工程常见输(火用)元的特性准则及其计算

输元是组成传递模型的基本单元.提出三类9项输元特性准则.研究确定传热传递、能量转换传递、传质传递三大类8种典型输元的特性准则,并给出了相应的计算式或表达式,为规范建立基本工程传递模型、简化复杂系统的工程传递分析提供了基础.     

Exergy transfer characteristics of forced convective heat transfer through a duct with constant wall temperature

The exergy transfer characteristics of fluid flow and heat transfer inside a circular duct under fully developed laminar and turbulent forced convection are presented. Temperature is kept constant at the duct wall. The exergy transfer Nusselt number is put forward and the analytical expressions for exergy transfer Nusselt number are obtained as functions of heat transfer Nusselt number, Reynolds number, Prandtl number, etc. The variations of the local and mean convective exergy transfer coefficient, non-dimensional exergy flux, exergy transfer rate, etc. with operating parameters are presented graphically. By reference to a smooth duct and taking air as working fluid, a numerical analysis of the influence of the Reynolds number and non-dimensional cross-sectional position on exergy transfer characteristics has been conducted. The results show that the process parameters and configuration in the fluid flow and heat transfer inside a duct should be properly selected so that the forced convection process could have the best exergy utilization. In addition, the results corresponding to the exergy transfer and energy transfer are compared.     

Exergoeconomic analysis of a combined heat and power (CHP) system

This study deals with exergoeconomic analysis of a combined heat and power (CHP) system along its main components installed in Eskisehir City of Turkey. Quantitative exergy cost balance for each component and the whole CHP system is considered, while exergy cost generation within the system is determined. The exergetic efficiency of the CHP system is obtained to be 38.33% with 51 475.90 kW electrical power and the maximum exergy consumption between the components of the CHP system is found to be 51 878.82 kW in the combustion chamber. On the other hand, the exergoeconomic analysis results indicate that the unit exergy cost of electrical power produced by the CHP system accounts for 18.51 US$ GW^?1. This study demonstrates that exergoeconomic analysis can provide extra information than exergy analysis, and the results from exergoeconomic analysis provide cost‐based information, suggesting potential locations for the CHP system improvement. Copyright © 2007 John Wiley & Sons, Ltd.     

Exergy analysis of a 420 MW combined cycle power plant

Combined cycle power plants (CCPPs) have an important role in power generation. The objective of this paper is to evaluate irreversibility of each part of Neka CCPP using the exergy analysis. The results show that the combustion chamber, gas turbine, duct burner and heat recovery steam generator (HRSG) are the main sources of irreversibility representing more than 83% of the overall exergy losses. The results show that the greatest exergy loss in the gas turbine occurs in the combustion chamber due to its high irreversibility. As the second major exergy loss is in HRSG, the optimization of HRSG has an important role in reducing the exergy loss of total combined cycle. In this case, LP‐SH has the worst heat transfer process. The first law efficiency and the exergy efficiency of CCPP are calculated. Thermal and exergy efficiencies of Neka CCPP are 47 and 45.5% without duct burner, respectively. The results show that if the duct burner is added to HRSG, these efficiencies are reduced to 46 and 44%. Nevertheless, the results show that the CCPP output power increases by 7.38% when the duct burner is used. Copyright © 2007 John Wiley & Sons, Ltd.     

湍流_传递方程及其应用

导出了湍流火用传递方程组 ,依此研究了壁面常热流对流换热管的火用传递 ,计算了由于粘性耗散、径向和轴向导热引起的火用损率分布。通过对单位体积总火用损率的计算表明 ,单位体积总火用损率是换热管几何参数和边界条件的多元函数 ,对于给定的几何参数 ,存在使单位体积总火用损率最小的边界条件 ,反之亦然。该结论对优化设计换热器及对给定边界条件的换热器优化选取具有一定的指导意义。     

原油管输不可逆过程火用的传递和转换规律研究

基于不可逆过程热力学的基本理论,探讨了原油管输过程各不可逆过程的强度量势场梯度驱动力作用下的火用流传递现象,结合原油管道输送过程的基本场平衡方程组和普遍化热力学体系的火用平衡动力学方程,推导了管输过程的热火用和压火用传递和转换方程,进一步建立管输过程的总火用传递方程。以某原油管道为例,对管道输送过程进行数值分析得到管输过程中热火用和压火用的传递和转换火用流分布规律,为将火用的传递转换规律应用到管道节能体系中提供理论基础和合理依据。     

