填料塔气体分布器二相流场计算流体力学数值模拟

填料塔内气体分布器对进料气流的分布作用和填料塔的分离效率,特别是对低压降、高效填料有重大影响。文中运用计算流体力学(简称CFD),采用欧拉-拉格朗日二相流模型建立了填料塔内双切向气体分布器内三维瞬态气液二相流模型,气体的湍流运动采用k-ε湍流模型计算。模型中考虑了二相之间的作用力,包括液滴所受的曳力和虚拟质量力。求解时时间项采用隐式格式,时间步长取1×10-4s,对流项采用二阶迎风格式,压力-速度耦合方程的求解采用了S imp lec方法。在不同操作条件下,模型计算得到的压降、夹带、气体分布不均匀度和文献报道的实验值吻合较好。从而可以看出,CFD模型可以较为准确地描述双切向环流式气体分布器内瞬时气液二相流场。     

气液两相流在文丘里管内的流动压降特性研究

本文选用数值模拟方法对文丘里管内气相与液相的混合流体的流动进行模拟。选取收缩管段的四个截面来分析文丘里管的压强变化情况,得到文丘里管内的气液两相混合流体的流场分布以及流量、气液比、收缩管长对压降的影响。     

塔板上流型变化对板效率影响的计算传质学

利用能够描述塔板上气液两相错流过程的流体力学模型,建立了同时模拟气液两相流动与传质过程的数学模型;通过对气液两相传质方程和流体力学模型方程的联立求解,计算得到了塔板上液相速度分布和气液两相浓度分布的数值解,考察了气相完全混合和气相部分混合两种条件下塔板上的气液两相浓度分布,同时考察了气相完全混合时流型变化对塔板效率的影响.     

带液滴辅助捕集结构的折板除雾器分离性能研究

采用Fluent对折板除雾器内气液两相流场、分离效率和压降进行数值模拟。气相采用SST k-ω模型,液滴相采用离散相模型。为改善分离性能,引入液滴辅助捕集结构,对比前后除雾器内的流场和液滴轨迹的区别,结果表明,后者气相湍动能增强、出口液滴轨迹线减少。通过改变各级捕集结构高度并进行组合,研究效率和压降随着进口粒径的变化。然后改变进口粒径分布,模拟27种不同高度组合下的分离效率和压降,得到最优的组合方式,对除雾器设计有一定指导意义。     

撞击式泡沫洗涤器流场数值模拟

采用k-ω湍流模型和拉格朗日两相流模型模拟了撞击式泡沫洗涤器内气液逆流接触的两相流场,通过分析中心截面的气相速度分布,可将气液两相相互作用区分为回流区、泡沫区和壁面环流区3个区域;探索用液相浓度分布来定量表征泡沫区即有效传质区的范围;考察了5种工况下洗涤器压降的模拟结果,并与试验结果相对比吻合较好(相对误差小于10%),验证了模拟的可靠性。     

旋转填料床气液两相流场的仿真分析

通过合理简化旋转填料床(RPB)结构,建立了三维物理模型,利用商用软件Fluent的计算平台,采用欧拉两相流模型和多孔介质模型对旋转填料床内的气液两相流场进行了仿真分析,深入分析了其压力场分布和速度场分布,并在此基础上对比了气相压降随旋转床转速变化的仿真结果与实验结果,两者变化趋势一致,表明所建立模型能近似地模拟旋转填料床的流场分布,并指导理论研究和实验研究进一步深入。     

微通道反应器内气液二相流压降的研究

以氮气和去离子水为研究体系,采用混合均质模型,在内径分别为900μm和500μm的圆形微通道中针对微通道反应器内气液二相流的压降进行研究。分析了黏度、气液表观速度等因素对微通道反应器中气液二相摩擦压降的影响。结果表明:均相流模型与分相流模型在微通道反应器内适用性均有限;采用Mc Adams黏度公式对微通道内的压降进行理论计算,其结果与实际测量所得压降值吻合良好;微通道反应器中的气液二相摩擦压降随气液二相表观速度的增大而增大;将实验结果与分相流模型的预测值进行比较,分相流模型中Lockhart-Martinelli关系式不能很好地预测微通道中气液二相流的摩擦压降。     

