变温热源布雷顿循环的功率密度优化

计入工质与高、低温侧换热器的热阻损失及压气机和涡轮机中的不可逆压缩和膨胀损失,用有限时间热力学方法,导出了恒温热源条件下不可逆布雷顿循环功率密度与压比间的解析式,借助于数值计算,研究了高、低温侧换热器的热导率分配和工质与热源间的热容率匹配对最大功率密度的影响。     

实际回热式布雷顿制冷机的性能优化

用有限时间热力学方法分析实际回热式布雷顿制冷机的性能特性,以制冷率和制冷系数为优化目标,优化了高低、温侧换热器和回热器的热导率分配以及工质和热源间的热容率匹配,并采用数值计算分析了各参数值对最优性能的影响特点.所得结果对工程制冷系统设计有一定的指导意义。     

两级中冷回热再热布雷顿热电联产装置的性能

应用有限时间热力学理论和方法建立了恒温热源不可逆两级中冷回热再热布雷顿热电联产装置模型,基于分析的观点,导出了装置无量纲输出率和效率的解析式。在给定总压比的情形下,通过数值计算分别研究了输出率和效率与两个中冷压比和两个再热压比的关系,当总压比变化时,发现输出率和效率对总压比存在最大值,并分别求出了两个相应的最佳的中冷压比和再热压比。分析了回热度、中冷度、再热度、压气机和涡轮机效率、压降损失等特征参数对装置性能的影响。最后发现分别存在最佳的用户侧温度使输出率和效率取得双重最大值。     

Four-Objective Optimizations for an Improved Irreversible Closed Modified Simple Brayton Cycle

An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, the cycle performance is optimized by taking four performance indicators, including the dimensionless power output, thermal efficiency, dimensionless power density, and dimensionless ecological function, as the optimization objectives. The impacts of the irreversible losses on the optimization results are analyzed. The results indicate that four objective functions increase as the compressor and turbine efficiencies increase. The influences of the latter efficiency on the cycle performances are more significant than those of the former efficiency. Then, the NSGA-II algorithm is applied for multi-objective optimization, and three different decision methods are used to select the optimal solution from the Pareto frontier. The results show that the dimensionless power density and dimensionless ecological function compromise dimensionless power output and thermal efficiency. The corresponding deviation index of the Shannon Entropy method is equal to the corresponding deviation index of the maximum ecological function.     

Experimental and numerical investigation on the exergy and entransy performance of a novel plate heat exchanger

There has been increased attention on various types of plate heat exchangers because of their high efficiency and compactness. This article presents an investigation of heat transfer and fluid flow performance of a novel plate heat exchanger based on numeric studies and experimental tests. Parameters of the novel plate heat exchanger are analyzed and discussed. The thermo-hydraulic transfer performance of different plate heat exchangers is comprehensively analyzed using the exergy and entransy principle. The results indicate that the novel plate heat exchanger has better thermo-hydraulic transfer performance than the smooth plate heat exchanger. The result of this study provides a paradigm for the optimal design of plate heat exchangers.     

采用化学链式燃烧的燃料电池联合循环及其性能分析

1课题背景高温燃料电池可与燃气轮机、蒸汽轮机等动力装置组成多重循环,实现能量的梯级利用,从整体上进一步提高能源利用率,为总能系统的发展提供了新的可行途径。氢能是一种高效、清洁、可再生的二次能源,被称为21世纪的能源。研究以氢为燃料、由高温燃料电池、燃气...     

Thermodynamic Analysis and Optimization of a Novel Power-Water Cogeneration System for Waste Heat Recovery of Gas Turbine

A power-water cogeneration system based on a supercritical carbon dioxide Brayton cycle (SCBC) and reverse osmosis (RO) unit is proposed and analyzed in this paper to recover the waste heat of a gas turbine. In order to improve the system performance, the power generated by SCBC is used to drive the RO unit and the waste heat of SCBC is used to preheat the feed seawater of the RO unit. In particular, a dual-stage cooler is employed to elevate the preheating temperature as much as possible. The proposed system is simulated and discussed based on the detailed thermodynamic models. According to the results of parametric analysis, the exergy efficiency of SCBC first increases and then decreases as the turbine inlet temperature and split ratio increase. The performance of the RO unit is improved as the preheating temperature rises. Finally, an optimal exergy efficiency of 52.88% can be achieved according to the single-objective optimization results.     