SLA (Second-law analysis) of transient radiative transfer processes

This paper concerns a SLA (second-law analysis) of transient radiative heat transfer in an absorbing, emitting and scattering medium. Based on Planck’s definition of radiative entropy, transient radiative entropy transfer equation and local radiative entropy generation in semitransparent media with uniform refractive index are derived. Transient radiative exergy transfer equation and local radiative exergy destruction are also derived based on Candau’s definition of radiative exergy. The analytical results are consistent with the Gouy–Stodola theorem of classical thermodynamics. As an application concerning transient radiative transfer, exergy destruction of diffuse pulse radiation in a semitransparent slab is studied. The transient radiative transfer equation is solved using the discontinuous finite element based discrete ordinates equation. Transient radiative exergy destruction is calculated by a post-processing procedure.     

试论工程(火用)传递的基本方式

基本Yong传递方式的科学确定,对复杂Yong传递过程或系统的研究极具价值。在分析评述现有研究成果的基础上,提出了作为基本Yong传递方式的充要条件。对多种复杂Yong传递系统的分解、分析,积累了丰富的Yong传递形式资料。据此提出四种基本Yong传递方式,作为应用列举了二个复杂Yong传递系统分解实例。     

管道热输原油过程的(火用)传递分析

在求解热油管道温度场、压力场的基础上,给出了其包括压Yong、压Yong流密度、压Yong传递系数及其常影响因子在内的Yong传递分析指标。对大庆油田某热油管道的应用数值模拟表明：Yong传递分析不仅可对管道输送过程主导势场Yong传递的时空变化规律进行描述,对温度场、压力场二基本势场的协同作用机制作以合理解释,还提出了诸如增大压力可有效提高输油管道的压Yong传递系数等改进输送过程的技术途径。     

Comparison of energy,exergy, and entropy balance methods for analysing double‐stage absorption heat transformer cycles

The energy, exergy and entropy balance methods are used to analyse a double‐stage LiBr‐water absorption heat transformer cycle. An energy balance comparing component energy transfer is used to determine energy calculations. An exergy balance is employed to evaluate exergy destruction, and an entropy balance to verify entropy generation. A comparison of the results by the second law exergy and entropy balances indicates that they are consistent in identifying the location and relative significance of key non‐idealities within the system. The results obtained clearly show the influence of irreversibilities of individual components on deterioration of the effectiveness and the coefficient of performance of the system. The second law analysis offers an alternative view of cycle performance and provides an insight that the first law analysis cannot. The differences between the first law analysis by energy balance method and second law analysis by exergy and entropy balance methods are illustrated quantitatively for the double‐stage absorption heat transformer cycle, and the limitations and advantages of these methods are presented and discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

一维非稳态导热过程(火用)传递的规律及计算

对平壁在导热第三类边界下的一维非稳态导热过程中的Yong传递进行计算，并将导温系数在定值与变值下的计算结果加以比较，以非稳态条件下Yong传递的时空分布规律进行分析。结果表明，Yong流密度随时间按指数规律递减，而Yong传递数却按指数曲线递增。在密度和比热近似不变的条件下，导温系数对温度场分布、Yong传递系数及Yong流密度有决定性的影响。     

富氧燃煤锅炉的效率分析

采用锅炉效率的分析方法对某电站300MW锅炉在O2/CO2气氛下的各项损失和锅炉效率进行了计算,并与相同条件的空气气氛下的各项损失和锅炉效率进行了比较。结果表明,采用O2/CO2的富氧燃烧技术可大大提高锅炉热效率,并相应提高锅炉的效率,而燃烧过程和传热过程的损失仍是锅炉的主要损失。     

An examination of exergy destruction in organic Rankine cycles

The exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy‐based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Entropy flow,entropy generation,exergy flux,and optimal absorbing temperature in radiative transfer between parallel plates

Taking nonequilibrium radiative heat transfer between two surfaces as an example, the nonequilibrium thermodynamics of radiation is studied and discussed. The formulas of entropy flow, entropy generation, exergy flux, and optimal temperature of absorbing surface for maximum exergy output are derived. The result is a contribution to the thermodynamic analysis and optimization of solar energy utilization and can be applied in more complex radiative heat transfer cases.     

