不可逆热机的最大功率和最大效率

在内可逆热机循环模型的基础上，建立了一类不可逆热机循环模型，并导出其最大功率及其相应的效率和最大效率及其相应的功率。所得结果可用以指导衩际热机的性能分析和优化。     

热漏对热机最佳功率与最佳效率特性的影响

对于有限时间热力学,以往文献对于卡诺热机最佳效率与最佳功率间关系的分析大多只考虑了热阻和装置热漏(本文称为外热漏),而没有考虑到工质热漏(本文称为内热漏)的影响。将热漏分为外热漏和内热漏两种方式,经过分析得出了由于内热漏损失使热机存在最佳功率和最佳效率两种不同工作状态,指出了内热漏的影响不同于外热漏,也不可将内热漏简单归结于内不可逆的重要结论。     

热漏对热机功率效率特性的影响

本研究热漏对热机最优性能的影响,导出存在热阻和热漏损失的定常态流不可逆热机的最佳功率、效率关系,所得结果不同于仅存在热阻损失的内可逆热机的功率效率特性关系,且与实际热机特性较为一致,由此指出了一些献的“不可逆循环”模型的不完备之处。     

不同热漏对热机功率效率特性的影响

建立了一个包含多种不可逆性的不可逆热机模型,并将热漏分为外热漏和内热漏两种方式。在此基础上求得存在热阻、热漏和内不可逆损失的定常态流不可逆卡诺热机的功率、效率关系。分析了两种热漏方式对热机最优性能的影响,发现内热漏对热机功率效率特性的影响不同于外热漏,而且与摩擦、涡流和非平衡等不可逆效应也不同;内热漏不能归结于外热漏作为整个热机的热漏或合并为除热阻和热漏外的其他不可逆性。分析表明,当有内热漏存在时,一定温比下热机的最佳功率和最佳效率工作状态分别对应不同的面积比。所得结果对热机设计具有一定指导意义。     

热漏对热机功率效率特性的影响分析

在以往文献的基础上,对定常态流不可逆卡诺热机的热漏模型进行了改进,将热机热漏分为外热漏和内热漏两种方式,分析两种热漏方式对不可逆热机最优性能的影响。分析得出内热漏对热机功率效率特性的影响不同于外热漏,也与摩擦,涡流和非平衡等各种不可逆效应不同,内热漏应单独作为影响热机特性的一种因素。并导出存在热阻和两种热漏损失的热机存在最佳功率和最佳效率两种工作状态,两种工作状态分别对应不同的面积比。所得结果对热机设计具有一定指导意义。     

包含7种热机模型的普适不可逆热机循环火用经济性能优化

用有限时间热力学方法分析了热漏、热阻和其他不可逆效应对工作在两恒温热源之间的普适定常流不可逆热机循环性能的影响,导出了由两个绝热过程、两个等热容加热过程以及两个等热容放热过程组成的循环的功率、效率和利润率的特性关系．并由数值计算分析了循环过程对循环性能的影响特点。所得结果包含了内可逆和不可逆Carnot、Diesel、Otto、Atkinson、Brayton、Dual、Miller循环的有限时 [火用]经济性能。     

恒温热源条件下不可逆闭式中冷回热布雷顿循环的功率优化

考虑高低温侧换热器、回热器和中冷器的热阻损失，以及压气机和涡轮中的不可逆损失，以功率为优化目标，借助数值计算，研究了恒温热源条件下不可逆闭式中冷回热布雷顿循环输出功率最大时高低温侧换热器、回热器和中冷器的热导率分配以及中间压力与总压比的关系。     

恒温热源不可逆闭式中冷回热燃气轮机循环的功率和效率

用有限时间热力学方法首次研究了恒温热源条件下不可逆闭式中冷回热燃气轮机循环的功率、效率以及中间压比特性，导出了无因次功率及效率的解析式。通过数值计算方法，分析了中冷度、回热度对循环最优功率、最优效率及其对应的中间压比分配的影响。     

补燃型不可逆联合循环热机的性能分析

在原有的不可逆联合动力循环模型的基础上,建立了一个存在热阻、热漏、补燃、内不可逆性的定常流联合卡诺热机循环模型。研究其在补燃作用下的功率和效率特性并对其进行优化,导出功率、效率的基本优化关系,分析了补燃对最优性能的影响。     

Efficient power analysis for an irreversible Carnot heat engine

In this paper, the finite‐time thermodynamic optimization is carried out based on the efficient power criterion for an irreversible Carnot heat engine. The obtained results are compared with those obtained by using the maximum power (MP) and maximum power density (MPD) criteria. The optimal design parameters have been derived analytically, and the effect of the irreversibilities on the general and optimal performances is investigated. Maximizing the efficient power gives a compromise between power and efficiency. The results showed that the design parameter at the maximum efficient power (MEP) condition leads to more efficient engines than at the MP conditions and that the MEP criterion may have a significant power advantage with respect to the MPD criterion. Copyright © 2007 John Wiley & Sons, Ltd.     

