汽轮发电机组突发性振动的部分原因分析

汽轮发电机组在运行中产生突发性振动情况较为复杂，需要根据出现振动的不同现象进行分析找出原因，再根据原因进行处理。本文就引起汽轮发电机组转子振动的部分原因进行了分析，并提出几点建议。     

Generalised theory of ENSO and related atmospheric phenomena

In this paper we develop a generalised theory of El Nino-Southern Oscillation (ENSO) phenomena as well as related atmospheric phenomena (e.g. quasi-biennial oscillations and the Madden-Julian oscillations) and use actual climatic records to demonstrate its credibility as well as validity. In particular, it is shown that the Southern Oscillation is primarily caused by large zonally moving heat waves at low latitudes whose zonal wavelength is approximately 360° longitude and which generally last for about one year, although some extend to over 10 years. These large zonally moving heat waves (LZMHW) are mostly formed by interactions at low latitudes among (seasonal) atmospheric patterns, zonal surface albedo patterns, incoming solar energy and its sampling sequences continuously executed by the Earth through its spinning motion. The temperature patterns associated with the LZMHW in turn generate the atmospheric pressure patterns associated with the Southern Oscillation through the well-known high correlation between ocean surface temperature and barometric pressure. The latter patterns in turn give rise to air circulation patterns and other corresponding meteorological processes. El Nino events, on the other hand, result when the peak of eastward-moving LZMHW reach the eastern part of the Pacific ocean and their heat content (at least partly) focuses onto a stretch of the ocean by the concave-shaped lining of the lofty Rocky-Andes mountains as indicated in the text. Finally the theory applies the above points to the possible existence at low latitudes of zonally moving heat/temperature (and associated meteorological) oscillations at each solar cycle period and also twice in each solar cycle period. This apparently explains the zonally moving heat/temperature waves (at a period of 11 years) which were deduced from meteorological records.     

Analysis of chemical-reaction-coupled mass and heat transport phenomena in a methane reformer duct for PEMFCs

Mass, heat and momentum transport processes are coupled with catalytic chemical reactions in a methane steam reforming duct. It is often found that endothermic and exothermic reactions in the ducts are strongly integrated by heat transfer from adjacent catalytic combustion ducts. In this paper, a three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, and the effects on various transport processes in a steam reforming duct. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The predicted results are presented and discussed for a composite duct consisting of a porous catalyst reaction layer, the fuel gas flow duct and solid layers. Parametric studies are conducted to reveal the importance of reformer designs and operating conditions. The results show that the variables, such as porous layer configuration, temperature and catalyst loading, have significant effects on the transport processes and reformer performance.     

Apparatus for investigating boiling phenomena in a fibrous porous medium

Recent advances in paper drying research have identified a phase-change process that offers significant improvements in drying rates and sheet solids contents. A fundamental study focusing on the hypothesized boiling process within the sheet required the development of an apparatus to perform boiling experiments in a bed of ceramic fibers. The apparatus is composed of a boiling cell, a heat supply system, a digital data acquisition system, and associated process control systems for control of heater surface temperature and cell pressure. Boiling curves measured with this system indicate that heat transfer is governed largely by the physical characteristics of the fiber bed. This paper presents a detailed explanation of the boiling apparatus.     

Integrated governor control for a diesel-generating set

This paper is concerned with the detailed implementation of real-time fuzzy logic speed control for a standby diesel-generating set. The implementation platform is that of the Mathworks xPC Target. This rapid prototyping scheme permits the automatic cross-compiling of the nonreal-time Simulink control system model into real-time C code, which is executable on the xPC target PC. The digital governor xPC target hardware consists of a desktop PC with a National Instrument Input/Ouput card and a Softing Controller Area Network Card. The paper details the fuzzy control model and the methods with which to communicate with the engine control module. Tests were conducted on a 50-kVA diesel-generating set. The results show that the fuzzy controller is superior to the variable gain PID-type governor used by the conventional engine control module.     

稻壳在循环流化床中燃烧现象的分析

为了研究稻壳在循环流化床中的燃烧特性，在生物质循环流化床试验台上对稻壳进行了燃烧试验。通过对试验过程中各测点温度及压力变化的分析，探讨了二次风和循环回料对稻壳在循环流化床燃烧炉内燃烧过程的影响。试验结果表明：二次风可以促进挥发分在稀相区的燃烧，对提升稀相区的温度作用明显；正常循环回料使得温度沿炉膛高度均匀分布。所得结论对生物质循环流化床的试验研究及实际运行有一定的参考意义。     

Understanding the role of energy consumption in human development through the use of saturation phenomena

A correlation is presented between the UN human development index and per capita energy consumption for 120 nations. A strong relationship between index values and energy consumption is observed for the majority of the world. Additionally, a distinct secondary trend emerges from the dataset, representing heavy energy exporters such as the Organization of the Petroleum Exporting Countries and some Former Soviet Union nations, among others. The preliminary observation is made that these two trends closely resemble saturation curves, exhibited by a variety of natural phenomena. For the primary trend, three regions are isolated: a steep rise in human development relative to energy consumption for energy-poor nations; a moderate rise for transitioning nations; and essentially no rise in human development for energy-advantaged nations, consuming large amounts of modern energy. These correlations suggest that tremendous gains in human development are possible for the world's poorest, with small incremental access to energy.     

