共查询到20条相似文献,搜索用时 15 毫秒
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导热系数低是影响相变储热材料应用的主要难题之一,而泡沫金属具有高热导率、高孔隙率以及高比表面积等特性,在相变材料中添加泡沫金属可实现强化传热。该文基于泡沫金属基3D微观结构W-P模型,重点分析了泡沫金属基复合相变材料有效导热系数与泡沫金属孔隙率以及孔径的关系,采用数值模拟方法利用该模型预测并验证了泡沫铝6101添加空气与水的有效导热系数,研究结果表明该模型能够精确预测泡沫金属材料有效导热系数,在此基础上预测了石蜡中添加泡沫铜的有效导热系数,结果表明,泡沫金属可以显著提高相变材料的导热系数,当泡沫铜的孔隙率为97.57%时,复合相变材料的导热系数与纯石蜡相比提高了13倍。研究结果对于相变储热材料的热物性强化研究具有一定参考价值。 相似文献
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建立了填充泡沫材料冰蓄冷板内冰融化过程的数学物理模型,该模型考虑了融化液态水自然对流的影响。分别数值模拟了填充开孔聚氨酯泡沫、泡沫铜的冰蓄冷板的融化过程,研究了泡沫材料冰蓄冷板融化过程的速率、温度分布、相界面移动等规律。进行了实验对比,验证分析了泡沫材料的孔隙参数对融化速率的影响。结果表明,填充低导热系数泡沫材料可有效延长冰蓄冷板的释冷时间,该时间随泡沫孔密度的减小而增加、随孔隙率的增大而略减。填充高导热系数泡沫材料可有效改善冰蓄冷板温度分布,可加快冰融化速率,该速率随着泡沫孔隙率的减少而增加、随孔密度的减少而略增。 相似文献
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研究了聚酰亚胺(PI)先驱体和发泡温度等工艺参数对PI泡沫结构的影响,采用DSC,TGA和光学显微镜对PI泡沫结构进行观察及表征.研究发现:先驱体的发泡温度应在150℃左右,随着发泡温度的升高,泡沫的密度降低;泡沫具有突出的开孔特性,开孔率高达93%以上;泡沫的密度主要取决于泡沫孔数和泡孔壁厚. 相似文献
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搭建了镓铟锡合金低温液态金属接触热阻实验平台,验证了实验系统的可靠性,对比了常规导热硅脂和液态金属的热阻特性,研究了压力、温度和界面特性对接触热阻的影响规律。实验结果表明,特征测点温度稳定变化且在稳态下具有很小的线性偏差(ε<6%),表明该实验系统具有较高的可靠性。与导热硅脂相比,在74 kPa的界面压力下液态金属的接触热阻降低约71%,且界面接触热阻随着压力的增加而降低。此外,界面温度的升高造成试件界面处液态金属导热系数降低,进而增加界面接触热阻。通过对铜表面镀镍处理能够有效防止液态金属对铜表面发生腐蚀,但镍层存在造成接触热阻增大。 相似文献
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《International journal for numerical methods in engineering》2018,113(9):1488-1506
In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method. 相似文献
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Steffen Müller-Probandt 《材料科学与工程:中英文B版...》2018,(4):161-177
We associate a variety of innovations with the term "Industry 4.0". The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di... 相似文献
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Janet Lang 《Materials and Manufacturing Processes》2017,32(7-8):857-866
ABSTRACTThe production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them. 相似文献
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A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils. 相似文献
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Standards are the basis for production enterprises to organize production ex-factory inspection trade 《中国标准化(英文版)》2008,25(1):24-25
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.…… 相似文献
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A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa. 相似文献
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S. K. Malhotra Paramanand Singh A. Thirunavukkarasu 《Materials and Manufacturing Processes》2006,21(7):652-657
Al2O3-ZrO2 nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness. 相似文献
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On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.…… 相似文献
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Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite
Vipin Sharma Yashpal Gupta Ujjwal Prakash 《Materials and Manufacturing Processes》2016,31(10):1384-1392
Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles. 相似文献