数码涡旋变容制冷系统冷凝器动态特性分析

针对数码涡旋压缩机的容量调节方式,将冷凝器内部流量的响应规律转化为外部一个变化的流量输入信号,建立数码涡旋变容制冷系统的冷凝器仿真模型;分析了热负荷、出风温度、制冷剂进口压力在不同容量输出下的动态变化特性。结果表明,在容量调节作用下,热负荷、出风温度呈现出周期性波动趋势,但其总体是随容量输出比例的降低而减小;而制冷剂进口压力变化不显著。     

排气冷却R290/CO_2复叠式制冷系统性能分析

通过对带排气冷却器的R290/CO_2复叠式制冷系统的性能分析,以及与不带排气冷却器的R290/CO_2复叠式制冷系统的性能进行比较,得出在相同的运行工况下,当排气冷却器的热负荷为1.4 kW,低温循环的冷凝温度为-20℃,制冷量为10kW时,排气冷却器在降低冷凝蒸发器CO_2的入口温度方面起到显著作用,高温循环制冷剂R290的质量流量减少11.4%,相应的高温循环压缩机的功耗和冷凝器的热负荷均降低11.4%,R290/CO_2复叠式制冷系统的COP提高8.8%。     

外绕微通道冷凝器空气源热泵热水器仿真与优化

空气源热泵热水器比燃气或电热水器更为节能。本文提出了一种外绕微通道冷凝器,可以减少制冷剂充灌量、提高换热效率、降低成本、提高安全性。建立了热泵热水器的准稳态系统模型,制冷剂侧采用稳态模型,水箱和水侧采用动态模型。通过实验证明了该系统模型可以准确地预测时变的系统功耗、水温,以及系统时均COP。通过仿真分析,发现水箱隔热层可以缩短水的加热时间、并提高系统COP约9.2%。增大冷凝器也可提升系统COP,但几乎不改变水的加热时间。最后提出了微通道冷凝器的三流程优化设计方法。     

基于冷凝器最佳温度的中央空调冷却水控制

本文从理论到实际的项目应用对基于冷凝器最佳中点温度的冷却水调节技术在中央空调能源管理系统中的可用性和节能性进行研究。中央空调制冷系统综合性能优化控制,就是以整个制冷系统总能耗最少为目标,寻找各种负荷下的冷却水最佳冷凝器中点温度值,并以此调节冷却水泵转速和冷水塔风机风速,使冷却水系统运行于该温度值,从而保证在部分负荷下整个制冷系统能效比COP最高,消耗的总功率最小。     

不同空气侧风速下微通道蒸发器换热特性实验研究

搭建微通道蒸发器性能实验台,采用控制变量法研究不同空气侧风速下微通道蒸发器表面温度分布、制冷剂进出口压力的变化规律,计算换热量和换热系数,从而分析空气侧风速对微通道蒸发器的流量分配特性和换热效果的影响。结果表明,随着风速增大,微通道蒸发器制冷剂流量分配不均匀性增大,进出口压力波动振幅和周期增加,压降增大,风速2 m/s时微通道蒸发器换热效果最佳。     

R290直接接触冷凝制冷循环性能分析对比

本文分析了R290直接接触冷凝(DCC)制冷循环的性能,并与R290常规单级压缩制冷循环的热力性能进行对比,得出:在最佳主循环冷凝温度下,R290直接接触冷凝制冷循环可获得最大性能系数和最低冷凝器热负荷。主循环过冷液体的过冷度增大,最优性能系数降低、最低冷凝器热负荷增加、蒸发器的制冷剂质量流量减少,同时,获得最优性能系数和最低冷凝器热负荷的最佳主循环冷凝温度升高。当蒸发温度为-15～-6℃,R290直接接触冷凝制冷循环相比R290单级压缩制冷循环的性能系数提高了7.5%～14.9%,冷间供冷设备蒸发器的制冷剂质量流量减少了26.5%～36.7%,冷凝器热负荷减少了1.5%～3.7%。结果表明R290直接接触冷凝制冷循环具有很好的发展前景。     

电动汽车热泵空调系统低温制热性能及优化

热泵空调系统在满足电动汽车冬季供暖需求方面发挥了重要作用。本文采用新型低GWP值的R1234yf为制冷剂?对电动汽车热泵空调系统在－20~7 ℃环境下的低温制热性能进行了测试?对电动汽车冬季热负荷进行标定,并且与制冷剂R134a进行了对比,研究了系统制冷剂充注量、制热量、COP和排气温度的变化,同时对系统各部件火用损失进行了分析计算并根据结果 确定系统优化方向。结果表明:该系统最佳制冷剂充注量为1406g,制热量与COP在大部分工况下达到2kW与18以上,能够满足低温制热需求;R1234yf 直接替代R134a时,系统制热量与COP比R134a系统低71％与66％,系统的排气温度比R134a平均低53 ℃,系统工作更稳定可靠;热泵空调系统内冷凝器与压缩机的火用损失占系统总火用损的80％以上,是重点优化方向;增大内部冷凝器换热面积、增大风量、提高压缩机转速可显著提升R1234yf系统制热性能,使之与R134a系统的制热性能相比大约相等或者更高。     

自复叠制冷系统中套管式冷凝器的应用研究

自复叠制冷系统广泛应用于小型制冷装置,制取-40℃~-150℃之间的低温环境。套管式冷凝器在自复叠制冷系统中常用作冷凝设备,其特性与结构深刻地影响着制冷装置系统。自动复叠制冷系统用套管式冷凝器为研究对象,研究其冷凝过程特性和结构尺寸;在冷凝压力2.0 MPa,当R600a和R23混合工质的质量分数为7∶3时,计算其冷凝负荷为1610 W;根据混合工质和冷却水的换热系数,确定套管式冷凝器长度为4.842 m。最后对不同冷凝水流量的吸气温度、排气温度、蒸发温度,以及冷却水进出口温度进行了对比分析。     

采用微通道冷凝器对商用空调系统制冷剂迁移的影响

针对采用微通道冷凝器的商用空调,对制冷剂在系统中的分布和迁移进行试验研究。并与采用铜管翅片冷凝器的商用空调制冷剂迁移现象进行对比。结果表明,在相同条件下,与采用铜管翅片冷凝器的商用空调相比,采用微通道冷凝器的商用空调在停机时制冷剂液体更容易从排气管回流到压缩机。     

电子膨胀阀在低温系统中的应用研究

研究了电子膨胀阀在低温系统中的应用特性，并对热力膨胀阀和电子膨胀阀在相近工况下进行降温特性的对比性试验。根据实验结果进行分析，可以看出电子膨胀阀在低温条件下的控温曲线也是非常平稳的，并可调节电子膨胀阀的不同开度，使低温箱体达到不同的降温速率及终温。另外通过改变电子膨胀阀开度以及在箱体内加入不同的热负荷，研究了在变负荷条件下，对制冷系统循环参数的影响，尤其是对蒸发器、压缩机、冷凝器进出口温度的影响。     

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.