小型热电站热电联产Yong分析及节能评价

采用Yong平衡分析法,分别对小型热电联产系统和分散锅炉房供热系统进行了Yong流分析,把两者计算所得Yong效率作一对比,从而得出热电联产系统是取代分散锅炉房供热的节能措施之一,同时还对热电联产系统内各环节中的Yong流损失进行计算,得出各热力设备的Yong效率,找出系统用能不合理的主要薄弱环节,为今后设备的工艺过程改进指出了方向。     

压缩式热泵系统Yong效率定义方法初探

对压缩式热泵系统Yong效率的定义式进行了分析，指出了该定义式在实际应用过程中存在的一些不足。即当低温热源为环境时，此定义式合理，否则即使热泵系统内部可逆，系统大用效率仍不为1，文中对产生这一问题的原因进行了分析。以热泵系统的Yong平衡方程为依据，参照Yong效率定义方法及Yong效率的基本特征，对压缩式热泵的系统Yong效率进行了重新定义。通过对两个不违背Yong效率定义特征的表达式的对比分析，确定了热泵系统合理的Yong效率表达式。最后说明，在压缩式制冷系统中当高温热源不为环境时，Yong效率定义也存在同样缺陷，改进方法与本文类似。     

制冷与热泵系统的Yong分析

介绍了制冷与热泵系统的Yong分析方法。通过对系统的各环节的Yong损失分析，进而得出系统的Yong效率，还介绍了减少Yong损失，提高Yong效率的措施。     

单元初始Yong效率和Yong流价值分布

分析了Yong的不等价性，在此基础上提出了Yong弹性系数、初始Yong损耗率等概念。以Yong弹性系数为计算基础，分析了在单一系统内各组元Yong效率对整个系统Yong效率的影响，导出了初始Yong损耗率的计算方法，并以实例进行了分析计算。分析表明：系统内各组元的单位Yong所消耗的初始Yong更能反映系统各组元的Yong耗特性，从而有利于更科学地分析系统各单元的节能潜力。     

天然气热、电、冷三联供的热经济性分析

提出系统Yong经济系数方法，对天然气热、电、冷三联供系统，天然气发电系统和天然气热电联供系统进行分析，计算出三系统的Yong经济系数，对其进行比较分析，指出天然气热、电、冷三联供系统具有较高的热经济性。进一步对天然气价格进行灵敏度分析，得出三系统在不同天然气价格下的Yong经济系数。图4表8参5     

楼宇冷热电联供系统的变工况及热力学分析

燃气轮机的楼宇冷热电联供系统是一种有前途的节能和环保的能源系统，该文对1个己运行了4年的系统进行了变工况和热力学分析计算，得出了该系统在夏季的设计负荷和变工况条件下能源效率和Yong效率的数据，并进行了讨论和给出了结论。     

基于能级概念的Yong经济学计价策略

正确合理地对Yong流计价，确定从燃料到产品Yong流的转换过程中费用形成及变化过程，是实现能量系统的炯经济学分析和优化的关键之一。将能级的概念引入热经济学计价体系。把供入能流按能级拆分，依据能级相近最大化相供的原则，解决能量取出与供入间的对应问题，提出了基于能级相近最大化相供的Yong流计价策略，以减少求解过程中所涉及的未知变量数。说明产品Yong流存在时的附加方程引入情况。最后以典型的热电联产系统(CGAM系统)的Yong经济分析优化中Yong流计价为例，介绍了该计价方法的应用。     

确定热电联产中热、电分摊比的折合Yong—Yong法

在热电联中,热电分摊比的合理制定是直接关系到热电厂和热用户双方利益的一种重要的问题。根据在供热过程中起到的作用,引入折合Yong的要领,考虑热电联产机组供热能量中的可能能占机组总可用能的比例,建立折合Yong－Yong法热电分摊比分析模型,并对几种典型的机组的实际运行工况进行了计算,本文提出了折合Yong－Yong法克服了京城 缺陷,物理意义明确,简单适用。     

