热源间热机的_全息_热效率_功率谱

本文定义了输出功率弱化系数π及π函数因子①,建立了二源间内可逆循环的“全息”热效率——功率谱。借助克氏微循环或有限元循环概念,该全息谱能概括一切可能的任意热源间热机循环,可供热源间热机循环工作参数合理性的有限时间热力学分析。     

以Dieterici气体为工质的两类热机循环性能分析

对Dieterici实际气体作了简要分析,并以Dieterici实际气体为工质,分别导出卡诺热机和斯特林热机的输出功和效率的一般表达式.最后通过数值计算,讨论了卡诺热机及斯特林热机的输出功和效率分别与体积和温度之间的关系.所得结论可为热机的运行条件和优化设计提供理论参考.     

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.     

On the Coexistence of Solar-Energy Conversion and Plant Cultivation

In this paper we propose a configuration of a solar, e.g., photovoltaic, power plant, which allows for additional agricultural use of the land involved, although the collectors are optimized for solar-energy conversion. If the collectors are not installed directly on the ground, but are elevated by about 2m above the ground with the periodic distance between collector rows of about three times the height of the collectors, one achieves nearly uniform radiation, (integrated over the day), on the ground of a value of about two-thirds of the global radiation without solar collectors. The mathematical relations allowing calculation of the fraction of light reaching the ground under the collector field are derived. Numerical calculations for both the direct and diffuse part of solar radiation are carried out yielding the seasonal and local dependence of this fraction. In addition, we give an outline of the various advantages offered by this configuration.     

一类不可逆卡诺热机最佳效率和功率间的关系

采用包括Ｄｕｌｏｎｇ－Ｐｅｔｉｔ非线性传热率和热漏的不可逆卡诺热机模型,导出其基本优化关系,并讨论了热机在最大输出功率时的效率问题。     

热机有限时间热力学_理论和应用

本文从以下几个方面介绍了热机有限时间热力学的研究现状:牛顿定律系统的研究,热阻和其它不可逆损失模型的影响,有限热容热源的影响,外部加热速率的影响,以及热机设计和评估中的应用。     

发动机效率及后处理技术进展综述

全面综述了过去几年汽车尾气温室气体和标准污染物减排的一些主要进展,讨论了针对改进发动机及后处理系统最新出台和即将出台的法规及正在研发的技术.介绍了轻型和重型车辆的全球主要市场的发展,及相关的法规和技术.     

AVL Indicom热力学计算及燃烧放热分析

介绍了热力学计算的基本原理及基于AVL Indicom的热力学计算的基本理论,探讨了内燃机燃烧放热基本过程与关键参数,并提出了一种利用燃烧放热基本参数更为迅速准确地判断最佳点火角的方法。     

气体燃料对内燃机充气效率的影响

气体燃料作为能源替代应用于内燃机时,会因其组分、温度的原因对内燃机充气效率产生影响。讨论了四种气体燃料对内燃机充气效率的影响,并基于一些基本假设,从理论上计算了影响的程度。结果表明,LPG燃料对充气效率的影响较小,氢气较大;气体燃料掺燃量越大,对充气效率的影响越大;过量空气系数大的内燃机所受到的影响较小。研究的四种气体燃料因温度对充气效率无影响或影响较小。     

卡诺热机的最佳利润与效率间的关系

本文导出牛顿定律系统卡诺热机的最佳利润与效率间的关系,并得到最大利润时的效率界限。其结果包含了最大功率和最小熵产率(也即最小损失)两种特例。籍此,作者首次提出了有限时间经济分析和有限时间经济性能界限的概念,为统一现代热力学的各分支研究开拓了方向。     

内燃机混合加热(Dual)循环有限时间热力学分析

对内燃机混合加热循环的特性做了进一步的分析与研究,使得对该循环的分析结果与内燃机实际热力过程的不可逆性充分接近,对内燃机的设计和理论研究工作具有重要意义;并运用有限时间热力学的方法,对135柴油机Dual循环进行了有限时间特性分析,得出了应用该方法对内燃机缸内热力过程不可逆性进行研究具有重要实际意义的结论。     