气液两相并流向下通过筛板孔口单元的压降特性

针对堆叠筛板填料的基本单元,采用12种不同规格的孔板,研究了气液两相并流向下通过孔口的压降特性,阐明了气液流量、孔板结构对压降的影响规律。结果表明：压降随气液流量的增加而增大;随孔径的增大而减小;在筛板常用厚度范围内,孔口锐缘效应使得压降随板厚减小而增大。根据孔口压降行为不同,以气相雷诺数Re_G=5000分界,建立了单一气相向下通过孔口的压降预测关联式;然后利用气相折算因子对关联式进行修正,得到了Re_G>5000时气液并流向下通过孔口的压降预测关联式;当Re_G<5000时,通过直接对单一气相阻力系数进行修正,得到了相应气相雷诺数范围内的气液两相压降预测关联式。     

颗粒负荷对小型旋风器性能影响的模拟分析

为探究颗粒负荷对小型旋风器内气固两相流动的影响,基于雷诺应力模型（RSM）和欧拉-欧拉方法的混合流模型（Mixture）进行气体-颗粒、颗粒-颗粒的相间耦合计算。采用粒径为0.5～5μm的颗粒组在40L/min、60L/min和80L/min的入口流量下模拟0~3kg/m³的5种不同颗粒浓度工况,通过对比旋风器内纯气相流场和颗粒负荷流场的不同,研究了颗粒的存在对流场的影响;探究了入口流量和浓度变化对旋风器内分离效率和压降特性的影响。基于模型有效性验证的数值模拟结果表明：较高颗粒浓度负荷使旋风器内的气相流场发生显著变化。随着入口流量的增大,旋风器的分离效率先增大后减小,压降呈非线性增大。随着颗粒浓度的增大,旋风器的分离效率逐渐增大,压降先减小后增大。     

气液螺旋环状流压降特性研究

考虑旋流衰减的影响,对气液螺旋环状流的压降特性进行研究并推导出了螺旋环状流压降预测模型。定义压降旋-直比系数为气液两相螺旋环状流和气液两相直流的压降之比,以此来表征旋流衰减对压降的影响。基于量纲分析的方法对压降旋-直比系数进行分析,推导出其表达式,压降旋-直比系数依赖于Lockhart-Martinelli 参数和气相Froude数变化。最终,得出了气液两相螺旋环状流的压降预测模型。在50 mm内径的水平管内对螺旋环状流的压降特性进行了实验研究,其中气相表观流速变化范围为10~16 m/s,体积含液率（LVF）变化范围为0.6%~4.8%。通过与实验数据进行对比,压降预测模型的相对误差在±15%以内,为工程应用提供了参考。     

双切向环流气体分布器结构优化的研究

双切向环流气体分布器性能的优劣与导流板和套筒结构的密切相关。优化导流板和套筒结构可强化双切向环流气体分布器的稳流性能,改善塔内流场分布。文中利用CFD软件采用k-ε湍流模型,对分布器内不同环形通道宽度下的流场分布进行了数值模拟。考察了套筒与塔壁的间距L变化对分布器性能的影响,并得出了在既定塔径下分布器性能达到最优时L的尺寸。通过模拟不同导流板数目和结构下塔内的流场分布,考察了分布器性能随导流板数目、轴向及径向倾角的变化趋势。分析得出使分布器压降最小,流场分布最优时挡板的结构参数。为工程设计时预测分布器的速度场及能量耗散提供参考。     

涓流床反应器泡帽分布板的两相流动及均布性能

用单泡帽装置可研究涓流床泡帽分布板的气液两相流动状态(Flow regimes)及压降性能.通过七个泡帽分布板的实验测定,得到均布所需的条件.本文证明:在喷射流动状态有利于液体分布,并提出简要的解释.泡帽分布板分布性能比降流营型好得多.对大型涓流床泡帽分布板的设计提出了有益的建议.     

