On the calibration and application of heat flux sensors on buried district heating pipes

A heat flux sensor (HFS) can be used to measure the heat loss from buried district heating (DH) pipes if the HFS is calibrated in conditions resembling the actual condition of use, i.e. not in one‐dimensional conditions. Owing to the fact that the thermal conductivity of the HFS often differs from the thermal conductivity of the surrounding media, the heat flux through the HFS will differ from the true heat flux. Consequently the development of compensated HFSs is discussed. The influence of how the HFS is fixed to the pipe casing is discussed as well as the influence of the casing diameter and the soil thermal conductivity on the calibration factor. The long‐term stability of HFSs is discussed with reference to measurements on a DH transmission line, which were carried out over a period of more than one year. Copyright © 2000 John Wiley & Sons, Ltd.     

用于跨声速叶轮性能计算的多种分裂格式的分析与比较

针对跨声速压气机叶片内复杂的三维流动,采用自行开发的三维CFD程序对跨音速轴流压气机NASA Rotor 37流场进行数值模拟,对比分析了L-F（Lax Friedrichs）、Steger Warming及Van Leer 3种通矢量分裂格式和AUSMDV混合格式在跨声速叶轮流场数值计算时的格式效应。研究表明：与其他格式相比,AUSMDV在设计工况下的计算结果与实验误差最小,对激波和叶顶间隙泄漏的捕捉能力最强,Van Leer格式次之;Steger Warming格式在计算过程中收敛性最好。     

黄河下游泥沙沉积汇对入海悬移质泥沙粒度的影响

黄河下游泥沙沉积汇在黄河流域系统的泥沙收支平衡(Sediment budget)中起着重要的作用。通过河床主槽中泥沙的淤积和冲刷,运动泥沙的组成发生变化;通过滩地上泥沙淤积和河岸坍塌,河漫滩上前期淤积的泥沙与洪水所挟带的泥沙发生交换,使悬移质泥沙的组成发生变化。泥沙冲淤量对不同粒径组入海泥沙百分比的影响是不同的。小于0.01mm细泥沙的百分比与下游河道淤积量呈正相关,0.025~0.05mm和大于0.05mm的较粗泥沙的百分比与下游河道淤积量呈负相关。入海泥沙平均粒径与深泓年摆幅之间也存在着负相关关系。自20世纪60年代,中期以来,特别是自80年代中期以来,由于黄河下游径流量显著减小,黄河下游河道发生萎缩,河宽减小,因而主流线的摆动幅度也显著减小。这使得原来十分强烈的河岸侵蚀和滩槽泥沙交换强度大为减弱,主槽洪水得到的来自河岸侵蚀的细粒泥沙越来越少,因而使入海泥沙粒径变粗。     

高温太阳能吸热管在非均匀热流下的温度研究及结构优化

对腔式管状集热器在非均匀受热条件下进行温度场和热应力场的模拟.研究发现周向温差的不同造成吸热管的热变形分布不同,且吸热管后半段热变形最大;同时,太阳能辐射量随时间变化导致热流密度和吸热管壁面上的周向温差都在发生变化.鉴于此,分别从腔式集热器吸热管的结构、工作介质物性等方面入手以解决非均匀热流带来的形变问题.通过改变吸热...     

Critical heat flux under conditions of high subcooling and high velocity at atmospheric pressure

A quantitative analysis of critical heat flux (CHF) under high mass flux with high subcooling at atmospheric pressure was successfully carried out by applying a new transition region model for a macro-water sublayer on heated walls to the existing model of a vapor blanket over the macro-water sublayer. The CHF correlation proposed in this study could predict well the experimental data obtained for water mass flux of 940 to 20,300 kg/m²s using circulate tubes 2 to 4 mm in diameter and 30 to 100 mm in length with inlet subcooling of 30 to 90 °C and rectangular channels heated from one side with gaps of 3 to 20 mm, length of 50 to 305 mm, and inlet subcooling of 30 to 77 °C and revealed a unique feature of CHF, namely, that the effects of wall friction of subcooled boiling flow and the velocity of the steam blanket above the macro-water sublayer at atmospheric pressure become the dominant factors while they were not dominant at higher pressures. © 1997 Scripta Technica, Inc Heat Trans Jpn Res, 26 (1): 16–29, 1997     

基于量化热能需求的热力系统精益化管理方案

介绍了潘三电厂工业水系统热负荷需求的特点,分析了影响热交换的主要因素,并将热能需求进行量化。着重分析了根据热能需求设计热力系统动力模型的思路及方法,并给出了具体的实践效果。结合运行实践,验证了通过量化热能需求提高系统运行效率的可行性及其所带来的经济效益。     