再论卡诺热机的输出功率与热效率间的关系

对卡诺热机输出功率与热效率间的关系再次进行了讨论，认为结构系数θ是影响卡诺热机性能的主要因素。研究最大功率与热效率间的关系以及最佳热效率与功率间的关系是没有实际意义的，有实际意义的仍然是功率与热效率间的关系。     

Exergoeconomic performance of an endoreversible Carnot heat pump with complex heat transfer law

The finite-time exergoeconomic performance of an endoreversible Carnot heat pump with a complex heat transfer law, including generalized convective heat transfer law and generalized radiative heat transfer law q∝ (Δ T ⁿ ) ^m , is investigated in this paper. The focus of this paper is to obtain the compromised optimization between economics (profit) and the energy utilization factor (coefficient of performance, COP) for the endoreversible Carnot heat pump, by searching the optimum COP at maximum profit, which is termed as the finite-time exergoeconomic performance bound. The obtained results include those obtained in much of the literature and can provide some theoretical guidance for the design of practical heat pumps.     

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。     

内燃机排气余热ORC中异丁烷-CO2混合工质的可燃性分析

针对内燃机高温排气与ORC工质的匹配问题,提出了一组安全且环保的烷烃/CO_2混合工质。为了解决混合工质泄漏后可燃的问题,按照美国ASTME681-2009标准提出测量异丁烷-二氧化碳混合工质可燃区域的实验手段。实验结果表明,异丁烷的可燃下限随阻燃剂二氧化碳的加入基本不变,可燃上限随着阻燃剂的加入迅速减小。并基于临界火焰温度理论建立了预测异丁烷-二氧化碳混合工质可燃极限的模型,与试验值相比较表明,预测模型可以较好地预测异丁烷的可燃下限,上限预测误差较大。     

温度对乙醇重整燃料发动机充气效率的影响

一种简化计算公式能够描述进气温度变化对内燃机充气效率的影响。同时采用工作过程仿真和笔者提出的计算公式比较,考虑了发动机负荷、转速、发动机排量、进气入口空气温度和乙醇重整燃料温度等因素,计算分析了温度对乙醇重整燃料发动机充气效率的影响。简化计算公式的计算结果与工作过程仿真的计算结果非常接近,二者的最大差值小于0.5%;计算结果表明,由于高温乙醇重整燃料引起的进气温度变化,导致充气效率下降3%~7%。     

Fluent在非常规内燃机设计中的应用

简单介绍典型非常规内燃机的工作原理及独特结构;计算方法的进步和计算机技术的快速发展促进了计算流体力学在内燃机研制中的应用,减少了实验工作量,降低了研究费用,缩短了研发周期,Fluent软件突破了内燃机专用软件中对内燃机结构的限制,提供了用户自定义函数这一用户接口,为非常规内燃机的瞬态数值仿真计算提供了平台。非常规内燃机为提升内燃机热效率提供了发展思路,在非常规内燃机开发中应用Fluent进行数值模拟可加快研发进程。     

The efficiency of endoreversible heat engines with heat leak

Finite-time thermodynamics are used for studying the performance of endoreversible heat engines with heat leak. A comprehensive formulation and a general solution methodology, valid for any mode of heat supply or release, are presented. Detailed analyses are conducted for several heat transfer modes and universal analytical and numerical results for the efficiency at maximum power are generated. Many established laws and major conclusions derived in several references are shown to represent very special cases of the new formulation. Furthermore, the nature of the leakage power law is found to deeply affect the efficiency at maximum power. Finally, for no leakage situations, if the heat to the engine is supplied and released via similar heat transfer modes, then the lowest efficiency at maximum power, when the only thermal resistance is between the working fluid and the hot reservoir, is found to be given by 1/n, n being the power of the heat transfer law.     

Thermodynamic and thermoeconomic analyses of an irreversible combined Carnot heat engine system

A combined cycle model which includes the irreversibilities of finite‐rate heat transfer in heat‐exchange processes and heat leak loss of the heat source is used to analyse the performance of a multi‐stage Carnot heat engine system. The efficiency, power output, ecological function and profit of operating the combined system are optimized. The optimally operating region of the combined system is determined. The optimal combined conditions between two adjacent cycles in the combined system are obtained. Moreover, the cycle model is generalized to include the internal irreversibilities of the working fluids so that the results obtained here become more general. Copyright © 2001 John Wiley & Sons, Ltd.