sensitive as the charge varies.

Nonuniversality of heat-engine efficiency at maximum power

We study the efficiency of a simple quantum dot heat engine at maximum power. In contrast to the quasi-statically operated Carnot engine whose efficiency reaches the theoretical maximum, recent research on more realistic engines operated in a finite time has revealed other classes of efficiencies such as the Curzon-Ahlborn efficiency maximizing the power. Such a power-maximizing efficiency has been argued to be always the half of the maximum efficiency up to the linear order near equilibrium under the tight-coupling condition between thermodynamic fluxes. We show, however, that this universality may break down for the quantum dot heat engine, depending on the constraint imposed on the engine control parameters (local optimization), even though the tight-coupling condition remains satisfied.It is shown that this deviation is critically related to the applicability of the linear irreversible thermodynamics.

Topological phase transition in quantum-heat-engine cycles

We explore signatures of a topological phase transition (TPT) in the work and efficiency of a quantum heat engine, which uses a single layer topological insulator, stanene, in an external electric field as a working substance. The magnitude of the electric field controls the trivial and topological insulator phases of the stanene. We investigate the effects of TPT in two types of thermodynamic cycles, with and without adiabatic stages. For the adiabatic case, we examine a quantum Otto cycle. We find that at the critical point of TPT both work and efficiency plots with respect to the strength of the electric field exhibit a kink. For a non-adiabatic case, we consider an idealized Stirling type cycle with two isothermal and two isoelectric processes. We find no signatures of the TPT unless a voltage bias is introduced to restrict the involved energy bands to the electronic manifold above the Fermi level. In this case, either above or below the critical point, both work and efficiency become zero depending on the relative magnitudes of the electric fields in the isoelectric stages.

Thermo-Economic Optimization of an Idealized Solar Tower Power Plant Combined with MED System.

Based on the reversible heat engine model, theoretical analysis is carried out for economic performance of a solar tower power plant (STPP) combined with multi-effect desalination (MED). Taking total revenue of the output power and the fresh water yield per unit investment cost as the economic objective function, the most economical working condition of the system is given by analyzing the influence of the system investment composition, the receiver operating temperature, the concentration ratio, the efficiency of the endoreversible heat engine, and the relative water price on the economic parameters of the system. The variation curves of the economic objective function are given out when the main parameter is changed. The results show that the ratio of water price to electricity price, or relative price index, has a significant impact on system economy. When the water price is relatively low, with the effect numbers of the desalination system increasing, and the economic efficiency of the overall system worsens. Only when the price of fresh water rises to a certain value does it make sense to increase the effect. Additionally, the threshold of the fresh water price to the electricity price ratio is 0.22. Under the conditions of the current price index and the heliostat (or reflector), the cost ratio and the system economy can be maximized by selecting the optimum receiver temperature, the endoreversible heat engine efficiency, and the optimum concentration ratio. Given the receiver surface temperature and the endoreversible heat engine efficiency, increasing the system concentration ratio of the heliostat will be in favor of the system economy.

Universal constraint for efficiency and power of a low-dissipation heat engine

The constraint relation for efficiency and power is crucial to design optimal heat engines operating within finite time. We find a universal constraint between efficiency and output power for heat engines operating in the low-dissipation regime. Such constraint is validated with an example of Carnot-like engine. Its microscopic dynamics is governed by the master equation. Based on the master equation, we connect the microscopic coupling strengths to the generic parameters in the phenomenological model. We find the usual assumption of low-dissipation is achieved when the coupling to thermal environments is stronger than the driving speed. Additionally, such connection allows the design of practical cycle to optimize the engine performance.

Thermal modeling and efficiency of a dual-stage sodium heat engine

A thermal design of an axisymmetric dual-stage sodium thermal electrochemical converter (Na-TEC) is presented, where a reduced-order finite-element model is used in conjunction with a Na-TEC thermodynamic model to determine the total parasitic heat loss of this dual-stage design. A number of simplifications are applied in the reduced-order model to decrease the computational time while maintaining acceptable accuracy. These include the use of effective thermal conductivities to account for complex corrugated geometries and apparent surface emissivities to accommodate the effect of radiation shields. Furthermore, a simplified analytical model is developed to account for conduction bypass through the Na-TEC liquid-return path. An iterative procedure between the finite-element and thermodynamic models is described in detail, and the thermal performance of the design proposed herein is analyzed. According to this analysis, a maximum efficiency of 29% and a maximum power output of 125 W can be achieved.

