海洋温差发电系统蒸发压力及工质优选分析

文章基于热力学原理,建立了海洋温差发电系统仿真模型,分析了R717,R134a和R600这3种工质系统的性能参数随蒸发压力的变化。研究结果表明:随蒸发压力的增大,不同工质系统的蒸发器和冷凝器的热负荷和海水泵功率均近似呈幂递减的变化趋势,不同工质系统的泵功率均近似呈指数递增的变化趋势,不同工质系统的质量流量均近似呈幂递减的变化趋势,不同工质系统的热效率均近似呈对数递增的变化趋势;蒸发压力越大,R717和R600工质系统的单位换热面积发电量越大,但R134a工质系统的单位换热面积发电量随蒸发压力的增加存在峰值;在不同工质的饱和蒸汽压力下,R600工质系统的单位换热面积发电量最大,但其透平进出口压降较小,乏汽温度高,工质流量大,导致透平尺寸较大;R717工质系统具有较大的蒸发压力操作范围,且其热效率较大,单位换热面积发电量在合适的范围内,适用于海洋温差能发电系统。     

海上油气平台余热朗肯循环发电系统热力学分析

海上油气平台存在大量的燃气轮机余热。通过建立海上平台余热朗肯循环发电系统仿真模型,开展平台余热发电热力学及热经济性分析。选取工质泵功率、发电机输出功率、系统热效率、换热面积和单位面积发电量等参数作为优化目标,研究不同冷凝温度下优化目标函数随蒸发器烟气进出口温差的变化规律。结果表明:随着蒸发器烟气进出口温差的增加,工质泵功率、发电机输出功率和系统APR先增大后减小。冷凝温度越高,工质泵功率越大,发电机输出功率和系统热效率越小。当冷凝温度为65℃时,系统APR最大。受透平出口蒸汽干度的限制,所研究工况下,系统发电机最大输出功率为7 496 kW,系统最大热效率和APR分别为14.16%和5 kW·m~(-2)。研究结果可为撬装化、集成化海上油气平台余热发电系统研制提供理论参考。     

基于粒子群算法的海洋温差能朗肯循环系统多目标优化

为提高海洋温差能发电系统的综合性能,以单位换热面积发电量和单位海水流量发电量为基础建立综合目标函数,选取蒸发温度、冷凝温度、蒸发器和冷凝器的海水出口温度为优化变量,利用粒子群算法对海洋温差能朗肯循环系统进行多目标参数优化。研究结果表明,在28℃温海水和5℃冷海水条件下,循环工质为R717时,蒸发器内的最佳蒸发温度为23.10℃,温海水出口温度为23.42℃;冷凝器内的最佳冷凝温度为12.31℃,冷海水出口温度为10.80℃;在换热器的海水进出口温差超过4℃时,换热器的海水出口温度对系统性能的影响较小。综上,采用多目标优化可实现对各评价指标间的协调,相比单目标优化的传统模型,多目标优化改善了系统的综合性能。     

基于海底黑烟囱的海洋温差发电热力循环系统研究

与传统的海洋温差发电系统不同,海底黑烟囱海洋温差发电系统是以海洋地热为热源,以深海冷水为冷源的发电系统。文章分别分析和计算了以水蒸气为工质的开式系统和以纯氨为工质的闭式系统的循环热效率、换热器负荷、泵耗以及循环净功等相关参数。结果表明,与以纯氨为工质的闭式系统相比,开式系统的热水泵功耗过大,降低高温海水的温度和提高闪蒸压力对开式系统是不利的;以水蒸气为动力循环工质有利于降低换热器的负荷,这对换热器的设计是十分有利的。     

