三叶转子气冷式罗茨真空泵的流场数值分析

本文利用数值模拟软件FLUENT建立三叶转子气冷式罗茨真空泵的二维计算模型,采用动网格技术对气冷式罗茨真空泵内部流动进行动态模拟。分析了转子在转动情况下泵内部流场的变化、内部流场的压强分布以及进排气腔的速度分布,得出泵内部流场的流动规律,为气冷式罗茨真空泵的设计和分析提供理论依据,同时可以用于气冷式罗茨真空泵的性能预测及优化设计。     

两叶与三叶转子气冷式罗茨真空泵气动噪声分析

气冷式罗茨真空泵的噪声主要由机械噪声和气动噪声组成,气动噪声具有强度高、危害大的特点,是气冷式罗茨真空泵的主要噪声.应用FLUENT软件动态模拟泵的内部流场,对两叶、三叶转子的气冷式罗茨真空泵的气动噪声进行比较,分析气动噪声产生的来源,为设计低噪声的气冷式罗茨真空泵提供参考.同时对两种转子的气冷式罗茨真空泵的噪声进行测试,三叶转子的气冷式罗茨真空泵的噪声明显低于两叶转子的气冷式罗茨真空泵.     

气冷式直排大气罗茨真空泵及机组的应用选型

本文介绍气冷式直排大气罗茨真空泵及机组的工作特点及应用选型。旨在通过范例的分析，为不同的用户使用气冷式直排大气罗茨真空泵，充分发挥该泵的抽速大、耐压高、无污染、低功耗的优点，提供可参考的范式。     

高压差工作用气冷式罗茨真空泵设计及其性能

在大型汽轮机转子真空动平衡机室设计中选用了气冷式罗茨真空泵作为其主泵以大大加快抽空速度。气冷式罗茨真空泵由于其特殊结构，在携带一泵外冷却器后，可在极高的压差下连续工作而不会超温。这种泵还具备无油压缩的优点，可防止油蒸汽对被抽气体的污染，可广泛应用于各种真空作业上。本文介绍了这种泵的设计及其性能。     

滑阀真空泵,罗茨真空泵及其真空机组

滑阀真空泵、罗茨真空泵及其真空机组谈治信（兰州物理研究所，兰州７３００００）分类号：ＴＢ７５２滑阀式真空泵（简称滑阀泵）和罗茨真空泵（简称罗茨泵）及其由该泵组成的真空机组近几年来随着真空冶金、真空热处理、真空冷冻干燥、真空镀膜等各种领域的发展需要而得...     

罗茨真空泵机组抽气速率分析

罗茨真空泵机组因配用前级泵不同和所处工作压力范围的差异，相应其抽气速率变化较大，设计中应根据具体工况条件及真空系统使用要求，力求使罗茨真空泵机组体现好的适用性和经济性。     

关于真空泵基础压力与罗茨真空泵特征性能指标的探讨

本文阐述了真空泵的极限压力与基础压力两者的概念和关系,对国际标准ISO21360-1:2012中有关基础压力的条款做了详细的解读。对影响中真空罗茨泵抽气性能的特性指标进行了分析,给出了用罗茨泵零流量压缩比K0和最大允许压差作为罗茨真空泵的抽气性能指标的合理性,建议选择罗茨泵零流量压缩比K0作为罗茨泵抽气能力的主要考核指标之一,将最大允许压差作为罗茨泵的辅助考核指标。     

我国主要容积式真空泵质量状况浅析

本文对容积式真空泵－旋片泵，滑阀泵，罗茨泵的总体情况进行了介绍，重点对其质量状况进行了分析，阐述了近几年容积真空泵的质量改进情况和目前仍存在的主要问题以及问题产生的原因和改进措施，并对真空泵普遍存在的共性问题进行了分析。     

罗茨泵噪声测量方法研究

罗茨真空泵噪声的测量一贯沿用GB/T 21271《真空技术——真空泵噪声测量》,没有充分考虑到罗茨真空泵噪声的发声特殊性,测量条件严重脱离了罗茨真空泵现实的安装和运行条件,不能真实反映罗茨真空泵的噪声水平,影响了泵噪声的研究和控制.经过多年研究和论证后,提出了在符合罗茨真空泵真实安装和运行状态下的、采用全矩形平行六面体测量表面的罗茨真空泵噪声测量方法,从而保证了泵噪声测量值的真实性和准确性.     

