Understanding the interfacial behaviors of benzene alkylation with butene using chloroaluminate ionic liquid catalyst: A molecular dynamics simulation

To better understand the benzene alkylation with chloroaluminate ionic liquids(ILs) as catalyst, the interfacial properties between the benzene/butene binary reactants and chloroaluminate ILs with varying cation alkyl chain length and different anions were investigated using molecular dynamics(MD) simulations. The results indicate that ILs can obviously improve the interfacial width, solubility and diffusion of reactants compared to H_(2)SO_(4). The longer alkyl chains of cations present a density enrichment at the interface and protrude into the binary reactants phase. Furthermore, the ILs consisting of 1-octyl-3-methylimidazolium cations([Omim]^(+)) and the stronger acidity heptachlorodialuminate anions([Al_(2)Cl_(7)]^(-)) are more beneficial to promote the interfacial width and facilitate the dissolution and diffusion of benzene in both the IL bulk and the interfacial region in comparison to the ones with shorter alkyl chains cations and weaker acidity anions. The information gives us a better guideline for the design of ILs for benzene alkylation.

MOLECULAR DYNAMICS SIMULATIONS OF FILLED AND EMPTY CAGE-LIKE WATER CLUSTERS IN LIQUID WATER AND THEIR SIGNIFICANCE TO GAS HYDRATE FORMATION MECHANISMS

Molecular dynamics simulations are performed to observe the evolutions of 512 and 51262 cage-like water clusters filled with or without a methane molecule immersed in bulk liquid water at 250 K and 230 K. The lifetimes of these clusters are calculated according to their Lindemann index δ (t) using the criteria of δ≥0.07. For both the filled and empty clusters, we find the dynamics of bulk water determines the lifetimes of cage-like water clusters, and that the lifetime of 512 62 cage-like cluster is the same as that of 512 cage-like cluster. Although the methane molecule indeed makes the filled cage-like cluster more stable than the empty one, the empty cage-like cluster still has chance to be long-lived compared with the filled clusters. These observations support the labile cluster hypothesis on the formation mechanisms of gas hydrates.

Influence of vacuoles with gas–liquid inclusions on the thermobaric destruction conditions of natural quartz under dynamic heating in an RF-TICP torch system

In the present work,the turbulent mixing process of a polydisperse quartz particle flow with a plasma stream generated by a radio-frequency(RF)inductively coupled plasma torch was numerically studied.The thermobaric stress in the quartz particles under dynamic heating in a heterogeneous plasma flow was determined by a two-stage approximation approach.The effect of the presence of vacuoles in natural quartz on the particle thermobaric destruction conditions was studied.It was found that the equivalent thermal and baric stresses in quartz particles may significantly increase in the presence of vacuoles within a small gas volume fraction.The influence of the regime and energetic working conditions of an RF inductively coupled plasma torch system on the particle thermobaric destruction conditions was examined,and a recommendation was given to promote the degree of thermobaric destruction of quartz particles,which is of substantial importance for improving the overall enrichment efficiency of quartz concentrates.

Numerical Simulation and Experimental Study on the Performance of Gas/liquid Spiral Separator

The gas/liquid spiral separator, a key component in the compressed air system, was used to remove liquid and oil from gas stream by centrifugal and gravitational forces. To optimize the design of the separator,the relationship between the performance and structural parameters of separators is studied. Computational fluid dynamics (CFD) method is employed to simulate the flow fields and calculate the pressure drop and separation efficiency of air-liquid spiral separators with different structural parameters. The RSM (Reynolds stress model)turbulence model is used to analyze the highly swirling flow fields while the stochastic trajectory model is used to simulate the traces of liquid droplets in the flow field. A simplified calculation formula of pressure drop in spiral structures is obtained by modifying Darcy's equation and verified by experiment.

Dynamic microwave-assisted extraction combined with liquid phase microextraction based on the solidification of a floating drop for the analysis of organochlorine pesticides in grains followed by GC

A convenient,cost-effective and fast method using dynamic microwave-assisted extraction and liquid phase microextraction based on the solidification of a floating drop was proposed to analyze organochlorine pesticides in grains including rice,maize and millet.Twelve samples can be processed simultaneously in the method.During the extraction process,10%acetonitrile-water solutions containing 110μL of n-hexadecane were used to extract organochlorine pesticides.Subsequently,1.0 g sodium chloride was placed in the extract,and then centrifuged and cooled.The n-hexadecane drops containing the analytes were solidifi ed and transferred for determination by gas chromatography-electron capture detector without any further filtration or cleaning process.Limits of detection for organochlorine pesticides were 0.97–1.01μg/kg and the RSDs were in the range of 2.6%–8.5%.The developed technology has succeeded in analyzing six real grains samples and the recoveries of the organochlorine pesticides were 72.2%–94.3%.Compared with the published extraction methods,the developed method was used to analyze organochlorine pesticides in grains,being more environmentally friendly,which is suitable for the daily determination of organochlorine pesticides.

