自然通风建筑内空气流动和污染物扩散的数值模拟

数值模拟了单体自然通风建筑模型内的空气流动和污染物扩散,考察了紊流施密特数Sct对污染物模拟值的影响。结果表明,选取的3种紊流模型对时均流速和紊动能的模拟值和风洞试验值基本一致,标准k-ε模型与realizable k-ε模型模拟的流场较相似,其浓度场结果也基本相同,当Sct为0.8～1.0时,模拟值和试验值吻合得最好。由于RNG k-ε模型对地面污染源附近的时均流动模拟不准确,导致其浓度模拟值和试验值相差较大,因此,选取合理的Sct时,应基于准确的流动模拟,而不能仅考察浓度模拟值和试验值的吻合程度。     

基于数字孪生及神经网络的电压扰动定位方法

提出一种基于数字孪生及神经网络的电压扰动定位方法。首先根据配电网中大量的监测点信息以及网架结构参数构建配电网数字镜像模型,然后采用人工神经网络对数字镜像模型的历史数据进行学习训练,得到反映节点电压与暂降发生位置之间映射关系的神经网络模型。该模型可以根据暂降后各节点的电压数据得到反映各节点故障特征的信息,进而实现对暂降源的定位。以河南某县30节点的配电网为例,对所提方法的有效性进行验证,结果表明该方法能够实现对电压暂降源的准确定位。     

宁夏典型工业园区污染物化学指纹数据库的建立

为评估工业园区污染状况及建立用于污染物溯源的数据库,以宁夏典型工业园区为研究区域,采集了7种不同行业类型的共398件土壤样品,检测了样品中的重金属和多环芳烃含量并建立污染物化学指纹数据库.结果 表明:除废弃资源综合利用业地块的二苯并[a,h]蒽外,样品中的重金属和多环芳烃均不超过第二类用地筛选值,但还是有部分污染物的含量超过宁夏土壤背景值和第一级标准值,污染现象依然存在.通过定义4种污染指纹等级,成功搭建了基于行业的污染物化学指纹数据库,为后期的污染治理及污染物的溯源提供了参考.     

宁夏典型工业园区污染物化学指纹数据库的建立

为评估工业园区污染状况及建立用于污染物溯源的数据库,以宁夏典型工业园区为研究区域,采集了7种不同行业类型的共398件土壤样品,检测了样品中的重金属和多环芳烃含量并建立污染物化学指纹数据库.结果 表明:除废弃资源综合利用业地块的二苯并[a,h]蒽外,样品中的重金属和多环芳烃均不超过第二类用地筛选值,但还是有部分污染物的含量超过宁夏土壤背景值和第一级标准值,污染现象依然存在.通过定义4种污染指纹等级,成功搭建了基于行业的污染物化学指纹数据库,为后期的污染治理及污染物的溯源提供了参考.     

宁夏典型工业园区污染物化学指纹数据库的建立

为评估工业园区污染状况及建立用于污染物溯源的数据库,以宁夏典型工业园区为研究区域,采集了7种不同行业类型的共398件土壤样品,检测了样品中的重金属和多环芳烃含量并建立污染物化学指纹数据库.结果 表明:除废弃资源综合利用业地块的二苯并[a,h]蒽外,样品中的重金属和多环芳烃均不超过第二类用地筛选值,但还是有部分污染物的含量超过宁夏土壤背景值和第一级标准值,污染现象依然存在.通过定义4种污染指纹等级,成功搭建了基于行业的污染物化学指纹数据库,为后期的污染治理及污染物的溯源提供了参考.     

