长外伸段转子动平衡辅助支承动力特性分析

辅助支承是长外伸段转子进行动平衡时避免振动过大的有效方法。其动力特性直接影响到动平衡试验的安全和质量。文章通过分析已投运的辅助支承的动力特性和运行情况,提出了辅助支承动力特性的设计准则。然后,采用镂空支承板结构设计了刚度大且质量轻的350 t动平衡试验台辅助支承。最后通过三维有限元法对其动力特性进行了分析,结果表明其具有优良的动力特性。     

关于我国汽轮机转子平衡标准中的若干问题

本文为我国机械工业部“汽轮机刚性转子动平衡标准”和‘汽轮机挠性转子动平衡标 准”的编写说明。其中主要对转子分类和转子动平衡的精度评定两大问题作了较详细的分析和阐述。对于转子分类,按动力特性上的差异,可分成刚性、准刚性、半挠性与挠性四种。由此规定刚性与准刚性转子可采用低速动平衡,而挠性转子必须采用高速动平衡,半挠性转子一般也可用低速动平衡,但有时也要求经过高速动平衡。对于平衡精度,文中分析了支承振幅、支承振动烈度、支承振动力、轴振幅与剩余振型不平衡量五种情况。最后根据向国际标准靠拢和结合国情两条原则,提出用支承振动烈度作为平衡精度的尺度,具体数值则采用国际标准。     

带有外伸悬臂端的汽轮发电机组动平衡方法研究

针对两台带有外伸悬臂端转子的发电机-励磁机转子动平衡问题,提出了一种高效动平衡方法.研究表明,尾部没有支撑的励磁机,受发电机转子二阶振型的影响,励磁机转子容易出现"甩轴"现象.振型分析表明,工作转速下,发电机转子较大幅度的对称分量由于外伸端不平衡所引起的可能性较大.悬臂端加重,在激发较大幅度对称分量同时,也会产生一定幅度的反对称分量.为了使发电机-励磁机这样带有外伸悬臂端转子各瓦振动同时达到优秀水平,可能需要在发电机两侧和励磁机尾部3个平面上同时加重.     

905毫米长叶片试验转子主轴段与轴头联接螺栓强度校核

1 概述为了对我厂新开发的905毫米长叶片进行动态试验,我厂耗资百万余元设计、制造用于进行长叶片动振动试验的转子。试验转子的叶轮结构尺寸与实物机组末级叶轮相似,叶轮上可对称地安装24只905毫米长叶片,叶片的根径达1716毫米。要使试验转子能在高速动平衡机上运转,试验转子的轴承档距离不得小于2800毫米,要制造如此庞大的试验转子,这给锻件的制造质量带来了较高的要求,而且试验转子的成本较高。为了尽可能地降低试验转子成本,试验转子采用组合式。整个试验转子由两个轴头和一个主轴段构成,安装试验叶片的主轴段与两个轴     

60Hz汽轮机转子高速动平衡探讨

对60Hz汽轮机低压转子高速动平衡试验数据进行了分析．并对动平衡所用设备及转子的平衡方法进行了介绍．为国产608z机组转子高速动平衡提供了可资参考和借鉴的经验。     

某60Hz、185MW汽轮机转子高速动平衡试验试重大小及位置探究

针对汽轮机转子个性化设计的特点,文章结合在250t试验台位上进行转子高速动平衡试验所积累的经验。对全新设计的某60Hz、185MW汽轮机转子厂内动平衡试验平衡块试加重量及方位角进行探究。实践证明．文章总结的方法可以有效地缩短转子动平衡时间,并可以推广应用到其它转子厂内高速动平衡试验上。     

2f—2h类准刚性转子的平衡

近年来挠性转子平衡问题的研究无论在理论上还是在试验技术上都已日趋完善;高速动平衡试验装置也正为许多研究和生产部门所装备并投入使用.挠性转子高速动平衡的功效和价值日益为更多的人所认识和接受.但是,高速动平衡试验设备价格昂贵,技术也较为复杂,有人不禁要问,是否所有挠性转子皆需采用高速动平衡?什么样的挠性转子或在什么情况下的挠性转子可以避开高速平衡,而采用改进的低速平衡技术,能同样保证转子在工作转     

