表面活性剂溶液粗粒化模型couette流动模拟

本文主要利用粗粒化分子动力学方法对不同浓度下表面活性剂水溶液在couette流动过程中胶束的形成、速度分布与流变性规律进行了研究。结果表明,对于相同浓度的表面活性剂溶液,随着剪切速率的增大,胶束完全动态平衡时间越来越小;而随着表面活性剂分子浓度的增加,胶束动态平衡时间也越来越小,形成胶束越来越快。在剪切速率与溶液剪切黏度关系方面,保持表面活性剂分子浓度不变情况下,随着剪切速率的增大,剪切黏度逐渐减小,呈现剪切稀化特征。     

黏性液体中单个气泡上升的形状特性

采用基于Level Set方法的直接数值模拟技术对黏性液体中单个气泡的上升运动进行三维模拟.数值模拟采用拟单相流模型处理气泡内外的气液两相流动,应用Level Set方法捕捉运动气泡的变形.针对Eo数从O(0)～O(2),Mo数从O(-11)～O(2)的流动范围,重点研究了上升气泡的形状特性,并与经典的气泡形状图谱进行了比较.模拟结果表明,上升气泡的形状与无量纲参数(Eo、Mo和Re)密切相关.在高Re的扁椭球区域,数值发现了气泡形状的周期性振荡行为.     

均匀磁场中磁性液体的磁表面张力系数实验研究

基于特殊性能的磁性液体增设了综合性设计性实验项目,根据项目式教学法初步实现了以学生自我训练为主的教学模式.本文设计了磁性液体磁表面张力系数智能测试仪,研究了均匀磁场中4种不同类型磁性液体的磁表面张力系数随磁感应强度的变化规律.随外加磁场磁感应强度的增强,磁性液体的磁表面张力系数增大,主要是磁场增强了磁性颗粒之间的相互作用力.磁感应强度相同时,载液质量对磁性液体的磁表面张力系数影响较大,载液质量越小,单位体积内融入的磁性颗粒数量越多,导致磁性液体的磁表面张力系数越大.表面活性剂种类对磁性液体磁表面张力系数的影响也较大,由于油酸对磁性颗粒的吸附作用比PBSI-941表面活性剂强,油酸官能团较早吸附在磁性颗粒表面,限制了磁性颗粒进一步长大,导致MFO-4磁性液体磁表面张力系数较小.     

高粘度流体中上升气泡的直接数值模拟

本文将基于Front Tracking方法求解气液两相界面迁移特性的直接数值模拟方法扩展到中低Re数情形 (1．89≤Re≤55．6),针对无边界以及垂直壁面附近高粘度流体中单个气泡(1．2 mm≤D≤6 mm)的上升过程进行模拟,研究气泡运动的机理以及气泡与壁面的相互作用。数值模拟准确再现了气泡的上升过程和变形,不同Re数下气泡的上升速度计算结果同经验关联式非常吻合,验证了该方法在中低Re数范围内的有效性。壁面附近流场的不对称引发壁面对气泡的升力是导致气泡逐渐偏离垂直壁面的原因,计算得到的壁面作用力系数同实验结果的对比也确定了本文参数范围内计算壁面对气泡作用力的模型。     

竖直矩形窄缝内流动沸腾压降实验与模型研究

本文实验研究了水在间隙为2.1、2.2、3.6 mm的垂直矩形窄通道内流动沸腾压降,包括入口过冷的情况,得到了在不同操作条件下压降随热流密度的变化曲线,同时分析了曲线变化的原因.实验结果发现:在实验参数范围内,流动沸腾的压降随着质量流速、热流密度和入口干度增加而增大;随着窄缝间隙的增大而减小.窄通道内的压降计算与大通道有显著不同,本文针对窄通道的特点,修正了传统的压降计算模型,模型预测值与实验结果比较,误差在±15.4%之内.     

