Experimental study of oscillation behaviors in confined impinging jets reactor under excitation

Dynamic behaviors in a three‐dimensional confined impinging jets reactor (CIJR) under excitation were experimentally studied by a flow visualization technique at 75 ≤ Re ≤ 150. The effects of inlet Reynolds numbers (Re), excitation frequencies and excitation amplitudes on the oscillation behaviors in CIJR have been investigated by a particle image velocimetry (PIV) and a high‐speed camera. Results indicate that the excitation in the inflow of the opposed jets can induce periodic oscillation of the impingement plane along the axis, whose oscillation frequency is equal to the excitation frequency. At Re ≤ 100, the induced axial oscillation can further cause a deflective oscillation with a frequency nearly equal to the excitation, and the scale of the vortex in the impingement plane is well regulated by the excitation frequency. At Re = 150, the excitation of amplitude less than 20% has insignificant effect on the deflective oscillation existing in CIJR. A semiempirical formula has been proposed to predict the oscillation amplitude of the impingement plane in CIJR under excitation. © 2014 American Institute of Chemical Engineers AIChE J, 61: 333–341, 2015     

基于制备超细复合含能材料的对置受限式撞击流反应器微观混合性能

由于对置受限式撞击流反应器较高的传热及混合效率,能够制备出粒径小、均匀且分布范围窄的超细颗粒。本文采用碘化物-碘酸盐平行竞争反应体系研究入射速度、结构尺寸对对置受限式撞击流反应器微观混合效果的影响规律,并将混合腔尺寸同等比例放大一倍进行对比研究。结果表明,随着入射速度的增大,离集指数减小,微观混合效果提高。喷嘴间距与喷嘴直径比的增大使得离集指数增大,微观混合效果降低。离集指数随着混合腔高度、混合腔出口尺寸的增大呈现先增大后减小的趋势,且混合腔高度对混合效果的影响较混合腔出口尺寸显著。将对置受限式撞击流反应器混合腔尺寸扩大一倍,离集指数增加到原来的2.4倍,微观混合效果显著下降,但是在较大入射速度下,两种结构的混合效果差距减小。研究结果可为纳米复合含能材料的制备提供高效、安全的技术支持。     

An elastic analog model for controlling the impingement point position in confined impinging jets

Confined impinging jets (CIJs) are highly efficient mixers. The scales of mixing in CIJs are controlled by the opposed jets interaction. A mechanistic model is described here, which accurately predicts the impinging position of the opposed jets for a large range of flow rate ratios. The impinging point position is shown to impact the dynamic properties of the flow and the achieved mixing quality. The opposed jets kinetic energy ratio is shown to have a critical impact on mixing, similar to the Reynolds number. A mixing chamber design relation is proposed and verified for the opposed injectors diameters ratio, , which enables to operate CIJs under optimum mixing conditions for large ranges of flow rate ratios, viscosity and density ratios between the opposed streams. Optimum values have asymptotes for large and small Reynolds number depending on the process stoichiometry, viscosity, and density ratios of the opposed jet streams. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2200–2212, 2016     

撞击流反应器撞击面稳定性研究进展

撞击流技术因其良好的混合特性近些年用于强化制备超细粉体反应中的混合过程。撞击面的稳定影响反应器内的混合效果,所以本文对撞击面稳定性的研究进行了综述。撞击流反应器不同结构形式包括平面撞击流、轴对称撞击流和微型撞击流等。文中简述了撞击流稳定性的实验研究手段,分析轴对称撞击流反应器的径向偏转振荡的起止条件和不同喷嘴间距下的轴向偏移振荡规律,并且分析平面撞击流反应器的撞击面偏转周期以及偏转振荡的起止条件。得出轴对称撞击流与平面撞击流撞击面驻点的振荡对混合都有促进作用,并且偏移振荡周期不定,轴对称撞击面偏移振幅与喷嘴间距和雷诺数相关。平面撞击流的偏转振荡周期与进口流速成反比,反应器结构参数是撞击流稳定性的影响因素之一。根据轴对称撞击流偏移振荡对混合的促进作用,本文提出一种新型的预设流量波形双组撞击流反应器。新型撞击流反应器的独特结构克服了物料反应通道单一缺点,通过预设波形控制其进口流量,增大其撞击面偏移振幅,消除撞击面无序振荡,使流动轨迹扩展,扩大混合区域,并设计实验装置与方法讨论动态流量撞击流反应器撞击面稳定性对混合效果的影响。最后,本文对轴对称撞击流反应器的混合性能研究前景进行展望。     