On the efficiencies of absorption heat pumps

Although commonly used, the coefficient of performance COP is not always an adequate measure to describe the effectiveness of a sorption heat pump. Equations for four different efficiencies are derived, discussed and compared for absorption heat pumps (AHP). A flow-sheeting computer program, developed for both design and evaluation simulations of arbitrarily complex absorption cycles, is used to exemplify the derived equations. The working fluid pair H₂OLiBr has been used in two different AHP configurations. The examples given clearly show that the COP can only be used to compare different AHPs operated at the same circulation ratio. The COP can be considered as an indicator of the effectiveness of heat exchange within and thermal insulation of a heat pump operated at a fixed circulation ratio. Nevertheless, it is an insufficient measure to compare different AHPs, even when they are operated at the same circulation ratio. On the other hand, the coefficient of performance for cooling Q_e/Q_g is better in this respect since it takes into account the real heat flow to the generator. The Carnot efficiency COP_rev takes into consideration both the real heat outputs from the absorber and condenser, and the temperature of heat sources and heat sinks. The thermodynamic efficiency E_th is shown to be a more logical measure of the heat pump efficiency, since it takes into account the real heat input the generator. The exergetic efficiency E_ex can be considered as an alternative to the thermodyanamic efficiency E_th but it offers a possibility to take into account any temperature level where heat energy may be considered worthless. However, both E_ex and E_th are not conventionally used since their numerical values are always less than 1.0. On the other hand, the exergetic index I_ex is directly related to E_ex but its numerical value shoul be considered as a more significant measure for evaluating the performance of AHP systems, since it properly takes into account the exergy losses which inevitably occur in the system. It may however be stressed that exergy analysis should be used as a compliment to the First Law analysis.     

耦合热泵换热器的原理及变工况性能研究

工业能耗占我国总能耗超过70%,而其能源利用效率不足50%,因此工业余热高效回收利用是节能减排的重要途径之一。热泵技术是提升能量品位的有效方法,但吸收式热泵需要配置三个不同温度品位的热源或热汇,而电动热泵受热力学循环、工质物性、压缩机耐温耐压限制以及避免润滑失效一般只能工作于有限温度范围(<100℃)之内,因此该研究将吸收式循环与压缩式循环进行深度耦合,用于直接回收工业余热制取高温热水,同时确保压缩机的安全稳定运行.该文首先分析耦合热泵换热器的运行原理,其次建立了耦合热泵换热器的数学模型,最后对模型进行求解分析了关键参数对耦合热泵换热器性能影响变化规律。在设计工况下,当制取133℃热水时,耦合热泵换热器COP达到3.6,压缩机排气压力为1.2 MPa,排气温度为79℃,远低于压缩机耐温耐压上限和润滑油失效温度,因此耦合热泵换热器在利用余热制取高温热水或蒸汽领域具有一定的应用潜力。     

给定边界条件下定常态制冷循环的最优化

给定边界条件下定常态制冷循环的最优化陈林根，孙丰瑞，龚建政，陈文振，赖锡棉（武汉海军工程学院三系，武汉海军工程学院基础部武汉４３００３３）关键词：有限时间热力学，卡诺制冷机，布雷顿制冷机，最优化一、前言实际工程问题主要是在给定的循环型式和运行边界条件...     

驻波型热声制冷机熵产分析

声制冷机是一种新型制冷机,具有无机械运动部件,可靠性高寿命长,采用惰性气体为工质无污染等优点．驻波型热声制冷机的声功泵热效应是不可逆过程,内部不可逆损失导致热声制冷机效率偏低,制约了热声制冷机的发展和应用．本文研究了线性范围内驻波型制冷机换热器和回热器内的可压缩振荡流动与传热过程的熵产,分析了板间距,振荡频率和温度梯度对熵产的影响。     

工质变比热条件下内燃机循环普适特性

用有限时间热力学的方法分析空气标准不可逆内燃机循环,导出了考虑工质变比热情况下,存在摩擦及传热损失时,由两个加热过程、两个放热过程和两个绝热过程组成的普适的空气标准不可逆内燃机循环的功率与压缩比、效率与压缩比以及功率和效率的最佳特性关系,同时由数值计算分析了工质变比热和循环过程对循环性能的影响特点,比较了工质恒、变比热时循环性能差异。所得结果包含了不可逆往复式Diesel、Otto、Brayton、Atkinson、Dual和Miller 循环的性能特性。     

换热器的综合效率分析

利用分析的方法对换热器进行了性能分析,推导出了综合评价换热器性能的公式;并以芳烃生产工艺中制苯工段的换热器为实例进行了具体的效率分析,得出了换热器的效率、单位面积的收益、损失及综合性能评价指标。结果表明:流体发生相变的换热器的性能要优于单相流体换热器的性能。     

Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.     