立窑Yong分析浅析

利用Yong分析的方法对立窑系统进行了Yong分析,得出了Yong效率,Yong变质系数,找出了立窑系统能量利用的薄弱环节,提出了节能挖潜措施。     

热泵定义及Yong效率计算方法探讨

热力学中对热泵的定义与工程实际中的热泵意义不一致。由此导致热泵用效率计算方法的出入，以至产生热泵Yong效率大于1的原则性错误，本文以热泵，Yong分析基本理论为依据，就热泵定义及热泵Yong效率计算方法问题进行了广泛深入的探讨，提出了新的热泵定义，给出了符合Yong分析理论原则的热泵Yong效率计算方法。     

Exergy analysis of lithium bromide/water absorption systems

Exergy analysis of a single-effect lithium bromide/water absorption system for cooling and heating applications is presented in this paper. Exergy loss, enthalpy, entropy, temperature, mass flow rate and heat rate in each component of the system are evaluated. From the results obtained it can be concluded that the condenser and evaporator heat loads and exergy losses are less than those of the generator and absorber. This is due to the heat of mixing in the solution, which is not present in pure fluids. Furthermore, a simulation program is written and used for the determination of the coefficient of performance (COP) and exergetic efficiency of the absorption system under different operating conditions. The results show that the cooling and heating COP of the system increase slightly when increasing the heat source temperature. However, the exergetic efficiency of the system decreases when increasing the heat source temperature for both cooling and heating applications.     

Exergetic evaluation of methods for improving power generation efficiency of a gas turbine cogeneration system

A cogeneration system generating both heat and power for district heating and cooling is required to be more efficient to improve its economy. In this paper, three typical methods for improving the power generation efficiency of a gas turbine cogeneration system are evaluated by examining exergy flow at various points of the system. The three methods investigated are: (a) to raise turbine inlet temperature, (b) to incorporate a regenerative cycle, and (c) to introduce a dual-fluid cycle. Exergy flows at various points of each cogeneration system have been evaluated. It has been shown through quantitve analyses of exergy flows (1) what kind of energy loss of the system can be reduced by introducing each efficiency-improving method, (2) that the method of incorporating a regenerative cycle is highly useful in improving exergy efficiency of the cogeneration system. © 1997 by John Wiley & Sons, Ltd.     

Performance and parametric investigation of a binary geothermal power plant by exergy

Exergy analysis of a binary geothermal power plant is performed using actual plant data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy diagram, and compared to the energy diagram. The sites with greater exergy destructions include brine reinjection, heat exchanger and condenser losses. Exergetic efficiencies of major plant components are determined in an attempt to assess their individual performances. The energy and exergy efficiencies of the plant are 4.5% and 21.7%, respectively, based on the energy and exergy of geothermal water at the heat exchanger inlet. The energy and exergy efficiencies are 10.2% and 33.5%, respectively, based on the heat input and exergy input to the binary Rankine cycle. The effects of turbine inlet pressure and temperature and the condenser pressure on the exergy and energy efficiencies, the net power output and the brine reinjection temperature are investigated and the trends are explained.     

Role of exergy in increasing efficiency and sustainability and reducing environmental impact

The use of exergy is described as a measure for identifying and explaining the benefits of sustainable energy and technologies, so the benefits can be clearly understood and appreciated by experts and non-experts alike, and the utilization of sustainable energy and technologies can be increased. Exergy can be used to assess and improve energy systems, and can help better understand the benefits of utilizing green energy by providing more useful and meaningful information than energy provides. Exergy clearly identifies efficiency improvements and reductions in thermodynamic losses attributable to more sustainable technologies. A new sustainability index is developed as a measure of how exergy efficiency affects sustainable development. Exergy can also identify better than energy the environmental benefits and economics of energy technologies. The results suggest that exergy should be utilized by engineers and scientists, as well as decision and policy makers, involved in green energy and technologies in tandem with other objectives and constraints.     