Ecological coefficient of performance analysis and optimization of an irreversible regenerative-Brayton heat engine

In this paper, a performance optimization based on the ecological coefficient of performance (ECOP) criterion has been carried out for an irreversible regenerative Brayton heat-engine. The results obtained were compared with those using the power-output criterion and alternative ecological performance objective-function defined in the literature. The design parameters, under the optimal conditions, have been derived analytically and their effects on the engine’s performance have been discussed. It is shown that, for the regenerative Brayton-engine, a design based on the maximum ECOP conditions is more advantageous from the point-of-view of entropy generation rate, thermal efficiency and investment cost.     

Performance evaluation of irreversible Miller engine under various specific heat models

In this paper, the performance of a Miller engine is evaluated under different specific heat models (i.e., constant, linear, and fourth order polynomial). Finite-time thermodynamics is used to derive the relations between power output and thermal efficiency at different compression and expansion ratios for an ideal naturally-aspirated (air-standard) Miller cycle. The effect of the temperature-dependent specific heat of the working fluid on the irreversible cycle performance is significant. It was found that an accurate model such as fourth order polynomial is essential for accurate prediction of cycle performance. The conclusions of this investigation are of importance when considering the designs of actual Miller engines.     

Optimization of the irreversible Stirling heat engine

The effects of inefficiencies in the compression, expansion and regeneration processes on engine performance have been evaluated theoretically for a Stirling heat engine operating in a closed regenerative thermodynamic cycle. The irreversible cycle has been optimized by using the maximum power density technique. Maximized power and maximized power density are obtained for different n_ex, τ, α_c, α_h, η_c, η_ex and η_reg values. The maximum efficiencies have been found very close to the values corresponding to the maximum power density conditions but far from the values at maximum power. It has been found that the engines designed by considering the maximum power density have high efficiencies and small sizes under the same prescribed conditions. Copyright © 1999 John Wiley & Sons, Ltd.     

Optimum operating conditions of irreversible solar driven heat engines

An optimal performance analysis of an internally and externally irreversible solar driven heat engine has been carried out. A Carnot-type heat engine model for radiative and convective boundary conditions was used to consider the effects of the finite-rate heat transfer and internal irreversibilities. The power and power density functions have been derived and maximization of these functions has been carried out for various design parameters. The optimum design parameters have been derived and the obtained results for maximum power (MP) and maximum power density (MPD) conditions have been compared. The effects of the technical parameters on the performance have been investigated.     

Optimal ratios of the piston speeds for a finite speed irreversible Carnot heat engine cycle

The performance of an irreversible Carnot heat engine cycle is analysed and optimized by using the theory of finite time thermodynamics based on Agrawal's [2009. A finite speed Curzon-Ahlborn engine. European Journal of Physics, 30 (3), 587–592] model of finite piston speed on the four branches and Petrescu et al.’s [2002b. Optimization of the irreversible Carnot cycle engine for maximum efficiency and maximum power through use of finite speed thermodynamic analysis. In: Proceedings of ECOS’2002, 3–5 July, Berlin, Germany, Vol. II, 1361–1368] model of a Carnot cycle engine with the finite rate of heat transfer, heat leakage from heat source to heat sink and irreversibilities caused by finite speed, friction and throttling through the valves. The finite piston speeds on the four branches are further assumed to be different, which is different from the model of constant speed of the piston on the four branches. Expressions of power output and thermal efficiency of the cycle are derived for a fixed cycle period and internal entropy generation rate. Numerical examples show that the curve of power output versus thermal efficiency is loop shaped, and there exist optimal finite piston speeds on the four branches which lead to the maximum power output and maximum thermal efficiency, respectively. The effects of the heat leakage coefficient and internal entropy generation rate on the optimal finite piston speed ratios are discussed.     

Finite-time thermodynamic modelling and analysis of an irreversible Otto-cycle

The performance of an air standard Otto-cycle is analyzed using finite-time thermodynamics. In the irreversible cycle model, the non-linear relation between the specific heat of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies, and the heat-transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are indicated by numerical examples. Moreover, the effects of internal irreversibility, heat-transfer loss and friction loss on the cycle performance are analyzed. The results obtained in this paper may provide guidance for the design of practical internal-combustion engines.     

线性唯象传热规律下广义不可逆卡诺热机生态学性能系数优化

以反映热机循环输出功率和火用损失率之比的生态学性能系数(ECOP)为目标,用有限时间热力学理论和方法研究广义不可逆卡诺热机的循环性能。导出了线性唯象传热规律(Q∝Δ(T-1))下ECOP的解析式,通过数值计算分析了各种目标极值条件下ECOP与循环功率、效率、熵产率、生态学函数E之间的关系,主要研究了热源温比对最优性能的影响。     

Frequency-dependent performance of an endoreversible Carnot engine with a linear phenomenological heat-transfer law

On the basis of an endoreversible Carnot heat-engine model, the frequency-dependent performance of the engine is analyzed when the heat transfers between the working fluid and the heat reservoirs obey a linear phenomenological heat-transfer law, i.e., Q ∝ (ΔT⁻¹). The relations among average power-output, efficiency, available temperature-drop, cycle frequency and ratio of the heat-transfer times are derived. They are different from those obtained with Newton’s law. The results can provide guidance for selecting the appropriate working points of heat engines.