Heat transfer regimes for a flow of water at supercritcal conditions in vertical channels

Heat transfer regimes observed in experiments with water at supercritical conditions flowing in vertical channels of various cross-sections (such as round pipes, annulus, or rod bundles) are analyzed. In accordance with the established practice, the normal and the deteriorated heat transfer regimes were singled out as the basic regimes specific for heat carriers with highly variable properties. At the same time, it has been established that most published experimental data on supercritical pressure water heat transfer along the length of test sections demonstrate combined (or transient) heat transfer regimes. The features can be presented as a superposition of characteristics of the above-mentioned basic regimes. The combined regimes are not stable in certain ranges of water flow conditions in which sudden transitions between the basic regimes can occur. A system of similarity criteria governing heat transfer rate in the vicinity of the critical point is examined. As applicable to cores of water-cooled reactors, due to a small hydraulic diameter of cooling channels, buoyancy forces acting in these channels are negligible as compared with the inertia effects caused by thermal acceleration of the flow and viscous force. This concept yields two integrated criteria whose use in the correction factors for the basic heat transfer equation, which we proposed previously for the normal regimes, adequately (with an error of 20–25%) describes the specific of the heat transfer coefficient in the normal, deteriorated, and combined regimes. A system of equations is proposed for design calculation of heat transfer in channels of nuclear reactors cooled with supercritical pressure water.     

Pattern recognition for modeling and online diagnosis ofbioprocesses

Bioprocesses are highly nonlinear and they operate within a wide range of operating regimes. Proper modeling and control of these processes necessitate real-time identification of these regimes. In this paper, the authors introduce an approach for the development of a fuzzy neural network (NN) model for a bioprocess based on decomposition of the process into its different regimes. The model consists of multiple linear local models, one for each regime, and its output is the interpolation of the outputs from the local models. Regime identification is performed using fuzzy clustering and NNs. The outcome of this identification technique is a set of membership functions which indicate to what degree the process is governed by the three operating regimes at any given point in time. The method is illustrated through the development of a real-time product estimation model for a simulated gluconic acid batch fermentation     

Control of an induction motor in restart of the pickup and retention quasi-stationary regimes

The concepts for implementing the control of an induction motor in quasi-stationary regimes are systematized. These concepts, which involve specification of the regulators of the automatic control system for asynchronous electric drives, enabled the development of the algorithms for the practical implementation of the regimes for maintaining the main movement of the executive device during short-time voltage drops in the supply mains: retention and restart, or pickup, of the rotating induction motor.     

Mechanism for self-synchronization of femtosecond pulses in atwo-color Ti:sapphire laser

An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model     

高压浓相变水分煤粉输送特性及香农信息熵分析

在输送压力可达4.0 MPa，固气比高达450 kg/m3的高压气力输送试验台上，用氮气进行煤粉高压浓相气力输送试验研究。分别在不同的总输送差压、煤粉含水率、压力和表观速度等条件下进行了输送试验，考察操作参数对煤粉质量流量和固气比等气力输送特征参数的影响，用信息熵分析试验过程中采集到的压力波动时间序列，探讨流动稳定性和流型变迁过程中信息化趋势，建立信息熵和流型之间的关系。结果表明，在总输送差压增大的过程中，固气比和香农(Shannon)信息熵均增大；流动相图与Shannon信息熵之间呈现较好的规律性；不同流动形态的Shannon熵差异较大，不同流型之间的Shannon熵区分度较好。随着煤粉含水率的增大，煤粉的质量流量和压损减小，Shannon信息熵值下降。Shannon信息熵分析为研究高压浓相气力输送流型、稳定性及其转变特性提供了一种行之有效的方法。     

锌银电池化成制度对银电极老化后性能的影响

主要研究了锌银电池化成制度对银电极老化后性能的影响。化成制度包括恒流充电、变电流充电、恒流充电后浅放一定的容量、卤素离子法、不对称交流充电和高温充电。并采用加速老化的方法,将实验银电极进行了加速老化处理。通过极化曲线测试、扫描电镜分析及实效放电等方法,分析了化成制度对银电极老化后性能的影响,主要包括电压、容量等,为锌银电池干贮存性能的提高提供一定的技术贮备。     

The effect of the operating regime of 6(10)-kV power cables on parameters of partial discharges in insulation

The effect of the operating regime of 6(10)-kV power cables of urban power-distribution networks on the parameters of partial discharges in insulation is investigated. Operating regimes of the cable, regimes after high-voltage testing and short circuits, and the ability to diagnose a single-phase fault in an urban 6(10)-kV power-distribution network are analyzed. Dependences of changes in partial discharge intensity in these regimes are defined.     

