Numerical computation of thermally controlled steam bubble condensation using Moving Particle Semi-implicit (MPS) method

In the present study, single steam bubble condensation behaviors in subcooled water have been simulated using Moving Particle Semi-implicit (MPS) method. The liquid phase was modeled using moving particles and the two phase interface was set to be a movable boundary which can be tracked by the topological position of the interfacial particles. The interfacial heat transfer was determined according to the heat conduction through the interfacial liquid layer and the coupling between momentum and energy was specially treated. Computational results showed that the bubble experiences various deformations at lower degrees of liquid subcooling while it remains nearly spherical at higher degrees of liquid subcooling. The bubble lifetime is nearly proportional to bubble size and is prolonged at higher system pressures. Bubble lifetime obtained from the MPS method agrees well with the experiments of 10 and 11, however it is lower than the predictions of Sudhoff et al. (1982). The underestimation is caused by severe bubble deformation at lower degrees of subcooling. The present study exhibits some fundamental characteristics of single steam bubble condensation and is expected to be instructive for further applications of the MPS method to evaluate more complicated bubble dynamics problems.     

小规格轮胎硫化模具的改进设计

对硫化罐硫化模具进行改进,设计用于双机型(硫化罐和四柱硫化机)的小规格轮胎[胎圈直径为13~16英寸(330.2~406.4 mm)]硫化模具。改进硫化模具外水嘴座孔中心距大于内密封圈底座孔中心距,外水嘴座孔与内密封圈底座孔相交;模具设有两套可独立使用且互不影响的并联内循环管路;模具外增设裙边和压板槽或者增加下模支承板和局部减少裙边。改进模具结构简单、易加工。     

多局部放电源定位中去除交叉定位虚假点的快速算法

针对测向交叉定位法在对放电信号进行分析以获得放电源位置信息时,存在多放电源情况下大量的虚假定位问题,利用3个传感器阵列,采用基准线最小距离法来排除交叉定位中的虚假点:首先使用多重信号分类对多个局部放电源进行观测和计算,得到各个信号源的方位;然后利用基准线最小距离法去除交叉定位中的虚假点.仿真结果表明了该方法的有效性和实用性.     

BP神经网络在新浇筑混凝土最高温度预测中的应用

鉴于在坝体混凝土开仓前准确预测新浇筑混凝土最高温度对防止大坝开裂的重要性,基于BP神经网络原理,以混凝土浇筑温度和冷却水管布置方式、通水温度、通水流量及气温、浇筑层厚度、混凝土龄期7个因素作为输入层,以实测混凝土浇筑仓内最高温度为输出层,利用Matlab神经网络工具箱,建立了新浇筑混凝土最高温度的BP神经网络预测模型,并通过实例对模型进行了验证分析。结果表明,冬季、夏季浇筑仓内混凝土最高温度的预测值和实测值之间的误差均约为0.5 ℃,二者吻合较好,可见该模型满足实际工程要求,也说明了BP神经网络在预测新浇筑混凝土最高温度方面具有可行性和实用性。     

制定PQM装置检测标准值得关注的几个问题

随着供用电双方对电能质量重视程度的不断提升,在电网侧和用户侧已安装大量电能质量监测装置(PQM),为了保证PQM装置正常运维和监测结果安全可靠,制定PQM装置检测标准已很有必要。从测量、检测、试验和检验等基本概念入手,通过综合分析对PQM装置进行检测和被检测PQM装置在不同场景下的技术性能指标,明确制定PQM装置检测标准的核心目标和主要范围,指出值得关注的几个基本问题,提出解决这些问题的原则性建议,希望能抛砖引玉,为本标准的制定和完善起到微薄作用。     

高填方地基沉降预测及方法研究

结合西南某高填方机场监测资料,分析高填方地基沉降几种预测方法的优缺点,根据填方体和原地基各自沉降规律的不同特征,运用三轴实验所得e-p曲线、对数模型、经验公式等方法对填方体沉降进行预测分析,用对数模型、分层总和法等方法计算原地基沉降,并与地表监测数据进行对比分析。     

