油田结垢原因分析及防垢措施研究

油田在生产过程中结垢现象严重,影响到其正常生产。在阅读大量文献的基础上对油田的结垢机理以及各主要影响因素进行了系统分析,并提出了一些国内外比较成熟的防垢建议及对策;分别从化学方法、物理方法以及改变油田生产工艺来达到防垢的目的。     

Investigations on heat transfer and hydrodynamics under pyrolysis conditions of a pilot-plant draft tube conical spouted bed reactor

This paper describes the hydrodynamic and heat transfer performance of a pilot-plant scale conical spouted bed reactor designed for the pyrolysis of biomass wastes. The spouted bed reactor is the core of a fast pyrolysis pilot plant with continuous biomass feed of up to 25 kg/h, located at the Ikerlan-IK4 facilities.The aim of this paper is to obtain a deeper understanding of the spouted bed reactor performance at pyrolysis temperatures, in order to operate under stable conditions, improve the heat transfer rate in the reactor and minimize energy requirements. The influence of temperature on conical spouted bed hydrodynamics has been studied and wall-to-bed and bed-to-surface heat transfer coefficients have been determined.     

Using positron emission particle tracking (PEPT) to study the turbulent flow in a baffled vessel agitated by a Rushton turbine: Improving data treatment and validation

Positron emission particle tracking (PEPT) is a relatively new technique allowing the quantitative study of flow phenomena in three dimensions in opaque systems that cannot be studied by optical methods such as particle image velocimetry (PIV) or laser Doppler anemometry (LDA). Here, velocity measurements made using PEPT in two sizes of baffled vessel (∼0.20 m and ∼0.29 m diameter) and two different viscosity fluids agitated by a Rushton turbine are compared for the first time directly in depth with some studies reported in the literature made by LDA for the turbulent regime in the equivalent geometry. Initially, the paper considers how the Lagrangian data obtained by PEPT can be converted into Eulerian in order to make the comparison most effective. It also considers ways of data treatment that improve the accuracy of both the raw PEPT data and the velocities determined from it. It is shown that excellent agreement is found between the PEPT and literature results, especially for the smaller vessel, except for the radial velocity just off the tip of the blade in the plane of the disc of the Rushton turbine. This difference is attributed to the very rapid changes in both magnitude and direction that occurs in that region and also to the different way of ensemble averaging in the two techniques. In addition, the results for the absolute velocities normalised by the impeller tip velocity for all the rectangular cross-section toroidal cells in each size of vessel and each fluid and a range of agitator speeds are compared in the form of frequency histograms. In this analysis, the velocities for each run are obtained from PEPT based on tracking a particle for 30 min and the mean and mode of the velocities each decrease slightly with decreasing scale and Reynolds number. The possible reasons for this variation in the mode and the mean are discussed. Overall, it is concluded that for the radial flow Rushton turbine the PEPT technique can be used to obtain accurate velocity data throughout the entire complex three-dimensional turbulent flow field in an agitated, baffled vessel except very close to the impeller in the radial discharge stream.     

城市设计视角的校园规划实践研究

该文针对当前国内校园建设中存在的“规模扩张下的超足度校园”、“形式主义下的平面化校园”、“封闭管理下的孤立式校园”等规划问题,从城市设计角度提出在校园环境城市化的背景下,校园规划应重视“足度与功能”、“密度与环境”、“封闭与开放”等设计理念的合理应用,并结合湖南工业大学、中央民族大学等校园规划方案提出在现实条件下校园规...     

