含二氧化硅气凝胶和相变材料三层玻璃窗热性能分析

为了研究含二氧化硅气凝胶和相变材料三层玻璃窗对严寒地区建筑能耗的影响,建立了相变材料层与其他透明壁层结合发生的传热数值模型。分析了含二氧化硅气凝胶和相变材料三层玻璃窗在不同二氧化硅气凝胶厚度、导热系数和不同保温材料下的动态热调节性能,得到了含二氧化硅气凝胶和相变材料三层玻璃窗内表面热流密度和液相率随时间的变化规律。结果表明:随着二氧化硅气凝胶厚度增加,总传热量降低和液相率增加,当二氧化硅气凝胶厚度为20～30 mm时,可以实现有效的利用太阳能;随着二氧化硅气凝胶导热系数增加,总传热量升高和液相率降低;当二氧化硅气凝胶的导热系数从0.022降低到0.014 W/(m·K)时,最大液相率从0.83增加到1.00。二氧化硅作为保温层比相变材料作为保温层具有更好的保温隔热作用。     

大功率集成LED热管散热器的传热性能

针对大功率集成LED单位热流密度高的特点,提出一种新型的翅片式重力热管散热器,并对其传热性能进行了实验研究,讨论了加热功率和充液率对散热器传热性能的影响。实验结果表明:在加热功率为150W、散热热流密度为37.5W/cm2时,翅片式重力热管散热器的系统热阻在0.08～0.33K/W,此时加热表面温度低于80℃,冷凝段管壁温度相差不超过3℃。该散热器不仅具有良好的均温性,且在工况变化时能快速重新达到稳定,满足大功率LED的散热需求。     

工况参数对X型桁架阵列通道流动与 传热性能影响的数值研究

针对不同工况参数下桁架阵列通道冷却性能优劣的问题，采用数值方法模拟了 X型桁架阵列通道内 的流动与传热特性，分析了不同？诺数下人口湍流度和壁面热流密度对D型桁架阵列通道流动与传热性能 的影响规律。结果表明:人口湍流度从5%增大到15%时，通道摩擦系数增大了 1.69% ~3.23%，通道平均努 塞尔数提高了 2.47% ~2.57% ;壁面热流密度从3 000 W ? m-2增大到10 000 W ?m-2 时，通道摩擦系数增大 了 3.39% ~6.45%，通道平均努塞尔数降低了 11.14% ~17.44%。随着？诺数的增大，人口湍流度和壁面热 流密度对通道流动与传热性能的影响程度都有所减弱。增大人口湍流度可以较小幅度地提升通道的综合热 力性能，增大壁面热流密度则会降低通道的综合热力性能。     

梯度孔密度金属泡沫的池沸腾传热性能研究

实验研究了梯度孔密度通孔金属泡沫的池沸腾传热性能。工质为去离子水,梯度孔密度金属泡沫材质为铜和镍, 孔隙率为0.98,泡沫厚度为4-14 mm。实验结果表明：相比于单层泡沫,梯度孔密度金属泡沫显著的增强了沸腾传热能力,但增强程度受孔密度变化梯度、泡沫厚度和材料的影响;梯度孔密度泡沫的池沸腾传热性能随着表面活性剂SDS浓度的增大而减小,而且SDS降低了梯度孔密度金属泡沫的临界热流密度; 添加Al2O3纳米颗粒严重的削弱了梯度孔密度铜泡沫的池沸腾传热能力。     

太阳能集热管内熔盐流动传热特性数值模拟

建立太阳能集热管物理模型,采用RNG κ-ε模型,基于CFD方法在不同热流边界条件下熔盐入口温度300℃,速度0.6~3.6 m/s,平均热流密度180 k W/m2参数范围内,对外径20 mm,壁厚2 mm的集热管内熔盐传热特性进行数值模拟研究。分析了集热管管壁温度分布规律和熔盐传热性能,对比了不同热流边界下管壁周向温度不均匀分布特性。研究结果表明:不同热流条件下集热管管壁温度分布规律差异较大,管内熔盐温度也存在较大差异;集热管内Nu随Re增大而升高,周向热流分布对Nu影响较大;非均匀热流边界下集热管壁温周向分布不均匀,周向热流越不均匀,壁面温差越大。     

