Development of supercritical water heat-transfer correlation for vertical bare tubes

This paper presents an analysis of heat-transfer to supercritical water in bare vertical tubes. A large set of experimental data, obtained in Russia, was analyzed and a new heat-transfer correlation for supercritical water was developed. This experimental dataset was obtained within conditions similar to those in supercritical water-cooled nuclear reactor (SCWR) concepts.The experimental dataset was obtained in supercritical water flowing upward in a 4-m long vertical bare tube with 10-mm ID. The data were collected at pressures of about 24 MPa, inlet temperatures from 320 to 350 °C, values of mass flux ranged from 200 to 1500 kg/m² s and heat fluxes up to 1250 kW/m² for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature.A dimensional analysis was conducted using the Buckingham Π-theorem to derive the general form of an empirical supercritical water heat-transfer correlation for the Nusselt number, which was finalized based on the experimental data obtained at the normal and improved heat-transfer regimes. Also, experimental heat transfer coefficient (HTC) values at the normal and improved heat-transfer regimes were compared with those calculated according to several correlations from the open literature, with CFD code and with those of the proposed correlation.The comparison showed that the Dittus-Boelter correlation significantly overestimates experimental HTC values within the pseudocritical range. The Bishop et al. and Jackson correlations tended also to deviate substantially from the experimental data within the pseudocritical range. The Swenson et al. correlation provided a better fit for the experimental data than the previous three correlations at low mass flux (∼500 kg/m² s), but tends to overpredict the experimental data within the entrance region and does not follow up closely the experimental data at higher mass fluxes. Also, HTC and wall temperature values calculated with the FLUENT CFD code might deviate significantly from the experimental data, for example, the k-? model (wall function). However, the k-? model (low Reynolds numbers) shows better fit within some flow conditions.Nevertheless, the proposed correlation showed the best fit for the experimental data within a wide range of flow conditions. This correlation has an uncertainty of about ±25% for calculated HTC values and about ±15% for calculated wall temperature. A final verification of the proposed correlation was conducted through a comparison with other datasets. It was determined that the proposed correlation closely represents the experimental data and follows trends closely, even within the pseudocritical range. Finally, a recent study determined that in the supercritical region, the proposed correlation showed the best prediction of the data for all three sub-regions investigated.Therefore, the proposed correlation can be used for HTC calculations in SCW heat exchangers, for preliminary HTC calculations in SCWR fuel bundles as a conservative approach, for future comparison with other datasets and for the verification of computer codes and scaling parameters between water and modelling fluids.     

A real-time classification method of power quality disturbances

This paper describes a real-time classification method of power quality (PQ) disturbances. With an acceptable computation burden, both the elementary parameters of the power signal and the types of the disturbances in the power signal are obtained easily. The proposed method addresses the selection of discriminative features for detection and classification of PQ disturbances. Five distinguished time-frequency statistical features of PQ disturbances are extracted using RMS (root-mean-square) method and discrete Fourier transform (DFT). Using a rule-based decision tree (RBDT), the nine types of PQ disturbances can be recognized easily and there is no need to use other complicated classifiers. Finally, the proposed method is tested using the simulated waveforms. And some preliminary experimental results of the accuracy characterization of an initial development instrument are reported. The simulation and application results validate the accuracy and efficiency of the proposed method.     

锯切参数对串珠绳振动特性的影响

利用六个激光位移传感器对锯切加工花岗石过程中串珠绳的振动进行跟踪,利用MATLAB软件分析采集来的振动信号,从频率和幅值两个方面来研究锯切过程对串珠绳振动的影响.试验结果表明,串珠绳在非切削过程中的振动信号含有多个主频率,但是进入切削过程后,其主要振动频率为串珠的冲击频率.切削过程的振动信号幅值比非切削过程中振动信号的...     

Microstructure,Mechanical, and Tribological Properties of CNx Thin Films Prepared by Reactive Magnetron Sputtering

The microstructure,mechanical,and tribological properties of the carbon nitride(CN_x) thin films with different nitrogen contents deposited on high-speed steel substrates by reactive magnetron sputtering were studied.CN_x films with nitrogen contents from 10.7 to 28.2 at.%had an amorphous structure composing of the carbon bonds of sp~2C-C,sp~2C-N,and sp~3C-N.The TiN inter-layer cause the adhesion of CN_x films enhancement.The more nitrogen concentration led to larger film hardness and friction coefficient against GCr15 steel balls,but the wear rates decreased.     

轴承异常声检测错判和漏判原因分析与对策

依据JB/T 10187—2000和JB/T 7047—2006中给定的有效值限值和峰值限值检测判定轴承静音等级时,存在理论上的错判和漏判,在分析、比较的基础上指出,采用峰值同有效值之比(波峰因数)或峰值同有效值之差可以有效地避免这种错判和漏判。     

基于dsPIC单片机的单相逆变电源的设计

本文介绍的是一个PI控制单相逆变电源的设计过程。根据单相电压型逆变器电路模型,建立了逆变器开环系统的传递函数,利用dsPIC单片机设计了一个单相逆变电源。逆变电源的仿真和实验结果表明:增加了电压有效值反馈闭环后,逆变器对输出电压的控制能力明显提高。     

基于SIFT特征匹配的全自动辐射归一化算法

分析了辐射归一化在遥感、航测领域中的重要性,针对辐射归一化线性校正法进行了研究,并提出了一种非人工干预、自动化程度高的基于SIFT(尺度不变特征Scale-Invariant Feature Transform)特征匹配的辐射归一化新方法。通过实验发现,基于SIFT特征匹配的辐射归一化方法能够减少由于大气、照度和传感器差异带来的辐射误差,与传统的方法相比具有结果稳定、自动化程度高的特点.     

一种基于小波变换的数字水印算法

目前有很多基于离散小波变换 (DWT)的水印算法,但很少讨论到水印嵌入子带的选择问题。介绍了一种新颖的基于DWT的水印算法,该算法通过在最大均方根 (RMS)值细节子带中嵌入水印取得了不错的结果,实验证明该子带中的水印在抵抗高斯噪声和JPEG压缩攻击时有较好的鲁棒性。     

RMS广域无线接入系统及其应用

利用成熟的RMS广域无线接入技术和现有的市话网络,使无线市话成为中国电信在通信领域的一个新的业务增长点,并且为偏远地区的用户提供一种更经济有效的通信解决方案。