罗茨真空机组预抽阶段的抽气特性比较研究

针对罗茨泵真空机组在启动预抽阶段的三种工作模式——旁通式、直通式和变频式,分别建立了简化计算模型,推导得出罗茨泵进入正常稳态工作之前罗茨机组的有效抽速计算公式,以及被抽容器的抽气时间计算方法.通过一个计算示例,对比得出了三种不同启动预抽方式的压力-时间曲线,结果表明,直通式、旁通式、变频式工作模式下容器的抽气时间依次减...     

具有多孔基体复合相变储能材料研究

本文提出了研制一种具有多孔基体的复合相变储能材料，通过实验分析了该储能材料的融解温度、融解热、热稳定性及微相结构等性能。该储能材料是由两种有机相变材料组成，通过物理吸附的方法将其复合在多孔基体材料中。在热分析中，用示差扫描量热仪(DSC)来测定储能材料的融点、融解热，用热重分析仪(TGA)测定其热稳定性，并用扫描电镜(SEM)观测了该储能材料的微相结构。测试结果表明该储能材料具有较高的相变潜热和较好的热稳定性，可被应用于储能和热能回收系统中。     

航天器用十一种热控材料热物理性质及其与显微组织和工艺因素关系的研究

应用自行研制的激光脉冲法热导仪、小平板稳态法热导仪、铜卡计和冰卡计法比热仪, 对航天器用的十一种热控材料的导热系数、导温系数和比热及其与材料显微组织和工艺因素的关系进行了实验研究. 结果表明, 在室温至1800℃温区内, 绝热材料和防热材料的导热系数均随温度升高而增大, 多孔绝热材料的有效导热系数是由多种导热因子相互作用的结果, 并存在对应于最小导热系数的最佳密度. 所得数据为热控材料的优选提供了科学判据, 亦为航天器的热控系统热设计提供了参数.     

Thermal stresses and fracture of thin plates during cutting and welding operations

In many technological processes involving cutting or welding of thin plates there is local thermal heating or cooling at the tip of the cut by a thermal source. In this paper we analytically investigate the stress distribution induced by the point thermal source moving with a constant velocity across an infinite elastic plate. Stress intensity factor for the cut formed by the moving thermal source is calculated. It is shown that for welding the value of the stress intensity factor due to thermal stresses induced by the thermal source is equal to zero. For cutting in the case of positive values of the power of thermal source the stress intensity factors will be negative. This means that the thermal field induced by the point thermal heat source will tend to close the cut in the vicinity of the tip. The opposite situation occurs when the cut tip is cooled by the thermal source. As an example, the theory under development is shown when applied to some strength issues of thermal beam cutting of brittle materials.     

Realizing the Accurate Measurements of Thermal Conductivity over a Wide Range by Scanning Thermal Microscopy Combined with Quantitative Prediction of Thermal Contact Resistance

Quantitative thermal performance measurements and thermal management at the micro-/nano scale are becoming increasingly important as the size of electronic components shrinks. Scanning thermal microscopy (SThM) is an emerging method with high spatial resolution that accurately reflects changes in local thermal signals based on a thermally sensitive probe. However, because of the unclear thermal resistance at the probe-sample interface, quantitative characterization of thermal conductivity for different kinds of materials still remains limited. In this paper, the heat transfer process considering the thermal contact resistance between the probe and sample surface is analyzed using finite element simulation and thermal resistance network model. On this basis, a mathematical empirical function is developed applicable to a variety of material systems, which depicts the relationship between the thermal conductivity of the sample and the probe temperature. The proposed model is verified by measuring ten materials with a wide thermal conductivity range, and then further validated by two materials with unknown thermal conductivity. In conclusion, this work provides the prospect of achieving quantitative characterization of thermal conductivity over a wide range and further enables the mapping of local thermal conductivity to microstructures or phases of materials.     