二氧化硅气凝胶制备条件对热导率的影响

二氧化硅(SiO2)气凝胶由于其内部的多孔网状结构与气体填充,热导率极低,可应用于多种保温隔热材料。本文通过实验研究了二氧化硅气凝胶的热学性能,并分析了不同水解时间、蒸馏水体积、反应物体积比、pH值对其热学物性参数的影响规律。结果表明,在所研究的范围内,随着水解时间的增加,二氧化硅气凝胶热导率减小;随着反应物体积比、蒸馏水体积和pH值的增加,二氧化硅气凝胶热导率先减小后变大。     

Al-Si合金与高温热管的传热性能试验

提出了一种基于太阳能碟式聚光器的Al-Si合金储能锅炉的构想,搭建了Al-Si合金与高温热管传热的实验平台。试验结果表明,Al-Si合金与高温热管之间的传热密度为54.4 kJ/m2。对Al-Si合金的传热温度分布进行模拟,以热流密度为54.4 kJ/m2,换热系数为200 W/(m2.K),空气温度25℃的对流边界条件时,模拟结果和试验测试结果比较吻合,为Al-Si合金储能锅炉设计提供了依据。     

双玻璃窗空气间层的最佳厚度

在直接受益式太阳房中,为减少直接受益窗的热损失,往往要使用双层玻璃窗。如果我们不考虑窗户冷风渗透,仪考虑双层窗的传热热损失,那么,双层玻璃窗空气间层多厚时其传热热损失最小呢?从传热学角度分析,我们可以把双层玻璃窗空气间层看成是二维封闭空间的传热问题,其外层玻璃是冷壁面,内层玻璃是热壁面,因此成为一个有限封闭空间内两壁面之间对流、辐射和导热的综合传热过程。可以进一步认为,当内外层玻璃温度一定时,两玻璃之间的辐射换热量不随它们之间空气间层厚度而变化,也就是说此时可以认为辐射换热量是一个常数。因此,确定最佳厚度归结为寻找使对流和导流传热量达到最小     

半周加热内螺纹管中超临界水传热特性的数值模拟及机理分析

为了研究700℃高效超超临界锅炉和超超临界循环流化床锅炉水冷壁管中工质水的流动传热规律和机理,采用SST k-ω湍流模型模拟了大比热容区内半周加热条件下长度为2 m、水力直径为19 mm的垂直上升四头内螺纹管中超临界水的流动传热特性。结果表明:半周加热条件下内螺纹管内壁温度和热流密度呈现类似抛物线分布,在内壁热流密度变化不大的局部区域(圆周角φ=0°～90°),内壁温度在肋底与背风侧交点处达到最大值,在肋顶与迎风侧交点处达到最小值,内壁热流密度的变化趋势与之相反,这是由内螺纹肋的旋流作用造成的,内壁热流密度的周向分布不是影响超临界水传热特性的唯一因素;超临界水发生传热强化现象主要是由于其在边界层内的比热容份额较大导致的,而与湍动能的大小无关。     

氨工质平板式环路热管的传热性能研究

为了解决平板式蒸发器环路热管面对高集成电子元器件在较长传热距离下的散热能力不足等问题,本文采用更大面积的毛细芯和蒸发器,研制了一个传热距离达到1.6m的氨-不锈钢环路热管系统并进行了大量实验.实验过程中,加热壁面温度控制在70℃以下.实验结果表明,在热沉温度为-10℃的情况下,该环路热管可以在2.5W到180 W的热负荷范围内稳定运行,相应的热流密度是0.15 W/cm2和10.8W/cm2.蒸发器热阻的最小值为0.096℃/W,系统热阻的最小值为0.252℃/W.系统存在变热导率和定热导率两种工作特性,实验过程中没有观察到明显的温度过冲和温度波动现象.在启动测试和变热负荷测试中,系统均能够快速响应,展现出优良的可靠性.研究表明,与一般的平板式蒸发器环路热管相比,该系统更好地兼顾了传热距离和传热能力,拓展了平板式蒸发器的应用场景.     

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．