Rheological behavior of multi-sized SiC inks containing polyelectrolyte complexes specifically for direct ink writing

In order to simultaneously improve both the solid loading and rheological behavior of ceramic ink during direct ink writing (DIW) process, the polyelectrolyte complexes have been used as rheological modifiers. Based on the Funk-Dinger function, the maximum solid loading of multi-sized SiC ink reached 63 vol%. The viscoelasticity of SiC inks with different [COOH]:[NH_x] molar ratios was investigated and the mechanism of polyionic chains on rheology was analyzed. When the [COOH]:[NH_x] molar ratio was 1:0.1, the SiC ink exhibited excellent thixotropic behavior and formability. The effect of particle size on rheological behavior of SiC ink was investigated to clarify the correlation between polyelectrolyte complexes and multi-sized SiC.     

基于加权分布熵的配电网电动汽车并网运行风险分析

针对电动汽车负荷接入配电网的运行风险分析问题,提出带有放大系数的损失严重度;以分布熵来量度配电网状态变量分布不确定性引起的风险,利用损失严重度对分布熵进行加权以建立加权分布熵,基于加权分布熵建立了电压风险指标和潮流风险指标;以元件重要度对加权分布熵进行加权求和来评估网络的电压风险和潮流风险,并综合2类风险建立了配电网运行风险综合评估指标。最后,以接入风电和光伏的改进IEEE 33节点配电系统为例,通过动态概率潮流仿真计算分析了加权分布熵相对于传统风险指标的优越性以及运行风险综合评估指标的合理性,并研究了运行风险随电动汽车负荷的接入位置和容量的变化情况,从而验证了所提指标和模型的有效性。     

Reduction of harmonics in grid-connected inverters using variable switching frequency

The increasing application of distributed power generation into the power system makes grid interconnection requirements of power quality more and more stringent. The reduction of current total harmonic distortion (THD) of grid-connected inverters to achieve the grid code by increasing of switching frequency in PWM of inverters is one of the popular methods, but this increases the switching loss. The aim of this paper is to propose a PWM technique with the function of variable switching cycle to reduce the current harmonics in grid-connected inverters. The weights of this function are determined by using a genetic algorithm under the constraint of constant switching loss. The simulation and experimental results of the proposed technique as well as the conventional constant technique are given and compared, which validate the performance of the proposed technique.     

Finite element analysis for phase change problem in polymer processing

Transient analysis of heat transfer with phase change in thermoplastic injection molding plays an important role to predict solidification in many material-manufacturing processes. Solidification results in a moving solid-liquid interface during filling. Two approaches of the finite element method, namely the apparent heat capacity model and the enthalpy model, for the solution of the Stefan problem in a fixed domain are examined. A two-dimensional, transient, non-newtonian and non-isothermal thermal field of a polymer in a rectangular domain is selected as study case.     

Reconstruction of a heat exchanger network under industrial constraints — the case of a crude distillation unit

Heat exchanger network retrofit using a pinch based approach is presented. In this approach, the criterion of minimum sensitivity of heat exchanger to fouling effects is accounted for. The present paper introduces this criterion without explaining its details that are described in the literature. A summary is given of HEN reconstruction in a crude distillation unit processing 4.2 million ton crude oil per year. While the total heat quantity of hot streams is 110 MW, the heat recovery in the existing HEN is 60 MW. Using Pinch Analysis, the target value of heat recovery at ΔT_min=10 K was determined at 91 MW. Measurements were carried out on the existing HEN with the aim to determine the influence of fouling effects on the heat transfer in the exchangers. Taking local constraints including fouling into account, HEN reconstruction was proposed. The heat savings in the reconstructed HEN was estimated at 75 MW.     

