一种微型膜分散式萃取器

结合现代化学工程学科的热点领域———微尺度化工过程,开发了一种微型膜分散式混合及传质设备。该微型传质设备以压力为推动力,以微孔膜作为相分散的介质,使二相达到微尺度的混合及传质。选择正丁醇-丁二酸-水体系为对象研究了该设备的传质性能。研究结果表明,该微萃取器结合了微尺度混合传质和处理量大的优势,具有高效萃取的特点,萃取效率为流量的函数,在很高的流量下仍能保持高萃取效率。微混合后相分离性能好,澄清时间在25s以内,是一种理想的萃取设备。     

不溶液-液分散在搅拌槽内的CFD模拟

液滴平均尺寸和液滴尺寸分布是描述不溶液-液分散程度的2个重要参数,决定着两相接触面积的大小,进而决定着相间的传质、传热和化学反应速率。利用CFD方法详细研究了水-油两相在搅拌槽内的分散过程,发现叶轮转速、分散相体积分数和连续相黏度对分散效果有显著影响。当两相组成一定时,增大叶轮转速和连续相黏度均有利于两相的分散。在一定范围内,液滴平均直径与叶轮转速、分散相体积分数均为对数线性关系,相关系数高达0.999。基于个数的液滴尺寸分布在不同转速和连续相黏度条件下出现了双峰分布,而基于体积的液滴尺寸分布则始终为单峰分布。     

Gas/liquid dispersion in a sequential split micromixer

Two different types of split–recombine micromixers have been tested for a gas/liquid dispersion. Mixing performances of two micromixers have been compared in terms of a mixing efficiency. The effects of liquid flow rates, the ratio of gas/liquid flow rate, bubble sizes, and bubble size distributions have been investigated. The sequential split micromixer and the caterpillar micromixer showed a consistent mixing performance at various flow rates. The sequential split micromixer has shown the smaller and narrower bubble size distribution than that of the caterpillar micromixer at a higher flow rate of 1.8 L/h.     

Kinetics of oil dispersion in the absence and presence of block copolymers

A phenomenological model proposed describes droplet breakup in the turbulently agitated lean oil-in-water dispersions and provides a correlation between the median droplet size in an agitated vessel of standard geometry and the time of dispersion. It was assumed that the droplet breakup takes place in the dispersion-only region and coalescence is negligible. The model described the data from this study and the literature quite satisfactorily under these conditions. The effect of adding triblock PEO/PPO/PEO copolymeric surfactants on the dispersion kinetics of oil was also investigated. Addition of surfactant reduced the median oil droplet size significantly, and the extent of this reduction was a strong function of surfactant concentration. Application of the model on these data demonstrated that the change in the median droplet size could be divided into two distinct regions. The breakage rate was high initially, most probably due to continuous adsorption of surfactant molecules at the oil/water interface. A lower breakage rate was attained at longer times, as the surfactant molecules were depleted from the solution. The time of transition between the two was affected strongly by the concentration of the surfactant added. Furthermore, the time of addition of the surfactant did not affect the final droplet-size distribution in the system.     

Utilization of Micromixers for Extraction Processes

The aim of the investigation was to evaluate the extraction performance of a mixer settler set‐up for miniplant technology using static micromixers as an alternative to conventional stirring apparatuses. A comprehensive experimental study was conducted at BASF AG to broaden the technology base for the “extraction” unit operation which is well established for miniplants in order to be utilized for microplant systems. The work proved that micromixers, or micromixer arrays, are highly efficient apparatuses for extraction purposes. The extraction efficiency was found to be a function of volume flow, which could be explained in light of the volume flow dependence of the mean droplet size and, hence, the specific surface area of the dispersions intermediately formed. At optimal flow conditions, one practical mixer settler stage was found to yield one theoretical plate for most systems investigated.     

