LOCAL NONLINEAR CHARACTERISTICS OF GAS LIQUID SOLID THREE PHASE SELF ASPIRATED REVERSED FLOW JET LOOP REACTOR

Hursts rescaled range (R/S) analysis and Wolfs attractor reconstruction technique have been adopted to estimate the local fractal dimensions and the local largest Lyapunov exponents in terms of the time series pressure fluctuations obtained from a gas liquid solid three phase self aspirated reversed flow jet loop reactor,respectively.The results indicate that the local fractal dimensions and the local largest Lyapunov exponents in both the jet region and the tubular region inside the draft tube increase with the increase in the jet liquid flowrates and the solid loadings,the local fractal dimension profiles are similar to those of the largest Lyapunov exponent,the local largest lyapunov exponents are positive for all cases,and the flow behavior of such a reactor is chaotic.The local nonlinear characteristic parameters such as the local fractal dimension and the local largest Lyapunov exponent could be applied to further study the flow properties such as the flow regime transitions and flow structures of this three phase jet loop reactor.

LOCAL CHAOS CHARACTERISTICS IN A SELF ASPIRATED REVERSED FLOW JET LOOP REACTOR

The local chaos characteristics of the time series pressure fluctuations of gas liquid two phase flow in a self aspirated reversed flow jet loop reactor are studied by the deterministic chaos analysis technique. It is found that the estimated local largest Lyapunov exponent is positive in all cases and the profile is similar to that of the local fractal dimension in this reactor. The positive largest Lyapunov exponent shows that the reactor is a nonlinear chaotic system. The obvious distribution indicates that the local nonlinear characteristic parameters such as the Lyapunov exponent and the fractal dimension could be applied to further study the flow characteristics such as the flow regine transitions and flow structures of the multi phase reactors.

FRACTAL STUDIES IN A SELF-ASPIRATED REVERSED FLOW JET LOOP REACTOR

1 INTRODUCTIONSelf-aspirated reversed flow jet loop reactors,characterized by a well defined flow pat-tern,well better dispersing effects,relatively low power consumption and a high masstransfer coefficient,are widely used in chemical engineering,especially in biochemicalengineering.The characteristics of such reactors are highly random or stochastic due tothe influence of a variety of phenomena such as jetting and bubbling of the

FLOW AND DIFFUSION IN SELF-ASPIRATED REVERSE FLOW JET LOOP REACTOR

1 INTRODUCTIONGas and liquid distributions in a self-aspirated reverse flow jet loop reactor dependchiefly on the aspiration and the breakup against gas phase by the liquid nozzle aswell as the redistribution in the draft tube.It has also been noted that effective diffu-sion or backmixing in the reactor has great influence on the flow and mass transferrates.In this case,accurate descriptions about the fluid flow and diffusion conditions inthe reactor are most necessary for effective amplification of them.

LOCAL LIQUID-PHASE OHARAOTERISTIOS OF THE SELF-ASPIRATED REVERSED FLOW JET LOOP REAOTOR

The local liquid--phase characteristics of the gas--liquid two-phase and gas--liquid--solid threephase self-aspirated reversed flow jet loop reactor with a concentric gas--liquid injection nozzle were studied experimentally. They facilitate the evaluation of local phenomena. The local instantaneous liquid velocities at different axial positions of the reactor were measured by using the modified pilot tube.The local liquid-phase turbulent structural parameters such as time-averaged velocity. turbulent nuctuating velocity and turbulent micro scale were calculated with the aid of the statistical theory of turbulence. In particular, effects of liquid jet flowrates and solid loadings on the profiles of the liquid--phase turbulent structural parameter both in the jet effective region and in the tubular region inside the draft tube were discussed.

Numerical simulation of preparation of ultrafine cerium oxides using jet-flow pyrolysis

Ultrafine rare-earth oxides(REOs) are widely applied in all fields of daily life,but the conventional preparation methods are limited by a long procedure,low efficiency and severe environmental pollution.Our team has independently developed a jet pyrolysis reactor for the preparation of ultrafine cerium oxides,and this process has theoretical significance and practical application values.In this study,gas-solid pyrolysis reactions inside the jet-flow pyrolysis reactor were numerically simulated.We performed a coupling computation of the combustion,phase transformation and gas-solid reaction on Fluent and userdefined functions.We characterized the flows of different phases as well as the compositions and distributive laws of the reactants/products in the reactor.The gas-phase inlet velocity and dynamic pressure/additional pressure were related by a quadratic function.The velocity at the throat inlet changed the most,and the outlet velocity was very stable.The CeO2 concentrations were obviously stratified.This study enriches theories of jet-flow pyrolysis and theoretically underlies the optimization and popularization of self-developed pyrolysis reactors.

