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1.
研究了热阻、回热损失和热漏等多种不可逆因素对以广义Redlich-Kwong气体为工质的斯特林热机性能的影响,给出了斯特林热机输出功率和效率的具体表达式并分析非理想回热特性及循环主要性能参数(如循环体积比及工质高低温比等)对循环输出功率和效率的影响.同时指出,只有在理想回热及无热漏的情况下,气体斯特林热机的效率才能达到卡诺效率. 相似文献
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An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output. 相似文献
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It is shown that the efficiency of a regenerative Stirling cycle can principally not reach that of a Carnot cycle operating
in the same temperature range. A relation is obtained between the degree of regeneration and the characteristics of regenerator.
The maximum efficiency of an ideal regenerative Stirling engine is obtained. 相似文献
4.
研究了以带有Dzyaloshinski-Mariya(DM)相互作用的两比特自旋体系为工质的量子纠缠Otto热机和量子Stirling热机.两种不同热机在各自的循环过程中,通过保持其他参量不变,只有DM相互作用发生改变,从而分析热机循环中DM相互作用与热传递、做功以及效率等热力学量之间的关系.研究结果表明:DM相互作用对两种热机的基本量子热力学量都具有重要的影响,但量子Stirling热机由于回热器的使用,其循环效率会大于量子Otto纠缠热机的效率,甚至会超过Carnot效率;得到了量子Otto纠缠热机和量子Stirling热机做正功的条件.因此,在这两个纠缠体系中,热力学第二定律都依然成立. 相似文献
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Quantum thermal machines make use of non-classical thermodynamic resources, one of which include interactions between elements of the quantum working medium. In this paper, we examine the performance of a quasi-static quantum Otto engine based on two spins of arbitrary magnitudes subject to an external magnetic field and coupled via an isotropic Heisenberg exchange interaction. It has been shown earlier that the said interaction provides an enhancement of cycle efficiency, with an upper bound that is tighter than the Carnot efficiency. However, the necessary conditions governing engine performance and the relevant upper bound for efficiency are unknown for the general case of arbitrary spin magnitudes. By analyzing extreme case scenarios, we formulate heuristics to infer the necessary conditions for an engine with uncoupled as well as coupled spin model. These conditions lead us to a connection between performance of quantum heat engines and the notion of majorization. Furthermore, the study of complete Otto cycles inherent in the average cycle also yields interesting insights into the average performance. 相似文献
7.
针对当前国家大力推行清洁能源技术和煤改气政策的供暖现状,本文探索了一种双效斯特林燃气热泵系统。全文基于热声学观点对系统进行了理论研究,并采用SAGE程序对其进行数值模拟和优化设计。计算表明,当加热、供热和冷端温度分别为923 K、333 K和273 K时,系统可获得的泵热量为7000 W,COPh为1.79,系统(火用)效率可达到45.67%;但谐振活塞位移对温度、压力以及谐振电机机械阻尼等参数变化具有敏感性,该特点将会严重制约系统的高效运行。为了降低系统的敏感性,本文采用谐振电机耦合斯特林发动机和斯特林热泵,通过对谐振电机电功输入和输出的调控来保持电机活塞工作状态的稳定。结果表明,谐振电机对于实现斯特林发动机和斯特林热泵的高效耦合以及降低系统敏感性具有可行性。 相似文献
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The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely. 相似文献
9.
The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely. 相似文献
10.
We analyze the efficiency of thermal engines (either quantum or classical) working with a single heat reservoir like an atmosphere. The engine first gets an energy intake, which can be done in an arbitrary nonequilibrium way e.g. combustion of fuel. Then the engine performs the work and returns to the initial state. We distinguish two general classes of engines where the working body first equilibrates within itself and then performs the work (ergodic engine) or when it performs the work before equilibrating (non-ergodic engine). We show that in both cases the second law of thermodynamics limits their efficiency. For ergodic engines we find a rigorous upper bound for the efficiency, which is strictly smaller than the equivalent Carnot efficiency. I.e. the Carnot efficiency can be never achieved in single reservoir heat engines. For non-ergodic engines the efficiency can be higher and can exceed the equilibrium Carnot bound. By extending the fundamental thermodynamic relation to nonequilibrium processes, we find a rigorous thermodynamic bound for the efficiency of both ergodic and non-ergodic engines and show that it is given by the relative entropy of the nonequilibrium and initial equilibrium distributions. These results suggest a new general strategy for designing more efficient engines. We illustrate our ideas by using simple examples. 相似文献
11.