Experimental and numerical characterization of viscous flow and mixing in an impinging jet contactor

The laminar flow in an impinging jet contactor is examined as a first step toward the development of new technology for fast mixing of viscous fluids. The flow, velocity, and stretching fields in an impinging jet contactor are quantified for low Reynolds number flow using three-dimensional numerical simulations and particle image velocimetry measurements. Computational and experimental velocity fields are in close agreement, as quantified by the velocity probability density functions. Two steady-state flow regimes are found to exist: for jet Reynolds numbers (Re_j) < 10, the jets do not impinge and the velocity field scales linearly with Reynolds number; for Re_j > 10, the jets begin to impinge and recirculation regions form above and below the impingement point. The magnitude of the rate-of-strain tensor is calculated as a function of Re_j. While areas of essentially zero stretching occupy most of the flow domain, very high rates of stretching occur at specific locations in the flow. The maximum and average rates of stretching in the contactor increase roughly linearly as a function of Reynolds number. Mixing simulations show that no mixing occurs for the steady flow in a symmetric-jet contactor. However, mixing is improved substantially by a slight modification of the impinging jet geometry that disrupts geometric symmetry.     

撞击流—旋转填料床反应器的微观混合性能研究

采用化学偶合法 ,对撞击流—旋转填料床反应器内微观混合进行了实验研究 ,得到了转速、喷嘴间距、射流速度及浓度等因素对离集指数Xs的影响规律 ,并对其进行了定性的分析。结果表明撞击流—旋转填料床反应器中微观混合能被极大地强化 ,可成为适合快速反应新型反应设备     

Characterization of micro-mixing in a novel impinging streams reactor

This paper presents an experimental investigation of a novel impinging stream reactor (ISR) with the aim of high mixing intensity. The integral mixing quality in the reactor was measured with the iodide-iodate reaction and showed excellent mixing performance. The impact of the operating parameters, such as fluxes, circulation and internozzle distances, was investigated in terms of segregation index. The results showed that the increase of flux, the decrease of inter-nozzle distance and a suitable circulation can improve the micro-mixing efficiency. Based on turbulence theory, it was estimated that the characteristic micro-mixing time was 0.002–0.02 s, which was much shorter than that in the stirred tank reactor. The micro-mixing time was related to the segregation index, which was in good agreement with those in the literature.     

Experimental investigation of flow regimes of axisymmetric and planar opposed jets

Dynamic behaviors of axisymmetric and planar opposed jets have been experimentally studied at 786 < Re < 6288. The flow patterns were investigated by a smoke‐wire technique, and the smoke‐wire photos were recorded by a high‐speed camera. Different flow regimes of axisymmetric and planar opposed jets have been identified. Axisymmetric opposed jets exhibit axial quasi‐periodic oscillations, stagnation point offsets, and steady states, while planar opposed jets exhibit both horizontal instabilities and deflecting oscillations. Effects of the nozzle separation and the exit Reynolds number on the dynamic characteristics of axisymmetric and planar opposed jets have been investigated and discussed. Maps of parameter spaces describing the flow regimes of axisymmetric and planar opposed jets at various nozzle separations and exit Reynolds numbers have been presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

小型受限撞击流反应器内混合特征及激励强化

利用平面激光诱导荧光技术(planar laser induced fluorescence,PLIF)研究了小型受限撞击流反应器(confined impinging jets reactor,CIJR)内混合特征及激励强化,射流入口Reynolds数范围为75~150。研究结果表明,在受限撞击流反应器内,由分离流模式向自持振荡模式转变过程中,两股流体间的混合效果逐渐提升;当流动为分离流模式时,激励能有效地强化两股流体间的混合,而当流动转变为自持振荡模式时,激励对流体混合的影响较小。     