Partial electrostatic discharge induced by precharged dielectricsurfaces

In this paper on partial discharges due both to applied Laplacian field and to charged surface of a plate-covering dielectric sheet, separate positive and negative precharging polarities were used in selective point-plane corona experiments in atmospheric air. At a finite point potential, three distinct regimes were encountered: (1) Trichel-like pulsing; (2) discharge quenching; and (3) inverse pulsing. A quenching-potential threshold separating regimes 1 and 2 and an inverse-pulsing triggering potential threshold separating regimes 2 and 3 were determined as functions of the precharging voltage for the physical parameters of the system used. In regime 3, inverse-pulsing current signatures indicate some features shared in common with the more familiar Trichel pulsing. Also noted is the phenomenon of pulse bunching, observed when conditions lie close to those of the threshold of inverse-corona pulsing, whereby groups of such pulses, typically a few in each, would recur in quick, but irregular succession     

基于生态径流指标的水文情势变化评估新方法

基于流量历时曲线计算生态径流指标的方法存在诸多不足,也未形成相应的河流水文情势变化评估方法。采用流量过程线重新定义了月、季和年三种时间尺度的生态径流,构建了包含12个月生态盈余和12个月生态赤字的生态径流指标体系,提出了衡量这些指标在建库前后变化度的计算公式,基于月生态赤字发展了月生态风险评估方法,形成了一种河流生态水文情势变化评估方法。将其用于长江宜昌站,评估三峡工程在建库前后的生态水文情势变化。结果表明：重新定义的月、季、年生态径流之间消除了不一致性,香农多样性指数与年生态赤字的年际变化具有更高的相似度,变化度计算公式完全适用于衡量建库前后的变化程度,生态风险图使生态径流指标的实用性大为增强。     

Study of reliability of the metal of the cast valve casing made of grade 20KhMFL steel subjected to recovery thermal treatment after 250000 h of operation

The effect of different regimes of recovery thermal treatment (RTT) on short and long-term mechanical properties and structure of the cast-casing elements that have exhausted their rated lifetimes are analyzed. A comparison of different RTT regimes is made, and the advantages and shortcomings of each regime are revealed. RTT parameters that provide optimal properties of the metal being treated are determined.     

Vector control of permanent-magnet synchronous motors

Schemes and algorithms are considered for vector control of a permanent-magnet synchronous motor by adjusting the stator-field vector magnitude and its angular misalignment relative to the rotor-field vector. The proposed algorithms provide a very varied view of motor mechanical characteristics, demonstrate low sensitivity to the dispersion of engine parameters, use a relatively small amount of computational procedures, and make it possible to implement quite easily a variety of static and dynamic drive operating regimes, including the modes of direct-current control, start, reverse, and others. Simulation results of the drive operation in static and dynamic regimes are given.     

International water and steam quality standards for thermal power station drum-type and waste heat recovery boilers with the treatment of boiler water with phosphates and NaOH

One of the ways for improving the operational reliability and economy of thermal power station equipment, including combined-cycle equipment, is to decrease the rates of the corrosion of constructional materials and the formation of scales in the water-steam circuit. These processes can be reduced to a minimum via the use of water with a minimum content of admixtures and the correction treatment of a heat-transfer fluid. The International Association for the Properties of Water and Steam (IAPWS), which unites specialists from every country of the world, has developed water and steam quality standards for power station equipment of different types on the basis of theoretical studies and long-term experience in the operation of power plants in 21 countries. Different water chemistry regimes are currently used at conventional and combined-cycle thermal power stations. This paper describes the conditions for the implementation of water chemistry regimes with the use of sodium salts of phosphoric acid and NaOH for the quality correction of boiler water. Water and steam quality standards and some recommendations for their maintenance under different operational conditions are given for each of the considered water chemistry regimes. The standards are designed for the water-steam circuit of conventional and combined-cycle thermal power stations. It is pointed out that the quality control of a heat-transfer fluid must be especially careful at combined-cycle thermal power stations with frequent startups and shutdowns.     