多室内环流反应器中液体循环量的试验验证与模拟

目的对液相氧化脱硫多室内环流反应器液体循环量的影响因素进行模拟和验证。方法采用CFD数值模拟,基于欧拉-欧拉多相流模型,对液相氧化脱硫多室内环流反应器进行气液两相流模拟,考查了酸气流量和空气流量对液体循环量的影响。结果利用数值模拟得到的液体循环量与利用靶式流量计测得的液体循环量误差小于10%。当酸气中H 2S体积分数不超过3%时,液体循环量(z)与酸气流量(x)、空气流量(y)之间的关系式为:z=-474.996+0.358 x+0.4873 y。结论欧拉-欧拉两相流模型能够准确地预测液相氧化脱硫反应器内液体循环量。

环流生物反应器降流区输氧浓度影响因素

环流生物反应器降流区输氧浓度主要受导流筒直径、导流筒溢流堰口高度及曝气量等因素影响,其对反应器污水脱氮除磷处理效果有重要影响。为考察以上影响因素对降流区输氧能力影响,采用数值模拟与实验结合的方法对环流反应器降流区输氧能力进行研究,通过自定义程序耦合Higbie传质理论模拟氧传质,对比不同曝气强度下反应器溶解氧浓度及溢流量模拟与实测值,结果显示误差在8%以内,表明数值模拟模型及方法正确可行。随后探究了曝气量、导流筒直径及导流筒溢流堰口高度对降流区输氧能力的影响。结果表明:曝气量由20 L/min增至50 L/min时,氧体积传质系数由2.04 h^(-1)增至4.45 h^(-1);导流筒直径由325 mm降至250 mm时,氧体积传质系数由3.99 h^(-1)增至4.42 h^(-1);导流筒溢流堰口高度由10 mm增至25 mm时,氧体积传质系数由4.17 h^(-1)降至4.00 h^(-1);增大曝气量和减小导流筒直径能明显提升降流区输氧能力。总之,可通过调整曝气量,导流筒直径及导流筒溢流堰口高度控制降流区输氧能力,以构建耗缺氧区域。通过响应面分析,得到导流筒直径250 mm、导流筒溢流堰口高度10 mm时,反应器降流区输氧能力较优。

一种连续流反应器内射流耦合搅拌流的混合特性

连续式搅拌反应器采用连续化工艺,可以保证生产过程的连续性,相较于传统反应器而言,连续式反应器内流场更复杂,进料口射流对于流场的影响较为明显。对传统的双层搅拌桨结构的微波反应釜进行连续化改造,基于计算流体力学CFD(Computational Fluid Dynamics)方法对不同射流方案下反应器内醇油混合液的流动及混合特性进行了数值模拟,得到反应器内混合液的流动特性和混合时间特征。结果表明:射流通过直接影响射流区的流场和改变反应器内的循环涡流位置间接影响全局流动;射流方向对于反应器内流型影响更大,逆时针射流时反应器内的速度梯度大,流体之间的剪切作用更强,混合性能最佳,相较于传统的间歇式搅拌反应器,混合时间缩短了33%。

气升式环流反应器实验及三维模拟

利用Fluent软件对气升式环流反应器进行三维全尺寸的数值模拟,采用欧拉多相流模型和标准κ-ε模型模拟反应器内气液两相流动,得到了反应器内流场的详细分布。在此基础上还结合FLOW 3D软件模拟物理流动现象,得到了直观的真实清晰动画,而传统的实验很难测得相关具体的数据。两种数值模拟结果与文献实验值吻合较好,说明了数值模拟的可靠性。

气-固环流反应器内瞬态流体力学特性的数值模拟

采用双流体模型和颗粒动力学理论,并考虑颗粒团聚现象对气固相间曳力的影响,对气-固环流反应器内的流体力学特性进行了数值模拟。模拟的时均固含率和颗粒速度与实验数据具有较好一致性,验证了模拟方法的可靠性。模拟结果表明:气-固环流反应器内瞬态固含率的分布具有典型聚式流态化的非均匀特征;压力脉动沿床层轴向的分布在一定程度上定性反映了气泡运动的信息;颗粒速度的时间序列和概率密度分布函数表明,床层各径向位置均存在颗粒的向上、向下运动,颗粒主体在床层内向上运动的同时还存在微观的内循环运动,模拟值为颗粒时均速度的径向非均一性宏观分布提供了合理的微观解释。

三相下喷式环流反应器的传质性能

在三相非牛顿型流体体系中，对下喷式环流反应器传质特性进行了实验研究。讨论了表观气速、能量耗散速率、导流筒直径与反应器直径比、喷嘴直径、导流筒下端距反应器底部的距离、固体装填量、羧甲基纤维素钠（ＣＭＣ）溶液浓度及其流变特性对它的影响。实验结果表明，容积传质系数随表观气速和能量耗散速率的增加有所增加，在实验条件下，发现最优的导流筒直径与反应器直径比在０．４～０．４５这一范围、固体装填量大约为３％（体积百分比）、导流筒下端距反应器底部的距离为０．０８ｍ左右。同时提出了容积传质系数的经验关联式。