阶梯式T型微通道内液滴、气泡分散规律

采用高速摄像仪对嵌入毛细管的阶梯式T型微通道内液滴和气泡的分散规律进行研究。考察了两相流量、黏度、表面活性剂浓度等因素对分散流型及分散尺寸的影响规律。结果表明,对于液滴分散过程,表面活性剂的浓度和连续相流量决定了分散流型,随二者增大,流型从dripping流向jetting流转变。对于气泡分散过程,实验范围内仅存在squeezing、dripping流型,表面活性剂的加入对气泡分散过程影响可忽略。嵌入毛细管的阶梯式T型微通道内获得的液滴、气泡直径小于微通道直径,根据实验结果基于两相流量和毛细管数分别建立了计算液滴、气泡分散尺寸的半经验模型,模型与实验结果符合良好。     

Influence of Atomizing Parameters on Droplet Properties in a Pulse Combustion Spray Dryer

A pulse combustor employed in a spray-drying system offers a new approach for liquid atomization that yields high-quality powders at low cost. Using a pulse combustion atomizer, there is no need for any form of nozzle dispersion and its atomization mechanism differs from those of conventional atomizers, such as rotary atomizers and pressure and pneumatic nozzles. In this work, based on the analysis of atomization mechanism, experiments of unsteady pulsating atomization were carried out in an experimental system of a Helmholtz-type pulse combustor. An optical analyzer was used for measuring the mean diameter of atomized droplet and droplet distribution. The effects of liquid feed rate, air flow oscillatory frequency, and liquid viscosity on atomized droplet size and size distribution were investigated and analyzed. The results indicate that the uniform droplet size distribution can be obtained under the conditions of a low feed rate, high-frequency pulsating flow, and moderate viscosity. The range of the droplets' Sauter mean diameter (SMD) is between 50 and 80 µm. The pulsating air flow from the pulse combustor can be used to atomize liquid or slurry without a nozzle and the atomizing quality can meet the requirements of spray drying.     

Influence of Atomizing Parameters on Droplet Properties in a Pulse Combustion Spray Dryer

A pulse combustor employed in a spray-drying system offers a new approach for liquid atomization that yields high-quality powders at low cost. Using a pulse combustion atomizer, there is no need for any form of nozzle dispersion and its atomization mechanism differs from those of conventional atomizers, such as rotary atomizers and pressure and pneumatic nozzles. In this work, based on the analysis of atomization mechanism, experiments of unsteady pulsating atomization were carried out in an experimental system of a Helmholtz-type pulse combustor. An optical analyzer was used for measuring the mean diameter of atomized droplet and droplet distribution. The effects of liquid feed rate, air flow oscillatory frequency, and liquid viscosity on atomized droplet size and size distribution were investigated and analyzed. The results indicate that the uniform droplet size distribution can be obtained under the conditions of a low feed rate, high-frequency pulsating flow, and moderate viscosity. The range of the droplets' Sauter mean diameter (SMD) is between 50 and 80 µm. The pulsating air flow from the pulse combustor can be used to atomize liquid or slurry without a nozzle and the atomizing quality can meet the requirements of spray drying.     

微孔膜制乳技术基本规律研究

在对制乳技术进行充分调研的基础上 ,选择水 -正丁醇和水 -煤油为实验体系 ,以十二烷基磺酸钠、Span85等表面活性剂为乳化剂。在 0 .2 μm的陶瓷膜中研究了压力、连续相流量等因素对乳液粒径大小、分布和分散相通量的影响。实验结果表明 ,用微孔膜可以制得分布均匀的乳状液。乳化剂的类型与用量对乳液的性质有显著影响。微孔膜对低界面张力及界面张力中等的体系可制得粒径小、分布窄的O/W乳液。连续相流量和膜两侧压差对于乳液粒径和粒径分布没有明显的影响 ;分散相通量随压差的增大而明显增大 ,但连续相流速对分散相通量影响不大。     

微通道内传递对液液分散过程的影响规律

在同轴环管微通道中,采用水/正辛醇形成两相体系,利用硫酸向水中传质并释放热量以实现伴随传质传热的微分散过程,研究了两相流速、硫酸浓度对两相流型和液滴大小的影响规律。结果发现,传递会引发O/W/O新流型的产生和流型分布区域变化。探讨了传递强度对于分散液滴尺寸的影响,通过计算液滴脱落时的动态界面张力,分析了传质和传热对于液液微分散影响的大小。     

CFD analysis of turbulence non-homogeneity in mixing vessels: A two-compartment model

