正戊烷热稳定性和材料相容性对超临界ORC系统设计的影响

有机朗肯循环(Organic Rankine Cycle,ORC)在可再生能源和工业余热领域都有着良好的应用前景,特别是超临界ORC系统目前得到广泛关注。工质的热稳定性和材料相容性是工质的重要物性,对系统设计有很大的影响。本文以正戊烷为例,对热稳定性和材料相容性对超临界ORC系统设计的影响进行研究。提出了一种冷凝器改造装置方案,并建立ORC系统仿真模型对其改善效果进行验证;计算结果表明本文提出的改造方案可以明显改善正戊烷热分解带来的负面影响。同时对中高温工况下正戊烷的材料相容性进行实验研究。实验结果表明,304不锈钢相对铜材料有更优的相容性,从材料相容性角度来说是更合适的蒸发器材料。三元乙丙橡胶(EPDM)被证明会吸收正戊烷,因此不能用于正戊烷超临界ORC系统中;聚四氟乙烯(PTFE)相比氟橡胶(FKM)有更优的相容性,从材料相容性角度来说是更合适的膨胀机出口密封材料。     

有机朗肯循环工质热稳定性研究进展

介绍了有机朗肯循环(ORC)工质热稳定性研究进展,总结归纳了ORC工质热稳定性在实验和理论两方面的研究成果,并对现有的ORC工质热稳定性实验方法进行了分析。结合分析结果对ORC工质热稳定性研究进行展望,指出未来可能的发展方向。     

内燃机余热回收有机朗肯循环系统研究综述

有机朗肯循环(Organic Rankine cycle, ORC)系统是一种回收内燃机余热的有效方案之一,目前受到越来越多的关注。由于内燃机余热形式多样,温度梯度大且存在变温特性,基本有机朗肯循环用于回收内燃机余热有一定难度。本文对内燃机有机朗肯循环系统的相关研究进行了综述,以余热最佳匹配循环为基础,分别从工质和系统结构方面对比分析了超临界ORC,混合工质ORC,双回路ORC和添加额外回路ORC四种方案。采用温熵(T-S)图映射法,根据有机朗肯循环与理想循环的接近度,总结了多种有机朗肯循环系统用于内燃机余热回收的潜力。分析发现在相同的循环系统下,具有较高临界点的工质和有较大的温度滑移的混合工质更有优势,相同工质下,双回路ORC和添加额外回路的ORC是解决内燃机余热波动的合理方案之一。     

R1233zd(E)热稳定性及热解机理的实验和理论研究

有机朗肯循环(ORC)是一种前景广泛的热电联产技术,R1233zd(E)是一种在ORC中表现良好的环保型有机工质,有机工质的热稳定性对于工质在ORC中的应用至关重要。本文采用实验和理论方法对其热稳定性及热解机理进行了研究。采用高温高压反应釜研究了热解气态产物、热解固态产物、热解温度区间和压力对热解的影响等。通过ReaxFF模拟方法研究了工质的主要热解路径、压力和分子结构对热解的影响。结果表明,R1233zd(E)热解的主要气态产物是HF和HCl,热解中有黑色固体生成,R1233zd(E)的热解温度区间为250～270?C,压力对R1233zd(E)热解速率无明显影响, R1233zd(E)的热解路径主要有均裂反应和抽提反应两大类。     

有机工质热稳定性的离解能预测方法

有机朗肯循环(Organic Rankine Cycle,ORC)在可再生能源和工业余热等领域有着广泛的应用,目前热源温度范围更高的超临界ORC由于其高效率、低损失等优势得到广泛的关注。随着热源温度的提高,有机工质的热稳定性成为更为重要的工质性质,是工质筛选工作中需要首先确定的关键因素。目前针对有机工质热稳定性的研究主要集中在实验方面,而要对上百种适用工质进行筛选,合适的理论预测方法是必要的。本文提出了一种对有机工质热稳定性进行预测的离解能预测方法,可以实现对于不同种类有机工质热稳定性的理论预测。计算结果表明工质的最小离解能能够很好的表征工质热稳定性的相对大小;同时选择HFE7100作为验证对象对预测方法进行实验验证,发现实验结果与预测结果相符合。同时通过对最小离解能的计算对不同官能团对工质热物性的影响以及不同种类工质在超临界ORC中的适用性进行了分析讨论。     