Not-quite-free shortcuts to adiabaticity

Given the increasing use of shotcuts to adiabaticity (STA) to optimize power and efficiency of quantum heat engines, it becomes a relevant question if there are any theoretical limits to their application. We argue that quantum fluctuations in the control device which implements the shortcut deflect the system from the adiabatic path. This not only induces transitions to unwanted final states but also changes the system energy, so that using the STA has a definite cost in terms of conventional work definitions. This may be the ultimate cost of an adiabatic shortcut, in the sense that it is present even for a frictionless, zero temperature driving. We estimate the effect, to lowest nontrivial order in the derivatives of the time-dependent frequency, on a parametric harmonic oscillator, thus providing a consistency condition for the validity of the classical approximation.

Phase transition and heat engine efficiency of phantom AdS black holes

Phase transition and heat engine efficiency of phantom AdS black holes are investigated with peculiar properties found. In the non-extended phase space, we probe the possibility of T–S criticality in both the canonical ensemble and grand-canonical ensemble. It is shown that no T–S criticality exists for the phantom AdS black hole in the canonical ensemble, which is different from the RN-AdS black hole. Contrary to the canonical ensemble, no critical point can be found for neither phantom AdS black holes nor RN-AdS black hole in the grand-canonical ensemble. Moreover, we study the specific heat at constant electric potential. When the electric potential satisfies A_0>1, only phantom AdS black holes undergo phase transition in the grand-canonical ensemble. In the extended phase space, we show that there is no P–V criticality for phantom AdS black holes, contrary to the case of the RN-AdS black hole. Furthermore, we define a new kind of heat engine via phantom AdS black holes. Comparing to RN-AdS black holes, phantom AdS black holes have a lower heat engine efficiency. However, the ratio {eta _{H}}/eta _C of phantom AdS black hole is higher, thus increasing the possibility of approaching the Carnot limit. This observation is obviously of interest. The interesting results obtained in this paper may be attributed to the existence of phantom field whose energy density is negative.

Accelerating AdS black holes as the holographic heat engines in a benchmarking scheme

We investigate the properties of holographic heat engines with an uncharged accelerating non-rotating AdS black hole as the working substance in a benchmarking scheme. We find that the efficiencies of the black hole heat engines can be influenced by both the size of the benchmark circular cycle and the cosmic string tension as a thermodynamic variable. In general, the efficiency can be increased by enlarging the cycle, but is still constrained by a universal bound 2pi /(pi +4) as expected. A cross-comparison of the efficiencies of the accelerating black hole heat engines and Schwarzschild-AdS black hole heat engines suggests that the acceleration also increases the efficiency although the amount of increase is not remarkable.

BTZ black holes in massive gravity

We analyze certain aspects of BTZ black holes in massive theory of gravity. The black hole solution is obtained by using the Vainshtein and dRGT mechanism, which is asymptotically AdS with an electric charge. We study the Hawking radiation using the tunneling formalism as well as analyze the black hole chemistry for such system. Subsequently, we use the thermodynamic pressure-volume diagram to explore the efficiency of the Carnot heat engine for this system. Some of the important features arising from our solution include the non-existence of quantum effects, critical Van der Walls behaviour, thermal fluctuations and instabilities. Moreover, our solution violates the Reverse Isoperimetric Inequality and, thus, the black hole is super-entropic, perhaps which turns out to be the most interesting characteristics of the BTZ black hole in massive gravity.

The saturated and supercritical Stirling cycle thermodynamic heat engine cycle

On the assumption that experimentally validated tabulated thermodynamic properties of saturated fluids published by the National Institute of Standards and Technology are accurate, a theoretical thermodynamic cycle can be demonstrated that produces a net-negative entropy generation to the universe. The experimental data on the internal energy can also be used to obtain a simple, empirical equation for the change in internal energy of a real fluid undergoing isothermal expansion and compression. This demonstration provides experimental evidence to the theory that temperature-dependent intermolecular attractive forces can be an entropic force that can enhance the thermodynamic efficiency of a real-fluid macroscopic heat engine to exceed that of the Carnot efficiency.

Holographic heat engine within the framework of massive gravity

Heat engine models are constructed within the framework of massive gravity in this paper. For the four-dimensional charged black holes in massive gravity, it is shown that the existence of graviton mass improves the heat engine efficiency significantly. The situation is more complicated for the five-dimensional neutral black holes since the constant which corresponds to the third massive potential also contributes to the efficiency. It is also shown that the existence of graviton mass can improve the heat engine efficiency. Moreover, we probe how the massive gravity influences the behavior of the heat engine efficiency approaching the Carnot efficiency.