Numerical investigation of thermal regimes in twin-tube-channel heat pipelines using conductive-convective model of heat transfer

The results of numerical investigation are reported on thermal regimes in the systems of heat transport based on the solution of the conjugative problem of conductive-convective heat transfer in the system •twin-tube-channel underground heat pipeline„ environmental medium. It is shown that the use of the proposed approach allows one to perform the comprehensive analysis of the heating regimes in such systems.     

Discovering price-load relationships in California's electricitymarket

This paper reports on characterizing price behavior in the California electricity market. Market participants, that is, producers, consumers and traders, are highly motivated by the potential for profits to develop strategies to explore, and exploit, the limits of system operation. These strategies should be reflected in the market as different price to load relationships. We show that a number of regimes, i.e., characteristic behaviors, exist in the price time series, and provide a brief analysis of each regime. Knowledge of the number of regimes, their characteristics and switching dynamics allows insight into the market and power system performance     

Specific features of the relay protection of magnetization-controlled shunt reactors for voltage of 110–500 kV

Based on the experience in design and calculation of operation regimes, specific features and general concepts of the relay protection for magnetization-controlled shunt reactors for voltage of 110–500 kV are described.     

Implementation of the Wigner-Boltzmann transport equation within particle Monte Carlo simulation

In this paper, we detail the main numerical issues of the Monte Carlo method developed to solve the Wigner-Boltzmann transport equation and simulate the quantum transport in semiconductor nanodevices. In particular, we focus on the boundary conditions regarding the injection of particles and the limits of integration for the calculation of the Wigner potential which are of crucial importance for the physical correctness of simulation results. Through typical examples we show that this model is able to treat correctly purely quantum coherent and semi-classical transport situations as well. It is finally shown that to investigate devices operating in mixed quantum/semi-classical regimes and to analyze the transition between both regimes, this approach takes advantage of its full compatibility with Boltzmann algorithm.     

The influence of the type of steam distribution in steam turbines of combined-cycle plants on the effectiveness of their operation

The paper is concerned with the comparative effectiveness of the use of nozzle and throttle steam distribution in steam turbines of combined-cycle plants equipped with heat recovery boilers. The influence of the type of steam distribution in the steam turbine on the reliability of startup regimes and the load control range of a combined-cycle plant on the effectiveness of the use of steam turbines in the regimes of the frequency and power control in a power system is analyzed.     

Comparison of electron and phonon transport in disordered semiconductor carbon nanotubes

Charge and thermal conductivities are the most important parameters of carbon nanomaterials as candidates for future electronics. In this paper we address the effects of Anderson type disorder in long semiconductor carbon nanotubes (CNTs) to electron charge conductivity and lattice thermal conductivity using the atomistic Green function approach. The electron and phonon transmissions are analyzed as a function of the length of the disordered nanostructures. The thermal conductance as a function of temperature is calculated for different lengths. Analysis of the transmission probabilities as a function of length of the disordered device shows that both electrons and phonons with different energies display different transport regimes, i.e. quasi-ballistic, diffusive and localization regimes coexist. In the light of the results we discuss heating of the semiconductor device in electronic applications.     

Electrostatic atomization of conducting liquids using ACsuperimposed on DC fields

The objective of this study is to investigate the possibility of using electrostatic atomization to produce fine ceramic particles starting from highly conducting ceramic precursor solutions. The work was directed towards carrying out experimental investigation for the production of uniform droplets formed by the breakup of a permanent jet extending from the capillary nozzle. To control the atomization process an AC field (sine wave) was superimposed on a DC field. For given parameters of electrostatic field, capillary diameters, resistivity of liquids, and flowrate, the jet formation and breakup process was investigated. Several regimes were observed to be in synchronization with the applied potentials and frequencies. In these regimes uniform droplets were produced. Optical techniques were employed to study the breakup process     

Focussing and defocussing regimes in the multistable optical response of single-crystal lead magnesium niobate

Abstract

Experimental observation of the static and dynamic response of monocrystalline lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), at moderate power c. w. laser irradiation shows five distinct regimes depending on the beamwidth and wavefront curvature of the incident Gaussian laser beam. In one of these regimes, the system exhibits multistability and transient aperiodic regenerative oscillations similar to those observed previously in ceramic PMN. In the other four regimes, thermal focussing and/or defocussing combine with nonlinear Fabry-Perot resonances to produce qualitatively different responses. The thermal relaxation time is calculated theoretically as 1 - 500 s, about 10³ longer than earlier estimates and in agreement with experiment. Damage thresholds are also discussed.