Experimental study and model predictions on helium release in an enclosure with single or multiple vents

This paper presents experiments performed at Canadian Nuclear Laboratories (CNL) to examine the dispersion behaviour of helium in a polycarbonate enclosure that was representative of a residential parking garage. The purpose was to gain a better understanding of the effect of buoyancy- or wind-driven natural ventilation on hydrogen dispersion behaviour. Although hydrogen dispersion studies have been reported extensively in the literature, gaps still exist in predictive methods for hazard analysis. Helium, a simulant for hydrogen, was injected near the centre of the floor with a flow rate ranging from 5 to 75 standard litres per minute through an upward-facing nozzle, resulting in an injection Richardson number ranging between 10^?1 and 10². The location of the nozzle varied from the bottom of the enclosure to near the ceiling to examine the impact of the nozzle elevation on the development of a stratified layer in the upper region of the enclosure. When the injection nozzle was placed at a sufficiently low elevation, the vertical helium profile always consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. To simulate outdoor environmental conditions, a fan was placed in front of each vent to examine the effect of opposing or assisting wind on the dispersion. The helium transients in the uniform layer predicted with analytical models were in good agreement with the measured transients for most tests. Model improvements are required for adequately predicting transients with primarily stratified profiles or strong opposing wind.     

Incorporating microgrids coupling with utilization of flexible switching to enhance self-healing ability of electric distribution systems

Electric distribution networks have to deal with issues caused by natural disasters. These problems possess unique characteristics, and their severity can make load restoration methods impotent. One solution that can help in alleviating the aftermath is the use of microgrids (MGs). Employing the cumulative capacity of the generation resources through MG coupling facilitates the self-healing capability and leads to better-coordinated energy management during the restoration period, while the switching capability of the system should also be considered. In this paper, to form and schedule dynamic MGs in distribution systems, a novel model based on mixed-integer linear programming (MILP) is proposed. This approach employs graph-related theories to formulate the optimal formation of the networked MGs and management of their proper participation in the load recovery process. In addition, the Benders decomposition technique is applied to alleviate computability issues of the optimization problem. The validity and applicability of the proposed model are evaluated by several simulation studies.     

Distribution performance of gas-liquid mixture in the shell side of spiral-wound heat exchangers

The non-uniformity of gas-liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers (SWHEs). Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side. In order to investigate the influences of these parameters, an experimental test system was built using water and air as mediums and a novel distributor named "tubes distributor" was designed. The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed, where the mass flow rate ranged from 28.4 to 171.9 kg·h^-1 and the content of gas changed from 0.2 to 0.8, respectively. The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow. It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4. Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.     

哈尔滨典型街谷空间PM2.5分布场与绿色界面指数相关性 研究

在城市化快速进程的背景下，城市 街区PM2.5污染日益严重，本文选取哈尔滨 在不同季节的典型街谷空间，对以叶面积密 度（LA D）、叶面积指数（LAI）为实测要素 的绿色界面指数以及PM2.5浓度进行实测对 比研究。通过对实测数据的分析和挖掘，最 终得出如下结论：首先，典型街谷空间PM2.5 时段浓度呈现上午比下午平均高37.75%，冬 季比夏季高4.7倍的特征；其次，街谷空间的 灌木界面对PM2.5浓度场平均积极贡献率为 18.62%；最后，对PM2.5的衰减率与实测街 谷绿色界面的叶面积密度（LAD）与叶面积 指数（LAI）进行相关性分析，结果显示街谷 绿色界面对PM2.5浓度的衰减作用与叶面积 密度（LAD）呈显著负相关关系，与叶面积指 数（LAI）的相关性程度较弱。     

Effect of sintering temperature on the transport properties of La2Ce2O7 ceramic materials