Large enhancement of thermoelectric performance in CuInTe2 upon compression

Thermoelectric materials can directly generate electric power by converting waste heat, and the efficiency is appraised by the figure of merit zT. A high zT value larger than three is required to achieve comparable efficiency of the traditional heat engines. Despite great efforts for over a century, the desired value of three is seemingly an upper limit, and many existing thermoelectric materials have the zT values less than one. If their zT values can be improved for several times to break through the upper limit, the energy revolution could be expected. Here, a p-type CuInTe2 is chosen as an example to show the extremely important role of pressure in enhancing the thermoelectric performance. Over five times increase of the zT value is realized by the application of pressure. Both the enhancement of the power factor and the reduction of the thermal conductivity account for this large enhancement. The former is due to the optimization of the carrier concentration and band structure, and the latter is attributed to the enhanced phonon anharmonicity. Our results offer an effective method to improve zT of the existing materials for the future technological applications.

Design of a high temperature (1350 °C) solar receiver based on a liquid metal heat transfer fluid: Sensitivity analysis

One approach to reducing the cost of concentrated solar power is to improve the heat engine efficiency by increasing its maximum operating temperature. To achieve higher operating temperatures, we have studied using a liquid metal heat transfer fluid in conjunction with a receiver made from a ceramic/refractory material. As a first step in the design of such a receiver, we conducted sensitivity analyses of several receivers, allowing us to determine what factors most significantly affect receiver performance. Material properties, natural convection from the receiver cavity, and the location of hot spots within the cavity were found to have the largest effect on receiver efficiency. It was also determined that stresses due to thermal expansion can exceed the fracture strength of the receiver material if care is not taken to minimize these stresses. Interestingly, the stress as opposed to performance considerations, set the most important constraints on the receiver geometry.

The Influences of Quantum Coherence on the Positive Work and the Efficiency of Quantum Heat Engine with Working Substance of Two-Qubit Heisenberg XXX Model

We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.

Estimating the cost of high temperature liquid metal based concentrated solar power

The current levelized cost of electricity from concentrated solar power is too high to directly compete with natural gas under current carbon emissions policies. An approximate 50% cost reduction is needed relative to current power tower technology based on molten nitrate salts, and one pathway to a major cost reduction is to operate the system at higher temperatures, enabling a more efficient heat engine. Here, we consider a future system that can operate at gas turbine inlet temperatures of ∼1300–1500 °C by using liquid metals as heat transfer and storage fluids with a ceramic based piping infrastructure. In general, ceramics are more expensive than the current stainless steels, but they are less expensive than the nickel alloys that are proposed to be used in higher temperature chloride molten salt plants. Considering various tradeoffs, it was not clear a priori whether or not the potential gains in heat engine efficiency would be negated by increased material costs or how much net reduction in levelized cost might be possible. This study answers this question by first detailing a base case molten nitrate salt power tower plant with published cost data. Then, a future liquid metal version of a power tower is modeled using similar specifications as the liquid salt plant to determine if there are any obvious costs that might negate the efficiency gains associated with operating well above 1000 °C. The results of the analysis showed that although the receiver and several other sub-systems become more expensive, there is a net cost reduction in the range of 20%–30%, depending upon the heat engine efficiency.

A Hybrid Electric and Thermal Solar Receiver

Summary Solar energy offers a promising renewable energy source; however, it is expensive to store electricity from photovoltaics (PV), the most widely deployed solar electricity technology. Solar thermal energy technologies can be paired with inexpensive thermal storage, but are more expensive overall. We have developed a solar receiver that combines PV and solar thermal systems to efficiently convert solar radiation to electricity (to be used immediately) and thermal energy (to be stored and converted to electricity on demand). This paper describes the Hybrid Electric And Thermal Solar (HEATS) receiver and models its performance. An idealized model predicts high solar-to-electricity efficiency (35.2%) with high dispatchability (44.2% of electricity from thermal energy) at an operating temperature of 775 K. Modeling using measured performance values for HEATS subcomponents predicts 26.8% efficiency and 81% dispatchability with silicon PV and 28.5% efficiency and 76% dispatchability with gallium arsenide PV, both operating at 700 K.

General relations between the power, efficiency, and dissipation for the irreversible heat engines in the nonlinear response regime.

We derive the general relations between the maximum power, maximum efficiency, and minimum dissipation for the irreversible heat engine in a nonlinear response regime. In this context, we use the minimally nonlinear irreversible model and obtain the lower and upper bounds of the above relations for the asymmetric dissipation limits. These relations can be simplified further when the system possesses the time-reversal symmetry or antisymmetry. We find that our results are the generalization of various such relations obtained earlier for different heat engines.