熵与yong及yong分析与yong传递

能量与能质寓于同一的客观属体——能，又分别表征能的不同的客观属性。热力学可划分为基础热力学和应用热力学两大类，相应地形成了分别以熵和yong为核心的两个热力学参数框架体系。yong理论的直接应用是，用分析法；其扩展应用是与经济学结合产生的热经济学，与传输学结合产生炯传递理论。     

考虑污垢时换热器热力学性能的评价

在分析污垢对换热器传热性能影响的基础上,在考虑污垢时采用Ｙｏｎｇ损率这一指标对换热器的热力学性能进行了评价,讨论了传热数和冷热流体热容量率比对其性能的影响,并把结果与不考虑污垢时的情况进行了比较,得到了一些有益的结论。     

Energetic and exergetic performance evaluation of a combined heat and power system with the micro gas turbine (MGTCHP)

This study deals with the energetic and exergetic performance assessment of a combined heat and power system with micro gas turbine (MGTCHP). Quantitative energy and exergy balance for each component and the whole MGTCHP system was considered, while energy and exergy consumption within the system were determined. The performance characteristics of this MGTCHP system were evaluated using energy and exergy analyses methods. The energetic and exergetic efficiencies of the MGTCHP system are calculated as 75.99% with 254.55 kW (as 99.15 kW—electrical and 155.40 kW—hot water_{@363.15 K}) and 35.80% with 123.61 kW (as 99.15 kW—electrical and 24.46 kW—hot water_{@363.15 K}), respectively. The maximum energy loss and exergy consumption occur at 44.03 kW in the stack gas and 129.61 kW in the combustion chamber, respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

Exergy loss analysis of heat transfer across the wall of the dividing-wall distillation column

The dividing-wall distillation column is thermodynamically equivalent to the Petlyuk column on the condition that no heat transfer is allowed across the dividing wall. However, better energy efficiency of the column may be obtained if heat transfer occurs within a certain part of the wall. The effects of heat transfer across the dividing wall can be analyzed by using the column grand composite curve (CGCC). The heat transfer potential across the wall can be observed by looking at the CGCC of both column sections alongside the dividing wall. However, the possibility of whether heat should be added or rejected at any stage is not clearly known ahead of the CGCC. Consequently, in this work, the exergy analysis is applied to the dividing-wall column in order to determine whether heat should be added or rejected at any particular stage. Also, the minimum exergy loss value in the column is set as the criterion for determining the heat load targets at any stage. These load targets can then be plotted as a T–H profile similar to the CGCC. This methodology was reported to successfully apply to the column with multiple feeds and products. After having identified the locations and quantities of the feasible heat transfer across the dividing wall, the benefits are discussed via three case studies.     

Energy,exergy and uncertainty analyses of the thermal response test for a ground heat exchanger

This paper presents energy, exergy and uncertainty analyses for the thermal response test of a ground heat exchanger. In this study, a vertical U‐shaped ground heat exchanger with 80 m depth and 20 cm borehole diameter is installed for the first time at the university premises in Saudi Arabia. A mobile thermal response apparatus is constructed and used to measure the performance of the ground heat exchanger. The thermal response test was carried out four times at different thermal loads from September 2007 to April 2008. The energy and exergy transports of these thermal response tests were analyzed using the experimental results obtained in this period. The analysis provides a better understanding of the overall performance of vertical ground heat exchangers, verifies the thermal response test results and improves the experimental setup. Copyright © 2008 John Wiley & Sons, Ltd.     

Enhancement of natural convection heat transfer from a vertical heated plate using inclined fins

An enhancement technique is developed for natural convection heat transfer from a vertical heated plate with inclined fins, attached on the vertical heated plate to isolate a hot air flow from a cold air flow. Experiments are performed in air for inclination angles of the inclined fins in the range of 30° to 90° as measured from a horizontal plane, with a height of 25 to 50 mm, and a fin pitch of 20 to 60 mm. The convective heat transfer rate for the vertical heated plate with inclined fins at an inclination angle of 60° is found to be 19% higher than that for a vertical heated plate with vertical fins. A dimensionless equation on the natural convection heat transfer of a vertical heated plate with inclined fins is presented. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(6): 334–344, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20168