Study of deep transportation and plugging performance of deformable gel particles in porous media

Deformable gel particles(DGPs) possess the capability of deep profile control and flooding. However, the deep migration behavior and plugging mechanism along their path remain unclear. Breakage, an inevitable phenomenon during particle migration, significantly impacts the deep plugging effect. Due to the complexity of the process, few studies have been conducted on this subject. In this paper, we conducted DGP flow experiments using a physical model of a multi-point sandpack under various injection rates and particle sizes. Particle size and concentration tests were performed at each measurement point to investigate the transportation behavior of particles in the deep part of the reservoir. The residual resistance coefficient and concentration changes along the porous media were combined to analyze the plugging performance of DGPs. Furthermore, the particle breakage along their path was revealed by analyzing the changes in particle size along the way. A mathematical model of breakage and concentration changes along the path was established. The results showed that the passage after breakage is a significant migration behavior of particles in porous media. The particles were reduced to less than half of their initial size at the front of the porous media. Breakage is an essential reason for the continuous decreases in particle concentration, size, and residual resistance coefficient. However, the particles can remain in porous media after breakage and play a significant role in deep plugging. Higher injection rates or larger particle sizes resulted in faster breakage along the injection direction, higher degrees of breakage, and faster decreases in residual resistance coefficient along the path. These conditions also led to a weaker deep plugging ability. Smaller particles were more evenly retained along the path, but more particles flowed out of the porous media, resulting in a poor deep plugging effect. The particle size is a function of particle size before injection, transport distance, and different injection parameters(injection rate or the diameter ratio of DGP to throat). Likewise, the particle concentration is a function of initial concentration, transport distance, and different injection parameters. These models can be utilized to optimize particle injection parameters, thereby achieving the goal of fine-tuning oil displacement.

Analyses on uniformity of particles under HPGR finished grinding system

In order to deal with the disadvantages of excessive grinding and non-uniformity in finished particle under high-pressure grinding rolls （HPGR） finished grinding system, four aspects were investigated, including evaluating indicators, effects of operating factors, effect of particle uniformity on the flotation and formation mechanism of particle uniformity. Experiment of HPGR finished grinding system, cationic reverse flotation experiment and simulation test of particle bed comminution under the condition of quasi-static were carried out. Theoretical analyses indicated that both of uniformity coefficient and average particle size should be included in the uniformity analysis of the mineral particles. The results show that the effect of circulation fan impeller speed on particle uniformity is the most evident, HPGR working pressure and roll gap are second and HPGR roller speed is the last. Average particle size has a more obvious effect on the grade of flotation concentrate while uniformity coefficient has a more obvious effect on the flotation recovery. Considering the two aspects of grade and recovery, the optimal uniformity coefficient for flotation is 1.1-1.2 and the optimal average particle size for flotation is 50-55 μm. The operating factors which promote the shielding effect and compact effect in the HPGR finished grinding system should be strengthened based on the uniformity of particles.

Multi-dimensional size effects and representative elements for nonpersistent fractured rock masses: A perspective of geometric parameter distribution

This study takes a fractured rock mass in the Datengxia Hydropower Station,China as an example to analyze the size effects and determine the representative elementary sizes.A novel method considering geometric parameter distributions is proposed in this work.The proposed method can quickly and simply determine the size effects and representative elementary sizes.Specifically,geometric parameter distributions,including fracture frequency,size and orientation,are generated on the basis of the Bernoulli trial and Monte Carlo simulation.The distributions are assessed using the coefficient of variation(CV),and the acceptable variations for CV(5%,10%and 20%)are used to determine representative elementary sizes.Generally,the representative element of rock masses is the representative elementary volume(REV).The present study extends the representative element to other dimensions,i.e.representative elementary length(REL)and representative elementary area(REA)for one and two dimensions,respectively.REL and REA are useful in studying the size effects of one-(1D)and twodimensional(2D)characteristics of rock masses.The relationships among multi-dimensional representative elementary sizes are established.The representative elementary sizes reduce with the increase in the dimensions,and REA and REV can be deduced by REL.Therefore,the proposed method can quickly and simply determine REL and further estimate REA and REV,which considerably improves the efficiency of rock mass analysis.