A Carnot cycle outside a Schwarzschild black hole is investigated in
detail. We propose a reversible Carnot cycle with a black hole being
the cold reservoir. In our model, a Carnot engine operates between a
hot reservoir with temperature T1 and a black hole with Hawking
temperature TH. By naturally extending the ordinary Carnot
cycle to the black hole system, we show that the thermal efficiency
for a reversible process can reach the maximal efficiency 1-TH/T1. Consequently, black holes can be used to
determine the thermodynamic temperature by means of the Carnot cycle.
The role of the atmosphere around the black hole is discussed. We
show that the thermal atmosphere provides a necessary mechanism to
make the process reversible. 相似文献
12.
The second law of thermodynamics has been proven by many facts in classical
world. Is there any new property of it in quantum world? In this paper, we
calculate the change of entropy in T.D. Kieu's model for quantum heat engine
(QHE) and prove the broad validity of the second law of thermodynamics. It
is shown that the entropy of the quantum heat engine neither decreases in a whole cycle, nor decreases in either stage of the cycle. The second law of thermodynamics still holds in this QHE model. Moreover, although the
modified quantum heat engine is capable of extracting more work, its
efficiency does not improve at all. It is neither beyond the efficiency
of T.D. Kieu's initial model, nor greater than the reversible Carnot efficiency. 相似文献
13.
It is demonstrated that the generally accepted treatment of the second law of thermodynamics is incorrect when the statement
of the maximum limiting efficiency of the forward Carnot cycle is applied to the reverse cycles. An analysis of reversible
cycles compared with the Carnot cycle shows that the reverse Carnot cycle has the lowest efficiency of all reverse cycles.
A new characteristic is proposed — the thermal efficiency of reverse cycles, and a generalized theorem is put forward for
the additivity of the thermal efficiencies of the forward and reverse cycles. A formulation of the second law of thermodynamics
is suggested from the point of view of the efficiency of reverse cycles.
Zh. Tekh. Fiz. 69, 11–14 (June 1999) 相似文献
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The aim of the paper is to present the performance characteristics of a Stirling refrigeration cycle in micro/nano scale, in which the working substance of cycle is an ideal Maxwellian gas. Due to the quantum boundary effect on the gas particles confined in the finite domain, the cycle no longer possesses the condition of perfect regeneration. The inherent regenerative losses, the refrigeration heat and coefficient of performance (COP) of the cycle are derived. It is found that, for the micro/nano scaled Stirling refrigeration cycle devices, the refrigeration heat and COP of cycle all depend on the surface area of the system (boundary of cycle) besides the temperature of the heat reservoirs, the volume of system and other parameters, while for the macro scaled refrigeration cycle devices, the refrigeration heat and COP of cycle are independent of the surface area of the system. Variations of the refrigeration heat ratio rR and the COP ratio rε with the temperature ratio τ and volume ratio rV for the different surface area ratio rA are examined, which reveals the influence of the boundary of cycle on the performance of a micro/nano scaled Stirling refrigeration cycle. The results are useful for designing of a micro/nano scaled Stirling cycle device and may conduce to confirming experimentally the quantum boundary effect in the micro/nano scaled devices. 相似文献
16.
A model of an irreversible quantum Carnot heat engine with heat resistance, internal irreversibility and heat leakage and
many non-interacting harmonic oscillators is established in this paper. Based on the quantum master equation and semi-group
approach, equations of some important performance parameters, such as power output, efficiency, exergy loss rate and ecological
function for the irreversible quantum Carnot heat engine are derived. The optimal ecological performance of the heat engine
in the classical limit is analyzed with numerical examples. Effects of internal irreversibility and heat leakage on the ecological
performance are discussed. A performance comparison of the quantum heat engine under maximum ecological function and maximum
power conditions is also performed. 相似文献
17.
A new model of micro-/nanoscaled heat engines consisting of two thin long tubes with the same length but different sizes of cross section, which are filled up with ideal quantum gases and operated between two heat reservoirs, is put forward. The working fluid of the heat engine cycle goes through four processes, which include two isothermal processes and two isobaric processes with constant longitudinal pressure. General expressions for the power output and efficiency of the cycle are derived, based on the thermodynamic properties of confined ideal quantum gases. The influence of the size effect on the power output and efficiency is discussed. The differences between the heat engines working with the ideal Bose gas and Fermi gas are revealed. The performance of the heat engines operating at weak gas degeneracy and high temperatures is further analyzed. The results obtained are more general and significant than those in the current literature. 相似文献
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A. N. Zaikin 《Moscow University Physics Bulletin》2008,63(5):344-348
The periodic regime of a stable limit cycle for a modified Carnot engine is realized through an algorithmic slide valve. The power, piston oscillation frequency, and efficiency of the engine have been determined in a quasi-harmonic approximation. The modified engine can operate in the regime of a triangular limit cycle (cycles with any number of angles larger than three are realizable). The developed approach to analyzing the dynamic regimes of a Carnot engine allows one to dispense with the concept of entropy. 相似文献