Experimental study of the fluidic mixing in a cylindrical reactor

An experimental study of fluidic mixing in a cylindrical reactor was conducted in order to determine the effects of jet position and liquid viscosity. The tests were carried out in a tank of 0.09 m³ liquid volume using eight conductimetric probes to measure the mixing time. Relative jet positions leading to an impinging flow structure have been found to be less efficient than shear flow configurations. Mixing time and inhomogeneity correlations extending the previous results of Simon and Fonade (1993) are put forward for mixing by steady or unsteady jets.     

Trapping region of impinging jets in a cross-shaped channel

This study follows our previous report (Zhang et al., Phys. Fluids, vol. 31, 2019, 034105) by describing the formation and evolution of the engulfment flow in the cross-shaped channel. First, the flow regimes were studied by planar laser induced fluorescence (PLIF). Results show the formation of a spiral vortex in the center of the chamber and the appearance of a well-mixed zone inside the spiral vortex. Second, we proposed a novel experimental method to analyze the residence time of the fluid in the chamber, and discover an unexpected trapping region inside the well-mixed zone. There is almost no fluid transport into or out of this region. Furthermore, three-dimensional numerical simulation is used to reveal the origination of this trapping region. Simulation results reveal that the fluid recirculates in the trapping region and the flow feature is caused by the bubble-type vortex breakdown.     

Turbulent mixing in the confined swirling flow of a multi‐inlet vortex reactor

Turbulent mixing in the confined swirling flow of a multi‐inlet vortex reactor (MIVR) was investigated using planar laser induced fluorescence (PLIF). The investigated Reynolds numbers based on the bulk inlet velocity ranged from 3290 to 8225, and the Schmidt number of the passive scalar was 1250. Measurements were taken in the MIVR at three different heights (¼, ½, and ¾ planes). The mixing characteristics and performance of the MIVR were investigated using instantaneous PLIF fields and pointwise statistics such as mixture fraction mean, variance, and one‐point concentration probability density function. It was found that the scalar is stretched along velocity streamlines, forming a spiral mixing pattern in the free‐vortex region. In the forced‐vortex region, mixing intensifies as the turbulent fluctuations increase significantly there. The mixing mechanisms in the MIVR were revealed by identifying specific segregation zones. At Re = 8225 the mixing in the free‐vortex region was dominated by both large‐scale structures and turbulent diffusion, while in the forced‐vortex region mixing is dominated by turbulent diffusion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2409–2419, 2017     

撞击流反应器用于甲醇合成反应

撞击流反应器用于气液固三相甲醇合成反应可以充分发挥其优良的传热、传质性能。在撞击流反应器内,催化剂浆料经喷嘴雾化后成微米尺度的液滴,气液相间接触面积远大于其他三相合成反应器。考察了温度、压力、气体流量、浆料循环量以及喷嘴个数对甲醇合成反应的影响,结果表明,当压力从3.8 MPa上升到5 MPa时,反应器的时空产率增长了近1倍,气体流量达22.4 L·min^-1后时空产率几乎不再变化,增加浆料循环量以及在同一循环量下采用多喷嘴对置都可以增加催化剂时空产率。同时,与固定床、搅拌釜和浆态鼓泡床甲醇合成进行了对比,结果表明,在低空速下撞击流反应器与其他反应器时空产率相当,而在高空速下要优于其他反应器。     