基于SWMM模型的青岛市典型工业园区径流污染特征分析

以沿海城市青岛市为研究对象,选取3场典型降雨对其典型工业园区道路径流污染物进行取样检测。分析区域径流污染物瞬时浓度,计算径流污染物的次降雨径流平均浓度(E_(MC))值,制作最小雨强的M(V)曲线图,拟合区域污染物冲刷量随径流量变化数据和污染物累积量,构建SWMM分析模型,确定冲刷模型参数。结果表明,初期雨强越大,径流污染物浓度越高;3场降雨中TN、TP、Cu、Zn的E_(MC)值均符合地表水环境质量Ⅴ类,COD、Pb的E_(MC)值存在超标情况;最小雨强依然(但不明显)存在初始冲刷现象;区域SS、COD、TN、TP、Cu、Zn、Pb的模拟结果与实测结果的标准偏差符合模拟要求,拟合的水质参数适应于SWMM模型径流模拟,为沿海城市径流污染的防治和径流模型的运用提供了技术支持。     

计算机网络对智能电网安全的有效保护机制分析

摘要： 传统的保护方法采用时帧分布调节方法实现智能电网网络信道交叉映射,实现过载保护和网络节点管理,容易导致智能电网计算机网络节点信道偏移,数据丢包率较高,安全性差。提出基于端到端数据融合滤波的具有容错性的计算机网络下智能电网安全保护机制。构建计算机网络下的电网节点优化分布模型,采用网格形式部署,对过载节点进行数据融合与滤波处理,提高电网节点的容错性能;采用预加重方法补偿智能电网计算机网络节点之间的系统功率衰减,实现安全保护优化。仿真结果表明,采用该算法能准确实现对智能电网中的网过载的失调节点定位,电网进行能量传输稳定性较高,抗干扰性能较好,有效实现了电网的安全保护。     

农村分散式污水处理模式的比较及应用

针对目前采用定性方法确定分散式农村生活污水处理设施存在的不足,按照以水定陆的污染防治思路,在分析污染源排放与入河机理的基础上,构建了农村分散式污水处理设施的定量化模式,即结合功能区水体纳污能力,确定水体的限制排污总量,再结合水功能区水质达标浓度,确定控制断面的污染物浓度,通过水环境数学模型的模拟,按照控制断面污染物浓度达标的要求,计算污染源的设计排放浓度,进而计算污水中污染物的去除率,根据去除率的范围确定农村分散式污水的处理规模与工艺。并将其应用于台州市新华村的生活污水处理中,最终通过定量计算选定生物滤池作为生活污水处理设施。     

基于Dijkstra算法的混联配电网故障区段定位方法

由于现有方法对数学工具过度利用而忽略了故障的具体特征,造成选线与定位不精准而存在偏差的问题,提出一种基于Dijkstra算法的对于混联配电网故障区段定位方法。对混联配电网进行分析研究,总结出发生相间短路、单相接地故障时配电网表现出的特征,随后以可能导致该故障的某一元件位置为起始点,通过Dijkstra算法进行搜索,为更准确获得下一搜索的节点位置,引入代价函数将算法的均等式优先搜索转化为启发式路径搜索,搜索终点所在线路分支即为发生故障区段。在仿真实验条件下,构建小电流接地系统模型,采用所提方法完成模型的故障区段定位,最大定位误差为0.08 km,最小定位误差为0 km,定位结果与真实情况一致,证明了所提方法具有一定的可行性和准确性。     

适用于非同步采样的含DG配电网多端 单相故障定位方法研究

为解决含DG配电网多端故障定位问题,并使定位结果不受非同步采样因素的影响,提出了一种适用于非同步采样的含DG配电网故障区间定位新算法。这种方法建立含DG配电网三相阻抗模型,分析并提取含DG配网三相阻抗模型下的故障特征。根据故障点故障特征值的特点,遍历所有节点,得到故障的关联节点。所定义的故障特征值计算只运用测量点信号幅值,而与测量相角无关,从源头上避免了非同步误差的引入,故可适用于非同步采样下的故障测距。通过在一个位于美国东南部的12.47 kV配电系统进行测试,验证了该方法的准确性。     

An experimental study on local interfacial area concentration using a double-sensor probe

Interfacial area concentration is an important parameter in modeling the interfacial transfer terms in the two-fluid model. In this paper, the interfacial area concentration, void fraction, and bubble Sauter mean diameter for air-water bubbly flow through a vertical transparent pipe with 40 mm internal diameter was investigated experimentally using both digital high-speed camera system and a double-sensor conductivity probe. Based on the experimental data of digital high-speed camera system, the statistical models derived by different researchers for local interfacial area concentration measurement using double-sensor conductivity probe were evaluated. The results show that there are obvious differences among the values of local interfacial area concentration calculated by different statistical models even from the same probe signals. The section-averaged values of the local interfacial area concentration calculated using the statistical model by Kataoka et al. agree best with experimental data of digital high-speed camera system. Therefore, the statistical model developed by Kataoka et al. is recommended for the local measurement of interfacial area concentration using a double-sensor conductivity probe in bubbly two-phase flow. Using the verified double-sensor probe method, we carry out experiment to study the local distribution characteristic of the interfacial area concentration and void fraction in air-water bubbly flow through a vertical pipe.     