ZrO2-Ni功能梯度材料的热冲击与热疲劳行为

通过抗热震参数分析和热循环试验研究了ZrO2-Ni功能梯度材料（FGM）的热冲击与热疲劳行为及其影响因素。结果表明,ZrO2-Ni FGM热热震参数呈梯度分布,ZrO2侧抗热冲击断裂能力强而富Ni区热疲劳抗力高。其热震破坏符合热疲劳损伤机理,裂纹的准静态扩展为其控制因素。热疲劳裂纹在梯度层内以微孔聚集、连接方式萌生和扩展,而在梯度层间无横向贯穿裂纹,克服了传统陶瓷／金属结合体的界面热应力剥离问题。     

导热高分子材料在包装印刷领域的研究进展

目的综述导热高分子材料在包装印刷领域的应用及研究现状,拓展导热高分子材料的应用领域。方法首先介绍2类导热高分子材料的制备方法,即本征型和填充型导热高分子材料;其次全面综述用于包装印刷领域的导热膜/纸、导热胶黏剂和导热油墨;最后总结常用的各类导热机理模型。结果与本征型导热高分子相比,填充型导热高分子具有加工简单、成本低廉、应用面广等优点,是目前研究最多的导热高分子材料。导热膜/纸、导热胶黏剂和导热油墨具有广泛的研究基础,市场需求旺盛。导热预测模型虽能够有效预测复合材料的热导率,但会受到填料含量和粒子形貌的影响。结论导热高分子材料在包装印刷领域拥有巨大的应用需求,开展导热高分子的研究具有重要的现实和理论意义。     

VIP绝热性能及其影响参数分析

真空绝热板（VIP）具有10倍于传统绝热材料的优异绝热性能。对VIP有效导热系数进行了分析，表明影响VIP绝热性能主要是固体导热和辐射传热，而气体导热和对流换热可忽略不计。影响VIP整体绝热性能的因素主要有温度、气体压力、含湿率、芯材密度及芯材颗粒度等参数。     

基于分形理论的碳泡沫有效导热系数研究

以煤焦油基中间相沥青为原料，在一定的温度和压力条件下升温发泡，然后再经碳化、石墨化便可以制得一种高导热系数的多孔材料——碳泡沫。应用分形理论讨论了这种新型多孔材料的导热特性，推导出了碳泡沫的面积分形维数，并在此基础上建立了石墨化碳泡沫材料的导热模型，采用热阻法导出了石墨化碳泡沫材料的等效导热系数的关系式，计算出了碳泡沫的有效导热系数，计算结果与碳泡沫样品的实测值基本一致，这种方法为更好地利用其优良的导热性能提供了理论基础。     

Thermal conductivity of inhomogeneous materials

The effective thermal conductivity is calculated from the rate of entropy production per unit volume. Thermal conductivity and the temperature field are expressed in terms of Fourier components and these are related. The rate of entropy production is then obtained in terms of the volume-averaged thermal conductivity and the Fourier components of thermal conductivity. A simple expression for the effective thermal conductivity is found. In the case of striations it leads to well-known results. The formalism is applied to solids with inhomogeneously distributed solutes. It is shown that the thermal conductivity is less than the volume-averaged thermal conductivity and that homogenization by diffusion increases the thermal conductivity. Similar results would apply to the electrical conductivity of inhomogeneous alloys.     

Thermal conductivity and thermal diffusivity analyses of low-density polyethylene composites reinforced with sisal, glass and intimately mixed sisal/glass fibres

The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe²⁺ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.