撞击流反应器内幂律流体流动特性的数值模拟

采用数值模拟方法对撞击流反应器内幂律流体的流动特性进行研究,分析了不同喷嘴间距和入口流速下清水和不同质量分数幂律流体的径向射流扩展率、径向速度衰减率、剪切应力、表观黏度等分布规律,研究表明：幂律流体中径向射流的径向速度分布规律与清水径向射流相似。随喷嘴间距的增大,扩展率增大,径向速度衰减率减小,平均剪切应力呈先增大后减小的变化规律,其中L=3D时平均剪切应力值最大,更利于流体混合。入口流速越大,扩展率越小,径向速度衰减率越大,平均剪切应力也随之增大。幂律流体的平均剪切应力大于清水,且随质量分数的增大,其扩展率增大,为清水扩展率的1.3~3.3倍,而幂律流体的径向速度衰减率从-1.268~-1.125降低到-1.144~-1.082,逐渐小于清水。幂律流体径向射流区域的剪切应力呈“M”形分布,表观黏度则呈“W”形分布,流体的流变性质对撞击流反应器内流体的流动规律影响显著。     

Application of an air‐operated two impinging streams extractor in liquid‐liquid extraction and comparison with other contactor types

Extraction of succinic acid by means of normal butanol from its aqueous solutions (BSW), acetic acid by means of distilled water from kerosene (WAK) and iodine by means of kerosene from its aqueous solution (KIW) have been investigated in an air‐operated two impinging streams extractor (AOTISE) with spray nozzles. The effects of air flow rate, solutions flow rate, extractor length and diameter as well as modes of operation and impinging streams on extraction efficiency have been investigated. These results indicate that AOTISE is an efficient device for extraction processes. In addition, the overall volumetric mass transfer coefficients (K_La) are reported. The latter coefficients are important in design and may be used to compare the performance capability of various kinds of extractors.     

三股对撞式撞击流反应器微观混合性能研究

采用高速数码相机对三股对撞式撞击流反应器不同入口雷诺数下的流场特征进行了研究,并采用碘化物-碘酸盐平行竞争反应体系,考察了不同喷嘴直径下的入口雷诺数、不同溶液体积流量比对离集指数的影响。结果表明:入口雷诺数、溶液体积流量比对离集指数有明显的影响。增大入口雷诺数,三股流体高速撞击破碎成的液滴粒径逐渐减小,液滴雾化程度增加,离集指数减小,微观混合效果增加;增大体积流量比,溶液局部浓度增大,导致混合不均匀,离集指数增大。与传统撞击流反应器相比,三股对撞式撞击流反应器离集指数为传统撞击流反应器的2/5,表现出了较好的微观混合性能,更适用于不等溶液体积流量比的液液快速混合反应。     

撞击流反应器内涡特性研究进展

撞击流技术具有良好的混合效果,广泛应用于能源、环保、化工等工程领域。由于撞击流反应器流场内存在大量无序的湍流涡结构,使其具有良好的混合效果。本文基于撞击流的混合原理,详细叙述了撞击流反应器内不同混合尺度下的混合过程以及涡的演变对混合的影响。结合实验和数值模拟等研究结果,阐述了不同类型撞击流反应器和撞击流反应器多相流场涡特性,归纳了撞击流反应器流场涡的特点。论述了撞击流反应器涡的产生和脱落机理。着重对圆柱射流、平板射流和撞击流流场内涡特性的本征正交分解（POD）分析进行总结,利用流场能量的角度揭示涡演化和消散规律。最后,对开发新型撞击流反应器、优化分析方法等研究前景进行展望。     

不同工作因数下方波冲击射流的换热特性

应用数值模拟方法研究了不同工作因数下方波冲击射流的换热及流动特性,并分析了冲击靶面换热特性的变化规律。研究了冲击靶面换热特性随Reynolds数、脉冲频率、喷嘴距冲击靶面距离与喷嘴直径之比等参数的变化规律,重点分析了不同工作因数对冲击射流滞止区域换热与流动特性的影响,并将数值计算结果与连续冲击射流、脉动冲击射流实验结果进行对比验证。计算结果表明:当工作因数为0.5与0.7时,冲击靶面滞止区域Nusselt数非常接近;当工作因数为0.5时,壁面射流区域Nusselt数比工作因数为0.7时提高了10%;工作因数为0.9时,冲击靶面Nusselt数比连续冲击射流提高3%;工作因数为0.7时,相对于工作因数为0.5、0.9及连续冲击射流时,冲击靶面滞止区域存在强烈的涡结构变化。