Investigation of flow phenomena in a kettle reboiler

Two-phase flow phenomena were investigated while boiling R113 and n-pentane in a 241-tube thin slice kettle reboiler. For heat fluxes between 10 and 40 kW/m², row pressure drop measurements were made in three columns and visual observations of the flow patterns were recorded by a video camera. The height of the two-phase mixture above the tube bundle was also varied. The results revealed that the height of the mixture had little effect on the row pressure drop distribution in each column. At heat fluxes below 10 kW/m², the pressure drops were reasonably constant. However, at heat fluxes greater than this, the row pressure drop continuously declined.Two one-point-five-dimensional models were developed, one to aid the investigation of static liquid driven lateral flow in the tube bundle, and another to aid the investigation of the cause of the change from reasonably constant to continually declining row pressure drop. The data and the analysis showed that the flow within the tube bundle was always two-dimensional and that the flow pattern was dominated by the static liquid at the tube bundle edge when the heat flux was less than 10 kW/m². This corresponded to the bubbly flow regime. At larger heat fluxes, the flow pattern changed to intermittent flow. The change occurred when the Kutateladze number was 1.09. Declining row pressure drops occurred in this latter flow regime.     

柴油发电机组安装架结构改进分析

为合理地选择柴油发电机组安装架的结构形式和支承位置,对柴油发电机组安装架在运用中出现的问题进行了分析,并结合安装架的受力特点,提出两种设计方案。为比较两种方案的可行性,采用有限元方法对两种设计方案安装架的强度和刚度进行计算、分析和比较。计算结果表明,两种方案的强度、垂向刚度均能满足设计要求,但方案二的扭转刚度明显优于方案一。     

Analysis of nanofluid transport through a wavy channel

Laminar forced convection of heat transfer and pressure drop of Al₂O₃ and CuO/water nanofluids flow through a horizontal tube and wavy channel under constant wall temperature boundary condition is numerically investigated. Two different models were employed in our study: single phase (homogenous and dispersion) and two phase (Lagrangian–Eulerian model or discrete-phase model (DPM) and the mixture). The effects of various parameters, such as particle concentration, particle diameter, particle type, constant or temperature-dependent properties, wave amplitude, Reynolds number and Peclet number on the thermal, and flow field of the Nanofluids are analyzed. Our results revealed that variable properties assumption play a dominant role in horizontal tubes and provide better predictions for the heat transfer enhancement. The difference between constant and variable properties becomes insignificant and can be ignored in wavy channel due to the high mixing and generated recirculation zones, whereas the difference between the DPM and the single-phase variable properties diminish as Peclet number and volume fraction increases. However, dispersion model shows an excellent agreement with the experimental data; the absence of the reference values for the adjustable factor C_d in the open literature put it in a questionable position. Therefore, DPM and homogenous single-phase model with well-chosen thermal conductivity and viscosity correlations can be considered as an accurate way and more dependable in nanofluid simulations especially the homogenous single-phase model because it requires less time, CPU, and memory usage. As expected, it is found that the heat transfer increases as the Reynolds number and particle volume fraction increases, but it is accompanied by a higher pressure drop. The obtained results have been successfully validated and compared with the experimental and numerical data available in the literature.     

Transport phenomena in the thin-film region of a micro-channel

A mathematical model to predict the flow and heat transfer characteristics for a thin film region of a micro-channel is proposed. Gradient of the vapor pressure and the capillary force are considered. The effects of channel height, heat flux and slip boundary condition at the solid-liquid interface are investigated. The length of the thin film region is calculated by comparing the magnitude of the capillary and disjoining pressures. The length and the thickness of the thin film region decrease exponentially with increasing heat flux. The channel height has no effect on the shape of film thickness. In the case of slip condition, the decreased film thickness causes the capillary and disjoining pressures to increase.     

Model of the commutation phenomena in a universal motor

An equivalent electrical circuit, characterized by the minimum coil sections number necessary to analyze the commutation in a universal motor, is discovered. The model parameters are also determined: in particular, the self and mutual inductance coefficients and the electromotive force induced in the coil sections (taking into account the magnetic saturation), the brush-commutator voltage drop, the electric arc. By means of a numerical solution of the equivalent circuit, the current waveforms are analyzed; the comparison between the computed and measured waveforms of the brush-commutator voltage drops allows to verify the model.     