Thermal conductivity of carbon nanotube nanofluid—Experimental and theoretical study

In this work, thermal conductivity of carbon nanotubes' (CNTs) nanofluid is studied both experimentally and theoretically. CNT nanofluids were stabilized using gum arabic (GA). The concentration of CNTs was varied from 0.01–0.1 wt% while the concentration of GA was varied from 1–2.5 wt%, respectively. The effect of particle volume fraction and temperature on the thermal conductivity enhancement of the nanofluids was also studied. A simple thermal conductivity model which demonstrates the effect of diameter and aspect ratio of the CNTs and takes into account the effect of temperature on thermal conductivity enhancement is presented. Good agreement between experimental and estimated values proves that the proposed model can provide precise prediction of the thermal conductivity of fluid containing CNTs. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20405     

Modelling electrode material utilization in the trench model 3D-microbattery by finite element analysis

A mathematical model for ionic transport in 3D-microbattery (3D-MB) using finite element analysis is presented here, based on concentrated solution theory, ionic and atomic diffusion and the Butler-Volmer equation. The model is used to study electrochemical processes taking place in the electrodes and electrolyte of a 3D-MB in the trench architecture, with a 10 μm thick electrolyte layer separating 10 μm thick graphite anode and LiCoO₂ cathode plates. The effect of changing conductivity of the positive electrode and the electrode plate height is also studied. Qualitative and quantitative data describing battery performance in terms of concentration gradient development and discharge curves points out the range for the most favourable electronic conductivity values of the electrodes: the values should not differ by more than order of magnitude. Furthermore, it is shown that also with optimal electrode conductivity values for electrodes, the Li ion diffusion in the electrodes during discharge is limiting the performance of the battery due to inhomogeneous lithiation and delithiation. Changing electrode height can be used to fine tune surface area usage, but has a limited effect on the overall battery performance.     

浑河流域沈阳段氨氮污染源核算及水质模拟分析

为研究氨氮污染源的排放情况,根据排污系数法核算了沈阳市浑河流域2015年各类点源、面源污染物情况,并利用QUAL2K模型对该流域氨氮进行模拟,得到氨氮在不同水期的变化趋势。结果表明,浑河沈阳段氨氮2015年入河总量为3 840.1t,氨氮主要来自农村非点源污染(占氨氮入河总量约92%,其中包括畜禽养殖污染67%、农业灌溉20%、农村生活污水4%),点源污染物占比仅8%;另外流域所包含两条河流浑河干流、蒲河支流的氨氮入河量分别为1 774.0、2 066.1t,且均以畜禽养殖污染为主。QUAL2K模型对氨氮的模拟结果与不同水期实测值相对误差在4%~20%之间,氨氮模拟浓度整体水平为枯水期>平水期>丰水期,其中浑河干流中游氨氮污染最为严重,枯水期氨氮浓度最大值3.6mg/L,为丰水期的12倍;而蒲河支流中下游污染情况较为复杂,在不同水期均存在超标风险。     

Effect of ball milling on the thermal conductivity and viscosity of Indian coal fly ash nanofluid

The present study investigates the effect of ball milling on thermal conductivity and viscosity of stable nanofluid of fly ash from Indian coal. The particle size of fly ash decreased from micron size to 89, 55.5, and 11.5 nm with reduction by 55, 90, and 434 times, respectively, due to ball milling for 30, 40, and 60 hours. The surfactant Triton X-100 was used to attain stability of 0.1% and 0.5% volume concentration of fly ash nanofluid. The samples were characterized by using scanning electron microscopy, dynamic light scattering, and zeta potential analysis. The outcome reveals that the thermal conductivity of fly ash nanofluid increases with temperature, volume concentration, and reduction in particle size. A maximum enhancement in thermal conductivity of 11.9% with 11.5-nm nanofluid sample and 5.4% with 89-nm nanofluid sample for 0.5% concentration at 60°C is observed. The viscosity of fly ash nanofluid increases with concentration and varies inversely with particle size and temperature. A difference of 1.6% in viscosity is observed between the values obtained with 11.5 and 89 nm nanofluid samples for 0.5% concentration at 30°C.     