Improvement of inductive power collection in null-flux maglev system

In the superconducting maglev system it is important to develop a non-contact on-board power source without environmental pollution such as noise and exhaust gases; therefore, inductive power collection (IPC), which utilizes a harmonic magnetic field generated by ground coils in EDS, is being studied. However, alteration to a null-flux EDS that has a high drag ratio reduces the power collecting capacity in the IPC system. In addition, power collecting coils are located on the cryostat of the superconducting coil (SC), so eddy currents at the cryostat also reduce the power collecting capacity. Therefore, an exclusive SC type that locates the exclusive SCs and IPC and power collecting coils so as to face the upper and lower coils of ground coils, respectively, is examined; but we aim to improve the conventional type. After analyzing the influence of eddy currents at the cryostat in detail and improving the composition of the power collecting coil and cryostat, we found that the conventional type has the same capacity as the exclusive SC type. In order to prove the above-mentioned result, we measured the induced voltage of the new-type coils in a test run at Miyazaki test track and confirmed the output of this IPC system in a full-scale synthetic bench test with a PWM converter and magnetic field simulator. © 1998 Scripta Technica. Electr Eng Jpn, 122(2): 48–60, 1998     

Effect of channel length on critical heat flux under conditions of high subcooling and high velocity in short heated channels

The characteristics of critical heat flux (CHF) in existing experiments under high subcooling and high velocity in short heated channels have, for the first time, been systematically and quantitatively investigated to provide a CHF correlation that can properly predict the effect of channel length, especially when the channel length-to-channel diameter ratio L/D is less than about 20. The major test conditions of existing CHF experiments investigated in this study were channel diameter 1 to 4 mm, L/D 1 to 25, 0.1 to 1.2 MPa pressure, 34 to 117°C inlet water subcooling and 500 to 40 700 kg/(m² · s) mass flux in circular channels, and 3 to 20 mm gap size, 6 to 40 L/D_e, 0.1 to 3.1 MPa pressure, 4 to 166°C inlet water subcooling, and 940 to 27,000 kg/(m² · s) mass flux in rectangular channels. The effect of L/D on CHF was evaluated referring to the analytical solution of CHF, which was previously derived by the author for the channel flow at high subcooling and high velocity. As a result, the effect of L/D was quantitatively clarified as an effect of magnitude in heat transfer of single-phase forced-convection flow, giving a larger CHF with a smaller L/D in the case of L/D less than about 20. The proposed correlation predicts CHF to within a ±35 percent error margin. ©1998 Scripta Technica, Heat Trans Jpn Res, 27(7): 509–521, 1998     

Spiral core made of grain-oriented electrical steel sheet

Spiral cores made of grain-oriented electrical steel sheets (GO) were developed to be used as a high performance motor core. All teeth directions are coincident with the GO rolling directions (easy magnetization axis) in the spiral cores. The GO spiral cores have excellent properties because the GO has very low iron loss and very high permeability in the rolling direction. In the GO spiral cores, the iron losses decrease to a quarter and the inductions are 0.2 T higher at 800 A/m as compared with conventional spiral cores made usually of SPCC. Because the thickness of conventional spiral cores generally varies, applications are limited to automobile alternator cores. The thickness of GO spiral cores changes little during a spiral deformation because the core sheets are deformed transversely to the rolling direction of GO, that is, <110>{011}; the <110>{011} deformation of Fe does not create sheet thickness. As the stiffness and packing factor of a GO spiral core are high in the order of no thickness change, GO spiral cores have high performance for motor cores. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (3): 58–66, 1997     

A generalized method of controlled voltage source-fed induction motor vector control using the observer theory

Vector control of induction motors is widely used for industrial applications. On-line parameter identification and speed sensorless control are being studied actively. A representative method for these problems is the application of an adaptive full-order observer. The rotor flux for vector control is estimated by a full-order observer and machine parameters, or the rotor speed is determined by an adaptive algorithm. In this paper, a new vector control scheme with parameter identification is proposed. This method is based on the adaptive full-order observer. However, the observed currents which are usually estimated in the voltage model are considered as command currents and the voltage model is used for the current controller. As a result, the proposed system is simpler than the conventional adaptive full-order observer system. Since the proposed system is composed of an induction motor model in a synchronously rotating reference frame, the well-known slip frequency control block is contained. The arrangement of the poles which are related to the torque transfer function is discussed. A linear model is derived taking into account the effects of the change of the stator and rotor resistances. The trajectories of poles and zeros of the torque transfer function are computed and discussed for various system parameters. Identification of stator and rotor resistances is confirmed by simulation using a nonlinear system model. The proposed idea is applied to a speed sensorless system; this system has a similar configuration to those of existing systems under some assumptions. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(4): 66–76, 1997