磁性液体旋转密封的关键问题研究进展北大核心CSCD

磁性液体是一种新型的功能材料,密封是磁性液体最成功的应用之一。磁性液体密封是一种利用磁场控制的新型流体密封技术,与其它的密封形式相比,具有零泄漏、长寿命、高可靠性、能承受高转速与黏性摩擦小等优点,因此在航空航天、机械工程、精密仪器等领域具有广阔的发展空间和重要的应用价值。本文针对磁性液体在大直径大间隙密封、高速密封与密封液体的应用中出现的关键问题进行了综述,分析了当前磁性液体在大直径密封、高速密封与密封液体方面存在的主要问题。基于目前的研究成果,提出了解决磁性液体密封关键问题的方法。最后,指出大直径密封、高速密封与密封液体是磁性液体密封未来的的重要发展方向,并总结了磁性液体密封需要进一步研究的热点问题。     

低温大直径磁性液体密封起动扭矩的研究

制约低温大直径磁性液体密封在实际应用中的关键因素之一是起动扭矩过大.为了使低温大直径磁性液体密封在实际中得到很好的应用,我们制备了耐低温磁性液体,测定了该磁性液体的粘温性能.以-40℃,直径为140mm的磁性液体密封为例,在低温室内研究了影响磁性液体密封起动扭矩大小的因素,如磁性液体注入量,密封的级数、常温(15℃)下放置的时间等.从一般形式的Navier-Stokes方程出发,考虑磁性液体在低温下的粘度变化,推导了低温大直径磁性液体旋转密封扭矩公式,并对实验结果进行了理论分析.利用这些研究结果所设计的低温大直径磁性液体密封被授予了国家发明专利,在某些领域得到了广泛应用.     

两种磁性液体密封结构耐压能力的比较

本文从实验和数值分析两个方面比较了对称型和非对称型两种磁性液体旋转密封结构的耐压能力大小.分析了导致这种结果的原因,指出非对称结构是更为有效的一种密封结构.     

磁流体密封件故障分析及结构改进设计

简要介绍了磁性液体组成，磁性液体密封件的基本元件及各元件的作用，说明了密封件的密封原理、耐压能力计算和实际测试结果，重点介绍 密封件的故障分析及采取的整改措施，以供有关人员参考。     

真空镀膜机双轴磁性液体密封的设计与实验研究

为了解决真空镀膜机双轴密封问题,对真空镀膜机双轴采用磁性液体密封,设计了磁性液体密封整体结构、密封极齿和永久磁铁。分析了双轴磁性液体密封的设计。还使用Ansys软件计算了双轴磁性液体密封的磁场分布。在实验上对所设计加工的双轴磁性液体密封进行了实验研究,得出了磁性液体密封耐压能力与加注磁性液体量的关系。     

磁性液体密封试验研究

本文在磁性流体密封理论的基础上计算了磁性流体密封的耐压能力，并进行了实验研究，酹明，当间隙在0．05－0．3mm之间时密封能力较好。     

磁性液体的理论与应用研究

在本研究工作中,作者制备出了性能稳定、具有实用价值,其综合性能指标达到先进国家水平的磁性液体;用有限元法计算了几种磁性液体密封件的磁场分布;设计、加工了往复式磁性液体密封实验台,并进行了静止耐压实验;首次在显微镜下观察并得出了往复运动密封中磁性液体的运动特征,推导出了往复运动密封磁性液体耐压公式,推导出了往复轴携带磁性液体量的计算公式,并用实验验证了该公式的正确性及实用性;作者研究出了磁性液体密封件的设计流程;推导出了磁性液体旋转密封的功率损失公式;成功地对某真空泵厂几类真空泵进行了动密封;首次对磁性液体密封润滑油的可行性及有关规律进行了研究;最后作者总结了自己多年从事磁性液体密封研究的经验和体会。     

重力对磁性液体密封性能的影响

磁性液体密封是磁性液体最重要最成熟的应用之一。通常,在分析磁性液体的密封性能时重力被忽略,但随着磁性液体应用的发展,有些工况重力会严重影响磁性液体密封的密封性能,甚至导致密封失效。本文通过实验研究了大直径大间隙的磁性液体密封的密封性能,分析了密封失效的原因,探讨了重力对密封性能的影响,提出了密封极限尺寸的概念。对于一般密封间隙的磁性液体密封,极限尺寸大约为1.57 m。随着密封间隙的增大,间隙里磁场的减弱,极限尺寸减小。     

干式罗茨真空泵磁流体密封的研究

本文设计了干式罗茨真空泵的磁流体密封 ,对磁流体密封磁场进行了有限元分析 ,针对不同文献中磁流体密封耐压公式的不严密甚至错误 ,作者对磁流体密封耐压公式进行了严密推导 ,在实验台上验证了磁流体真空密封的效果、耐压能力及转速对真空度的影响。本设备近十年的连续运转证明 :在干式罗茨真空泵采用磁流体密封效果良好     

气体隔离式磁流体液体旋转密封的耐压能力研究北大核心CSCD

磁流体旋转密封用于密封液体时,直接接触的磁流体与被密封液体相互作用导致两种流体界面不稳定性发生和增长,耐压能力较差。为提高磁流体对液体介质的密封性能,设计了可避免磁流体与被密封液体直接接触的气体隔离式磁流体密封,对结构中不同密封间隙内的磁场分布进行了仿真分析,得到了该结构各间隙下的最大理论耐压能力,搭建了气体隔离式磁流体密封实验台,在该实验台上进行了磁流体密封液体介质的耐压能力实验。理论与实验研究结果表明,气体隔离式磁流体密封结构对液体介质的耐压能力近似于磁流体密封对气体介质的耐压能力。气体隔离式磁流体密封有效提高了磁流体密封液体的耐压能力。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

卧式金属罐容量的测量结果不确定度

本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。     

盐酸浓度不确定度的评估

通过对盐酸浓度标定的过程分析，找出影响结果的各个分量，进行不确定度的评定，按照计量技术规范给出标准的表示法。     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.