弹性支承高速转子的动力学分析

阐述了一种有限元动力学分析方法,该方法从本质上对动力学分析的各项条件进行设定,更加侧重转子系统零部件之间连接条件和陀螺力矩的影响,为更加准确的进行高速转子的分析提供了正确的理论方法.该方法不但可以对转子进行模态和动平衡响应分析,而且还可以通过改变弹性支承和阻尼的参数来对转子模型进行优化设计,这样就为高速转子系统的结构参数优化设计提供了重要的理论依据.     

9FA重型燃气轮机转子高速动平衡研究

本文对9FA重型燃气轮机转子高速动平衡试验方法、平衡方法、平衡设备等做了详细的介绍,同时也介绍了GE公司的低速平衡方法,为9FA燃气轮机转子今后的高速动平衡提供了可资参考和借鉴的经验.     

某60Hz汽轮机转子高速动平衡试验研究

针对目前150 MW容量60 Hz机组高中压转子的高速动平衡试验进行了研究,采用基于有限元的转子轴承动力学软件Dyrobes建立了转子-轴承-摆架系统模型,在进行无阻尼临界转速及振型分析的基础上,结合模态振型平衡和影响系数平衡的特点,根据转子实测不平衡振动形式,合理选择平衡校正面和加重形式。最后,通过高速动平衡试验验证表明,该方法能有效减少启停机次数,节约平衡费用,同时可为这类国产小容量60 Hz汽轮机组转子高速动平衡提供技术参考和经验借鉴。     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Coupling a two-temperature model and a one-temperature model at a fluid-porous interface

We study a convective heat transfer problem in a fluid-porous domain in the case of the local thermal non-equilibrium assumption (LTNE). The issue of this study is to determine appropriate boundary conditions to model heat transfer, while using models with a different number of equations: a two-temperature model in the homogeneous porous region versus a one-temperature model in the free region. To proceed, a two-step up-scaling approach is used, which has the particularity to provide closed jump relations depending on intrinsic characteristic of the interface. Thus, the use of jump or continuity conditions depend only on the interface location inside the fluid-porous transition region. The pertinence of the approach is illustrated on a 2D convective heat transfer problem considering a solid heat source in the porous medium.     

Studies on a two-staged micro-combustor for a micro-reformer integrated with a micro-evaporator

A new micro-combustor configuration for a micro fuel-cell reformer integrated with a micro-evaporator is studied experimentally and computationally. The micro-combustor as a heat source is designed for a 10–15 W micro-reformer using the steam reforming method. In order to satisfy the primary requirements for designing a micro-combustor integrated with a micro-evaporator, i.e., stable burning in a small confinement and maximum heat transfer through a wall, the present micro-combustor is a simply cylinder, which is easy to fabricate, but is two-staged (expanding downstream) to control ignition and stable burning. The aspect ratio and wall thickness of the micro-combustor substantially affect ignition and thermal characteristics. For optimized design conditions, a pre-mixed micro-flame is easily ignited in the expanded second-stage combustor, moves into the smaller first-stage combustor, and finally is stabilized therein. The measured and predicted temperature distributions across the micro-combustor walls indicate that heat generated in the micro-combustor is well transferred. Thus, the present micro-combustor configuration can be applied to practical micro-reformers integrated with a micro-evaporator for use with fuel cells.     

Using a fin with a parabolic concentrator

The consequences of using a fin collector in focusing solar collectors is examined and is found to have merits.     