Piezotronic effect on the output voltage of P3HT/ZnO micro/nanowire heterojunction solar cells

We report the first observation of piezotronic effect on the output voltage of a flexible heterojunction solar cell. The solar cell was fabricated by contacting poly(3-hexylthiophene) (P3HT) with one end of a ZnO micro/nanowire to form a p-n heterojunction on a flexible polystyrene (PS) substrate. The open-circuit voltage V(oc) of the solar cell was characterized by tuning the strain-induced polarization charges at the interface between ZnO and P3HT. The experimental data were understood based on the modification of the band structure at the p-n junction by the piezopotential, which is referred as a result of the piezotronic effect. This study not only provides an in-depth understanding about the effect but also is useful for maximizing the output of a solar cell using wurtzite structured materials.     

Development of a thermal–hydraulic analysis code for the Pebble Bed Water-cooled Reactor

The Pebble Bed Water-cooled Reactor (PBWR) is a water-moderated water-cooled pebble bed reactor in which millions of tristructural-isotropic (TRISO) coated micro-fuel elements (MFE) pile in each assembly. Light water is used as coolant that flows from bottom to top in the assembly while the moderator water flows in the reverse direction out of the assembly.Steady-state thermal–hydraullic analysis code for the PBWR will provide a set of thermal hydraulic parameters of the primary loop so that heat transported out of the core can match with the heat generated by the core for a safe operation of the reactor. The key parameters of the core including the void fraction, pressure drop, heat transfer coefficients, the temperature distribution and the Departure from Nucleate Boiling Ratio (DNBR) is calculated for the core in normal operation. The code can calculate for liquid region, water-steam two phase region and superheated steam region. The results show that the maximum fuel temperature is much lower than the design limitation and the flow distribution can meet the cooling requirement in the reactor core. As a new type of nuclear reactor, the main design features with a sufficient safety margin were also put forward in this paper.     

Regional Distribution and Prospects of Potash in China

China was formed by amalgamation of several small continental blocks (cratons), micro,blocks and orogenic belts in different paleoclimatic settings. It may be correlated with other continental blocks but has its own specific characteristics; therefore the tectonic environments of China's marine and continental saline basins and salt, and potash, forming environment have some specific characteristics: multiple phases of salt formation, difference in salt, forming ages, migration and concentration of salt forming processes and diversity of component materials, as well as small sizes of marine saline basins and great changes of saline basins in the late stage and occurrence of abundant liquid mineral resources. The nature of the tectonic basement exerted a key controlling effect on the formation of potash basins. The stable tectonic region was favorable for potash concentration in a quasi, stable region, and quasi, and the quasi-stable region was favorable for salt concentration and potash formation in a local stable tectonic region. Most China's major ancient saline basins occur in "quasi, cratons (continental block)"; especially all the marine saline basins occur in continental blocks with the Precambrian basement. These regions are the key ones for potash search. Most relatively large, scale soluble salt deposits are developed in relatively stable continental nuclei. According to the characteristics of the tectonic domains where China's salt, forming basins are located, the North China Yangtze and Tarim, Qaidam salt minerogenetic domains and the nortbern Qiangtang, western Yunnan salt minerogenetic belt may be distinguished. Their salt and potash prospects wiU be discussed separately.     

基于支持向量机的纯电动公交车充／换电站日负荷预测

讨论了基于相似日选取的支持向量机电动汽车日负荷预测方法。通过对北京现有纯电动公交车充/换电站充电负荷的大量调研,分析了公交车充电站充电负荷的数据特征,采用关联分析方法提取了影响电动公交站充电负荷的因素,基于相关因素应用灰色关联理论构建相似日的小样本集合,而后建立多输入单输出的支持向量机预测模型。针对支持向量机预测模型,提出了两阶段确定模型参数的方法,首先直接确定不敏感损失参数ε,再通过遗传算法寻找最优核参数p和正则化参数C,以提高参数ε选取范围设置较大时的预测精度。实例测试结果表明,日负荷预测的均方根误差为10.85%,能基本满足有序控制的要求;与其他预测方法相比,改进方法具有较高的预测精度和稳定性。