分布式脉冲热源的冷却模型与数值分析

建立了分布式脉冲热源的物理模型,并对其进行了数值模拟和计算,得到了热源各层的中心点在冷却过程中前两分钟、前两小时及全过程的温度变化,计算得出整个热源的冷却时间。结果表明分布式脉冲热源的冷却是个比较缓慢的过程,在冷却过程后期,对冷却速度起决定性作用的是热源所处的温度梯度而非导热性能。     

热泵在海水养殖中的应用探讨

指出了海水养殖传统的冷热源设置方案存在的问题，提出了用热泵作为海水养殖冷热源的合理方案，并对该方案的经济性进行了分析。以热泵作为热源和冷源来完成海水的加热和冷却，是一种低能耗、无污染的加热冷却技术，经济可行，值得推广应用。     

地源热泵有限长线热源模型简化负荷计算方法的修正

通过对土壤源热泵有限长线热源周期脉冲负荷和简化计算负荷计算结果的比较,发现简化计算负荷的计算虽然迅速,但与周期性脉冲负荷计算结果相比存在误差,尤其在钻孔壁处误差较大.因此,文章对两种计算方法进行分析比较,给出了简化计算负荷方法针对钻孔壁处的修正公式,并用实例对修正公式进行了验证.结果表明,修正公式可以很好地缩小计算误差,提高计算的准确性,有利于有限长线热源模型更为广泛的应用.     

921A舰船钢激光–MAG复合焊接过程数值模拟分析

目的 对厚度为16 mm的921A舰船钢进行激光–MAG复合焊接,得到最佳工艺参数,从数值模拟的角度验证焊接工艺的可靠性。方法 利用SYSWELD+Visual–Environment软件对激光–MAG复合焊接过程进行数值模拟,选用3D高斯热源与双椭球热源相结合的复合热源模型对激光–MAG复合焊接过程进行仿真,绘制不同时刻及不同焊缝区域的时间–温度曲线,采用热弹塑性有限元法对应力变形场进行仿真计算。结果双椭球热源模型与3D高斯热源模型相结合的复合热源模型能够获得较为理想、接近真实热源形貌的热源形态;焊缝区域的焊接热源在行进过程中温度稳定,模拟热源温度可达3 200℃,具有典型的焊接热循环曲线特征,且距离焊缝越远,升温速率和冷却速率越慢;焊接残余应力主要集中在焊缝处,约为440 MPa,且焊缝两端的结合部位具有较高的残余应力。结论 复合热源模型适用于16 mm厚的921A钢激光–MAG复合焊接数值模拟,焊后板材的残余应力低于材料的屈服强度,冷却后板材的变形程度较小,最大变形量为1.13 mm,表明激光–MAG复合焊接方法及工艺适用于16 mm厚921A钢的焊接。     

导热油在工业换热过程中的应用

在工业换热过程中．除非采用热源(冷源)直接对工艺介质进行加热(冷却)的换热方式，一般均采用中间传热介质在热源(冷源)和工艺介质之间作为媒介进行换热。这种通过中间介质进行换热的方式称为间接换热．间接换热的最大优点是可在换热过程中对被加热的工艺介质进行精确的温控。有利于实现工艺过程的有效控制和产品及其质量的精细化。而实现间接换热方式最大优点的关键是在热源(冷源)的工作方式和工艺需求之间找到一种适合的中间传热介质。     

基于并层单元的大体积混凝土水管冷却温度场热-流耦合精细计算

热-流耦合精细算法能准确反映冷却水管附近温度梯度,从而精确计算大体积混凝土水管冷却温度场,然而该方法在有限元计算中存在前处理规模大、计算效率低的缺点;依据混凝土的热力学参数随龄期变化特性和混凝土水管冷却温度场分布规律,开发了一整套热-流耦合精细计算的前、后处理程序,在计算过程中依据龄期特性对混凝土单元不断进行并层处理,从而实现了大体积混凝土水管冷却温度场整体-局部一致模型的快速建立和高效精确数值模拟。数值计算算例表明该方法能在保证计算精度的同时,极大地降低有限元计算过程中的单元规模,有效地节约了计算时间,提高了计算效率,使得大体积混凝土温度场全过程精细数值仿真得以实现。     

一种空压机余热回收技术的实践

空压机在压缩空气过程中会产生大量的热量，使用者需要配备冷却系统来保证其稳定运行。为了回收这部分热量同时减少制冷系统的能量消耗，介绍了一种余热回收技术，使回收的热量代替用于其它生产工艺中的热源，从而减少了用于空压机冷却以及生产工艺加热的能耗，同时减少了温室气体的排放。以一个工厂为例计算得出了此种余热利用技术的节能效果。具有良好的经济和社会效益。     

冷却电子芯片的平板热管散热器传热性能研究

通过采用均匀与非均匀热量分布的两种热源对平板热管散热器在冷却电子芯片中的传热性能进行了实验研究，了解其在不同热源加热条件下的传热特性。对比均匀加热条件的铜柱而言，硅质芯片作为热源可以更切实际地模拟计算机微处理器的热源边界条件。非均匀热量分布的芯片内部设置了3个受热区，其中热点的最大热流密度为690W／cm^2。实验表明平板热管散热器工作过程中蒸发段的热传导和汽液两相之间的相变换热起重要作用。研究结果说明蒸发热阻在不均匀的加热条件下与均匀加热条件相比变化不明显，但与热源芯片的传热量成反比。     

塑料板材热成形过程三维温度场有限元分析潜热处理技术的研究

对塑料板材热成形过程的三维温度场进行有限元分析时采用动态内部热源的方法对潜热进行了处理。在成形过程中利用Ａｖｒａｍｉ方程来解出型坯结晶时任意时刻结晶度的大小，进而求得各单元释放的潜热量。在利用Ｃａｌｅｒｋｉｎ有限元公式求解温度场时采用动态内部热源的方法计算了潜热时温度的影响，对塑料半球形件的温度场进行了计算，并对是否考虑潜热两种情形的温度场进行了比较。     

平行板脉冲等离子体推力器工作过程的双温K-B模型仿真

为了提高脉冲等离子体推力器的效率,必须深入理解推力器的物理机理。本文在K-B模型中加入双温能量交换率项,并将该双温放电模型用于模拟平行板脉冲等离子体推力器加速通道中的等离子体激发及加速过程。该模型能够帮助我们更好地理解PPT中的等离子体激发及能量平衡过程,同时获得推力器的性能信息。运用该模型对实验室用平行板电极PPT工作过程进行了模拟计算。通过计算结果获得了放电过程中温度、能量以及密度等各种等离子体参数的变化细节。计算结果表明,高初始电容能量对应着出口速度、密度以及推力器表面温度的高脉冲峰值。在推力器放电过程中,大部分的中性成分出现在脉冲时间末期,这部分组分具有较低的速度,是造成推力器低效率的主要因素。为了提高PPT的性能,应该延长电流脉冲峰值的持续时间,同时在脉冲电流峰值结束后,对推进剂表面进行更好的冷却。     

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.     

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.……     

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.     

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...     

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.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

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.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...