Numerical simulation of gas–liquid flow in the bubble column using Wray–Agarwal turbulence model coupled with population balance model

In this paper,an improved computational fluid dynamic(CFD)model for gas-liquid flow in bubble column was developed using the one-equation Wary-Agarwal(WA)turbulence model coupled with the population balance model(PBM).Through 18 orthogonal test cases,the optimal combination of interfacial force models,including drag force,lift force,turbulent dispersion force.The modified wall lubrication force model was proposed to improve the predictive ability for hydrodynamic behavior near the wall of the bubble column.The values simulated by optimized CFD model were in agreement with experimental data,and the errors were within±20%.In addition,the axial velocity,turbulent kinetic energy,bubble size distribution,and the dynamic characteristic of bubble plume were analyzed at different superficial gas velocities.This research work could provide a theoretical basis for the extension of the CFD-PBM coupled model to other multiphase reactors..

Quantitative research of the liquid film characteristics in upward vertical gas, oil and water flows

The study of liquid film characteristics in multiphase flow is a very important research topic, however,the characteristics of the liquid film around Taylor bubble structure in gas, oil and water three-phase flow are not clear. In the present study, a novel liquid film sensor is applied to measure the distributed signals of the liquid film in three-phase flow. Based on the liquid film signals, the liquid film characteristics including the structural characteristics and the nonlinear dynamics characteristics in three-phase flows are investigated for the first time. The structural characteristics including the proportion, the appearance frequency and the thickness of the liquid film are obtained and the influences of the liquid and gas superficial velocities and the oil content on them are investigated. To investigate the nonlinear dynamics characteristics of the liquid film with the changing flow conditions, the entropy analysis is introduced to successfully uncover and quantify the dynamic complexity of the liquid film behavior.

A new model for predicting the critical liquid-carrying velocity in inclined gas wells

Based on the assumption of gas-liquid stratified flow pattern in inclined gas wells,considering the influence of wettability and surface tension on the circumferential distribution of liquid film along the wellbore wall,the influence of the change of the gas-liquid interface configuration on the potential energy,kinetic energy and surface free energy of the two-phase system per unit length of the tube is investigated,and a new model for calculating the gas-liquid distribution at critical conditions is developed by using the principle of minimum energy.Considering the influence of the inclination angle,the calculation model of interfacial friction factor is established,and finally closed the governing equations.The interface shape is more vulnerable to wettability and surface tension at a low liquid holdup,resulting in a curved interface configuration.The interface is more curved when the smaller is the pipe diameter,or the smaller the liquid holdup,or the smaller the deviation angle,or the greater gas velocity,or the greater the gas density.The critical liquid-carrying velocity increases nonlinearly and then decreases with the increase of inclination angle.The inclination corresponding to the maximum critical liquid-carrying velocity increases with the increase of the diameter of the wellbore,and it is also affected by the fluid properties of the gas phase and liquid phase.The mean relative errors for critical liquid-carrying velocity and critical pressure gradient are 1.19%and 3.02%,respectively,and the misclassification rate is 2.38%in the field trial,implying the new model can provide a valid judgement on the liquid loading in inclined gas wells.

Understanding the interfacial properties of benzene alkylation with 1-dodecene catalyzed by immobilized chloroaluminate ionic liquids using molecular dynamics simulation

Benzene alkylation catalyzed by immobilized ionic liquids(ILs)on solid carriers is considered as a heterogeneous reaction,in which the interfacial properties play an important role.Hence,the interfacial characteristics between benzene/1-dodecene mixture and immobilized chloroaluminate ILs with different alkyl chain length on the silica substrate were investigated by molecular dynamics simulation.The grafted ILs can obviously promote the enrichment of benzene near the interface,leading to a higher ratio of benzene to dodecene,and the interfacial width increases slightly with increased alkyl chain of grafted cations.At the same time,the grafted cations can also enhance the benzene diffusion and suppress the dodecene diffusion at the interface,which probably helps to inhibit the inactivation of catalysts.This work provides deeply insights into the rational design of novel immo-bilized ILs catalysts for the benzene alkylation.