Investigation on Settling Characteristics of Floes in the Changjiang Estuary, China

Settling characteristics of floes, including relative settling velocity, relative flocculation coefficient and flocculation exponent, are obtained by the suspended load equations for different size fractions. Data of the Changjiang Estuary suggest that level of flocculation changes from river section, river mouth (turbidity maximum) to offshore area in sequence of low, very high and high. The settling characteristics of floes reflected by in situ estimation performs a similar feature as that obtained from still water experiment.

Thermal properties of open-celled aluminum foams prepared by two infiltration casting methods

Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size;along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process.

Structural and Electrochemical Performance of Additives-doped a-Ni(OH)_2

The additives-doped α-nickel hydroxides were prepared by supersonic co-precipitation method. The crystal structure and grain size of the prepared samples were characterized by X-ray diffraction （XRD） and Particle size distribution （PSD）, respectively. Cyclic voltammetry （CV） tests show that Al-Co-Y doped Ni（OH）2 has better reaction reversibility, higher proton diffusion coefficient than those of Al-Co doped Ni（OH）2. Al-Co-Y doped Ni（OH）2 also has lower charge-transfer resistance as shown by electrochemical impedance spectroscopy （EIS）. Charge/discharge tests show that the discharge capacity of Al-Co-Y doped Ni（OH）2 reaches 328 mAh/g at 0.2 C and 306 mAh/g at 0.5 C, while Al-Co doped Ni（OH）2 can only discharge a capacity of 308 mAh/g at 0.2 C and 267 mAh/g at 0.5 C.

Determ ination of Even Degree of Animal Population

The even degree of animal population is generlay measured by the coefficient of variation of major economic characters.Facing the coefficient of variation,a statistic with complex properties,we achieved indirectly the determination of confidence interval for even degree of an animal population by analysing the reciprocal of the statistic.The sample size which is suitable to the determination of the even degree of an animal population was probed into within the extent of permissive estimation error.

Molecular Dynamic Regulation of Na and Mg Ions on Lithium Carbonate Crystallisation in Salt Lakes

Lithium carbonate (Li_(2)CO_(3)) was synthesised by adding sodium (Na) and magnesium (Mg) ions into a lithium chloride solution at different concentrations,followed by the addition of an appropriate sodium carbonate solution.Then,the morphology,purity and particle size of Li_(2)CO_(3) crystals were investigated.The Na and Mg ions had negligible and remarkable effects,respectively,on the product purity;however they both greatly influenced its morphology.Their effects on the nucleation and growth rates,the radial distribution function and the diffusion behaviour of the synthesised Li_(2)CO_(3) were investigated via molecular dynamics methods;the Na ions slowed down the crystal nucleation and growth rates,while the Mg ions accelerated them.Moreover,the Mg ions rendered the system short-range ordered and long-range disordered and also increased the diffusion coefficient.The results of this study showed that Mg ions are one of the most important factors influencing the purity and yield of Li_(2)CO_(3).

The Scattering of SH Wave in a Nano Hole Embedded the Infinite Inhomogeneous Medium

Scattering of the shear waves by a nano-sized cylindrical hole embedded the inhomogeneous is investigated in this study. The Helmholtz equation with a variable coefficient is transformed the standard Helmholtz equation by the complex function method and the conformal mapping method. By wave function expanding method, the analytical expressions of the displacement field and stress field in the inhomogeneous medium are obtained. Considering the surface effect and using the generalized Young-Laplace equation, we obtain the boundary conditions at nano arbitrary-shaped hole, then the field equations satisfying boundary conditions are attributed to solving a set of infinite algebraic equations. Numerical results show that when the radius of the cylindrical cavity shrinks to nanometers, surface energy becomes a dominant factor that affects the dynamic stress concentration factor (DSCF) around the cylindrical cavity. The influence the density variation of the inhomogeneity on the DSCF is discussed at the same time.