一维液态泡沫渗流实验研究及表面能和粘性耗散分析

液态泡沫由大量气泡密集堆积在微量表面活性剂溶液中形成，是远离平衡态的软物质. 泡沫强制渗流在微观上是指以恒定流率输入的液体在气泡间隙内的微流动过程，是影响泡沫稳定的主要因素之一. 采用在表面活性剂溶液中添加微量色素以显示泡沫中液体流动的方法，确定了透射率与液体分率的对应关系，测量得到了一维液态泡沫强制渗流中渗流波传播规律以及液体分率的演变规律；理论推导了泡沫基本单元，即开尔文单元结构(Kelvin cell)的粘性耗散能表达式，并依据Surface Evolver软件计算得到了不同液体分率时开尔文单元结构对应的的表面能，并计算出了与实验系统对应的开尔文单元结构的表面能和粘性耗散. 基于开尔文单元结构内液体分率演变的准静态假设，分析了表面能和粘性耗散的演变规律.     

垂直圆管氮气-磁性液体两相流电磁感应现象

基于磁性液体与非磁性气泡磁导率的差异,理论分析与实验研究了氮气-磁性液体两相流的电磁感应现象。以颗粒体积浓度为3.83%的水基Fe₃O₄磁性液体为工质,同时采用物性与其相近的去离子水进行流型的可视化对比研究。研究结果表明,当管内为泡状流、弹状流、搅拌流时均能产生毫伏级的感应电压,且感应电压的峰峰值随着气体流量的增加而增大,另外根据感应电压随时间变化的波形可以辨识出管内的流型。     

CTAC表面活性剂水溶液的流变特性

在25℃条件下,测量了质量分数w=0.007%～0.15%范围内表面活性剂水溶液的流变特性。实验结果表明,表面活性剂稀溶液在剪切作用下出现剪切增稠转变,随着溶液浓度的增加,剪切增稠转变越来越弱。当浓度达到某一临界饱和浓度时,不再有剪切增稠转变发生,该浓度所对应的流变曲线称为最大黏度线;对于表面活性剂稀溶液,剪切诱导时间和剪切平衡时间均是剪切速率的幂函数,幂指数为-1.0;剪切增稠转变结束后,表面活性剂稀溶液的稳态黏度随浓度增大而增大,当w>0.05%时,稳态黏度逼近最大黏度线,继续增大浓度,稳态黏度几乎保持不变。     

不同溴化锂溶液浓度及添加剂对气泡泵工作特性影响的实验研究

实验分析研究了溴化锂溶液驱动的气泡泵。实验中保持12 mm管径、960W加热功率、1244 mm提升高度不变,改变溴化锂溶液浓度、浸没高度和添加剂质量分数来测试分析气泡泵性能。浸没高度为378～528 mm。溴化锂溶液浓度为45.5%～59.5%。选取异辛醇作为添加剂,添加的质量分数为（40～70）×10^-6。实验结果表明,溴化锂溶液浓度对气泡泵的工作性能影响很大而异辛醇影响很小。     

剪切和温度作用下表面活性剂溶液流变特性

在10~70℃下,1~300 s~(-1)剪切速率范围内,对质量分数为0.001%~0.015%的CTAC/NaSal表面活性剂水溶液(CTAC与NaSal摩尔比为1:1)的流变性质进行了测试分析。研究发现,表面活性剂水溶液在不同的浓度下均存在临界剪切速率和临界温度,且温度和剪切对黏度的作用强度不同。对于同一溶液,温度和剪切的协同作用使黏度变化复杂,对于浓度相对高的溶液出现高温、高剪切区二次增稠的现象。     

What tells gravity on the shape and size of an electron

Gravitational field of an electron, fixed by experimental values of its mass, spin, charge and magnetic moment, is given by the metric of Kerr-Newman (KN) solution. Unexpectedly, this metric contains a singular ring of the Compton radius, which should be regulated resulting in a weeak and smooth source. The consistent source takes the form of an oblate vacuum bubble, bounded by a closed string of the Compton radius. The bubble turns out to be relativistically rotating and should be filled by a coherently oscillating Higgs field in a false vacuum state.     

