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1.
Based on the state equation of an ideal quantum gas, the regenerative loss of a
Stirling engine cycle working with an ideal quantum gas is calculated. Thermal
efficiency of the cycle is derived. Furthermore, under the condition of quantum
degeneracy, several special thermal efficiencies are discussed. Ratios of thermal
efficiencies versus the temperature ratio and volume ratio of the cycle are made. It
is found that the thermal efficiency of the cycle not only depends on high and low
temperatures but also on maximum and minimum volumes. In a classical gas state
the thermal efficiency of the cycle is equal to that of the Carnot cycle. In an ideal
quantum gas state the thermal efficiency of the cycle is smaller than that of the
Carnot cycle. This will be significant for deeper understanding of the gas Stirling
engine cycle. 相似文献
2.
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
3.
The performance in finite time of a quantum-mechanical Brayton engine cycle is discussed, without intro- duction of temperature. The engine model consists of two quantum isoenergetic and two quantum isobaric processes, and works with a single particle in a harmonic trap. Directly employing the finite-time thermodynamics, the efficiency at maximum power output is determined. Extending the harmonic trap to a power-law trap, we find that the efficiency at max/mum power is independent of any parameter involved in the model, but depends on the confinement of the trapping potential. 相似文献
4.
T. D. Kieu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):115-128
We introduce a class of quantum heat engines which consists of
two-energy-eigenstate systems, the simplest of quantum mechanical
systems, undergoing quantum adiabatic processes and energy exchanges
with heat baths, respectively, at different stages of a cycle. Armed
with this class of heat engines and some interpretation of heat
transferred and work performed at the quantum level, we are able to
clarify some important aspects of the second law of thermodynamics.
In particular, it is not sufficient to have the heat source hotter
than the sink, but there must be a minimum temperature difference
between the hotter source and the cooler sink before any work can be
extracted through the engines. The size of this minimum temperature
difference is dictated by that of the energy gaps of the quantum
engines involved. Our new quantum heat engines also offer a
practical way, as an alternative to Szilard's engine, to physically
realise Maxwell's daemon. Inspired and motivated by the Rabi
oscillations, we further introduce some modifications to the quantum
heat engines with single-mode cavities in order to, while respecting
the second law, extract more work from the heat baths than is
otherwise possible in thermal equilibria. Some of the results above
are also generalisable to quantum heat engines of an infinite number
of energy levels including 1-D simple harmonic oscillators and 1-D
infinite square wells, or even special cases of continuous spectra. 相似文献
5.
The performance of a two-state quantum engine under different conditions is analyzed.It is shown that the efficiency of the quantum engine can be enhanced by superposing the eigenstates at the beginning of the cycle.By employing the finite-time movement of the potential wall,the power output of the quantum engine as well as the efficiency at the maximum power output(EMP) can be obtained.A generalized potential is adopted to describe a class of two-level quantum engines in a unified way.The results obtained show clearly that the performances of these engines depend on the external potential,the geometric configuration of the quantum engines,and the superposition effect.Moreover,it is found that the superposition effect will enlarge the optimally operating region of quantum engines. 相似文献
6.
An irreversible cycle model of the quantum Bose Brayton engine is established, in which finite-time processes and irreversibilities in two adiabatic processes are taken into account. Based on the model, expressions for the power output and the efficiency are derived. By using a numerical computation, the optimal relationship between the power output and the efficiency of an irreversible Bose Brayton engine is obtained. The optimal regions of the power output and the efficiency are determined. It is found that the influences of the irreversibility and the quantum degeneracy on the main performance parameters of the Bose Brayton engine are remarkable. The results obtained in the present paper can provide some new theoretical information for the optimal design and the performance improvement of a real Brayton engine. 相似文献
7.
We calculate the relaxation rate of a scalar field in a plasma of other scalars and fermions with gauge interactions using thermal quantum field theory. It yields the rate of cosmic reheating and thereby determines the temperature of the “hot big bang” in inflationary cosmology. The total rate originates from various processes, including decays and inverse decays as well as Landau damping by scatterings. It involves quantum statistical effects and off-shell transport. Its temperature dependence can be highly non-trivial, making it impossible to express the reheating temperature in terms of the model parameters in a simple way. We pay special attention to the temperature dependence of the phase space due to the modified dispersion relations in the plasma. We find that it can have a drastic effect on the efficiency of perturbative reheating, which depends on the way particles in the primordial plasma interact. For some interactions thermal masses can effectively close the phase space for the dominant dissipative processes and thereby impose an upper bound on the reheating temperature. In other cases they open up new channels of dissipation, hence increase the reheating temperature. At high temperatures we find that the universe can even be heated through couplings to fermions, which are often assumed to be negligible due to Pauli-blocking. These effects may also be relevant for baryogenesis, dark matter production, the fate of moduli and in scenarios of warm inflation. 相似文献
8.
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
9.
C. Klingshirn J. Fallert O. Gogolin M. Wissinger R. Hauschild M. Hauser H. Kalt H. Zhou 《Journal of luminescence》2008,128(5-6):792-796
In linear optics, we report on measurements of the absolute external quantum efficiency of bulk ZnO and powders using an integrating sphere. At low temperature the near band edge emission efficiency can reach 0.15 in the best samples. For deep center luminescence this value may be even higher. When going to room temperature (RT) the quantum efficiency drops by about one order of magnitude. From time resolved luminescence measurements we deduce the lifetime of the free and bound excitons to be in the sub ns regime and find for the latter a systematic increase with increasing binding energy.Concerning lasing, we discuss the role of excitonic processes and the recombination in an inverted electron–hole plasma (EHP). While excitonic processes seem well justified at lower temperatures and densities, doubts arise concerning the concept of excitonic lasing at RT in ZnO. The densities at laser threshold at RT are frequently close to the Mott density or above but below the density at which population inversion in an EHP is reached. We suggest alternative processes which can explain stimulated emission in this density regime in an EHP at RT. 相似文献
10.