Breast milk lead and cadmium levels from suburban areas of Ankara

The objectives of this study were (1) to evaluate levels of lead (Pb) and cadmium (Cd) in the breast milk at 2 months postpartum, (2) to investigate the relationship between Pb and Cd levels in breast milk and some sociodemographic parameters and (3) to detect whether these levels have any influence on the infant's physical status or on postpartum depression in the mothers. Pb and Cd levels in breast milk were determined by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The median breast milk concentrations of Pb and Cd were 20.59 and 0.67 μg/l, respectively. In 125 (87%) of 144 samples, Pb levels were higher than the limit in breast milk reported by the World Health Organization (WHO) (> 5 μg/l). Breast milk Cd levels were > 1 μg/l in 52 (36%) mothers. The mothers with a history of anemia at any time had higher breast milk Pb levels than those without a history of anemia (21.1 versus 17.9 μg/l; p = 0.0052). The median breast milk Cd levels in active and passive smokers during pregnancy were significantly higher than in non-smokers (0.89, 0.00 μg/l, respectively; p = 0.023). The breast milk Cd levels of the mothers who did not use iron and vitamin supplements for 2 months postpartum were found to be higher than in those who did use the supplements (iron: 0.73, 0.00 μg/l, p = 0.023; vitamin: 0.78, 0.00 μg/l, p = 0.004, respectively). Breast milk Cd levels at the 2nd month were correlated negatively with the z scores of head circumference and the weight for age at birth (r = − 0.257, p = 0.041 and r = − 0.251, p = 0.026, respectively) in girls. We found no correlation between the breast milk Pb and Cd levels and the Edinburgh Postpartum Depression Scale scores. Breast milk monitoring programs should be conducted that have tested considerable numbers of women over time in view of the high levels of Pb in breast milk in this study.     

Study of scale effect on intact rock strength using particle flow modeling

Based on the extensive review of the UCS versus specimen size test data and the various empirical relations between the UCS and the specimen size, a new expression is proposed to describe the dependence of the UCS on specimen volume. The proposed new relation can fit the UCS versus specimen size test data of different rocks very well. Then, a numerical study of the scale effect on UCS is conducted using a numerical model in which the intact rock is represented by particles bonded to each other at contact points, with the contact bonds having both normal and shear strength components. The bond can break if the normal or shear contact stress exceeds the corresponding bond strength. To simulate the initial micro-fractures (flaws or cracks) in the rock, the smooth-joint contact model is used. The fractures are considered to be randomly orientated and located disks. The size and number of fractures are described by an exponential expression derived using fractal theory. The numerical model is calibrated using the test stress–strain curves of 80 mm×40 mm×40 mm prism Yamaguchi marble samples. Then, the calibrated model is used to predict the UCS of Yamaguchi marble samples at different sizes. The predicted UCS values are in good agreement with the experimental values. The numerical simulations show that to capture the scale effect on UCS of intact rock, initial fractures with sizes increasing faster with the specimen size must be considered in the modeling.     

基于大涡模拟方法的二冲程发动机缸内冷态流场的模拟研究

应用大涡模拟方法对一台二冲程发动机缸内冷态湍流流场进行了三维瞬态数值分析。探索缸内流场的速度、压力及温度的变动情况,并与PIV流场测试结果进行了对比。三维模拟的缸压曲线与试验及一维模拟均吻合较好,但在速度概率密度函数方面与试验存在一定差异。模拟结果表明:本文建立的三维模型能够自然再现缸内冷态流动的随机大尺度涡流情况,模型可靠有效。模拟能够较好地反应火花塞位置附近速度随机波动情况,其结果对于后续研究缸内大尺度涡流对燃烧循环变动的影响机理具有一定的指导意义。     

自由曲面的高精度匹配技术研究

研究自由曲面的高精度匹配技术。采用两步法即粗匹配和精匹配对曲面匹配进行逐步求精:采用微分进化算法进行粗匹配,获得下一步精匹配迭代过程的初始点,解决了迭代最近点算法(ICP)存在的容易收敛于局部最优点的问题,并克服了遗传算法收敛速度较慢的缺陷;基于最小二乘准则和最小条件原则,分别采用单纯形法和坐标轮换法循环计算进行精匹配,同时对设计变量进行尺度变换,改善了优化设计数学模型的性态。以Visual C++6.0为开发工具,编程实现了自由曲面的高精度匹配。运行实例表明,上述算法是可行和有效的。     

Continuous Transesterification with Acidic Ionic Liquids as Homogeneous Catalysts

Ionic liquids (ILs) are recyclable acid catalysts for transesterification reactions. In the present study, different acidic ILs were examined in this reaction, with special focus on their recyclability. Furthermore, the IL‐catalyzed transesterification reaction was realized in continuous operation. A miniplant reactor with technically representative design and operating characteristics was used for this study. The applied rig has a volume of 5 L and an external thermosyphon reboiler. The miniplant reactor can be operated in batch and in continuous mode. ILs functionalized with a sulfonic acid group were found to be the most suitable IL catalysts for the transesterification reactions under investigation. Using these ILs, reaction rates as high as for H₂SO₄ could be realized. Moreover, the IL catalyst was demonstrated to be active for at least 1000 h of operation time.