Oscillation of the convective flow around an air bubble in a vertically stratified surfactant solution

The appearance of oscillatory modes of the concentration convection around an air bubble in an aqueous solution with a vertical gradient of surfactant concentration was revealed experimentally. The solution filled a thin vertical layer containing an air bubble in the form of a short horizontal cylinder with a free lateral surface. Due to a small layer thickness, two-dimensional flows and concentration distributions were generated in the liquid. Their evolution was investigated using an interferometric technique. It was found that the flow oscillation was caused by a specific interaction between the diffusion and two solutal (capillary and gravitational) mechanisms of convective mass transfer, which had quite different characteristic times. The time variation of the oscillation period was analyzed in relation to the surfactant concentration gradient, the average solution concentration, and the concentration Marangoni number. It was shown that the ratio of the dimensionless oscillation frequency to the Marangoni number is time independent and is the same for different liquids and various orientations of the concentration gradient. Published in Russian in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 130, No. 2, pp. 363–370. The text was translated by the authors.     

Simulation of a bubble chain in a container of high aspect ratio exposed to a magnetic field

The influence of a homogeneous magnetic field acting in the direction of gravity on a bubble chain is studied with phase-resolving numerical simulations. The bubbles rise in a narrow container filled with liquid metal. Individual bubbles are represented by an immersed boundary method with the bubble shape being described by spherical harmonics and deformed by the surrounding liquid metal. A Gaussian bubble size distribution is realized as suggested by corresponding experiments. Bubble-bubble and bubble-wall interactions are modelled based on a repelling potential. With a magnetic field, the averaged trajectory of the bubble chain becomes more rectilinear, and the transverse dispersion is reduced. The average rise velocity decreases under the impact of the field.     

Tuning the band gap of self-assembled superparamagnetic photonic crystals in colloidal magnetic fluids using external magnetic fields

The model of tunable superparamagnetic photonic crystals self-assembled in colloidal magnetic fluids under externally applied magnetic fields is established. The mechanisms, which are in charge of the tunability of the band gaps with magnetic fields are clarified. The band structures of the triangularly-arrayed two-dimensional photonic crystals with limited heights of magnetic columns are calculated with the experimental data of structures and refractive indices in the literatures. The field-dependent properties of the first band gaps are gained for the z-odd and z-even modes, respectively. Simulation results indicate that the mid frequencies of the first band gaps of the z-odd modes can be easily tuned by the external magnetic fields, while those of the z-even modes bear relatively weak dependence on the external magnetic fields. Simultaneously, the first band gaps of both kinds of modes become wide along with the increase of the magnetic fields. The results presented in this work give a guideline for realizing the tunable photonic crystals with magnetically colloidal materials and magnetic stimuli.     

Dynamic rheological properties of viscoelastic magnetic fluids in uniform magnetic fields

The dynamic rheological properties of viscoelastic magnetic fluids in externally applied uniform magnetic fields are investigated by a laboratory-made cone-plate rheometer in this study. In particular, the effects of the magnetic field on the viscoelastic properties (the complex dynamic modulus) of the viscoelastic magnetic fluids are studied. In the investigation, three viscoelastic magnetic fluids are made by mixing a magnetic fluid and a viscoelastic fluid with different mass ratios. As a supplementation to the experimental investigation, a theoretical analysis is also presented. The present study shows that the viscosity and elasticity of the viscoelastic magnetic fluids are significantly influenced by the magnetic field and the concentrations of the magnetic particles in the test fluids. Theoretical analysis qualitatively explains the present findings.     

Scattering measurements from a dissolving bubble

A laboratory-scale study on acoustic scattering from a single bubble undergoing dissolution in undersaturated fresh water is presented. Several experiments are performed with the acoustic source driven with five-cycle tone bursts, center frequency of 120 kHz, to insonify a single bubble located on axis of the combined beam of the set of transducers. The bubble is placed on a fine nylon thread located in the far field of the transducer set, arranged in bistatic configuration, in a tank filled with undersaturated water. Backscattered waveforms from the bubble target are acquired every few seconds for several hours until the bubble has completely dissolved, and detailed dissolution curves are produced from the acoustic data. The rate of bubble dissolution is calculated using the solution developed by Epstein and Plesset [J. Chem. Phys. 18, 1505-1509 (1950)]. The results of the experiments performed are in agreement with the calculations.     

