等温热源微通道单相液体层流换热特性

对Dh=0.82mm的矩形微通道阵列内等温热源作用下层流传热特性进行了实验和数值模拟。实验中使用常温自来水提供等温热源。微通道流体流动雷诺数Re=100～900,传热温差50K,将所得数据与常规尺度均匀壁温加热下N-S方程的数值解法结果进行对比。结果表明,在Re300时,Nu数随着Re数的增加而增加;而在Re350时,实验所得Nu数近似为常数。将发展入口条件的数值模拟结果与实验结果比较,前者比后者高7.2%。     

固宝床层中四种不同粒径柱状活性炭流动阻力特性

采用活性炭脱硫制酸,床层阻力是活性炭床层在工程技术设计中一个重要的特征数据,通过测量4种不同粒径活性炭的阻力特性,为工程设计提供了依据.实验表明在层流区时,平均阻力系数随Re数的增大而减小,层流向紊流过渡区时,平均阻力系数随Re数的增大而增大.入口效应仅在低Re数、床层总阻力较小时对床层平均阻力系数影响较大.在层流区时小颗粒直径的活性炭(1mm)床层平均阻力系数随床层高度增大而增大,大颗粒直径活性炭(3mm,6mm,10mm)床层平均阻力系数随床层高度的增大而减小.过渡区中大颗粒直径活性炭的平均阻力系数随床层高度增大而增大.     

带肋壁与气膜孔内流通道中肋高度对流量系数的影响

在根据相似理论放大的模型上,测量了同时带肋壁与气膜孔内流通道中沿主流流向分布的各气膜孔的流量系数Cd。实验在内流通道进口雷诺数Re为20000～80000,通道总出流比SR为0 30～0 60,肋截面高宽比h/e为1 0和2 0以及肋角为60°的范围内进行,重点分析了肋高度对Cd的影响规律,并且进行了相应的数值模拟研究。结果显示:在低进口雷诺数Re(20000)和低通道总出流比SR(0 3),沿内流通道布置的各出流孔Cd通道前半部是上升的,在第五对孔时达到最大值,然后又沿通道而下降;在相同流动状况下,随肋高度的增大,肋所诱导的二次流强度增大,对带60°肋的通道而言,气膜孔流量系数降低。     

R32在水平强化管内的流动沸腾换热特性研究

为研究制冷剂在内螺纹管内的换热情况,搭建集蒸发冷凝性能测试于一体的实验台,研究了替代工质R32在水平内螺纹管内的流动沸腾换热特性和压降特性。实验测试管外径分别为7和8 mm,进口过冷度和出口过热度为3～5℃,制冷剂质流密度为300～700 kg/(m~2·s),饱和温度保持在5～10℃,实验段水侧雷诺数为12 000～20 000,热平衡误差保持在5%以内。结果表明:制冷剂侧表面换热系数随制冷剂质流密度的增大而增大,随饱和温度的增大而减小,而水侧雷诺数Re对其并无影响;总传热系数随制冷剂质流密度、水侧雷诺数Re的增大而增大,随饱和温度的增大而减小;试验段压降随制冷剂质流密度的增大而增大,随饱和温度的增大而减小,水侧雷诺数对其无影响;在相同工况下,7 mm管比8 mm管的制冷剂侧换热系数以及总传热系数都大,但是其压降也比8 mm管大。     

矩形微通道内流体流动特性的数值研究

对矩形微通道实体模型进行简化处理,并建立微通道内流体流动的数学模型.设定矩形微通道水力直径Dh=120～480 μm,入口雷诺数Re=ll.9～3 817.1,以20℃蒸馏水为流动工质,借助FLUENT分别对不同水力直径的三组矩形微通道内流体流动特性展开数值模拟研究,并将数值模拟结果与理论预测值及其他学者的研究结论进行对比.结果表明:随着微通道水力直径的减小,摩擦阻力系数、速度梯度和压强梯度都呈现增大趋势;在微尺度下,矩形微通道内临界Re提前,而且水力直径越小,临界Re值越小.     

矩形波状壁面二维层流运动阻力特性的研究

采用有限体积法对雷诺数Re＜2 000的层流流态下周期性矩形筋条波状壁面阻力特性进行了数值模拟,针对不同无量鲷波幅a/h与各种雷诺数的组合,计算了壁面应力分布特性.通过实验与数值法论证结果表明,波状壁面下水流的形状阻力、摩擦阻力随雷诺数增加而增大,提出了周期性矩形波状波边界层流沿程平均水头损失系数ξ的概念,可获平均阻力系数随雷诺数和筋条几何参数间的变化规律,具有实用价值.     

水平位置对突扩通道内横掠圆管对流换热的影响

采用非稳态数学模型对突扩通道内横掠圆管流动与换热进行了数值模拟。分别对不同雷诺数Re以及圆柱的不同水平位置情况进行数值模拟。结果表明,随着Re的变化,数值解有稳态和周期振荡。同时随着雷诺数的增加,圆管附近的换热不断增强。对于圆管不同的位置,当10≤Re100和Re=300时,圆管的换热随着Xc的增加而变弱;当100≤Re≤200时,圆管换热并不单调减弱。     

扰流肋柱在流动方向排列密度对矩形通道表面传热影响的数值研究

运用数值计算的方法将流动方向扰流圆柱排列密度对涡轮叶片尾缘冷却通道中流动传热的影响进行了三维数值研究。研究了流动雷诺数、流动方向圆柱排列密度对肋柱扰流矩形通道表面传热影响的规律。计算结果表明:在研究范围内,肋柱表面的平均Nu均随着Re的增大而增大。在Re相同的情况下,随X/D取值的增大,肋柱表面平均Nu有所减小。Nu在通道进口附近逐渐增加,然后达到充分发展值。传热在迎向流动方向的圆柱侧较强,在流动向背侧表面传热较弱。沿圆柱高度方向在中部传热较强。     

两种波纹通道内周期性充分发展对流换热的数值研究

应用数值方法研究了流体在正弦型和三角型两种波纹通道内周期性充分发展的层流流动与换热特性，分析了恒壁温条件下，雷诺数Re对流动与换热性能的影响，并对两种通道的摩擦阻力系数厂与努谢尔特数Nu分别进行了比较。结果表明：两种通道流动阻力的相对大小因雷诺数Re的大小而异；正弦型波纹通道的换热速率比三角型通道的换热速率大，因此换热器通道表面的选择应综合考虑。     

并列双柱绕流的格子Boltzmann模拟

采用格子Boltzmann方法模拟研究了并列双圆柱的绕流现象,利用非平衡外推法进行边界条件处理,基于C++编制程序,获得了不同雷诺数Re和柱间距比H/D下的流速及回流区分布,并分析了并列双柱绕流的流动特性。结果表明,随Re的增大,流场由层流向卡门涡街转变,回流区长度先增大后减小,临界值为Re=50;随H/D的增大,可将流动模式分为单体模式、交替翻转模式、同相模式及反相模式四种,回流区长度在这四种模式下随H/D的增大而增大。     

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     

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。     

我国车用柴油机的技术现状及发展趋势

本文根据国内外信息和资料，分析了我国目前车用柴油机制造技术方面与国际水平所存在的差距，预测今后若千年内车用柴油机要向节能降耗、应用增压技术、提高可靠性、降低排放、采用电控技术方面发展，以尽快接近和赶上国际先进水平．