Shi-jian Gu 《Frontiers of Physics》2012,7(2):244-251
Let a general quantum many-body system at a low temperature adiabatically cross through the vicinity of the system’s quantum critical point. We show that the system’s temperature is significantly suppressed due to both the entropy majorization theorem in quantum information science and the entropy conservation law in reversible adiabatic processes. We take the one-dimensional transverse-field Ising model and the spinless fermion system as concrete examples to show that the inverse temperature might become divergent around the systems’ critical points. Since the temperature is a measurable quantity in experiments, it can be used, via reversible adiabatic processes at low temperatures, to detect quantum phase transitions in the perspectives of quantum information science and quantum statistical mechanics. 相似文献
12.
《Revue Generale de Thermique》1998,37(7):549-555
The temperatures which are present in a heat transformation device play a very important part: at first, the temperatures determine the maximum performance or efficiency of the cycle via the first and second laws of thermodynamics. Secondly, the temperatures determine the heat transfer area which is required to put a given heat flux through the system. Consequently, they relate power to investment cost. In order to elaborate further on these interdependencies, in this paper basic relationships between technically and thermodynamically relevant temperatures, as they are present in the heat exchangers, are being derived. To this end, we will define several temperature differences as usual: the temperature glide, the driving mean temperature difference and the thermodynamic or entropic mean temperature difference. The logarithmic temperature mean is significant for determining the heat transfer. It will be shown that, as long as the temperature gradient between external and internal fluids is larger than the difference in glide of both fluids, the log-mean can be substituted by the difference of the arithmetic mean temperatures. Consequently, it is almost identical to the entropic temperature difference. The entropic temperature difference is a measure of efficiency whereas the logarithmic temperature difference is a measure of first cost. As both temperature differences deviate only marginally from each other in most technical applications it will easily be possible to establish a relationship between performance and investment. 相似文献
13.
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
14.
Non-linear charge and heat transport through a single-level quantum dot in the Coulomb blockade regime is investigated within the framework of non-equilibrium Green function formalism and power output and efficiency of the device are studied. It is found that maximum power as well as efficiency depends on the relative orientation of magnetic moments in electrodes and can vary with polarization factor p. In general, power output is suppressed in magnetic systems and decreases with polarization. The highest efficiency can be attained in antiparallel configuration, and moreover, it does not depend on p. Spin power as well as spin efficiency of the system is introduced and discussed. It is also shown that in the Coulomb blockade regime the (spin) efficiency of the device operating under maximum power conditions varies with temperature bias in a non-monotonic way and shows a flat maximum for low ΔT. 相似文献
15.
A new thermodynamic inequality is derived which leads to the maximum work that can be extracted from multi-heat-baths with the assistance of discrete quantum feedback control. The maximum work is determined by the free-energy difference and a generalized mutual information content between the thermodynamic system and the feedback controller. This maximum work can exceed that in conventional thermodynamics and, in the case of a heat cycle with two heat baths, the heat efficiency can be greater than that of the Carnot cycle. The consistency of our results with the second law of thermodynamics is ensured by the fact that work is needed for information processing of the feedback controller. 相似文献
16.
The spontaneous and the stimulated emission of both undoped and n-type CdTe crystals have been studied in a wide temperature range under dye laser excitation. Optical gain spectra have been also measured. The competition among the cooperative processes resulting in luminescence of CdTe is governed by the sample temperature and the doping level. When the exciton—electron collision is dominant, i.e. in n-type samples, the highest quantum efficiency is also achieved. 相似文献
17.
1前言采用燃气轮机排气做为再循环烟气并向燃烧室回注水等措施,不仅可保证一定的透平进气温度,而且可有效的减少NOx生成及压缩机耗功。但还有以下问题有待解决:(1)若再循环烟气温度较高,不利于提高系统效率。(2)如果燃烧室回注水取自周围环境,造成系统水消耗大。因此即要能使再循环烟气降温又能使系统用水尽量来自系统本身。冷凝式换热器可适应上述要求,通过把烟气冷却至露点以下,烟气中的水蒸气凝结为水,然后汽水混合物进入气水分离器,产生较低温度的再循环烟气,同时分离出液态水,经泵加压后作为燃烧室回注水使用。本文在… 相似文献
18.
Quantum entanglement can cause the efficiency of a heat engine to be greater than the efficiency of the Carnot cycle. However, this does not mean a violation of the second law of thermodynamics, since there is no local equilibrium for pure quantum states, and, in the absence of local equilibrium, thermodynamics cannot be formulated correctly. Von Neumann entropy is not a thermodynamic quantity, although it can characterize the ordering of a system. In the case of the entanglement of the particles of the system with the environment, the concept of an isolated system should be refined. In any case, quantum correlations cannot lead to a violation of the second law of thermodynamics in any of its formulations. This article is devoted to a technical discussion of the expected results on the role of quantum entanglement in thermodynamics. 相似文献
19.