工质变比热对不可逆矩形循环性能的影响

考虑工质线性变比热特性、传热损失和摩擦损失,用有限时间热力学方法研究了不可逆矩形循环。循环功率与压缩比、效率与压缩比和功率与效率的特性关系均由数值计算给出,分析可知矩形循环性能受工质变比热特性及传热、摩擦损失影响较大。考虑工质变比热特性的循环模型更加接近工程实际,所得结果对矩形循环的应用具有一定的理论指导意义。     

工质变比热对内可逆Lenoir循环性能的影响

用有限时间热力学理论和方法分析内可逆Lenoir循环,建立了存在工质变比热和传热损失时的循环模型,由数值计算得到了循环的临界压缩比范围,给出了功与压缩比、效率与压缩比以及功和效率的特性关系,并分析了传热损失和工质变比热对循环性能的影响特点,通过分析可知变比热特性和传热损失对Lenoir循环性能有较大影响,对该循环的应用具有一定指导意义。     

工质变比热和传热损失对Otto循环性能的影响

用有限时间热力学的方法分析空气标准Otto循环，由数值计算给出了存在传热损失和工质变比热时循环功率与压缩比、效率与压缩比以及功率和效率的特性关系，并分析了传热损失和工质变比热对循环性能的影响特点。通过分析可知传热和变比热特性对Otto循环性能有较大影响，所以在实际循环分析中应该予以考虑。     

工质线性变比热内可逆矩形循环功率密度和有效功率特性

应用有限时间热力学理论基于已有文献建立的模型,以功率密度和有效功率为优化目标,分析工质比热随温度线性变化条件下,存在传热损失的内可逆矩形循环性能特性,得到循环无因次功率密度Pˉd、无因次有效功率Wˉep与循环膨胀比γ和效率η之间的关系.结果表明,循环Pˉd-γ和Wˉep-γ关系曲线均为类抛物线型,Pˉd-η和Wˉep-...     

内可逆工质恒比热Meletis-Georgiou循环有限时间热力学建模与性能优化

应用有限时间热力学理论建立内可逆工质恒比热Meletis-Georgiou(MG)循环模型,导出循环各点温度、循环功、效率等性能参数表达式,并对MG循环性能进行分析和优化。应用数值计算方法,得到循环功与效率特性关系;分别以循环功和效率为目标,对压缩比、转换比、过膨胀比进行优化并得到一系列优化结果;分析了传热损失及循环各参数对循环性能与优化结果的影响。所得结果对实际MG发动机的设计优化有一定指导作用。     

内可逆矩形循环有限时间热力学分析

应用有限时间热力学理论分析了空气标准矩形循环的性能,导出存在传热损失的空气标准矩形循环的功与膨胀比、效率与膨胀比以及功和效率的特性关系,同时分析了传热损失及循环各参数对循环性能的影响。     

非理想气体工质对内可逆Otto循环功率、效率性能的影响

基于有限时间热力学理论和内可逆Otto循环模型,进一步考虑非理想气体工质比热模型,对循环的功率和效率性能进行研究。通过数值计算分析比热模型、气体分子自由度d和传热损失B对循环最大功率P_{ot max}、最大效率η_max、P_{ot max}对应的最佳压缩比(γ_opt)_p和效率η_P、η_max对应的最佳压缩比(γ_opt)_η和功率P_η的影响。结果显示：循环性能η_max、(γ_opt)_η和η_p随着B的增大而减小;工质比热模型对循环性能不产生定性影响,仅产生定量影响,非理想气体比热模型条件下的循环P_{ot max}、(γ_opt)_p、η_max、(γ_opt)_η、η_p     

工质变比热对混合加热循环功率密度特性的影响

以功率密度为目标函数,导出存在摩擦和传热损失时,工质变比热条件下由2个加热过程、2个绝热过程和1个放热过程组成的混合加热循环的功率密度解析表达式,分析功率密度和压缩比、效率及功率的特性关系,并通过数值计算的方法分析工质变比热特性和工质压缩比对混合加热循环功率密度目标函数的影响。     

内可逆Rallis循环的最优功率和效率性能研究

运用有限时间热力学理论建立存在传热损失的空气标准内可逆Rallis循环模型,导出循环功率(P)和效率(η)的解析式;以P和η为优化目标,将等温过程膨胀比作为优化变量,对循环性能进行优化;分析传热损失(B)、压缩比(ε)、增压比(λ)和预胀比(ρ)对P、η特性的影响。结果表明:内可逆Rallis循环的P、η与等温过程膨胀比的关系曲线均呈类抛物线形,存在最佳膨胀比(σ_P和σ_η)使循环P、η分别达到最大值(P_max和η_max);循环过程的P-η关系曲线呈现过原点的扭叶形;随着ε、λ和ρ的增加,P_max、σ_P、η_max和σ_η均增加;随着B的增加,η_P和η_max均减小。     

Ecological performance analysis of an endoreversible modified Brayton cycle

An endoreversible closed modified simple Brayton cycle model with isothermal heat addition coupled to variable-temperature heat reservoirs is established using finite-time thermodynamics. Analytical expressions of dimensionless power output, thermal efficiency, dimensionless entropy generation rate and dimensionless ecological function are derived. Influences of cycle thermodynamic parameters on ecological performance and optimal compressor pressure ratio, optimal power output, optimal cycle thermal efficiency and optimal entropy generation rate corresponding to maximum ecological function are obtained and compared with those corresponding to maximum power output. The results show that cycle thermal efficiency improvement and entropy generation rate reduction are obtained at the expense of higher compressor pressure ratio and a little sacrifice of power output at maximum ecological function. The compromises between power output and entropy generation rate and between power output and cycle thermal efficiency, respectively, are achieved.     