联合液化空气储能的有机朗肯循环研究

有机朗肯循环(ORC)是中低温余热资源的一种有效利用方式,但其平均吸、放热温度差值较小,使得系统的循环效率不高,经济性不够理想,从而严重制约其发展.液化空气储能(LAES)是近年兴起的一种新型储能技术,其电力恢复阶段需要热量的输入。若通过合理的设计,将液化空气储能技术与ORC技术相结合,则可降低现有ORC系统的冷凝温度,提升其发电效率.本文以基本的ORC循环系统为基础,对比分析了丙烷、R-134a及R-22三种工质在常规冷凝和结合液化空气储能技术冷凝条件下的循环性能.结果表明,联合液化空气储能的ORC循环效率大幅高于常规ORC。     

循环参数对微型有机朗肯循环系统性能的影响

为探究ORC系统循环参数对系统性能的影响,以R123为工作流体,在热力学分析的基础上对微型ORC系统建立数学模型,探究工质质量流量、冷却水流量以及热源温度对ORC系统性能特征的影响,结果表明三者的增加均能提升系统循环净功、循环热效率、发电功率以及发电效率,从而有助于提高系统的热力性能,系统循环净功与发电功率最大值分别为0.558 kW、0.167 kW;系统所达到最大热效率和最大发电效率分别为8.96%和2.61%。     

基于HFOs工质的有机朗肯循环系统热经济性能分析

本文建立了150℃地热水驱动的有机朗肯循环(ORC)系统热经济性能分析模型,对7种氢氟烯烃类(HFOs)工质和3种含HFOs的混合工质开展优化分析。以系统净现值(NPV)为优化目标,采用遗传算法对蒸发温度、过热度、蒸发/冷凝过程夹点温差和冷源出口温度等五个系统参数进行优化,分析各参数对系统热经济性能的影响。并将HFOs工质的热经济性能与R134a、R600a和R245fa进行对比。结果表明,R515A和R1234ze(E)的热经济性能最优,且均优于三种对比工质;其中,R515A的系统净输出功最大,R1234ze(E)的NPV最大,而R452B和R1234yf的热经济性能较差。     

有机朗肯循环系统及其透平设计研究

本文对可用于工业低温余热回收的有机朗肯循环(ORC)热力系统进行简述,采用热力学第一定律、热力学第二定律分析ORC热力系统及其效率,并对有机工质动力透平的特点及设计造型进行概述。最后采用F11,R123,R245ca,R600和R600a为工质,设计有机朗肯系统回收某一工业余热,并以R123为工质进行有机工质透平的气动设计、造型设计和CFD模拟计算研究,并对透平进行造型优化。研究表明,以R123为工质的有机朗肯循环系统能有效可靠利用该工业余热,所设计的有机工质透平基本达到设计要求,透平造型的优化设计能有效改善透平叶轮内部流动。     

R245fa有机朗肯循环发电系统运行性能实验研究

有机朗肯循环(ORC)利用低温热源实现热电转化的技术特点,是实现余热有效回收利用的重要途径。基于R245fa为循环工质的ORC发电系统,研究低温热源温度变化对系统循环热效率与发电效率的影响。结果表明:在冷却端温度不变的工况下,热源温度的提高使循环蒸发压力上升,膨胀比增大,等熵效率提升,膨胀做功能力增强,系统循环热效率、熵效率、发电效率均增大。夏季运行,冷却水进水水温为(30±1)、(35±1)℃,热源温度从89.6℃升至112.5℃时,系统发电效率分别由6.9%、5.8%升到8.7%、7.4%,系统■效率分别由43.4%、38.8%升到62.7%、62.3%。     

二元混合工质的氧化分解机理研究

基于量子化学密度泛函理论对低全球变暖潜值工质R152a与R600a进行了氧化分解机理研究. 通过对它们的主要起始反应路径分析及能量变化情况计算,结果表明：R152a与R600a热分解的起始反应可以分为工质自身热分解和与氧气碰撞分解两类,其中工质自身热分解的反应能垒比工质与氧气反应的能垒高,并且R600a比R152a更容易发生氧化分解;在二者混合后的起始反应阶段,R600a更容易先发生分解,而链式反应中R152a与自由基的反应更占优势;两种工质与自由基的反应大部分为放热反应,可以向反应体系提供热量,促进链式反应的进行. 相关结果可为新型混合工质的氧化分解机理研究提供参考.     