A two-compartment model has been developed for calculating the droplet/particle size distribution in suspension polymerization reactors by taking into account the large spatial variations of the turbulent kinetic energy and its dissipation rate in the vessel. The two-compartment model comprised two mixing zones, namely an impeller zone of high local energy dissipation rates and a circulation zone of low kinetic energy. Computational fluid dynamics (CFD) was employed for generating the spatial distribution of energy dissipation rates within an unbaffled mixing vessel agitated by a flat two-blade impeller. A general methodology was developed for extracting, from the results of the CFD simulations, the volume ratio of the impeller over the circulation zone, the ratio of the average turbulent dissipation rates in the two zones, and the exchange flow rate between the two compartments. The effect of agitation rate, continuous phase viscosity, impeller diameter, and mixing vessel scale on the two-compartment model parameters was elucidated. The two-compartment model was then applied to a non-homogeneous liquid-liquid dispersion process to calculate the time evolution of the droplet size distribution in the mixing vessel. An excellent agreement was obtained between theoretical and experimental results on droplet size distributions obtained from a laboratory-scale reactor operated over a wide range of experimental conditions.     

Droplet characteristics in the multi-staged high speed disperser with single inlet

Droplet characteristics in the cavity zone of a multi-staged high speed disperser with single inlet were studied in this paper. The influences of both the operating and structural parameters on the mean droplet diameter, size distribution and liquid flux distribution were quantitatively analyzed. The result showed that the mean droplet diameter decreased with the increase of rotational speed and the number of rotors;whilst there is little influence on the inlet flow rate. In the experimental range, the minimum value of mean droplet diameter is 0.57 mm, 0.48 mm, 0.41 mm in the two-staged, three-staged and four-staged rotors, respectively. The Rosin–Rammler(R–R) distribution could describe the droplet size distribution appropriately, and it became uniform with the increase of rotational speed and the number of rotor, while the inlet flow rate had little effect on the droplet size distribution. The liquid flux distribution curves were always unimodal. With the increase of rotational speed, the location of maximum liquid flux ratio moved from zone 3 to zone 4 and this value decreased from 22.1% to 18.1%. Using Coefficient of Variation(CV) to indicate the uniformity of liquid flux distribution, it was found that the CV decreases from 47.5% to 22.7%when the number of rotor increased from 2 to 4.     

Droplet breakage and coalescence models for the flow of water-in-oil emulsions through a valve-like element

An experimental and theoretical study was carried out regarding the evolution of droplet size distributions for the flow of water in oil emulsions through a valve-like element that simulates a mixing valve. The water droplets had diameters in the 0.1–100 μm range, which includes droplets that are either smaller or larger than the Kolmogorov length scale for the experimental conditions. Droplet breakage and coalescence models that can be used for this size range were proposed. A simplified population balance model was developed to interpret the experimental data and solved by the method of classes. The model parameters were estimated by the orthogonal distance regression method. The simplifying assumption of the model was verified by global optimization using a parallel implementation of the particle swarm optimization method. The agreement between simulated and experimental droplet volume size distributions was good. The predictions of the DeBroukere mean diameter, d₄₃, were unbiased with mean errors of 8%.     

Modeling fluid behavior and droplet interactions during liquid-liquid separation in hydrocyclones

A mechanical separation process in a hydrocyclone is described in which disperse water droplets are separated from a continuous diesel fuel phase. This separation process is influenced by droplet-droplet interaction effects like droplet breakup and coalescence resulting in a change of droplet size distribution. A simulation model is developed coupling the numerical solution of the flow field in the hydrocyclone based on computational fluid dynamics with population balances. The droplet size distribution is discretized and each discrete droplet size fraction is assumed to be an individual phase within a multiphase-mixture model. The droplet breakup and coalescence rates are defined as mass transfer rates between the discrete phases by the aid of user-defined functions. All model equations are solved with the CFD software package FLUENT™. The investigations show the impact of the cyclone geometry on the coupled population and separation dynamics. Cyclone separators with an optimized geometry show less steep velocity gradients increasing the coalescence rates and improving the separation efficiency. The calculated droplet size distributions at the cyclone overflow and at the underflow show good accordance with experimental data. The basic modeling approach can be extended and adapted to other disperse multiphase flow systems.     