普适内可逆热机循环模型的(火用)经济性能优化

用有限时间热力学方法分析工作在恒温热源TH、TL之间内可逆普适热机循环模型的经济性能,导出循环利润率与工质温比、热效率与工质温比的关系式;以及利润率和效率的特性关系。所得结果包含了内可逆D iese、lO tto、A tk inson和B rayton循环的有限时间经济性能。     

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.     

Performance of an Atkinson cycle with heat transfer,friction and variable specific-heats of the working fluid

The performance of an air standard Atkinson cycle with heat-transfer loss, friction-like term loss and variable specific-heats of the working fluid is analyzed using finite-time thermodynamics. 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 derived by detailed numerical examples. Moreover, the effects of variable specific-heats of the working fluid and the friction-like term loss on the irreversible cycle performance are analyzed. The results show that the effects of variable specific-heats of working fluid and friction-like term loss on the irreversible cycle performance should be considered in cycle analysis. The results obtained in this paper provide guidance for the design of Atkinson engines.     

Optimal performance of an endoreversible chemical pump with diffusive mass transfer law

The performance of an isothermal endoreversible two-reservoir chemical pump, in which the mass transfer obeys diffusive law, is analysed and optimised in this paper. The relation between the rate of energy pumping and the coefficient of performance of the isothermal chemical pump is derived by using finite-time thermodynamics. Moreover, the relation between the minimum power input and the coefficient of performance, and the relation between the minimum entropy production rate and the rate of energy pumping are obtained. The results obtained herein can provide some new theoretical guidelines for the optimal design of a class of apparatus such as mass exchangers, as well as electrochemical, photochemical, solid-state devices, and the fuel pumps for solar-energy conversion systems.     

热漏对内可逆四热源制冷系统的影响

在恒温热源内可逆四热源吸收式制冷循环的基础上，建立不可逆吸收式制冷循环的模型，考虑环境热源到制冷空间的热漏以及工质与外部热源间的热阻损失，导出牛顿定律下循环的制冷率和制冷系数的基本优化关系、最大制冷系数及相应的制冷率和最大制冷率及相应的制冷系数；并通过数值计算分析了循环参数对循环的制冷率、制冷系数的影响。     

甲醇乙醇混合工质振荡热管传热性能研究

混合工质可为振荡热管带来独特的传热性能．比较甲醇、乙醇纯工质以及甲醇-乙醇混合工质振荡热管在不同充液率时的热阻随加热功率的变化情况,结果发现：在小充液率（45％）时甲醇-乙醇混合工质和乙醇振荡热管开始烧干时的加热功率高于甲醇工质振荡热管;在加热功率不是很大（低于65W）和大充液率（62％～90％）时,甲醇以及甲醇-乙醇混合工质振荡热管的传热性能优于乙醇振荡热管;在大加热功率（高于65W）和大充液率（62％～90％）时甲醇以及甲醇-乙醇混合工质振荡热管的热阻十分接近,均低于乙醇工质振荡热管的热阻,且热阻随着充液率的增加曲线变化越来越平缓．     

Impact of EGR fraction on diesel engine performance considering heat loss and temperature‐dependent properties of the working fluid

Exhaust gas recirculation (EGR) to reduce feed gas NO_x emission is common practice in modern diesel engines. Dilution of the intake air with cooled recirculated exhaust gas limits the production of in‐cylinder NO_x due to a lowering of the adiabatic flame temperature and a reduction in oxygen content of the intake mixture. EGR also reduces the mixture‐averaged ratio of specific heats (γ) of the combustion charge leading to a reduction in the thermodynamic cycle efficiency. This trade‐off between minimizing NO_x production and maximizing cycle efficiency is of critical importance when calibrating EGR control schemes. Modeling tools that allow a quantitative analysis of this trade‐off can be very beneficial in tuning EGR systems over a range of operating conditions. In this study, the systematic development of a model that allows an assessment of the impact of EGR on three parameters, namely (a) the thermodynamic cycle efficiency, (b) the mixture temperatures during the cycle and (c) the mixture‐averaged γ, is presented. This is accomplished through a numerical solution of the energy equation while considering the effects of heat loss and temporally varying mixture‐averaged values of γ. Results for a simple phenomenological model relating fuel‐burn rate with EGR fraction and the impact of EGR fraction on NO_x reduction are also included. Copyright © 2008 John Wiley & Sons, Ltd.