Contact angle and stability of interfacial nanobubble supported by gas monolayer

Since solid-liquid interfacial nanobubbles(INBs)were first imaged,their long-term stability and large contact angle have been perplexing scientists.This study aimed to investigate the influence of internal gas density and external gas monolayers on the contact angle and stability of INB using molecular dynamics simulations.First,the contact angle of a water droplet was simulated at different nitrogen densities.The results showed that the contact angle increased sharply with an increase in nitrogen density,which was mainly caused by the decrease in solid-gas interfacial tension.However,when the nitrogen density reached 2.57 nm^(-3),an intervening gas monolayer(GML)was formed between the solid and water.After the formation of GML,the contact angle slightly increased with increasing gas density.The contact angle increased to 180°when the nitrogen density reached 11.38 nm^(-3),indicating that INBs transformed into a gas layer when they were too small.For substrates with different hydrophobicities,the contact angle after the formation of GML was always larger than 140°and it was weakly correlated with substrate hydrophobicity.The increase in contact angle with gas density represents the evolution of contact angle from macro-to nano-bubble,while the formation of GML may correspond to stable INBs.The potential of mean force curves demonstrated that the substrate with GML could attract gas molecules from a longer distance without the existence of a potential barrier compared with the bare substrate,indicating the potential of GML to act as a gas-collecting panel.Further research indicated that GML can function as a channel to transport gas molecules to INBs,which favors stability of INBs.This research may shed new light on the mechanisms underlying abnormal contact angle and long-term stability of INBs.

固液界面热阻的温度依赖特性模拟研究

基于非平衡态分子动力学模拟方法,研究了系统温度及固液结合强度对固液界面传热的影响规律。模拟结果表明,固液界面热阻随着系统温度的升高而降低,并且亲水性界面的界面热阻温度依赖性较弱。基于微观热流密度计算式的分析表明,随着系统温度升高,动能项和维里项的贡献均逐渐增大,因而固液界面传热增强,但是动能项占比逐渐增大,维里项占比逐渐降低;随着固液结合强度逐渐增大,界面吸附效应增强,维里项贡献明显增大,这是较强的固液相互作用能够强化界面传热的主要原因。

外电场作用下纳米结构表面的固-液界面传热特性

在固体表面布置纳米结构是一种强化固-液界面传热的简单有效的方法.但是,当固-液界面相互作用较弱时,由于纳米结构并不能被液体浸润,纳米结构的存在反而会弱化固-液界面之间的传热,而外电场的施加则可以解决这一问题.本文基于分子动力学模拟的方法,研究了纳米结构固-液界面在外电场作用下的传热特性.通过在2块平行金属板布置数量相同的正负电荷,产生垂直于板面的均匀电场,并在下层金属板上布置了不同尺寸的纳米结构.结果表明:在外电场作用下,纳米结构处会产生电润湿现象,固-液界面的润湿状态能够从Cassie态变为Wenzel态,界面处的Kapitza热阻长度明显减小,因而热流密度显著增大;当电荷量增至发生电冻结的临界值,液态水会产生电冻结现象,其热导率骤增至1.2 W/(m·K),热流密度也随之发生骤增;继续增加电场强度,由于电冻结现象的发生,固-液界面热阻则基本保持不变.

探索微纳尺度润湿动力学:长针式原子力显微镜的应用与进展

“如何在微观层面测量界面现象”是微纳尺度实验流体力学的关键科学问题,被列入世界前沿125个科学问题名单(Sanders S,Science,2021).由于光学衍射极限的限制,传统光学手段很难直接测量微纳尺度下的流动与界面现象.利用原子力显微镜的精准操控和小尺度力学测量等优势,结合长针式探针组装成的微流变计可以直接测量气-液-固三相接触线上的毛细力,并监测探针在垂直方向运动中力的动态变化.通过该技术手段,可以实现对流体界面的动力学行为以及各类材料在液体环境中力学性质在微纳尺度的精确表征.文章将系统介绍长针式原子力显微镜技术的实验原理和方法,及其在微纳尺度非理想界面润湿动力学中的最新研究进展,包括低能垒表面毛细力的速度依赖性与非对称性、无序粗糙表面接触线黏滑运动的统计学规律、柔性表面接触线动力学的状态与速度定律、以及离子液体-金属界面处电场对接触角迟滞的调控等,最后展望了该技术在新兴领域中的应用.该实验手段为检验各类理论模型与数值模拟提供了可信数据,为探究界面上复杂现象的物理本质提供参考.

气液搅拌槽内气泡尺寸与局部气含率的CFD模拟

采用在欧拉-欧拉双流体模型的基础上耦合气泡数密度(BND)函数模型,引入气泡破碎和聚并函数,对双层组合桨气液搅拌槽内的气泡尺寸和局部气含率进行了计算流体力学(CFD)模拟,同时采用双电导电极探针法对搅拌槽内局部气液分散特性进行了实验测量,并和CFD模拟结果进行了对比.结果表明:较高通气量条件下搅拌槽内气泡尺寸和局部气含率分布很不均匀,气泡尺寸在叶轮排出流区较小,且沿着排出流方向逐渐增大;在两桨间区域和上层桨以上区域气泡以聚并为主;局部气含率在循环涡涡心、叶轮和挡板后部较高,叶片后部存在明显气穴.

