浅谈油品减阻剂的发展现状及趋势

油品减阻剂具有用量小、效果显著、对油品性质影响小等优势,因此对减阻剂的研究显得尤为重要,文章主要介绍了油品减阻剂的分类、减阻机理及其影响因素,同时对其发展趋势进行了展望。     

Code performance with improved two-group interfacial area concentration correlation for one-dimensional forced convective two-phase flow simulation

In gas–liquid two-phase flow simulation for reactor safety analysis, interfacial momentum transfer in two-fluid model plays an important role in predicting void fraction. Depending on flow conditions, a shape of the two-phase interface complicatedly evolves. One of the proposed approaches is to quantify the gas–liquid interface information using interfacial area transport equation. On the other hand, a more simplified and robust approach is to classify bubbles into two-groups based on their transport characteristics and utilize constitutive equations for interfacial area concentration for each group. In this paper, interfacial drag model based on the two-group interfacial area concentration correlations is implemented into system analysis code, and void fractions were calculated for the evaluation of numerical behaviors. The present analysis includes (1) comparison of one-group and two-group relative velocity models, (2) comparison with separate effect test database, (3) uncertainty evaluation of drag coefficient, (4) numerical stability assessment in flow regime transition, and (5) transient analysis for simulating the prototypic condition. Results showed that utilization of interfacial drag force term using constitutive equations of two-group interfacial area concentration yields satisfactory void fraction calculation results. The proposed solution technique is practical and advantageous in view of reducing the computational cost and simplifying the solution scheme.     

液滴降落过程表面曳力及其形状改变规律

在单颗粒液滴-气流体系中,采用计算流体力学方法对速度发展段的输运现象进行数值模拟。研究液滴在气流中逆流运动的形态变化规律与局部传递特征。获得在30相似文献   

一种界面活性剂减阻溶液的流变特性

利用ARES流变仪对具有湍流减阻作用的阳性界面活性剂CTAC/NaSal水溶液的剪切黏度进行了测量。溶液的质量浓度范围为5×10-5 ～2×10-4,温度范围为20～40℃。对实验数据的分析发现,Giesekus模型可较好地拟合不同浓度和温度下界面活性剂溶液的剪切黏度。得到了不同溶液浓度下Giesekus模型参数与温度的关联式,从而揭示了溶液减阻特性与其流变特性的内在联系。利用对向喷嘴装置RFX流变仪对CTAC/NaSal水溶液的拉伸黏度进行了测量。     

用单元胞模型数值模拟气泡群中气泡的运动

用数值方法模拟了气泡群中Reynolds数为50的气泡的运动,以单元胞模型体现气泡群中气泡间的相互作用。数学模型用完全的流体力学方程、以流函数-涡度为变量来描述变形气泡周围的液体流动,控制方程在贴体正交坐标系中、以有限差分法离散后数值求解。模拟结果表明,气含率对气泡阻力系数和气泡偏心率有很大的影响,与理论分析较符合。但单元胞模型预测的阻力系数与基于爬流中球形气泡的理论值相比,在数值上偏高很多。采用无剪切为外边界条件比用无涡度为外边界条件的模型预测更接近理论公式。预计单元胞模型经进一步改进后可成为处理气泡群的有效工具。     

典型超高层建筑风荷载幅值特性研究

本文对10个典型的超高层建筑刚性模型进行了测量表面风压的风洞试验,获得了各测量层的阻力、升力和扭矩系数的平均值和根方差。讨论了各测量层风荷载系数随风向角的变化规律,以及高宽比和断面长宽比对方形及矩形建筑风荷载的影响。结果表明,倒角方形、Y形和三角形建筑的风荷载均小于方形与矩形建筑;方形建筑高宽比的增大导致升力系数的根方差明显增大;矩形建筑断面长宽比的增大则使阻力系数的平均值、根方差减少,而升力系数的根方差增大;D类和B类风场中的平均气动力系数相近,而D类风场中脉动气动力系数的根方差大于B类风场。     

大直径单桩竖向荷载传递及影响因素

分析大直径单桩的竖向荷载传递机理与传递形状,其变形特征为缓变型.不具有明显的破坏特征点,由此论述了荷载传递形状随有关因素的变化,并详述了影响大直径桩竖向承载力的各种因素.     

仿生非光滑旋成体表面减阻特性数值模拟

在前期进行的仿生非光滑旋成体模型低速风洞试验的基础上,将非光滑形态在旋成体模型上的排列方式固定为矩形布置,非光滑的尺寸固定为直径或宽度为1 mm,深度或高度为0.5 mm,在风速为44 m/s时,对布置在模型尾部的凸包形、凹坑形和棱纹形三种非光滑模型与表面光滑模型进行了对比模拟试验。试验结果表明,布置在尾部的非光滑结构能够有效地降低模型的压差阻力,尤其是棱纹状非光滑形态模型,压差阻力降低了25.3%,总阻力降低了11.12%。     

基于结构曳力的吸收塔内部气液流动模拟

湿法脱硫系统中的吸收塔为多尺度结构构成的复杂系统,其中介观结构对液滴和烟气在塔内流动有重要影响。而液滴和烟气的流动状况直接关系着脱硫系统的脱硫效率及运行阻力。本文基于吸收塔内部结构,建立基于介观结构的曳力模型,并将该模型耦合到多相流模型中,结合商业软件Fluent对吸收塔内部烟气和液滴流动状况进行模拟预测。在模拟结果中,通过对吸收塔二维、三维的压降、速度和液滴分布的模拟计算结果分析和对比,表明模拟结果准确预测了烟气和液滴在吸收塔内流动结构,充分说明了基于介观结构的曳力模型可以很好反映液滴和烟气之间的作用力。     

Experimental and numerical investigation of sands and Geldart A biomass co-fluidization

This article investigated the fluidization of sands and small Geldart A biomass mixtures. The mixture fluidized like Geldart A type particles with a uniform bed expansion regime before bubbling. The video recorded color distance between pure sands and sands–biomass mixtures was used to estimate the sands–biomass mixing. The coarse-grained computational fluid dynamics–discrete element method with a hybrid drag model which couples the Syamlal–O'Brien drag and a filtered drag can capture the mixing while the simulation with Gidaspow drag predicted a segregated bed. The simulations were further validated with experimental measured pressure drops. The time averaged pressure drop equals the weight of the bed material, however, its fluctuation is about three times of the bed material fluctuation.