Study on bubble formation in non-Newtonian fluids by laser image technique

A laser image system for studying bubble formation at the orifice submerged in liquid was established. The process of bubble formation can be directly visualized and real-time recorded through computer by means of He–Ne laser as light source using the beam expanding and light amplification technique. The behaviors of bubble formation in polyacrylamide (PAM) aqueous solutions were investigated at temperature 293.15 K and orifice diameters 1, 1.5 and 2 mm, respectively, the chamber volume was 90 cm³ and the gas flowrate from 0.1 to 0.6 cm³/s. The influences of mass concentration of solution and orifice diameter on bubble detachment volume were investigated experimentally and the results show that bubble detachment volume increases with solution concentration and orifice diameter in the experimental range of this work.     

基于几何遮蔽效应和法拉第旋光效应耦合的磁流体偏振光透过率

根据几何遮蔽效应和法拉第旋光效应耦合原理给出的解析表达式,通过数值模拟计算,研究了磁流体的纵场诱导偏振光透过率及磁流体的浓度、液态介电常量、磁性颗粒磁偶极矩热能比和单位磁性颗粒团聚体所含磁性颗粒数量四个参量的变化对其偏振光透过率的影响.结果表明,磁流体的浓度、液态介电常量和磁性颗粒磁偶极矩热能比对其偏振光透过率有显著影响,低浓度样品的偏振光透过率随着纵向磁场强度的增大而线性增加,而高浓度样品则随着纵向磁场强度的增大呈现振荡变化的特性.在一定范围内,磁流体偏振光透过率随其液态介电常量εliquid和磁性颗粒磁偶极矩热能比μd/(kT)的变大而增加.而单位磁性颗粒团聚体所含磁性颗粒数量对其偏振光透过率没有影响,磁流体参量依赖的偏振光透过率在低磁场区域和高磁场区域有明显区别.提出了磁流体纵场诱导偏振光透过率在几类光子器件中的可能应用.     

基于几何遮蔽效应和法拉第旋光效应耦合的磁流体偏振光透过率

根据几何遮蔽效应和法拉第旋光效应耦合原理给出的解析表达式,通过数值模拟计算,研究了磁流体的纵场诱导偏振光透过率及磁流体的浓度、液态介电常量、磁性颗粒磁偶极矩热能比和单位磁性颗粒团聚体所含磁性颗粒数量四个参量的变化对其偏振光透过率的影响.结果表明,磁流体的浓度、液态介电常量和磁性颗粒磁偶极矩热能比对其偏振光透过率有显著影响,低浓度样品的偏振光透过率随着纵向磁场强度的增大而线性增加,而高浓度样品则随着纵向磁场强度的增大呈现振荡变化的特性.在一定范围内,磁流体偏振光透过率随其液态介电常量ε_liquid和磁性颗粒磁偶极矩热能比μ_d/(kT)的变大而增加.而单位磁性颗粒团聚体所含磁性颗粒数量对其偏振光透过率没有影响,磁流体参量依赖的偏振光透过率在低磁场区域和高磁场区域有明显区别.提出了磁流体纵场诱导偏振光透过率在几类光子器件中的可能应用.     

Laser image measurement of twin bubbles formation in shear-thinning fluids

A laser image system for investigating twin bubbles formation in shear-thinning fluid was established. The process of twin-bubble formation could be directly visualized and real-time recorded through computer by means of He–Ne laser as light source using the beam expanding and light amplification technology. The shape and size of bubbles generating in carboxymethylcellulose (CMC) aqueous solutions were studied experimentally at orifice diameter 1 mm, 1.6 mm and 2.4 mm, the orifices interval 1D_o, 2D_o and 3D_o (D_o: orifice diameter) and the gas flow rate from 0.1 to 1.0 ml/s, respectively. The effects of solution mass concentration, orifice diameter and orifice interval on bubble detachment volume were investigated. The results reveals that twin bubbles gradually touch each other and then deviate from the vertical axis crossing the middle point of the line joining the two orifice during the formation process. However compared with the perfect teardrop terminal shapes in glycerol solution, the bubbles formed in CMC solutions are stretched vertically due to the shear-thinning effect of fluids. The bubble detachment volume increases with the solution mass concentration, whereas decreases with orifice diameter. The detachment volume generated at twin orifices is less affected by orifices interval, but still smaller than that at single orifice.