Prediction of interphase drag coefficient and bed expansion using a variational model for fluidization of small spherical particles

In this study,we applied the variational model to fluidization of small spherical particles.Fluidization experiments were carried out for spherical particles with 13 diameters between dp=0.13 and 5.00 mm.We propose a generalized form of our variational model to predict the superficial velocity U and interphase drag coefficientβby introducing an exponent n to describe the different dependences of the drag force Fd on fluid velocity for different particle sizes(different flow regimes).By comparing the predictions with the experimental results,we conclude that n=1 should be used for small particles(dp<1 mm)and n=2 for larger particles(dp>1 mm).This conclusion is generalized by proposing n=1 for particles with Ret<160 and n=2 for particles with Ret>160.The average mean absolute error was 5.49%in calculating superficial velocity for different bed voidages using the modified variational model for all of the particles examined.The calculated values ofβwere compared with values of literature models for particles with dp<1.0 mm.The average mean absolute error of the modified variational model was 8.02%in calculatingβfor different bed voidages for all of the particles examined.

六硝基六氮杂异伍兹烷微球的声流控制备工艺及性能表征

针对当前六硝基六氮杂异伍兹烷(CL-20)微球制备中粒径较大且均匀性差的问题,提出了一种能够控制液滴生成模式的声流控技术。该技术将液滴微流控技术与声表面波技术相结合,提高了含能乙酸乙酯液滴的尺寸均匀性,利用溶剂-非溶剂重结晶法制备了微米级CL-20/NC含能微球。采用高速相机对液滴生成过程进行监测,结果显示,声表面波技术能有效控制液滴生成模式的转变,避免液滴生成过程中因材料析出和通道堵塞等原因引起的液滴生成模式的不可控转变,实现了液滴均匀连续的生成。使用场发射扫描电镜对具有不同CL-20含量、不同NC含量和不同粒径的微球形貌进行了表征,结果显示,通过降低CL-20含量、增加NC含量或增大微球粒径等方式,可以降低微球的表面粗糙度,减少表面缺陷,同时在声表面波技术辅助下,微球粒径变异系数从39.33%降至7.51%,极大地提高了微球的均匀性。通过X射线衍射仪和热质量分析仪对具有不同粒径的CL-20/NC微球的晶体结构和热力学性能进行了表征,结果显示,中位粒径为20μm的微球(分解峰温为229.04℃)的热稳定性优于中位粒径为7μm的微球(分解峰温为228.22℃)的热稳定性,而中位粒径为7μm的微球的反应剧烈程度与能量密度较大,其损失质量率(84.3%)和放热量(12.05 mW/mg)均高于中位粒径为20μm的微球的损失质量率(80.2%)和放热量(8.84 mW/mg)。声流控技术成功制备了粒径更小且均匀性显著提高的CL-20/NC含能微球,为高能量密度材料的优化设计与应用提供了重要参考。

Influence of particle size on the aggregation behavior of nanoparticles: Role of structural hydration layer

More and more attention has been paid to the aggregation behavior of nanoparticles, but little research has been done on the effect of particle size. Therefore, this study systematically evaluated the aggregation behavior of nano-silica particles with diameter 130–480 nm at different initial particle concentration, pH, ionic strength, and ionic valence of electrolytes. The modified Smoluchowski theory failed to describe the aggregation kinetics for nano-silica particles with diameters less than 190 nm. Besides, ionic strength, cation species and p H all affected fast aggregation rate coefficients of 130 nm nanoparticles. Through incorporating structural hydration force into the modified Smoluchowski theory, it is found that the reason for all the anomalous aggregation behavior was the different structural hydration layer thickness of nanoparticles with various sizes. The thickness decreased with increasing of particle size, and remained basically unchanged for particles larger than 190 nm. Only when the distance at primary minimum was twice the thickness of structural hydration layer, the structural hydration force dominated, leading to the higher stability of nanoparticles. This study clearly clarified the unique aggregation mechanism of nanoparticles with smaller size, which provided reference for predicting transport and fate of nanoparticles and could help facilitate the evaluation of their environment risks.

Effects of type, level and time of sand and gravel mining on particle size distributions of suspended sediment

Monitoring the sediment transport behavior induced by different interventions, particularly sand mining from rivers, is needed to adaptively manage the watersheds. The particle size distribution of the sus-pended sediment in up and downstream of rivers is one of the main indicators to know about fate of sediments, which may be varied in different conditions. We investigated the effect of some types of sand and gravel (i.e., manual and low, semi-heavy, and heavy machinery) mining on particle size distribution of suspended sediment in the Vaz-e-Owlya, Vaz-e-Sofla and Alesh-Roud riverine mines located in Ma-zandaran Province, northern Iran. The study was conducted on a monthly basis from February, 2012 to January, 2013. Laser granulometry was used to analyze the particle size distribution of suspended se-diment samples taken from up and downstream sections of the study mines. The results revealed that the level and intensity of mining activity affected particle size distribution of suspended sediments. Further statistical assessments in up and downstream sections of the mines proved that sorting, D50, mean, D90, kurtosis, skewness and D10 of the suspended sediment were not significantly influenced by mining activities at levels of 0.09, 0.11, 0.12, 0.15 to 0.69, 0.15–0.69, 0.77, 0.87, 0.97, respectively. While it was not statistically significant, we found that the type of mine and the level of the exploitation changed the particle size distribution of the suspended sediment.

