瞬态热丝法测量纳米流体的导热系数

推导了用双铂丝测量流体导热系数的瞬态热丝法的实验关联式,并据此设计实验装置,分析误差因素,给出了系统误差修正系数.用该装置测量了几种纳米流体的导热系数并作了相关分析.     

金属氧化物纳米流体的导热性能研究

采用瞬态热线法测量了4种不同种类、不同体积份额配比的纳米流体的导热系数,分析了纳米颗粒属性、体积分数、悬浮稳定性及温度等因素对纳米流体导热系数的影响.实验结果表明,在流体中加入纳米颗粒将显著提高流体的导热系数.     

TiO_2球-管混合纳米流体的稳定性及导热性能

以TiO_2纳米球(TiNSs)和纳米管(TiNTs)为分散相,去离子H_2O为连续相,通过"两步法"制备混合TiO_2-H_2O纳米流体,研究了TiNSs和TiNTs浓度比以及纳米粒子总浓度对混合纳米流体稳定性和导热性能的影响。采用相对吸光度变化评价了混合纳米流体的稳定性,使用闪光法导热仪测量了混合纳米流体的导热系数。结果显示,混合纳米流体相对吸光度变化随TiNTs浓度增大先减小后增大,说明混合纳米流体稳定性先提高后下降;TiNSs和TiNTs浓度比相同时,混合纳米流体相对吸光度变化随纳米粒子总浓度增加而减小,说明其稳定性有所提高。制备完成后静置,混合纳米流体导热系数相比单组份TiNSs纳米流体下降幅度较小。从TiNSs和TiNTs间的空位作用力及粘度变化的角度分析了混合纳米流体稳定性变化的原因。     

采用3ω法测量多壁纳米碳管悬浮液的导热系数

为了减小瞬态热线法测量纳米流体导热系数时易受电磁干扰和自然对流等因素的影响,更好地探究新型换热工质的强化传热机理,研制了3ω法实验台,采用锁相放大器测得交流加热铂丝的3倍频电压响应,拟合算出待测液体的导热系数.先通过对常规液体蒸馏水、乙二醇以及酒精溶液的测量,验证了实验台的精度和可靠性.然后采用两步法合成了稳定性较高的多壁纳米碳管悬浮液,测得其各体积分数和各温度下的导热系数.实验结果表明,3ω法具有较好的电磁兼容性,测量时温升不超过0.5K,可以有效地减小对流传热和辐射传热的影响,且可以通过1ω电压来判断纳米流体的稳定性;纳米碳管悬浮液的导热系数比基液和Hamilton-Crosser预测值明显提高,并且分别随纳米碳管含量的增加和温度升高而加大.     

Cu-水纳米流体的分散行为及导热性能研究

通过测定Cu-水纳米悬浮液的Zeta电位和吸光度,采用Hotdisk热物性分析仪测量了其导热系数,探讨了不同pH值和分散剂浓度对Cu-水纳米悬浮液分散稳定性和导热性能的影响.结果表明,pH值和分散剂加入量是影响Cu-水纳米悬浮液分散稳定和导热系数的重要因素.最优化的pH值和分散剂加入量能显著提高水溶液中Cu表面Zeta电位绝对值,增大了颗粒间静电排斥力,悬浮液分散稳定性较好,导热系数较高.从分散稳定和导热系数提高两个方面来考虑,pH=9.5左右被选为最优化值,在0.1%Cu-H2O纳米流体中,0.07%SDBS被选为最优化浓度.另外,Cu-水纳米流体的导热系数随纳米粒子质量分数的增大而增大,呈非线性关系,且比现有理论(Hamilton-Crosser模型)预测值大.     