Transport properties of n-type CuGaSe2

Hall effect, electrical conductivity, and charge carrier mobility of n-type CuGaSe₂ single crystals are studied in the temperature range between 2 and 300 K. The experimental data, analyzed within the framework of a simple model of a semiconductor with two types of carriers of one sign, indicate the existence of an impurity band. The values of the gap between the main and impurity band, the concentration of donors, and the concentration of the compensating acceptors are calculated. The mobility above 100 K is described by scattering of conduction band electrons at phonons and impurities. The sharp drop at low temperatures is explained by a crossover to Mott-type variable-range hopping in the impurity band.     

Improving parameter estimates obtained from thermal response tests: Effect of ambient air temperature variations

This paper presents a method of subtracting the effect of atmospheric conditions from thermal response test (TRT) estimates by using data on the ambient air temperature. The method assesses effective ground thermal conductivity within 10% of the mean value from the test, depending on the time interval chosen for the analysis, whereas the estimated value can vary by a third if energy losses outside the borehole are neglected. Evaluating the same test data using the finite line-source (FLS) model gives lower values for the ground thermal conductivity than for the infinite line-source (ILS) model, whether or not heat dissipation to ambient air is assumed.     

Direct determination of transference numbers of LiClO4 solutions in propylene carbonate and acetonitrile

Transference number measurements were determined by a direct method for LiClO₄ solutions in propylene carbonate and acetonitrile at 25 °C. A comparison is reported between theoretical calculations of transference numbers using a model based on the Lee–Wheaton theory with values of conductometric parameters, and thermodynamic ion pairing constants determined from previously reported conductivity data.     

Experimental investigation and development of new correlations for thermal conductivity of CuO/EG–water nanofluid

In the present study, the thermal conductivity of CuO/EG–water nanofluid in different solid concentrations and temperatures has been experimentally investigated. Using a two-step method, the nanofluid has been produced in different solid concentrations ranging from 0.1% to 2% and temperatures up to 50 °C. The thermal conductivity of the nanofluid has been experimentally measured using the KD2 Pro instrument. Based on the experimental data, new correlations for predicting the thermal conductivity of CuO/EG–water at different temperatures have been proposed. The results show that with the increase of the solid concentration, the thermal conductivity of the nanofluid increases. Furthermore, the thermal conductivity of the nanofluid increases while the temperature increases. This increase is by far more noticeable in higher solid concentrations compared with lower solid volume fraction. This means that it is the presence of nanoparticles in the base fluid that causes the increase of the effect of temperature on the thermal conductivity.     

Generalized Procedure for Improved Accuracy of Thermal Contact Resistance Measurements for Materials With Arbitrary Temperature-Dependent Thermal Conductivity

Thermal contact resistance (TCR) is most commonly measured using one-dimensional steady-state calorimetric techniques. In these experimental methods, a temperature gradient is applied across two contacting beams and the temperature drop at the interface is inferred from the temperature profiles of the rods that are measured at discrete points. During data analysis, thermal conductivity of the beams is typically taken to be an average value over the temperature range imposed during the experiment. Here, a generalized theory is presented that accounts for temperature-dependent changes in thermal conductivity. The procedure presented enables accurate measurement of TCR for contacting materials whose thermal conductivity is any arbitrary function of temperature. For example, it is shown that the standard technique yields TCR values that are about 15% below the actual value for two specific examples of copper and silicon contacts. On the other hand, the generalized technique predicts TCR values that are within 1% of the actual value. The method is exact when thermal conductivity is known exactly and no other errors are introduced to the system.