跨临界二氧化碳蒸气压缩/喷射制冷循环性能比较

本文从系统的COP、制冷量和有效能分析三个方面比较了跨临界CO2蒸气压缩／喷射循环、蒸气压缩／回热制冷循环和常规的蒸气压缩制冷循环的性能．结果表明,在本文研究工况下,喷射循环的性能系数最大值比回热循环高 18．6％,比常规循环高22．0％．喷射循环的制冷量比回热循环高8．2％,比常规循环高11．5％。有效能分析表明喷射循环极大地减小了节流损失,冷却放热损失和压缩损失也有相应的减少．     

冷热联供的空气制冷不可逆循环分析

本文分析了压气机排气余热利用的冷热联供回热空气制冷不可逆循环,并建立了仅忽略系统内所有换热器流动阻力损失的循环工作性能系数(COP)计算方程式。用该方程分析研究了透平膨胀机与压气机等熵效率、压缩机排气余热度、降温比、传热温差、压比等参数对系统COP值的影响,发现膨胀透平等熵效率提高对COP值的贡献远大于压气机效率同样提高的功效;在其它参数确定时,存在最佳压比,可使系统工作性能系数在该条件下达极值。在优化参数配置下,用于空气调节的冷热联供回热空气制冷不可逆循环的COP值可达2左右。     

有限大低温热源混合工质节流制冷循环特性分析

通过深入分析和比较各种单级压缩混合工质节流制冷循环在低温热源为有限大热源时的热力学性能,揭示了不同循环型式之间的内在热力学关系,阐明了该类节流制冷机能够实现深度制冷的内在原因是利用了制冷机的内部热交换来减少节流制冷机所固有的节流过程的不可逆损失,并用实验进行了验证。     

Utilization of geothermal waters for heating by heat pumps

This paper treats the solution to the problem of the connection of heat exchanger and heat pumps in geothermal district heating systems. A numerical solution for the theoretical Rankine heat pump cycle is presented to determine the thermodynamic process efficiency as a criterion of quality of energy flow in the process of its transformation. This allows a reduction in the losses caused by irreversibility of real processes and saves energy. The results in graphical form are used in practice for technical and economic optimization of various geothermal heating systems employing heat pumps.     

铅基堆超临界CO2复合循环发电系统热力学分析

本文对比了再压缩超临界CO2 (S-CO2)循环、蒸汽朗肯循环、He布雷顿循环分别应用于铅基堆的最优热学性能,明确了S-CO2循环与铅基堆结合较传统循环的热力学优势。为进一步提高再压缩S-CO2循环的效率,以跨临界CO2 (T-CO2)循环为底循环构建了再压缩S-CO2/T-CO2复合循环,探讨了不同顶循环透平入口温度、压力和压缩机入口温度条件下系统性能的变化规律,对比了S-CO2/T-CO2复合循环和S-CO2循环的热学性能。结果表明:铅基堆再压缩S-CO2循环发电系统较传统循环形式具有更高的热效率;构建的S-CO2/T-CO2复合循环能够有效提高S-CO2循环的效率,在所研究参数范围内,S-CO2/T-CO2复合循环的热效率和效率比S-CO2循环分别最大可提高约4.8%和8.3%;再压缩S-CO2循环和S-CO2/T-CO2复合循环热学性能随顶循环关键参数变化规律具有一致性。     

利用LNG冷(火用)与工业余热的闭式Brayton循环的进一步分析

以超临界状态的LNG作为冷源,以工业余热作为热源的闭式Brayton循环,可以有效的利用LNG的冷(?)并回收工业余热。本文以(?)效率为评价准则,兼顾LNG冷(?)和工业余热的利用,对该循环进行了热力学分析。在分析过程中,利用以前分析所得的结论[1],选取的循环自变量数为4,针对不同的自变量、不同的LNG冷(?)和工业余热利用情况,对多种循环方案作了进一步(考虑了循环与冷、热源的匹配)较详细的热力学分析,并得出较明确的性能表达。