以柠檬酸钠为分散剂一步法合成Cu-水导热纳米流体

以柠檬酸钠为分散剂,KBH4为还原剂,CuSO4·5H2O为氧化剂,采用一步法直接合成了Cu-水导热纳米流体。其最佳合成工艺条件为:n(CuSO4·5H2O)∶n(KBH4)=2.5∶1,柠檬酸钠的用量为0.07mol/L,温度为40℃,反应时间为100 min。TEM表征表明该导热纳米流体中Cu纳米粒子分散较均匀;经激光光散射仪粒度分析得其分散粒子平均尺寸为1.1nm;在25℃时测得该导热纳米流体的导热系数为0.7812 W/(m·K),比纯水的导热系数提高30%。     

纳米流体强化对流换热的实验研究

建立了纳米流体对流换热系数的实验测试系统,利用实验系统测量YCu-H2O纳米流体的对流换热系数,探讨了纳米颗粒质最分数、Re数和轴向比对Cu-水纳米流体对流换热性能的影响.结果表明:Cu-水纳米流体的对流换热系数随纳米粒子质量分数的增人而增人,但其对流换热系数的增加明显低于导热系数的增加.随着雷诺数的增人,纳米流体的对流换热系数基本呈线性提高.纳米流体在实验管进口段的对流换热系数提岛值明显高于流体在充分发展段的提高值.纳米流体的导热系数、粘度和纳米颗粒迁移是影响纳米流体对流换热系数的主要因素.     

Cu-水纳米流体对流换热特性研究

建立了测量纳米流体流动与对流换热性能的实验系统,探讨了不同pH值、分散剂浓度和纳米粒子质量分数对Cu-水纳米流体对流换热性能的影响。结果表明:pH值对Cu-水纳米流体对流换热系数的影响较小,这个现象启发了我们将纳米流体应用到未来工业中,可以不考虑pH值对纳米流体对流换热性能的影响。分散剂加入量是影响Cu-水纳米流体对流换热系数的重要因素,从分散稳定、导热系数和对流换热系数提高三个方面来考虑,在0.1%Cu-H2O纳米流体中,0.07%十二烷基苯磺酸钠被选为最优化浓度。另外,Cu-水纳米流体的对流换热系数随纳米粒子质量分数的增大而增大,但其对流换热系数的增加明显低于导热系数的增加。     

SiO2-H2O纳米悬浮液的导热及其机理分析

采用"两步法"分别将50 nm、500 nm粒径的SiO2纳米颗粒加入去离子水中制备纳米悬浮液,采用稳定性分析仪测试SiO2-H2 O纳米悬浮液的分散稳定性.结果显示:SiO2-H2O纳米悬浮液的不稳定性指数低于0.37,说明SiO2纳米颗粒在去离子水中分散稳定.在此基础上,采用Hotdisk导热系数仪分别测试SiO2-H2 O纳米悬浮液在25℃、-20℃下的导热系数,就颗粒浓度和粒径的影响进行研究.结果显示:SiO2-H2 O纳米悬浮液在25℃下的液相导热系数随颗粒浓度的增大、粒径的减小而上升;在-20℃下由于冰的导热系数比SiO2纳米颗粒大,SiO2-H2 O纳米悬浮液的固相导热系数转而下降.采用Maxwell、Bruggeman、Yu and Choi和Xie提出的导热系数模型计算SiO2-H2 O纳米悬浮液的液相和固相导热系数,与测试结果对比发现:导热系数模型能相对较好地预测SiO2-H2 O纳米悬浮液的固相导热系数,但对悬浮液液相导热系数的预测存在很大偏差.分析认为,在纳米颗粒自身导热性能和其微观布朗运动对SiO2-H2 O纳米悬浮液的导热强化中,纳米颗粒的微观布朗运动起到主要作用.     

3ω法测量流体的导热系数

3ω法已成功应用于体态、薄膜等材料导热系数的测量,但还很少应用于流体领域。由于3ω法具有良好的测试性能,为此尝试将此法用于流体导热系数的测量。自行研制了流体导热系数的测量装置,采用锁相放大器获取3ω电压与频率的关系,并借助最小二乘法,算出待测试样的导热系数。通过对10#变压器油和去离子水等流体试样的测量,实验误差控制在5%之内,表明本实验具有一定的可行性。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

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.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

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...     

Roman iron and steel: A review

ABSTRACT

The 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.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

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.     

Flow calorimeter for enthalpy increment measurements on condensed gases

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.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

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.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

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.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

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.