Molecular dynamics study for dissociation phenomena of a gas molecule on a metal surface

The dissociation phenomena of a gas molecule on a metal surface were analyzed by the molecular dynamics method. A platinum (111) surface and hydrogen were chosen as the metal surface and the gas molecule, respectively. The embedded atom method was used as the interaction between atoms in order to express the dependence of electron density. The parameters were determined so that the results such as the electron density, adsorption energy of an H atom on a Pt(111) surface, and the interaction between H atoms of an H₂ molecule obtained by the EAM method were consistent with those obtained by the density functional theory or empirical function. Collisions between a hydrogen molecule and the platinum surface were simulated by the molecular dynamics method, and the dissociation probability was obtained. Using these results, the effect of the motion of the surface atoms or the hydrogen molecule on the dissociation probability was analyzed. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20222     

Experimental Investigation of Self—sustained Oscillation in a Traveling Wave Thermoacoustic System

A traveling wave thermoacoustic engine consisting of a loop tube with a resonator has been tested. The onset characteristic together with the transition of oscillation mode from traveling wave to standing wave and the periodic shifting between modes in this system are investigated experimentally. The process of self-sustained thermoacoustic oscillation in this heat engine is described and analyzed through phase space distribution reconstructed from the time series of acoustic signal.     

Dynamic simulation of backdraft phenomena in a townhouse building fire

A backdraft is a unique and extremely dangerous fire phenomenon in buildings with limited ventilation. Backdraft can generate the powerful fire and heavy smoke that hinders firefighter rescues and those escaping the fire. This study investigates a deflagration fire and smoke spread in a townhouse fire that occurred in Taiwan. The fire is reconstructed using the CFAST (ver. 6.0.10) zone model, FDS (ver. 4.0.7) field model, and full‐scale fire tests for motorcycles. Computational results reasonably agree qualitatively with the post‐accident reports. Simulation analysis for backdraft phenomena demonstrated that window size in the limited‐ventilation compartment fire influenced smoke leaking from vents, deflagration induction time, and fire intensity from a new opening. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(3): 153–164, 2008; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/htj.20196     

Analysis of parameter effects on transport phenomena in conjunction with chemical reactions in ducts relevant for methane reformers

Various transport phenomena in conjunction with chemical reactions are strongly affected by reformer configurations and properties of involved porous catalyst layers. The considered composite duct is relevant for a methane steam reformer and consists of a porous layer for the catalytic chemical reactions, the fuel gas flow duct and solid plate. In this paper, a fully three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, with purpose to reveal the importance of design and operating parameters grouped as three characteristic ratios. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The results show that the characteristic ratios have significant effects on the transport phenomena and overall reforming reaction performance.     

集群风电区域振荡原因分析及对策研究

由于新疆某集群风电场的各个风电场间无功补偿装置(SVC)控制不合理,导致低频振荡频繁,低电压穿越而发生大面积机组停机。文章结合新疆电网实时运行数据,考虑SVC间协调配合和动态响应时间,对其集群风电场送出线路功率、电压的影响进行仿真分析。仿真结果表明:SVC投切会引起系统低频振荡,导致并网点电压跌落使风机进入低电压穿越状态;同时SVC动态响应不及时易使风机过电压停机。文章提出相关的改善建议,为保证集群风电场稳定运行提供参考。     

Chemical reacting transport phenomena in a PEM fuel cell

A three-dimensional mathematical model for the PEM fuel cell including gas channel has been developed to simulate fuel cell performance. A set of conservation equations and species concentration equations are solved numerically in a coupled gas channel and porous media domain using the vorticity-velocity method with power law scheme. Detailed development of axial velocity and secondary flow fields are presented at various axial locations. Polarization curves are demonstrated by solving the equations for electrochemical reactions and the membrane phase potential. Compared with experimental data from published literatures, numerical results of this model agree closely with experimental results.     

A new dynamic model for predicting transient phenomena in a PEM fuel cell system

In this paper, a mathematical model is developed to simulate the transient phenomena in a polymer electrolyte membrane fuel cell (PEMFC) system. At present many electrochemical models are available to the fuel cell designers to capture steady state behavior by estimating the equilibrium voltage for a particular set of operating conditions, but models capable of describing transient phenomena are scanty. In practical applications such as powertrains of land-based vehicles or submarines, the output power from the fuel cell system undergoes large variations especially during acceleration and deceleration. During such processes, many transient dynamic mechanisms become significant, while simple empirical models are unable to represent the transient dynamics caused by such as diffusion effect and double layer capacitance at the interface between the electrodes and the electrolyte. Hence, a novel dynamic fuel cell model is developed in this paper which incorporates the effects of charge double layer capacitance, the dynamics of flow and pressure in the anode and cathode channels and mass/heat transfer transient features in the fuel cell body. This dynamic model can predict the transient response of cell voltage, temperature of the cell, hydrogen/oxygen out flow rates and cathode and anode channel temperatures/pressures under sudden change in load current. The proposed model is implemented in SIMULINK environment. The simulation results are analyzed and compared to benchmark results. Lab tests are carried out at Connecticut Global Fuel Cell Center and a good agreement is found between tests and simulations. This model will be very useful for the optimal design and real-time control of PEM fuel cell systems.