一起锅炉严重结垢事故的启示

分析了卧式内燃燃气锅炉在使用检验过程中发现的结垢和排污问题,提出了在研制、安装使用和检验时解决问题的具体方案。     

继电器的动态接触特性研究

本文主要研究触点带低电平负载时,继电器的动态接触特性。为此,在不同的环境应力下,对继电器的动态接触电阻及其弹跳情况进行了数据采集及处理,得到了一些新的试验结果。     

一种有限元自适应剖分的误差计算方法的实现

本文在总结有限元自适应剖分的误差计算方法的基础上,提出了一种新的误差定义,并通过计算实例证明其可行性。文中还定性地讨论了预置的误差控制值ε对计算效果的影响。     

Optimum thermoeconomic and thermodynamic performance characteristics of an irreversible three-heat-source heat pump

The coefficient of performance and specific heating load of an irreversible three-heat-source heat pump are given by using a general cycle model affected by the finite-rate heat transfer, heat leak and internal irreversibility of the cyclic working fluid. The heat pumping load divided by the total cost per unit time is taken as a new objective function and used to investigate the performance of the heat pump. The thermoeconomic and thermodynamic performance characteristics of the heat pump are discussed in detail. Some important performance parameters such as the thermoeconomic objective function and coefficient of performance are optimized. The optimally operating regions of the heat pump and the bounds of several performance parameters are determined. Finally, it is pointed out that the Carnot heat pump may be taken as a special case of a three-heat-source heat pump and consequently its optimal performance can be directly derived from the results obtained here.     

Long-term behavior of cooling fluid in a vertical cylinder

The long-term behavior of cooling an initially quiescent isothermal Newtonian fluid in a vertical cylinder by unsteady natural convection with a fixed wall temperature has been investigated in this study by scaling analysis and direct numerical simulation. Two specific cases are considered. Case 1 assumes that the fluid cooling is due to the imposed fixed temperature on the vertical sidewall whereas the top and bottom boundaries are adiabatic. Case 2 assumes that the cooling is due to that on both the vertical sidewall and the bottom boundary whereas the top boundary is adiabatic. The long-term behavior of the fluid cooling in the cylinder is well represented by T_a(t), the average fluid temperature in the cylinder at time t, and the average Nusselt number on the cooling boundary. The scaling analysis shows that for both cases θ_a(τ) scales as , where θ_a(τ) is the dimensionless form of T_a(t), τ the dimensionless time, A the aspect ratio of the vertical cylinder, Ra the Rayleigh number, and C a proportionality constant. A series of direct numerical simulations with the selected values of A, Ra, and Pr (Pr is the Prandtl number) in the ranges of 1/3 ? A ? 3, 6 × 10⁶ ? Ra ? 6 × 10¹⁰, and 1 ? Pr ? 1000 have been carried out for both cases to validate the developed scaling relations, and it is found that these numerical results agree well with the scaling relations. These numerical results have also been used to quantify the scaling relations and it is found that C = 1.287 and 1.357 respectively for Case 1 and 2 with Ra, A and Pr in the ranges of 1/3 ? A ? 3, 6 × 10⁶ ? Ra ? 6 × 10¹⁰, and 1 ? Pr ? 1000.     

在建筑中设置分布式供能系统站房的安全技术分析及对策

分析了原动机在民用建筑物内设置、运行可能产生的危险因素，根据这些危险因素分析阐述了机房设置的安全技术原则是预防为主，通过提供安全可靠的技术设备、多种检测手段及良好的通风环境，使发生事故的可能性降至最低。同时加强建筑物的安全措施做好准备，万一发生事故，能使事故产生的损失减小到最低限度。     

Thermodynamic analysis of representative power generation cycles for low‐to‐medium temperature applications

This study is focused on the analysis of representative thermodynamic cycles for power generation at low‐to‐medium temperatures (with the highest cycle temperature from 450 to 700 K). The natural working fluid of carbon dioxide is selected for the current tests and comparisons with suitable operation ranges. Energy balance and exergy loss models are established and applied to 10 selected representative thermodynamic cycles. One modified efficiency parameter is also defined for better comparison of performances, which has considered the effects of both specific thermodynamic process and cycle complexity. Based on the modified efficiency parameter, it is found that Rankine cycle yields the highest performance at 450–500 K among the 10 representative cycles, while regenerative Brayton cycle shows better behavior for 550–700 K. Detailed behaviors and optimal principals of regenerative Brayton cycles are also identified and compared in this study. Also, a new cycle is also proposed in this study, which combines the advantages of Rankine cycle and Brayton cycle. The new cycle is proved to have better work output potential but higher system complexity factor. In addition, based on the thermodynamic analysis, possible future directions of low‐to‐medium temperature power cycles are summarized. It is hoped that the results can be of help for related power generation system designs. Copyright © 2014 John Wiley & Sons, Ltd.     

陕西电网电力供求现状及形势展望─—兼论陕西电网加快调峰电源建设的必要性

本文根据西北和陕西电网近１０年来的运行状况，对２０００年及以后２０年间陕西电网的电力供求前景和电源配置等进行预测和分析，并具体提出了陕西电网在不同发展阶段的电源配置和调峰电源建设方面的建设。     

基于迁移学习的唐诗宋词情感分析

随着计算社会学的兴起,利用数据挖掘分析社会情感是近期的研究重点.当前的研究主要针对现代文本,对于古代诗歌这类短文本的情感分析相对较少.本文提出了一个基于短文本特征扩展的迁移学习模型CATL-PCO,通过分析诗歌情感对当时社会及文化进行进一步了解.该模型首先基于频繁词对对古文特征向量进行扩展,再通过迁移学习方式,建立三个分类器并投票得出最后的情感分析结果.CATL-PCO模型首先能够解决古文短文本特征稀疏的问题,在此基础上进一步解决由于现代译文信息匮乏所导致的古代诗歌情感分析困难问题,从而准确的分析古诗词情感倾向,从计算社会学的角度,增进对中国历史的认识.实验表明,当训练集为中国唐诗时,本文提出方法能够准确的对唐代诗歌进行情感分类,并能应用于唐代和宋代各个时期情感分析及代表流派分析.     

Instantaneous Frequency Estimation of Nonlinear Frequency-Modulated Signals Under Strong Noise Environment

Instantaneous frequency (IF) is the most important parameter of a signal, which is an important representation of non-stationary signals, such as frequency-modulated signals. Usually, signals are received with noises. Under noise environment, the conventional IF estimation methods for nonlinear frequency-modulated (NLFM) signal cannot work. In this paper, we focus on how to extract IF of NLFM signal under strong noise environment. First, a modified S-method (SM) is proposed to represent the time–frequency (TF) characteristic. The modified SM uses an adaptive smooth window. The symmetric window is used for multi-component signals and asymmetric window for mono-component signals. The modified SM enhances the TF energy concentration and suppresses the cross-terms effectively. Then, the Viterbi algorithm is used to extract the IF from the TF plane. Viterbi algorithm is a hidden Markov chain approach, which is proposed here as the IF estimator. The proposed method is utilized for various types of NLFM signals. Simulation results demonstrate the efficiency and validity of the proposed method under strong noise environment.