The flow behavior of droplet adsorption on a liquid-liquid interface accompanied by cross-linking reaction and phase separation in a microchannel

The adsorption process of droplets on the liquid-liquid interface and phase separation process can regulate the spatial distribution of the fluid system,which are crucial for chemical engineering.However,the cross-linking reaction,which is widely used in the field of polymers,can change the physical properties of the fluids and affect the flow behavior accordingly.A configuration of microchannels is designed to conveniently generate uniform droplets in one phase of the parallel flow.The flow behavior of the adsorption process of sodium alginate droplets on the liquid-liquid interface is investigated,and the subsequent process of phase separation is studied.In the process of droplet adsorption,the crosslinking reaction occurs synchronously,which makes the droplet viscosity and the elasticity modules of the droplet surface increase,thus affecting the dynamics of the adsorption process and the equilibrium shape of the droplet.The variation of the adsorption length with time is divided into three stages,which all conform to power law relationship.The exponents of the second and third stages deviate from the results of the Tanner's law.The flow pattern maps of droplet adsorption and phase separation are drawn,and the operating ranges of complete adsorption and complete separation are provided.This study provides a theoretical basis for further studying the flow behavior of droplets with cross-linking reaction in a microchannel.

Formation dynamics and size prediction of bubbles for slurry system in T-shape microchannel

The bubble formation dynamics and size manipulation in the slurry of polystyrene microspheres in the microfluidic T-junction were visually investigated by a high-speed camera.Based on the evolution of the bubble neck with time,the formation process of bubbles is divided into three stages:filling,squeezing and pinch-off.The particle concentration has an obvious effect on the squeezing stage,while less impact on the filling and pinch-off stages.In the squeezing stage,the evolution of the dimensionless minimum neck width of bubbles with time could be described by a power-law relationship.The increase of the particle concentration or continuous phase flow rate could lead to the increase of body flow of the continuous phase and the enhancement of the squeezing force acted on the bubble neck,correspondingly,the power-law index a in the squeezing stage enlarges.Moreover,the bubble size increases with the increase of the gas phase flow rate and the decrease of the particle concentration and continuous phase flow rate.However,the effect of the particle concentration on the bubble size weakens with the increase of the continuous phase flow rate.In addition,a new prediction correlation of the bubble size for the slurry system in a T-shape microchannel was proposed with good prediction accuracy.

Slug bubble deformation and its influence on bubble breakup dynamics in microchannel

The deformation of moving slug bubbles and its influence on the bubble breakup dynamics in microchannel were studied.Three bubble morphologies were found in the experiment:slug,dumbbell and grenade shapes.The viscosity effect of continuous phase aggravates the velocity difference between the fluid near the wall and the bubble,resulting in that the continuous phase near the bubble head flows towards and squeezes the bubble tail,which causes the deformation of bubbles.Moreover,the experimental results show that the deformation of bubbles could significa ntly prolo ng the bubble breakup period at the downstream Y-junction.There exists the critical capillary number Ca_(Cr )for the asymmetric breakup of grenade bubbles,Ca_(Cr )increases with the rise of flow rate and viscosity of the continuous phase.

Mass transfer intensification and mechanism analysis of gas–liquid two-phase flow in the microchannel embedding triangular obstacles

An effective mass transfer intensification method was proposed by embedding different triangular obstacles to improve the gas-liquid mass transfer efficiency in microchannel.The influences of triangle obstacles configuration,obstacle interval and flow rate on the volumetric mass transfer coefficient,pressure drop and energy consumption were investigated experimentally.The enhancement factor was used to quantify the mass transfer enhancement effect of triangle obstacles.It was found that the isosceles or equilateral triangle obstacles are superior to the rectangular obstacles.The maximum enhancement factor of equilateral triangle obstacles was 2.35.Considering comprehensively mass transfer enhancement and energy consumption,the isosceles triangle obstacle showed the best performance,its maximum enhancement factor was 2.1,while the maximum pressure drop increased only 0.41 kPa(22%)compared to the microchannel without obstacles.Furthermore,a micro-particle image velocimetry(micro-PIV)was utilized to observe the flow field distribution and evolution,in order to understand and analyze the enhancement mechanism.The micro-PIV measurement indicated that the obstacle structure could induce the formation of vortex,which promotes convective mass transfer and thins the flow boundary layer,accordingly,the gas-liquid mass transfer efficiency is remarkably improved.This study can provide theoretical guidance and support for the design and optimization of microchannel with triangular obstacles.

