高温肋板式蓄热器蓄/放热特性的数值模拟

采用计算流体动力学方法对高温不锈钢肋板式相变蓄热器的蓄/放热特性进行了数值模拟。分析了多孔肋片和锯齿肋片对蓄热器蓄/放热特性的影响以及载热体入口温度和流量对相变材料熔化和凝固速度的影响,计算结果表明:在该新型肋板式相变蓄热器中,多孔翅片的性能优于锯齿肋片;随着蓄热器传热温差的增大和载热体流量的增加,蓄热器的蓄/放热性能越好;肋片作为换热元件可以很好的提高蓄热器的蓄/放热性能。所得结论可为高温肋板式蓄热器的优化设计提供有益的参考。     

管翅式相变蓄热器性能的实验研究

为了改善光管螺旋式相变蓄热器的蓄放热效果,在圆管上加装了矩形翅片,并通过选择复合体系的相变蓄热材料,实验研究了翅片螺旋式相变蓄热器的蓄热特性。实验结果表明:以80%Na2SO4·10H2O+20%Na2HPO4·12H2O的复合体系为蓄热介质,矩形翅片螺旋相变蓄热器的蓄热速度比光管式蓄热器提高了1/3,蓄热时间缩短了1/3,具有良好的蓄放热性能。     

列管式相变蓄热器性能强化的模拟

基于列管式换热器具有传热面积大、结构紧凑、操作弹性大等优点,使其在相变储能领域具有广阔的应用前景。本文建立一种新型列管式相变蓄热器模型,在不考虑自然对流的情况下,利用Fluent软件对相变蓄热器进行二维储热过程的数值模拟。本文主要研究斯蒂芬数、雷诺数、列管排列方式、肋片数以及相变材料的导热系数对熔化过程的影响,并对熔化过程中固液分界面的移动规律进行了分析。模拟结果表明,内肋片强化换热效果明显,特别是对应用低导热系数相变材料[导热系数小于1 W/(m·K)]的列管式蓄热器,相对于无肋片结构,加入肋片(Nfn=2)可缩短熔化时间52.6%。     

新型管壳式相变蓄热器的设计与数值模拟

设计了新型具有内外双螺旋结构的翅片管式蓄热换热器,通过Gambit软件建立三维蓄热体相变蓄、放热过程的物理模型和数学模型,运用Fluent软件对换热器的蓄、放热过程进行模拟。研究表明新型换热器的蓄、放热效率要比光管、仅有外螺旋翅片以及仅有内螺旋翅片的换热器高。最后对相变材料和外螺旋翅片的间距进行了优化,结果得出添加0.5%膨胀石墨/石蜡的复合相变材料要比纯石蜡蓄热时间缩短34%,翅片螺距对蓄热器的蓄热性能有重要的影响。     

蓄热蒸发型空气源热泵蓄热器特性实验研究

以所研制的相变温度为30℃的圆柱形螺旋盘管相变蓄热装置为研究对象,实验分析其在不同室外温度下的蓄、放热特性和除霜特性。研究结果表明:该相变蓄热装置具有良好的蓄放热能力,可满足蓄热蒸发型空气源热泵在低温工况下的供热需求,可有效解决空气源热泵系统的热量供需矛盾,同时缩短除霜时间达50%,提高热泵系统的供热效果。但蓄热器的蓄热速度慢,在有限时间内的蓄热量少,为实现热泵系统在极低温环境下的高效工作,须采取措施强化该蓄热器的换热。     

肉豆蔻酸/膨胀石墨复合相变材料的制备及性能研究

以肉豆蔻酸(MA)为相变材料,膨胀石墨(EG)为基体,通过膨胀石墨对肉豆蔻酸的吸附作用制备一系列肉豆蔻酸/膨胀石墨(MA/EG)复合相变材料,发现肉豆蔻酸与膨胀石墨的最佳质量比为15∶1。通过SEM、DSC和蓄/放热实验对复合相变材料的微观结构和热性能进行分析表征。研究结果表明,MA均匀分布于EG的网状多孔结构中。MA/EG复合相变材料的相变温度和相变潜热分别为53.19℃和191.75 J/g,且与MA相比变化不大。蓄/放热实验结果表明,MA/EG单元蓄热时间比MA单元缩短了32.25%,放热时间比MA单元缩短了49.07%,MA/EG相变单元的蓄/放热速率较MA有很大提高。     

Numerical simulations on performance enhancement of a cross-flow latent thermal energy storage heat exchanger

基于列管式换热器具有传热面积大、结构紧凑、操作弹性大等优点,使其在相变储能领域具有广阔的应用前景。本文建立一种新型列管式相变蓄热器模型,在不考虑自然对流的情况下,利用Fluent软件对相变蓄热器进行二维储热过程的数值模拟。本文主要研究斯蒂芬数、雷诺数、列管排列方式、肋片数以及相变材料的导热系数对熔化过程的影响,并对熔化过程中固液分界面的移动规律进行了分析。模拟结果表明,内肋片强化换热效果明显,特别是对应用低导热系数相变材料[导热系数小于1 W/(m·K)]的列管式蓄热器,相对于无肋片结构,加入肋片（N_fn=2）可缩短熔化时间52.6%。     

管壳式太阳能相变储热器传热特性的数值研究

通过焓-孔隙法建立数值模型,研究石蜡RT50在管壳式太阳能储热器的传热特性,并分析储热器安装形式、不同管径和管外肋片结构对相变储热过程的影响规律。结果表明,立式储热器在管径较大时（相变材料区域厚度较薄时）熔化速度比卧式储热器快;而在管径较小时（相变材料区域较厚时）熔化速度比卧式储热器慢。卧式储热器相变材料熔化过程的初始时间段和末尾时间段热传导占主导地位,而中间时间段自然对流换热占主导地位,且熔化速度主要由自然对流换热决定。此外,管外侧安装肋片能够显著提高传热系数,缩短熔化时间。相较于无肋片管道,卧式储热器采用环肋管道可缩短熔化时长31.6%;采用直肋管道可缩短熔化时长42.1%。直肋比环肋具有更好的传热效果,主要原因为直肋能够强化熔化过程中的自然对流。     

采用肋片强化相变蓄热器传热的模拟分析

为了增加同心套管式相变蓄热器的蓄能效果,采用环形肋片强化相变储能设备的传热,利用Fluent软件模拟了这种结构中石蜡相变的融化过程,得到了石蜡熔化过程温度场分布及熔化时间的规律,根据这些规律分析了肋片间距及厚度等参数对贮热管放热效果的影响。分析结果表明：石蜡的总融化时间随肋片间距增加而延长即传热效果变差,但是随着肋片厚度的增加而缩短,即传热效果变优,但是当或肋间距超过40mm和厚度超过2mm后,进一步增加肋片间距或者厚度对传热效果的影响变得不明显。     

直接接触式/间接接触式加肋蓄热器性能比较研究

将直接接触式加肋蓄热器应用于移动蓄热系统,结合蓄热材料赤藻糖醇的特点设计便于运输的水平圆柱状直接接触式蓄热器。通过观察材料熔化凝固趋势、测量测点温度的方法研究蓄热器的充放热性能,并与间接接触式加肋蓄热器进行比较,结果表明:直接接触式蓄热器充热过程材料由上部向下部熔化,放热过程材料由上部和下部向中间凝固;增加导热油流量可以缩短蓄热器充放热时间;蓄热材料的熔化凝固趋势与进油管的位置有关。直接接触式蓄热器与间接接触式加肋蓄热器相比,具有更高的充放热速率、热利用率以及更低的运输成本,在移动蓄热系统中应优先考虑。     

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．