微生物菌液物质油水界面扩张黏弹性研究

采用小幅低频振荡法,研究了常温菌与高温菌菌液物质在油-水界面上的扩张黏弹特性及动态界面张力,阐述了菌液物质黏弹模量随扩张频率及温度的变化规律,获得了菌液物质油水界面吸附动态微观信息,并将扩张流变性质与动态界面张力相关联,定量考察了菌体本身对油水界面性质的影响.研究结果表明:菌液物质黏弹模量随扩张频率的增加而增加,随温度的升高而降低;菌体本身具有界面活性,能够降低界面张力和黏弹模量,改变油水界面性质,提高原油流动性能.但其活性受温度的影响,存在最佳活性温度.现场应用时应注意油藏温度与菌液最佳活性温度一致.

折流式旋转床气液比表面积的实验研究及CFD模拟

气液比表面积对折流式旋转床(RZB)的传质起到关键的作用。本文采用NaOH溶液化学吸收混合气体中CO_2的方法对折流式旋转床的气液比表面积进行了研究,通过计算流体力学(CFD)技术来模拟转子内液体的流动行为。分析转子转速、气体流量和液体流量对气液比表面积的影响。结果表明:折流式旋转床的比表面积在100~350m^2/m^3范围内,折流式旋转床的气液比表面积随液量的增大而增大,随气量的增大明显增大,随转速的增加先缓慢增大后迅速增大。CFD模拟表明,随液量的增加,动静圈之间的液滴数量明显增多,并且静圈上更多的表面被液膜覆盖;随气量的增大,更多的液体被碎成细小的液体,液滴的数量成倍增加;随转速的增大,动圈施加给液体的剪切力和离心力增大,液体被更好地分散,并且离开动圈的液滴尺寸变得更小。RZB与其他类型填充旋转床(RPB)的气液比表面积进行对比,发现RZB的比表面积低于分段进液式RPB、常规不锈钢金属网RPB、镍泡沫填料RPB、新型多个叶片转子RPB,接近于板式填料和挡板PRB。

接触角迟滞和气-液界面张力温度敏感性对液滴蒸发动态特性的影响

基于润滑理论和滑移边界条件,构建了考虑接触角迟滞时液滴在均匀加热固体壁面上蒸发的数学模型,探讨了接触角迟滞对蒸发液滴动力学的影响,并分析了不同气-液界面张力温度敏感性的液滴蒸发特征.研究结果表明:接触角迟滞对液滴蒸发过程有较大影响,随接触角迟滞增大,液滴的接触线钉扎时间延长,铺展阶段和去钉扎阶段时长缩短,液滴蒸发显著加快;迟滞角的增大使前进接触角增加,后退接触角减小,且后退接触角减小的幅度大于前进接触角增加的幅度.提高气-液界面张力对温度的敏感性系数可通过减小后退接触角,改善液滴在壁面上的润湿性,从而加强液滴传热,致使加快液滴蒸干.因此,改变接触角迟滞和气-液界面张力对温度的敏感性均可实现对液滴运动的调控,从而控制其蒸发进程.

表面电荷及外电场对液固界面热阻的影响

采用非平衡分子动力学方法模拟了外电场及固体表面电荷对水与固体间界面热阻的影响.结果表明,外加电场平行于界面时,其对界面热阻几乎没有影响,而垂直于界面时,界面热阻将随着电场强度的增大而减小.壁面带正电荷或负电荷都将使得界面热阻减小.界面热阻与表面电荷密度及电场强度均满足二次函数关系.模拟结果表明施加外电场和表面电荷是控制液固界面热阻的有效方法.

近自由面水翼性能分析

为了研究近自由面下水翼附近的黏性流动,通过有限体积法对雷诺时均N-S方程进行数值求解,速度压力耦合方式采用SIMPLEC解法,用流体体积函数模型来捕捉自由液面。首先将数值计算结果与实验值进行对比以验证所用数值方法的可行性,随后进一步研究了水翼的兴波、表面压力分布以及其水动力性能,并针对翻卷波现象进行了分析。从计算结果可以看出,距离自由面越近,水翼的升力和阻力越小。当水翼距离自由液面4倍弦长距离后,自由液面的影响基本可以忽略。

微液膜厚度及气液界面波动特性测量技术分析

气液两相流设备的性能受限于临界热流密度,开展流动微液膜厚动力学特性相关研究及气液分层流界面波动稳定性的精准表征是深入理解流动沸腾机理及其强化的关键。本文针对气液两相流设备中加热表面微液膜厚度及其波动特性为研究对象,对现有的液膜厚度与气液界面波动特性诊断技术进行测量原理说明,并对光学法测量范围、精度、可操作性等性能指标进行对比分析。