矩形微槽道饱和沸腾临界热流密度特性

对矩形微槽中的流动沸腾临界热流密度进行了实验研究。研究CHF随质量流速、进口过冷度和出口干度的增加而出现的变化趋势,以及槽道尺寸对CHF的影响。搭建试验平台,在不同槽道当量直径、较大范围的质量流速和不同进口过冷度条件下,获得以去离子水为工质两相沸腾传热的实验数据。由于常规尺寸槽道CHF预测关联式并不具有普遍性,所以提出了一个适用于微槽道饱和沸腾CHF的预测模型。并通过与该文以及参考文献中实验数据进行对比,验证了该模型的适用性。     

Effect of electric field on the enhanced heat transfer characteristic of an evaporator with multilayered sintered copper mesh

In this paper, it was investigated experimentally that the effect of different kinds of working fluid on the thermal performance of evaporator with capillary wick consisted by multilayered sintered copper mesh under different electric field strengths at the operating pressure of 1.01 × 10⁵ Pa R141b and R123 were used as the working fluids. The electric field strength in this study was in the range of 0kV/m–1600 kV/m, respectively. The experimental results showed that the applied electric field strength has significant effect on heat transfer characteristic. The heat transfer enhancement effects increased with the increase of the electric field. Under the applied electric field strength, the maximum heat transfer enhancement factors could reach as high as 1.5 and 1.32 for the two kinds of working fluids in the experiment.     

EXPERIMENTAL STUDY OF A PULSATING HEAT PIPE USING FC-72, ETHANOL,AND WATER AS WORKING FLUIDS

Experimental studies were performed on a pulsating heat pipe (PHP), consisting of a heating section, an adiabatic section, and a condensation section incorporating a heat sink. The capillary tube used in this study has an inside diameter of 1.18 mm and a wall thickness of 0.41 mm. The experiments were conducted under the condition of pure natural convection, for heating powers from 5 to 60 W, fill ratios from 60% to 90%. Three working fluids—FC-72, ethanol, and deionized water—were used. The thermal oscillation of the thin wall surface was recorded by a high-speed data acquisition system. Such thermal oscillation waves are random for some run cases due to the randomly distributed vapor plug and liquid slugs inside the PHP. The thermal oscillation amplitude is much smaller for FC-72, due to its lower surface tension, than for ethanol and water, while the oscillation cycle period for FC-72 is shorter than for the other two fluids, indicating the faster oscillation movement in the channels, possibly due to the lower latent heat of evaporation for FC-72. The unlooped PHP is not helpful for the fluid circulation and the PHP does not work. For the looped PHP, there is a minimum heating power that initiates the PHP working. Such minimum heating power is strongly dependent on the working fluid, and is considerably smaller for FC-72 compared with water. The optimal filling ratio is around 70% for all three working fluids. The looped PHP with water as working fluid provides better overall thermal performance once the heating power is greater than a minimum value. However, FC-72 is suggested to be used for low-heat-flux situations, due to its lower minimum heating power.     

不同工质中汽泡周围电场特性研究

为探明外加电场作用下,不同工质对强化沸腾换热的影响,本文采用了FC-72、R11、R113和R123四种工质,定量研究了两相系统中汽泡周围电场分布特性,探讨了工质介电常数对汽泡的作用规律．结果表明:随着工质介电常数的增加,电场非均匀性增强,电场对汽泡的作用加剧．这为不同工质对EHD沸腾强化效果不同提供了理论依据．     

升膜式板式换热器的换热性能研究

升膜蒸发是在换热器表面形成一层薄液膜,薄膜蒸发能够强化换热。文中研究采用光滑铜板的板式升膜蒸发器,以去离子水作为介质,在不同进水流量、不同加热量(热流密度)下,测定换热器某些点的局部换热系数,计算出总的换热系数,研究影响板式换热器升膜蒸发的因素和变化趋势。     