导流筒结构对气升式环流反应器内气液两相流动的影响

使用欧拉-欧拉两流体模型研究了导流筒结构对气升式环流反应器内气液两相流动的影响。对物理模型进行了网格独立性的考察,使用Chisti关系式验证计算流体力学数值模型的可靠性,并在此基础上预测环己烷氧化反应器内导流筒直径、导流筒在反应器内的高度以及导流筒喇叭口的开度对反应器内气液两相流动的影响。模拟结果表明,导流筒上部增加喇叭口可有效提高反应器的气液分离能力,喇叭口直径增大,气液分离效果增强;导流筒直径增大,液相循环量增大,液相混合效果增强;随导流筒在反应器内的位置升高,液相表观速度和液相循环量呈增加的趋势并趋于稳定,而气含率则变化不大。

气升式环流反应器内气液两相流动计算流体力学的模拟

采用欧拉-欧拉两流体模型模拟了气升式环流反应器内部气液两相流动过程,考察了液相速度和气含率随表观气速的变化,液相速度和气含率模拟值的关系与两种经验关系式的计算值进行了比较,两者取得了很好的一致,证明了模型的正确性。在此基础上,使用计算流体力学模拟的方法考查了反应器内的导流筒直径和导流筒高度对反应器内两相流动的影响,导流筒直径增大,液相循环量增大,上升段气含率增大;导流筒位置升高,液相循环速度和循环量均增大,上升段气含率减小。所获得的结果对气升式反应器的设计优化具有指导意义。

反向流动垂直喷淋式MOCVD反应器设计与数值模拟

本文分析了现有的MOCVD反应器存在的不足,提出了一种新型的反向流动垂直喷淋式反应器:反应气体从基片上方的许多平行小喷管喷入反应区,反应后的尾气又从基片上方出口排出,从而减少了反应物浓度沿衬底径向的不均匀性。通过对反应器进行三维数值模拟,改变喷管的中心距、喷管端与衬底的距离、流量、气体压强等参数,确定了反应室内衬底上方温度场与浓度场为最佳时的参数组合。

带导流筒的下喷环流反应器的模拟及研究

本文通过引入二维拟均相κ－ε模型方程，建立了描述气液下喷环流反应器内管流区流体流动规律的数学模型，并进行了求解，模型值与试验值吻合较好。以空气－水－玻璃球为研究物系，对有导流筒的下喷式环流反应器中局部液相性能进行了较深入研究。

反应堆主泵压水室出口收缩角对水力性能的影响

针对国内某百万千瓦核反应堆主泵的水力性能要求,完成主泵叶轮和导叶的设计;为研究出口收缩角对水力性能的影响,设计了13种压水室出口收缩角,采用三维软件Pro/E完成了三维造型;利用计算流体力学（CFD）软件Fluent进行定常与非定常三维数值模拟,得到内部流场特性及计算点的压力脉动情况,并对其进行分析。结果表明：收缩角对压水室与出口交接处的前后区域影响显著,收缩角在12°~16°范围内,主泵效率均在70%以上,=15°时效率达最大值74.2%;在=15°且其他结构参数不变的情况下,随着流量的降低,主泵叶轮进口前和导叶出口处回流区域逐渐扩大;随着流量的增加,叶轮进口前回流区域逐渐向叶轮进口偏移;回流是引起压水室与出口交接处压力脉动的主要原因;偏离工况越大,压水室出口处的压力脉动波动越严重。

下喷自吸环流反应器内气相局部流动特性

The local gas phase flow characteristics of the gas-liquid two phase selfaspirated reversed flow jet loop reactor such as the radial profiles of gas holdup,bubble mean velocity and bubble size,using a miniature dual-sensor resistivity probe,were studied experimentally.A new digital processing method,based on threshold combinations of level and slope,was proposed for phase identification by the resistivity probe.In particular,the effects of the liquid jet flowrates on the local gas phase flow parameter profiles in the jet region and the tubular flow region inside the draft tube were discussed.

气体分布器结构对气升式环流反应器内气液两相流动的影响

使用欧拉两流体模型研究气体分布器结构对气升式环流反应器内气液两相流动的影响,预测了环己烷氧化反应器内单环结构、三环结构、五环结构的气体分布器时反应器内液相速度分布、气含率分布、液相循环速度以及液相微观混合特性。模拟结果表明,在等量的进气流量下,气体分布器环数增加,液相速度分布和气含率分布更趋均匀;气体分布器环数增加,液相推动力增加,从而使得液相循环速度增加,液相的宏观混合效果增强;气体分布器环数增加,导流筒内外的平均气含率增加。随机游走模型模拟结果表明,气升式环流反应器与普通鼓泡床反应器对气体分布器结构要求不同。

不同结构均质阀内流场的数值模拟与对比研究

根据相关实验数据,应用商用CFD软件Fluent对Stansted均质阀、射流均质阀、倒Z环均质阀内部流场的压力和速度等参数进行数值模拟研究.结果表明:任何一种均质阀流场内,压力骤减均发生在流道最窄处的始端附近,在流道最窄段均质压力沿流道释放;压力梯度不能唯一决定均质破碎效果;在流道最窄段的始端位置,速度变化与压力骤变明显对应,在其它位置,速度变化主要与流道结构以及固壁影响有关;复杂的固壁边界,引起流动的剧烈变化,增强剪切、撞击等作用,有利于均质作用的微细化效果.