陶瓷微滤膜制备水包油型乳液的研究

乳液制备一直是化工领域中的一个重要的研究课题,本文选择水－正丁醇实验体系,以十二烷基碘酸钠为乳化剂,分别采用０．２μｍ和０．８μｍ的陶瓷膜为分散介质制备水包油型乳液。实验研究了压力、连续相流量等因素对乳液粒径大小、分布和分散相通量的影响。结果表明,用微滤膜可以制得分布均匀的乳状液。微滤膜的孔径较小时,连续相流量和膜两侧压差对于乳液粒径和粒径分布没有明显的影响;当膜孔径增大后,乳液滴的直径分布变宽,     

T型微通道内液滴尺寸的实验测定与关联

利用高速摄像仪对不同深宽比的T型微通道内液滴尺寸进行了实验研究。分别采用3种不同尺寸(深度×宽度)的微通道:400 μm×400 μm、400 μm×600 μm、400 μm×800 μm。以环己烷为分散油相,含0.3%表面活性剂十二烷基硫酸钠(SDS)的蒸馏水-甘油(质量分数分别为20%、40%、60%)溶液为连续相。考察了弹状流、过渡流和滴状流流型下微通道尺寸、两相流率、物性对液滴尺寸的影响。结果表明:液滴尺寸随微通道深宽比、连续相流率、黏度和毛细数的增加而减小,随分散相流率的增加而增加。用毛细数、两相流量比和通道深宽比对微通道内液滴尺寸进行了关联和预测,预测值与实验结果吻合良好。     

Experimental investigation and model improvement on the atomization performance of single-hole Y-jet nozzle with high liquid flow rate

Y-jet nozzle, as an efficient multi-hole internal-mixing twin-fluid atomizer, has been widely used for liquid fuel spray in many industrial processes. However, single-hole Y-jet nozzle with high liquid flow rate is indispensable in some confined situations due to a small spray cone angle. In this paper, the atomization performance of single-hole Y-jet nozzles with high liquid mass flow rates ranging from 400 to 1500 kg/h for practical semidry flue gas desulfurization processes was investigated by the laser particle size analyzer, and the effects of spray water pressure, atomizing air pressure and air to liquid mass flow ratio on the liquid mass flow rate and the droplet size distribution were analyzed. Moreover, the secondary atomization model was modified on the basis of previous random atomization model of Y-jet nozzle. The predicted results agreed well with the experimental ones, and the improved atomization model of Y-jet nozzle was well validated to design the nozzle geometry and to predict the droplet size distributions for single-hole Y-jet nozzle with high liquid mass flow rate.     

Intensification of production of O/W emulsions using oscillatory woven metal micro-screen (WMMS)

Using high porosity woven metal micro-screen (WMMS), a novel design oscillatory emulsifier had been used for intensification of production of relatively narrow size distribution oil in water (O/W) emulsions. The average droplet size increased with increasing the dispersed phase flow and decreased with increasing both the oscillation frequency and amplitude. The emulsion polydispersity decreased with increasing both oscillation intensities as well as dispersed phase flux. Although the change in droplet size with oscillation was reasonably predicted using a simple torque balance model based on Stokes oscillatory flow, both the flow patterns and the surface phenomena are more complex, and the final droplet size is affected by interactions between different operating and physical parameters.     

Particle formation mechanism in radical polymerization in miniemulsion based on in situ surfactant formation without high energy homogenization

Conventional radical polymerization of styrene at 70 °C in aqueous miniemulsion generated using the in situ surfactant technique, without use of high energy mixing, has been investigated in detail. The surfactant potassium oleate was formed in situ by reaction between oleic acid and potassium hydroxide at the styrene/water interface. The particle formation mechanism was investigated by use of pyrene as a probe, revealing that under suitable conditions with an oil-phase initiator, particle formation occurs primarily via monomer droplet nucleation. The droplet/particle stability is however inferior to that in a typical miniemulsion generated employing ultrasonication, as manifested by a marked increase in droplet/particle size with conversion and a bimodal droplet/particle size distribution by weight. The droplet/particle stability increases with increasing amount of oleic acid, hexadecane, water, and the ratio potassium hydroxide:oleic acid, respectively.     

Stabilization of Water Droplets in an Oily Matrix Exclusively by Gel Formation

As droplets in emulsions are thermodynamically unstable, surfactants are required for their stabilization. However, these additives often are unwanted due to legal restrictions and possible health threats. Gelling of the aqueous phase poses one promising alternative. Only droplet‐forming processes like microfluidic devices are known to successfully work so far for stabilization by gelling. As these processes are hard to scale‐up and tend to foul, a technical alternative based on commonly used high‐pressure homogenization is investigated. A nozzle was adapted by adding a micromixer directly behind the orifice outlet. This allowed gelling and stabilizing the droplets by feeding a cold oil stream immediately after droplet breakup. Up to 40 wt‐% droplets with Sauter mean diameters down to the micrometer range could be successfully stabilized.