以R134a为工质的OTEC朗肯循环热力计算软件开发

以海洋温差热能转换（OTEC）的热力循环为研究对象，为给循环分析提供方便准确的性能计算工具，采用Python程序设计语言，开发了OTEC朗肯循环热力计算软件。软件可以完成简单朗肯循环、再热朗肯循环、抽气回热朗肯循环等3种循环的热力计算，输出结果包括循环最高限制压力、冷凝压力、工质泵功、膨胀机功、蒸发器热负荷、冷凝器热负荷、循环净功以及循环热效率等朗肯循环性能参数。工质热力性质采用R134a的最新国际标准关联式，计算结果足够精确，在蒸发温度24.34℃、冷凝温度8.14℃，泵效率和透平效率均为1.0的工况下，与采用NIST提供的热物性数据进行循环计算结果对比表明，二者完全一致，循环热效率均为5.15%。软件可作为OTEC发电装置的热工设计参考，也可用于R134a工质的 -103.15℃~426.85℃之间的亚临界朗肯循环、跨临界朗肯循环和超临界循环等领域的应用，软件的成功开发对我国OTEC发电应用领域的发展具有相当程度的技术保障与引领作用。     

以R508B与R23为低温工质的复叠循环理论模拟

在医用超低温场景下,研究了以R404A为高温级工质,分别以R508B与R23为低温级工质的复叠循环的理论循环性能。通过计算,模拟了高温级冷凝温度、高温级蒸发温度和冷凝蒸发器换热温差对系统COP的影响。得到结论,随着高温级冷凝温度的升高,复叠系统的COP逐渐下降;随着高温级制冷系统蒸发温度的升高,复叠系统的COP呈现出先上升后下降的变化趋势;而随着冷凝蒸发器换热温差的升高,复叠系统的COP出现逐渐下降的趋势。综合来看,应优先考虑R508B作为低温级制冷工质。     

海洋温差能发电循环系统热力学分析

对海洋温差发电朗肯循环系统进行分析,分别研究蒸发压力、氨水浓度、冷热海水温度等参数对系统热效率和?效率的影响,对比分析纯氨和二氟一氯甲烷工质系统热效率和?效率,为海洋温差能开发及商业级发电系统研建提供技术支撑。结果表明:系统热效率和?效率与密切相关,氨水浓度的影响较小;纯氨质量流量远小于二氟一氯甲烷,且其热效率和?效率均大于二氟一氯甲烷系统,是海洋温差发电系统较为理想的循环工质。     

对流热采油页岩过程低温余热ORC系统热力分析

为回收利用对流热采油页岩过程中产生的低温余热蒸汽,提出并设计有机朗肯循环(ORC)系统进行热力发电。在特定余热蒸汽参数条件下,基于R245fa循环工质,编制计算程序模拟分析了ORC系统变工况参数对该系统热效率及输出功率的影响规律。数值模拟结果表明:设定汽轮机背压为0.25MPa时,工质最高蒸发压力为2.566MPa,在此范围内,系统热效率随蒸发压力升高单调增加,增幅减缓;取蒸发器出口温度85℃时,对于不同的蒸发压力系统允许运行工质流量范围不同,在同一蒸发压力下,由于热源限制导致系统热效率并未随工质流量增加显著提高,但可得到更多输出净功;蒸发压力为1.5 MPa时,随余热排放温度的降低,系统输出净功显著提高;随汽轮机背压的降低,系统热效率得到明显改善,但汽轮机背压的降低增加了工质冷凝的困难,合适的背压值取0.2MPa。     

亚临界有机朗肯循环系统的热经济分析与优化

以系统发电成本(electricity production cost,EPC)为评价指标,对用于回收工业锅炉烟气余热的有机朗肯循环(ORC)系统进行了热经济分析与优化。结果表明,随着蒸发器和冷凝器节点温差的增大,系统发电成本先减小、再增大,即存在一组最优的蒸发器和冷凝器节点温差使发电成本最小。分别以纯工质R245fa和R236ea、非共沸混合工质R141b/RC318和乙烷/丁烷为循环工质,得到了最小发电成本时有机朗肯循环系统的最优工作参数,以及对应的系统净输出功、热效率和火用效率。     

低温余热有机朗肯循环发电系统热经济性分析

针对工业中排放的低温烟气,建立有机朗肯循环发电系统的热经济分析模型,分析蒸发压力、热源温度及蒸发器最小传热温差对系统经济性能的影响。分析结果表明:热源温度为140℃,循环采用R123的经济性最佳,相应的发电成本与动态投资回收期分别为0.142元(/kW.h)与3.68年。余热发电系统存在一个经济性最高的蒸发压力,不同工质对应的最佳蒸发压力也不同。蒸发器内最小传热温差为15℃时,系统的经济性较好。烟气温度在100～180℃时,系统采用R123的投资回收期最短,而烟气温度高于180℃时,R141b的经济性更高;不宜采用有机朗肯循环发电技术回收温度低于100℃的低温烟气。     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