Potential of thermoelectric waste heat recovery in a combined geothermal,fuel cell and organic Rankine flash cycle (thermodynamic and economic evaluation)

The present work aim is performance improvement of an integrated geothermal system by proposing the integration of organic Rankine flash cycle (ORFC) with the Proton exchange membrane fuel cell (PEMFC) and waste heat recovery from condensers using thermoelectric generator (TEG) modules. To achieve this goal, a novel integrated system is proposed, thermodynamically modeled, investigated, and compared with the conventional system. To assess the performance of proposed system, thermodynamic and economic evaluations are performed. The results indicate that R123 as working fluid, has the best performance for the conventional and proposed systems. The findings demonstrate that with employing TEG modules an increase of 2.7% and 2.8%, for the first and second law efficiencies can be obtained respectively. Additionally, the results of parametric analysis indicate that however the geothermal fluid temperature increment decreases the first and second law efficiencies of the system, it leads to the net output power enhancement. Also, enhancement of the flash vessel pressure ratio increases the first and second law efficiency as well. Additionally, the simple payback method showed that a payback time between 1.25 years and 25 years according to the TEG modules cost can be achieved.     

Comprehensive influences measurement and analysis of power converter low frequency current ripple on PEM fuel cell

To deeply understand the influences of power converter's low frequency current ripple (LFCR) and harmonics on a proton exchange membrane fuel cell (PEMFC) in its power conditioning system (PCS), a comprehensive measurement and analysis of the influences of LFCR and harmonics on PEMFC's performance and durability is investigated in this paper. Based on an equivalent circuit model of PEMFC stack and a mechanism model for evaluating the LFCR effects on the PEMFC, this paper studies primarily and systematically the comprehensive influences of LFCR and harmonics on PEMFC performances and durability, such as (1) degrading the PEMFC performance, (2) shortening the lifetime of PEMFC, (3) reducing the stack output power, (4) lowing its availability efficiency, (5) producing more heat and raising the PEMFC temperature, (6) consuming more fuel, and (7) decreasing the fuel utilization. Finally, a Horizon 300 W PEMFC stack is implemented and tested.     

Estimation of shielding failure number of transmission lines for different trace configurations using leader progression analysis

The electrogeometric model (EGM) is a technique used for analyzing the termination of lightning flashes on transmission lines and masts, etc. When using the EGM for modeling the lightning stroke to transmission lines, the power line has normally been represented by a set of horizontal wire and both the sag of the wire, the existence of the towers and effect of uneven way have been ignored. This approach has serious short comings including inability to determine the percentage of the strokes terminating on the towers, failure to correctly predict the effect of height, and giving an approximate value for the number of collected strokes. This paper presents the development of a method for estimating the shielding failure number of power transmission lines in different trace configurations by using the charge simulation method. The effects of towers, sags of conductors, and a perfectly conducting ground are represented in 3-D computation. In addition, the stepwise descending nature of a downward negative leader–streamer systems taken into account by using an appropriate progression model. Upward leader inception and propagation is also modeled utilizing critical equivalent streamer-length criterion. The method is applied to compute the shielding failure of power transmission line for different trace configurations. In this paper the 3-D method is extended by modeling the effect of sloppy trace, trees on both and one side of the transmission line with extensive simulation results. Also, in this paper the effect of variation of tree height, its distance from transmission line and the number of trees on SFN are analyzed and results are shown in curves.     

发电厂并网考核与辅助服务补偿细则评价指标体系

在《发电厂并网运行管理实施细则》和《并网发电厂辅助服务管理实施细则》在国内几个区域电力系统逐步实施的背景下,建立了这2个细则的评价指标体系。首先选取合理性、科学性和实效性为二级指标,并定义了11个定量三级指标。之后,采用模糊层次分析法对2个细则进行综合量化评价:用模糊集方法确定每个指标对不同评价等级的隶属度,应用层次分析法计算各级指标的权重。最后,采用广东电力系统的实例来说明所构建的评价指标体系和采用的评价方法的有效性和实用性。     

基于S变换的配电网故障选线和区段定位

提出S变换的暂态能量法结合零序无功方向的故障选线及区段定位方法。将各馈线终端单元采集到的故障零序电流信息上传至主站,主站对全网故障信息进行信号分析,运用S变换获取表征故障信号的主导特征频率,比较此频率下各馈线的暂态能量及馈线之间的零序无功方向实现故障选线。根据故障线路上故障点前后波形差异,采用上述方法实现区段定位。仿真结果分析表明,选线和区段定位方法准确、可靠,且不受故障合闸角、噪声干扰等因素影响。