Conversion of low-grade heat from FCC absorption-stabilization system to electricity by organic Rankine cycles: Simulation and optimization

In this study, the organic Rankine cycle (ORC) is applied to be integrated into the fluid catalytic cracking (FCC) absorption-stabilization system to extract and convert the low-grade process heat to electricity. This newly integrated system is simulated by the Aspen Plus software. For the simulation, eleven different dry and isentropic working fluids are selected to investigate the energy conversion performance of the incorporated ORC system. It is found that, the performance depends highly on the operational parameters, such as mass flow rate and the evaporation pressure of the working fluids, outlet temperature of the process stream. After optimization, the working fluids R124 and R227ea are determined to be the best candidates due to their highest output net work in HCT (high critical temperature) and LCT (low critical temperature) working fluids, respectively. A further optimization has been conducted based on the economic evaluations (i.e., electricity production cost (EPC) and total annual profit (TAP)). Results show that, for the HCT working fluids, the use of working fluid of R245fa allows the EPC to be the lowest, while the application of R124 obtains the highest TAP. For the LCT working fluids, R227ea is the best choice due to its lowest EPC and highest TAP.     

Modern development on the features of magnetic field and heat sink/source in Maxwell nanofluid subject to convective heat transport

Nanofluids are forthcoming new generation heat transfer fluids, which have been scrutinized precisely, in current years. Thermophysical assets of these fluids have noteworthy impact on their heat transfer features. In this current investigation a mathematical relation for two dimensional (2D) flow of magnetite Maxwell nanofluid influenced by a stretched cylinder is established. To visualize the stimulus of Brownian moment and thermophoresis phenomena on Maxwell fluid Buongiorno's relation has been considered. Moreover, heat sink/source and convective condition are also presented for heat transport mechanism. The homotopic scheme has been developed for the solutions of nonlinear ordinary differential equations (ODEs). The achieved outcomes are planned and consulted in aspects for somatic parameters. It is noteworthy that the velocity of Maxwell fluid display conflicting performance for curvature parameter and Deborah number. It is also reported that the liquid velocity decays for magnetic parameter, whereas the nanoliquid temperature and concentration field enhance for magnetic parameter. Furthermore, the liquid temperature intensifies for the progressive values of thermophoresis parameter and Brownian motion. Additionally, endorsement of current significances is organized via benchmarking with earlier famous limiting situations and we pledge a marvelous communication with these outcomes.     

Thermal stability of atmospheric plasma sprayed (Ni, Cu, Co)–YSZ and Ni–Cu–Co–YSZ anodes cermets for SOFC application

This paper reports the results of the thermal stability study of M–YSZ (M=Ni, Cu, Co, Cu–Co, Ni–Cu–Co) SOFC anode cermets materials at different heat treatment temperatures. The cermets were elaborated by atmospheric plasma spraying (APS) with optimized conditions and then submitted to heat treatments at 800 and 1000 °C, respectively. Scanning electron microscopy and X-ray diffraction were used to characterize, respectively, the morphology and structure of obtained films, before and after thermal annealing. A correlation was made between the differential scanning calorimetry analysis results and those obtained by X-ray diffraction. Focusing, in this study, on YSZ matrix thermal stability, the obtained results were as follows: the monometallic cermets with the lowest amount of metal and the trimetallic one exhibited a good stability at 800 °C, whereas at 1000 °C, all considered cermets were unstable with a eutectoid decomposition of YSZ matrix.     

数据机房热管空调系统的实验研究

结合数据机房环境的特点,选取R22和R134a为工质,实验研究了数据机房热管空调系统的换热性能和工质的最佳充液率。结果表明,热管空调系统具有工作温差小、制冷能效比高的特点,随着热负荷的升高,所需排热温差逐渐增大;对比实验发现,工质为R22时空调系统的平均换热能力比R134a为工质时高19.2%,而两种工质的最佳充液率均为80%左右。通过对热管回路中工质温度分布的测量与分析,阐明了充液率过大或过小引起系统换热性能下降的原因。