Kenics型静态混合器中幂律流体与颗粒混合过程分析

针对Kenics型静态混合器内固体颗粒在幂律流体中的孤岛现象的产生机理进行研究。运用Fluent数值模拟固相颗粒与CMC水溶液在Kenics静态混合器中的混合过程,并利用浓度变异系数(COV)对颗粒分布特性进行量化分析。研究表明:提高流体表观黏度和流体入口速度,颗粒停留时间缩短,COV值降低,混合效果提高。在第4~8个扭旋叶片中间截面上均形成了两对对称的无粒子孤岛,降低流体表观黏度和提高流体入口速度,孤岛边界更清晰。扭旋叶片诱导的内流涡旋和近壁面涡旋有较高的涡量,涡旋中心局域形成无粒子孤岛,相邻叶片交错区域,随着涡旋耗散孤岛消失。

基于图像分析的掘进工作面粉尘颗粒检测方法

基于光散射原理测定粉尘质量浓度只能定时定点手动检测,实时性差,且只能检测出粉尘质量浓度,并不能给出粒径分布范围。目前基于图像分析的粉尘颗粒检测研究主要是针对粉尘质量浓度或粒径分布进行单方面研究,并不能实现粉尘质量浓度和粒径分布范围的同时检测。针对上述问题,提出了一种基于图像分析的掘进工作面粉尘颗粒检测方法,探究图像特征与粉尘质量浓度、粒径分布间的关系。通过粉尘样本收集及图像采集装置,采集粉尘颗粒图像并获取采集图像时的粉尘质量浓度。编写粉尘样本图像处理算法,提取图像的灰度特征、纹理特征、几何特征相关参数。对提取的图像特征与实测粉尘质量浓度进行相关性分析,选取相关性较大的图像特征作为参数建立回归数学模型。提取粉尘颗粒对象像素点个数,结合转换系数,基于几何当量等效面积径计算粉尘粒径大小及分布范围。实验结果表明:实测粉尘质量浓度与建立的图像特征多元非线性回归模型数学模型计算值间的平均相对误差为12.37%,标准实测粒径与几何当量等效面积径得到的粒径分布间的最大相对误差为8.63%,平均相对误差为6.37%,验证了基于图像特征的粉尘质量浓度回归数学模型和基于几何当量等效面积径分布数学模型的准确性。

不同粗骨料粒径混凝土动态压缩强度的离散性研究

为了研究粗骨料粒径差异引起的动态压缩试验离散性问题,制备了最大粒径分别为8 mm、14 mm和26 mm的混凝土与砂浆试件,通过动静态压缩试验,得到不同应变率下各试样的应力-应变曲线和应变率-动态增长因子曲线。为了更直观地分析由粗骨料粒径差异引起的试验离散性问题,定义粒径系数λ为粗骨料最大粒径d与试件直径D之比,引入变异系数CV,运用数理统计方法量化离散性,得到λ与CV关系图,直观反映试验离散性与粗骨料粒径关系。分析表明:λ=0.34为混凝土材料异质性临界点;当粒径系数λ<0.34时,混凝土材料异质性影响不明显;当λ>0.34时,粗骨料的粒径过大已经影响到了混凝土的动态响应,材料异质性明显增强。该结论的得出对今后工程与试验中粗骨料粒径的选取有指导意义。