Bioconvection in a squeezing flow of a micropolar fluid in a horizontal channel

The bioconvection flow of an incompressible micropolar fluid containing microorganisms between two infinite stretchable parallel plates is considered. A mathematical model, with a fully coupled nonlinear system of equations describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms is presented. The governing equations are reduced to a set of nonlinear ordinary differential equations with the help of suitable transformations. The resulting nonlinear ordinary differential equations are linearized using successive linearization method, and the resulting system of linear equations is solved using the Chebyshev collocation method. The detailed analysis illustrating the influences of various physical parameters, such as the micropolar coupling number, squeezing parameter, the bioconvection Schmidt number, Prandtl numbers, Lewis number, and bioconvection Peclet number on the velocity, microrotation, temperature, concentration and motile microorganism distributions, skin friction coefficient, Nusselt number, Sherwood number, and density number of motile microorganism, is examined. The influence of the squeezing parameter is to increase the dimensionless velocities and temperature and to decrease the local Nusselt number and local Sherwood number. The density number of motile microorganism is decreasing with squeezing parameter, bioconvection Lewis number, bioconvection Peclet number, and bioconvection Schmidt number.     

Exploration of heat transfer effect in a magnetohydrodynamics flow of a micropolar fluid between a porous and a nonporous disk

An analysis is carried out for the flow characteristics of a conducting micropolar fluid. The fluid was passed in between two parallel disks of infinite radii. The novelty of the study is to consider one of the disks as porous and the other one as nonporous, and the external magnetic field is applied along the transverse direction of the flow. The flow phenomena for the polar fluid characterized by the magnetic effect in conjunction with the temperature equation reduce to a set of coupled nonlinear ordinary differential equations using the requisite transformations and nondimensionalization. An analytical approach such as the variation parameter method is employed to tackle the system efficiently. To emphasize the effect of various physical parameters contributing to the flow phenomena, that is, non-zero tangential slip, Reynolds number, Prandtl number, magnetic parameter, and material parameter on the flow profiles of axial and radial velocities, the microrotation and temperature profiles are presented graphically. To validate the simulated results, a comparison with established results is made, and it is concluded that both are in good correlation.     

Development of a system model for a hydrogen production process on a solar tower

An attractive path to the production of hydrogen from water is a two-step thermo chemical cycle powered by concentrated sunlight from a solar tower system. In the first process step the redox system, a ferrite coated on a monolithic honeycomb absorber, is present in its reduced form while the concentrated solar energy hits the ceramic absorber. When water vapour is fed to the honeycomb at 800 °C, oxygen is abstracted from the water molecules, bond in the redox system and hydrogen is produced. When the metal oxide system is completely oxidised it is heated up for regeneration at 1100–1200 °C in an oxygen-lean atmosphere. Under those conditions and in the second process step, oxygen is set free from the redox system, so the metal oxide is being reduced and after completion of the reaction again capable for water splitting.Since the overall process consists of two core reaction steps, which need to be carried out sequentially in a reactor unit at two different temperature steps, a special process and plant concept had to be developed enabling the continuous supply of product regardless of the alternating nature of the solar reactor operation. The challenge of the process control is to keep the two core reaction temperatures constant and to ensure regular temperature switches after completion of the individual process steps, independent of the weather conditions, like DNI fluctuation, clouds and wind speed. Also start-up, the fast switching after completion of half-cycles and the shutdown must be controlled. State of the art is the manual switching of heliostats to fulfil those control tasks.This paper describes the development and use of a system model of this process. The model consists of three main parts: the simulation of the solar flux distribution at the receiver aperture, the simulation of the temperatures in the reactor modules and the simulation of the hydrogen generation. It can be used for the analysis of the operational behaviour. The model is intended to be used in the future for the control of the whole process.     

Evaporating characteristics of a microlayer under a bubble

Using the Hallinan‐Ervin model, the flow and evaporation in a bubble microlayer were theoretically analyzed, and the dryout characteristics and Staub's criterion were discussed in detail. It was revealed that the critical dryout radius is associated with the wettability of the heated surface, and that the dominant role for microlayer evaporation is disjoining pressure, not surface tension gradient. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 456–462, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10052     

Solidification of a liquid about a cylindrical pipe

The temperature distribution and the rate of removal of heat by a coolant are predicted for the process of solidification of a liquid about a cold, isothermal pipe. The heat balance integral method incorporating spacial sub-division is used. It is found that acceptable results can be obtained by using only a small number of sub-divisions together with a piece-wise, linear profile. Furthermore, the results illustrate that the sensitivity which is normally associated with the heat balance integral method is overcome.