La₂Ce₂O₇ (LCO) based materials are of a paramount importance since they can be utilized for ammonium production, thermal barrier application, catalysts, hydrogen production and solid oxide fuel cells (SOFCs). In this work, a nano crystalline LCO powder was prepared using glycine-nitrate combustion method and then its properties were comprehensively characterized. The structural analysis of the synthesized LCO was carried out using conventional X-ray diffraction (XRD) and Raman spectroscopy. In a disordered phase, LCO is a biphasic mixture composed of C- and F-type phases. Densification studies were performed by sintering LCO pellets at different sintering temperatures. A densification of ≥95% was observed in all the samples with a very little variation. Sintering temperature had a marked effect on the electrical conductivity of LCO. The LCO sintered at 1100 °C showed the highest conductivity (3.68 mS/cm at 700 °C in air). The electrical conductivity was found to be decreasing with an increase in sintering temperature from 1100 to 1400 °C. To understand the behavior, the analysis of distribution function of relaxation times (DFRTs) utilized for correct separation of grain and grain boundary resistances. The presence of C- and F- type phases calculated from Raman spectra plays a crucial role in deciding conduction behavior of LCO. The results suggest a strong relationship between history of the ceramics preparation and their electrical properties.     

Development of a Hydrogen Refueling Station Design Tool

In the last couple of decades, there has been a growing concern in what effects fossil fuels are having on the environment, resulting in governments and governing organizations issuing stringent emission standards in an effort to curve their environmental damage. To meet these new standards, the transportation industry has been conducting research into alternative fuels, such as hydrogen, but one critical problem utilizing hydrogen is that there is almost no infrastructure. A network of hydrogen refueling stations similar to modern gasoline stations will be required to be constructed to meet future demand. The hydrogen refueling station model was created to aid in designing hydrogen facilities, thus accelerating their development while reducing design cost. A model was created using Simulink consisting of an electrolyzer that generates hydrogen, a compressor, numerous storage tanks, a dispensing unit that transfers hydrogen, and a vehicle component that consumes hydrogen fuel. The model was validated using data from existing hydrogen refueling stations, and the data obtained from testing the previous version of the hydrogen refueling station model to determine model accuracy and if the model has improved. The model has demonstrated that it can produce reasonable results for a station's performance and has improved compared to the previous version.     

电力系统自动化发展方向分析

计算机技术、控制技术及信息技术的发展,电力系统自动化面临着空前的变革,多媒体技术、智能控制技术将迅速进入电力系统自动化领域。     

Quality improvement and backorder price discount under controllable lead time in an inventory model

The proposed study investigates a continuous review inventory model with order quantity, reorder point, backorder price discount, process quality, and lead time as decision variables. An investment function is used to improve the process quality. Two models are developed based on the probability distribution of lead time demand. The lead time demand follows a normal distribution in the first model and in the second model it does not follow any specific distribution but mean and standard deviation are known. We prove two lemmas to obtain optimal solutions for the normal distribution model and distribution free model. Finally, some numerical examples are given to illustrate the model.     

DG planning with amalgamation of economic and reliability considerations

Distributed generation has been playing a vital role in dealing with issues related to distribution systems. This paper presents an approach which provides the distribution system operator with a set of solutions for DG placement to optimize reliability and total cost of power consumed by the distribution system. Optimal location of a Distributed Generator is evaluated based on the performance indices derived for reliability index and total cost of power consumed by the system. The proposed approach is applied to a 15-bus radial distribution system and a 18-bus radial distribution system and the results are analyzed.     

两阶段领域自适应学习

针对领域自适应问题中源域和目标域的联合分布差异最小化问题,提出两阶段领域自适应学习方法.在第一阶段考虑样本标签和数据结构的判别信息,通过学习一个共享投影变换,使投影后的共享空间中边缘分布的差异最小.第二阶段利用源域标记数据和目标域非标记数据学习一个带结构风险的自适应分类器,不仅能最小化源域和目标域条件分布差异,还能进一步保持源域和目标域边缘分布的流形一致性.在3个基准数据集上的实验表明,文中方法在平均分类准确率和Kappa系数两项评价指标上均表现较优.