铀矿尾矿氡射气系数测量方法及主要影响因素研究

放射性矿物以及放射性伴生矿物在开采过程中,由于岩石破碎处理,改变了矿石原有的物理结构,引起氡气射气系数和迁移特性的改变,造成尾矿氡气排放超标等环境问题。测定尾矿射气系数以及研究射气系数主要影响因素,对尾矿氡气防护与治理具有重要意义。本文以铀矿尾矿射气系数为研究对象,搭建了射气系数测量装置,并利用装置测量了不同粒径和温度条件下样品的射气系数。依据实验数据建立了射气系数与温度和粒径的关系和经验公式。实验结果表明,在5目~30目的粒径范围内,射气系数与样品成幂指数关系,随着样品粒径减小而增大;射气系数与温度存在正相关性,在20~40℃范围内,存在线性关系。得到的经验公式可用于铀矿尾矿氡气浓度模拟计算,为尾矿氡气治理提供基础数据。

少层石墨烯纳米流体的球磨法制备及其导热性能

针对高频化电子器件对散热技术日益增高的迫切需求,该文提出利用物理-机械手段,以天然膨胀石墨为原料,依靠机械碰撞和电荷相互作用,通过改变研磨时间,制备出不同粒径的少层改性球磨石墨烯,并通过水溶液分散技术获得了不同浓度的少层石墨烯纳米流体.利用XRD、Raman、TEM和激光粒度仪对所制备的少层石墨烯形貌、结构和粒径分布进行了表征.结果表明,所制备的少层石墨烯层数约为6~7层,其微晶尺寸较小,且具有规则的层状结构,粒径集中分布在80 nm附近且分布均匀.借助自主搭建的导热测试平台,研究了在浓度和粒径影响下少层石墨烯纳米流体的导热性能.研究发现,少层石墨烯纳米流体的热阻随着质量分数的增大而减小,导热系数明显大于基液且随着少层石墨烯粒径的减小而增大,在热管中的平均传热功率随质量分数的增大而增大.粒径为83.72 nm,质量分数为0.1%的少层石墨烯纳米流体的热阻比水降低10.96%,导热系数提高27.31%,平均传热功率提高193.1%.因此,这一方法未来将对电子器件、芯片散热技术的优化和提升具有重要的指导价值.

含铯废水中亚铁氰化物的粒径分布及组成分析

亚铁氰化物是处理含Cs^(+)离子放射性废水的一种重要方法。为了研究亚铁氰化物处理Cs^(+)离子时的置换机理以及基础性质,本文按照M^(2+)/Fe(CN)64-=1.33的比例投加共沉淀剂(其中M^(2+)代表了Ni^(2+)、Cu^(2+)、Co^(2+)、Cd^(2+)),在不同的模拟水样中制备了亚铁氰化物。利用激光粒度分布仪器考察了M(NO_(3))_(2)与亚铁氰化钾形成共沉淀物的粒径分布。利用高氯酸和加热装置对制备的亚铁氰化物进行溶解以分析其组成。结果表明:共沉淀物的粒径几乎全部处于0.1~10μm;Cs^(+)和Mg^(2+)离子主要取代K^(+)和部分取代M^(2+)离子,Na^(+)离子只取代K^(+)离子;对1.00 mg/L Cs^(+)离子的去除率高于99%;对其吸附容量高达310mg/g以上。总之,亚铁氰化物粒径较小,Na^(+)和Mg^(2+)存在不会影响亚铁氰化物对Cs^(+)离子的去除。

渗流条件下夹层砂土中细颗粒迁移沉积特性试验研究

夹层砂土中细颗粒迁移-沉积问题广泛存在于地下水回灌、堆积体入渗、反滤层设计及注浆等工程中。采用室内一维砂柱试验系统,选取3种典型粒径砂土,开展了2种夹层位置及厚度下砂土中悬浮颗粒迁移-沉积特性试验研究。结果表明:在夹层砂柱中,粒径对细颗粒迁移-沉积过程影响显著。粒径比大于1时,悬浮颗粒穿透曲线峰值更高,在夹层处产生细颗粒沉积量突增现象;夹层位置越靠近注水端,厚度越小,其峰值和沉积突增量越大。粒径比小于1时,悬浮颗粒穿透曲线峰值较低,夹层处无颗粒富集;夹层越靠近出水端,厚度越大,穿透曲线的峰值也越高。试验过程中,悬浮颗粒的迁移沉积会引起渗透系数变化。渗透系数变化过程与穿透曲线变化相对应,过程分为沉积、剥离迁移和动态平衡三种。细颗粒在砂土中以吸附方式沉积,并在吸附处堆积。