Second law analysis of wind turbine power plants: Cesme, Izmir example

In this study, the energy and exergy efficiency results of the Wind Turbine Power Plants (WTPPs) are presented. Exergy, energy and technical availability analysis are performed. The case study includes the actual system data taken from the system in Cesme, Izmir WTPP. General energy, exergy and other performance parameters are also presented. Investigated WTPP is Turkey’s first installed (1998) wind plant (1.50 MW) located in Izmir. Exergy efficiency of the power plant found to be between 0% and 68.20%. The monthly average technical availabilities are 96.11%, 98.71%, 98.52% for turbine 1, turbine 2, and turbine 3, respectively. Furthermore, authors developed some correlations, which are capable of predicting the values of exergy efficiencies of the WTPP for different power factor value.     

Exergy analysis of a dual-level binary geothermal power plant

Exergy analysis of a 12.4 MW existing binary geothermal power plant is performed using actual plant data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy flow diagram, and compared to the energy flow diagram. The causes of exergy destruction in the plant include the exergy of the working fluid lost in the condenser, the exergy of the brine reinjected, the turbine-pump losses, and the preheater–vaporizer losses. The exergy destruction at these sites accounts for 22.6, 14.8, 13.9, and 13.0% of the total exergy input to the plant, respectively. Exergetic efficiencies of major plant components are determined in an attempt to assess their individual performances. The exergetic efficiency of the plant is determined to be 29.1% based on the exergy of the geothermal fluid at the vaporizer inlet, and 34.2% based on the exergy drop of the brine across the vaporizer–preheater system (i.e. exergy input to the Rankine cycle). For comparison, the corresponding thermal efficiencies for the plant are calculated to be 5.8 and 8.9%, respectively.     

An exergy analysis of a solar-driven ejector refrigeration system

Exergy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m², an evaporator temperature of 10 °C, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 °C as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 °C.     

Thermodynamic assessment of photovoltaic systems

In this paper, an attempt is made to investigate the performance characteristics of a photovoltaic (PV) and photovoltaic-thermal (PV/T) system based on energy and exergy efficiencies, respectively. The PV system converts solar energy into DC electrical energy where as, the PV/T system also utilizes the thermal energy of the solar radiation along with electrical energy generation. Exergy efficiency for PV and PV/T systems is developed that is useful in studying the PV and PV/T performance and possible improvements. Exergy analysis is applied to a PV system and its components, in order to evaluate the exergy flow, losses and various efficiencies namely energy, exergy and power conversion efficiency. Energy efficiency of the system is calculated based on the first law of thermodynamics and the exergy efficiency, which incorporates the second law of thermodynamics and solar irradiation exergy values, is also calculated and found that the latter is lower for the electricity generation using the considered PV system. The values of “fill factor” are also determined for the system and the effect of the fill factor on the efficiencies is also evaluated. The experimental data for a typical day of March (27th March 2006) for New Delhi are used for the calculation of the energy and exergy efficiencies of the PV and PV/T systems. It is found that the energy efficiency varies from a minimum of 33% to a maximum of 45% respectively, the corresponding exergy efficiency (PV/T) varies from a minimum of 11.3% to a maximum of 16% and exergy efficiency (PV) varies from a minimum of 7.8% to a maximum of 13.8%, respectively.     

A longitudinal analysis of the UK transport sector, 1970–2010

This paper presents an overview of the resource consumption and environmental impact of the United Kingdom's transport system for the period between 1970 and 2010. For the purpose of this analysis the concept of exergy has been employed both to quantify and aggregate the energy used and the atmospheric emissions arising from the sector. Our analysis illustrates and elucidates the disproportionate increase of the overall exergy consumed by the transport sector when compared to that of other UK economic sectors. Furthermore, its environmental impact and, in particular, the trends in the emission of the main ambient air pollutants and greenhouse gases is discussed. Exergy efficiency and intensity time series are also calculated and recommendations are made in order to minimize the sector's environmental impact and to facilitate a shift towards a more sustainable transport system.