太阳能柱式吸热器非均匀受热的数值模拟

塔式太阳能热发电站中的吸热器是光热转换的重要设备,其由多根无间隙排列的集热管组成。通常集热管表面接收的太阳辐射能流极不均匀,当水/蒸汽作为集热管内的传热工质时,管内工质状态为复杂的沸腾两相流动,因此研究其受热特性具有重要价值。本文基于Fluent平台,利用VOF(Volume of Fluid)方法,建立了不均匀能流边界条件下水/蒸汽集热管的数值模型。模拟分析呈现了管内汽液两相的流动特性;得到了集热管管内工质和管壁的温度分布和集热管内壁面的努塞尔数分布。     

LNG绕管式换热器管侧冷凝流型数值模拟

为了对液化天然气(LNG)用绕管式换热器管侧冷凝流型变化进行预测,本文用数值模拟的方法建立了基于VOF多相流、RSM湍流模型和Lee相变模型的冷凝计算模型,模拟了管侧三股流的冷凝流型,结果表明天然气在超临界压力下冷凝,气液物性接近,流型均具有均匀混合的特性,可采用均相流方法来计算;预冷段和液化段轻烃混合冷剂的冷凝流型主要有雾状流、环状流和分层流,流速越大环状流占的比重越大。     

进口边界条件对边壁进风鼓泡床流动的影响研究

为了探寻速度进口边界条件对边壁进风鼓泡流化床床内气泡行为的影响,根据欧拉-欧拉双流体模型,应用标准kε-方程模型处理气体湍流流动,分别采用均匀进风速度边界条件、脉动项按正态分布和脉动项按正弦分布的脉动进风速度边界条件,对鼓泡床内的气固两相流动过程进行了数值模拟.结果表明：采用脉动进风速度边界条件时,在非射流孔道处气体可形成气泡,气泡的上升速度比匀速进风时小;气体能够充分地与固体颗粒相互作用,床层中的空隙率主频较小;在设置边界条件时考虑脉动能够更合理地预测和分析床内气泡的尺寸、速度等特性.     

水平U型和Z型集箱系统的两相流流量分配特性实验研究

在模拟直流锅炉集箱系统的空气－水试验台上，对分配集箱入口装设加速管和不装设加速管的水平Ｕ型和Ｚ型集箱系统的两相流流量分配特性进行了对比性实验研究。研究发现：在相同的两相流量条件下，在分配集箱入口装设加速管，能够有效地改进原有集箱系统的分配特性。当分配集箱入口的两相流流速达到破膜速度的０．４５倍左右时，集箱系统的两相流量分配已基本均匀。     

单面加热竖直窄通道内环状流沸腾传热特性

基于汽芯的动量方程和液膜的质量和动量方程,建立了单面均匀热流竖直窄通道内环状流沸腾传热模型,利用数值法对方程组进行求解,得出了环状流区域的液膜厚度,并进一步预测了环状流两相沸腾传热系数。研究表明:模型预测的两相沸腾传热系数比Mahmound关联式计算值偏小;将不同工况下的291组环状流两相沸腾传热系数实验值与模型预测值进行对比,平均绝对误差为12.7%。     

流化床内气固两相绕流单沉浸管的流体动力计算

应用贴体坐标系，基于颗粒相采用颗粒动力学的气固两相双流体模型，数值模拟单沉浸管流化床内颗粒及气泡的行为，计算得到的瞬时颗粒浓度和速度揭示了气泡绕流沉浸管时出现的合并和破裂过程．瞬时颗粒浓度的功率谱密度表明，颗粒脉动的主频率为0．4-1．0Hz，大于床内无沉浸管颗粒的频率值，数值模拟得到的气泡频率与文献中实测值相吻合。     

DSG吸热管内插入扭带的汽水动力学数值模拟

文章使用欧拉多相流模型对插入扭带后的DSG吸热管的汽水动力学特性进行数值模拟。该数值模型充分考虑了DSG吸热管表面上非均匀热流密度的影响。基于此,文章分析了当吸热管内两相区插入扭带后,管内的汽水两相分布情况、壁面温度以及壁面温度梯度等。研究结果表明:y=4扭带扰乱了吸热管内的分层流型,这使得吸热管内蒸汽分布更为均匀;插入y=4扭带使得DSG吸热管管壁周向温度与温度梯度相对减小,吸热管周向壁面的最大温差减少33.3%;插入y=4扭带使得吸热管周向角度θ=120°处的壁面径向温差减少35.9%,径向最大温度梯度减少74.1%,壁面温度分布更加均匀。     

平行流蒸发器内气液两相流分配均匀性实验研究

平行流蒸发器内气液两相(特别是液相)在各扁管间的分配对其传热性能影响较大,如果各扁管间的气液分配不均匀其传热性能将显著地下降.在不同气-液流量下实验研究了6种不同形式的平行流蒸发器的分支管液体流量分配情况,实验中观察到流型以环状流为主.研究发现,对于竖直向下流动和竖直向上流动,用通过增加管径的方法不能改善液体流量在各分支管的分配,而主管中气液入口的位置对于流量分配均匀性影响较大.     

基于反问题理论的汽液两相上升流流型预测与实验研究

汽液两相流流型的测量在两相流研究中占有重要地位。应用均相流模型建立了圆管内汽液两相上升流压力分布,基于反问题理论反演了汽液两相的物性参数,将反演结果与流型图结合,精确地预测了管内流型,计算结果与实验结果进行了对比,误差小于5%。提出的反演流型的方法,可以推广到水平管、螺旋管,为工程上的汽液两相流设备安全性分析、稳定性分析等提供了一种简单可靠的技术方法。     

基于OpenFOAM的旋转管道螺旋流水力特性数值研究

为进一步深入研究旋转管道产生的螺旋流对流场水力特性的影响,基于开源软件OpenFOAM,构建了水箱-管道出流气液两相流数值计算模型,模拟了竖直管、55°和45°螺旋管三种情况下的水流运动过程,通过分析、比较选定断面处速度分布、断面平均压强、湍动能随时间及空间位置的变化,总结了螺旋流对水平管段水力特性的影响。结果表明,相较于直管道,两组螺旋管道使水平管段螺旋流湍动能明显减小,压强变化趋于平缓不易产生负压,且管道内断面流速分布更加均匀。     

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。