Coalescence dynamics of two droplets of different viscosities in T-junction microchannel with a funnel-typed expansion chamber

The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).

Formation characteristics of Taylor bubbles in a T-junction microchannel with chemical absorption

This study focuses on the effect of chemical absorption on the formation dynamic characteristics and initial length of Taylor bubbles.The temporal evolutions of neck width and length of gaseous thread and initial length with and without chemical absorption were investigated with the Capillary number and Hatta number between 0.0010–0.0073 and 1.8–5.8 respectively.The squeezing regime with typical three stages,expansion,squeezing and pinch off is observed for both two processes.Compared with the nonabsorption process,the increase of formation time in the chemical absorption process arises mainly from the expansion stage,and the decrease of initial length is from the necking stage.In addition,the temporal length evolution satisfies the power-law scale with the same exponent but a smaller pre-exponential factor.The correlations of neck width for stage transition and initial length with Hatta number demonstrate the enhancement effect of chemical absorption on bubble formation dynamics and initial length at relatively high chemical reaction rates and long formation time.This study provides insight into the bubble formation mechanism and helps to regulate the bubble initial size with chemical absorption.

微液滴强化传质与化学反应的研究进展

气–液/液–液两相体系广泛存在于多种化工过程中,如精馏、吸收、萃取、多相反应等.传统宏观的两相接触方式存在接触面积小、传质效率低、反应速率慢等问题,而微液滴具有比表面积大、生成频率高、液滴系统相对独立等诸多优点,可极大强化相间传质和化学反应.将微液滴作为传质和反应的媒介,能够有效改善两相宏观接触的局限,已被广泛应用于各类化工单元操作中.本文综述了近年来关于微液滴强化相间传质与多相化学反应的研究进展,并对未来的研究方向进行了展望.

微通道内流体压力降研究进展

从微通道构型出发,总结了恒定截面通道、变径通道、复杂通道内流体压降研究的最新进展,介绍了哈根-泊肃叶定律用于恒定截面通道的研究进展,提出了变径通道的截面变化对压降的影响,总结了复杂构型微通道内流体压降研究的难点,讨论了粘度、滑移、特征尺寸及其测量方式对压降的影响,为构建压降预测模型提供了思路.对该领域今后主要的研究方向进行了展望.

Studies on the liquid-liquid interfacial mass transfer process using holographic interferometry

This paper aims at the interfacial phenomena of liquid-liquid mass transfer and its characteristic.By using the real-time holographic technique,the concen-tration distributions on the aqueous side were obtained according to holographic diagrams of mass transfer of ethanol through the interface of oil and water at different initial concentrations.Furthermore,the concentrations near the interface and the mass transfer coefficients were attained.A correlation of concentration near the interface to the concentration of the solute in the oil side was proposed.An approach of interfacial energy with solute concentration was established,and the calculated results are at good agreement with the experimental data.It is indicated that the liquid-liquid mass transfer process is approximately in accordance with two-film theory,the interfacial performance may be changed by the addition of the solute,and the interface of liquid-liquid is non-equilibrium thermodynamically during the mass transfer process.

Effect of fine solid particles on absorption rate of gaseous CO_(2)

The influence of the properties of solid particles in slurry on the absorption of CO_(2) in the slurry was inves-tigated in a stirred thermostatic reactor.The absorption experiments were carried out in three different slurries con-sisting of water,cyclohexane and soybean oil,respectively,and three kinds of solid particles(active carbon,active alu-mina and silica gel)were incorporated into each of the above mentioned slurries separately.The experimental results show that the active carbon particles could enhance the absorption rate of gaseous CO_(2) in the aqueous slurry,while in the cyclohexane slurry,active carbon particles indi-cated no the absorption enhancement effect.However,it was observed that the active alumina and silica gel particles could enhance the absorption rate of CO_(2) in the cyclohex-ane slurry.These phenomena indicate that the solid part-icles,which could enhance the gaseous CO_(2) absorption rate,should possess two properties simultaneously,i.e.they rejected the solvent and had higher adsorption capacity for the solute.The experimental results also show that,as for those solid particles which could enhance the gas absorption rate,the enhancement increased quickly with the increase of solid concentration in slurry at first,and then reached a constant value gradually.It was also found that the enhancement factor was related to the coverage fraction of solid particles on the gas-liquid interface,and due to the reduction of surface fraction with increasing stirred speed,the enhancement factor decreased.