Economie d'énergie en trigénération

Trigeneration is defined as the production of three useful forms of energy—heat, cold and power—from a primary source of energy such as natural gas or oil. For instance, trigeneration systems typically produce electrical power via a reciprocating engine or gas turbine and recover a large percentage of the heat energy retained in the lubricating oil, exhaust gas and coolant water systems to maximize the utilization of the primary fuel. The heat produced can be totally or partially used to fuel absorption refrigerators. Therefore, trigeneration systems enjoy an inherently high efficiency and have the potential to significantly reduce the energy-related operation costs of facilities. In this paper, we describe a model of characterization of trigeneration systems trough the condition of primary energy saving and the quality index, compared to the separate production of heat, cold and power. The study highlights the importance of the choice of the separate production reference system on the level of primary energy saving and emissions reduction.     

Mineralogical characterization of the intraseam layers of Lofoi lignite deposits in Florina basin (western Makedonia,northwest Greece)

The mineralogical composition of intraseam layers from Lofoi lignite deposits (northwest Greece) is the subject of the present study. The samples were examined by means of X-ray diffraction (XRD), thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA), and Fourier transform infrared (FT-IR) spectrometry. The clay minerals prevail in most samples, with illite-muscovite being the dominant phase, and kaolinite and chlorite being the other major clay components. No smectite was found. Quartz and feldspars, dominate in two cases. The studied materials are characterized as clays to clayey sands, showing significant similarities with the intraseam layers of the adjacent Achlada lignite deposits.     

Innovative methodologies in renewable energy: A review

This paper is concerned with innovative approaches to renewable energy sources computation methodologies, which provide more refined results than the classical alternatives. Such refinements provide additional improvements especially for replacement of fossil energy usages that emit greenhouse gas (GHG) into the atmosphere leading to climate change impact. Current knowledge gap among each renewable energy source calculation is rather missing fundamentals of plausible, rational, and logical explanations for the interpretation of results. In the literature, there are rather complicated and mechanically applicable methodologies, which require input and output measurement data match with missing physical explanations. The view taken in this review paper is to concentrate on quite plausible, logical, rational, and effectively applicable innovative energy calculation methodologies with simplistic fundamentals. For this purpose, a set of renewable energy methodological approaches is revisited with their innovative structures concerning solar, wind, hydro, current, and geothermal energy resources. With the increase in the renewable energy utilizations to combat the undesirable impacts of global warming and climate change, there is a need for better models that will include physical environmental conditions and data properties in the probabilistic, statistical, stochastic, logical, and rational senses leading to refined and more reliable estimations with application examples in the text. Finally, new research directions are also recommended for more refined innovative energy system calculations.     

Constrained Optimization of Heat Transfer from an Extended Surface

Two different zero‐order optimization techniques are used to maximize the rates of heat transfer from a fin assembly of a specified cost and in the shape of several annular fins that are mounted on a central stem. The problem is formulated to account for two‐dimensional steady‐state heat transfer that is limited by several inequality constraints. The dimensionless governing equations are used to identify the relevant decision variables. The number of fins making up the assembly is treated as an input parameter. A digital computer is used to determine the required temperature distributions and to implement the optimization search algorithms. Three different fin materials are assessed—aluminum, copper and carbon steel. Design optimizations of the extended surface assembly were made over a range of operating conditions, encompassing several different convection heat transfer coefficients that are representative of free and forced convection in air, and several different overall temperature differences between the substrate surface and air. A few recommendations based on trends in the predicted results are given. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(6): 504–521, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21093     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

CY6D78Ti型柴油机的开发研制

本文介绍了CY6D78Ti型柴油机的开发研制过程及现状,CY6D78Ti型柴油机能满足国内中、重型卡车和豪华客车市场对柴油机动力性、经济性、可靠性的需求。由于该机型的高档配置,保证了其排放达到欧Ⅱ标准,同时为进一步提高性能、降低排放,采用电控及高压共轨等技术手段搭建了平台。