布风板对磷矿混合颗粒流化特性与还原反应的影响

针对现有窑法磷酸工艺中磷矿还原率低、热质传递差、结圈堵料等问题,将流态化技术应用于磷矿的还原反应。通过对布风板压降、操作弹性、流化质量、高温流态化还原磷矿反应的研究,考察了4种布风板的性能,并与固定床的热模实验结果进行了比较。实验结果表明:随着气速的增加,直孔布风板的压降以二次函数的形式增长,斜孔布风板则呈现一次函数的关系,且斜孔布风板的阻力损失与床层压降均高于直孔布风板;对于圆面斜孔布风板,曲线压力波动最小,流化质量最好;斜孔布风板的磷矿还原率均高于直孔布风板,说明斜孔孔道有利于磷矿的还原反应;在硅钙摩尔比为3.0、反应温度1 300℃时,圆面斜孔布风板的还原率可达98.26%,且流化床还原磷矿较固定床好。     

SCX超细分级机进料管内气固两相流数值模拟

以两相流理论为基础,对SCX超细分级机进料管改进后内部的气固两相流动特性进行了数值模拟。分析了气相压力、速度、湍动能和固相颗粒浓度的分布情况,得到了进料管内气固两相的分布规律。结果表明,加入导流片之后,进料管内气相压力、速度、湍动能径向梯度减小,偏流现象减弱;导流片阻碍了固相颗粒的横向运动,改变了颗粒的运动轨迹,使得颗粒浓度分布更加均匀,为后续的分级提供了良好的基础。     

流化床管式分布器内流场模拟和布气性能分析

以催化裂化装置（FCCU）再生器的管式气体分布器为研究对象,对流化床管式气体分布器的布气性能进行了分析。首先,对气体分布器分支管内的流场进行数值模拟,计算结果表明沿分支管内气体流动方向,压力逐渐增大,截面流量逐渐减少,沿程喷嘴流量逐渐增大;同时分支管上游入口还存在着明显的偏流现象,从而导致了上游喷嘴的出口流量小于设计流量,下游喷嘴的出口流量高于设计流量,造成流化床内非均匀布气。然后,依据分支管的变质量流动特点,将一般变质量流动的动量方程用于分析分支管内的流动过程,表明分支管的流动过程属于“动量交换控制模型”,具有始端静压低末端静压高的特点,固有压力分布不均匀的特征。这种不均匀的压力分布导致了喷嘴布气不均匀和磨损等系列问题。最后,结合流化床内的压力特点,综合分析气体分布器的分支管压降和喷嘴压降,明确了喷嘴出口流量与分支管压力分布的关系,喷嘴临界压降与设计压降的关系,结论表明分支管的结构改进可以优化和改善分布器的布气性能。     

Modeling of the pressure drop and flow field in a rotating fluidized bed

Rotating fluidized beds (RFB) have found applications as dust filters, dryers, particle coaters, and granulators, and recently as catalytic reactors for the clean up of diesel exhaust. However, successful design and operation of an RFB requires an in-depth understanding of the fundamentals of the fluid dynamics involved. In this study, mechanistic models have been developed to account for the pressure drop relationship with respect to rotating speed, flow rate, properties of the granular particles, and fluidization conditions in the RFB. The models show that the total pressure drop across the bed is quadratically dependent on the rotating speed as well as the flow rate. These quadratic relationships have also been validated experimentally. The pressure drop relationship has further been validated through a full flow field numerical simulation of flow through a rotating bed with a slotted cylindrical distributor but without granular particles in the bed. Using our analytical model together with experimental results from three different types of distributors, a slotted cylinder with a thin metal screen, a perforated cylinder with a thin metal screen, and a sintered metal cylinder, three semi-empirical quadratic equations are obtained to predict the pressure drop across these distributors. A comparison of the distributor pressure drop with that across the fluidized bed (granules only) shows that the pressure drop across the distributor is appreciable and cannot be neglected in RFB applications. The higher the rotating speed, the more significant the pressure drop across the distributor.     

双锥导流式进气分布器内流场的数值模拟

双锥导流式进气分布器是针对大型反应器开发的进气均布装置,今利用FLUENT软件采用κ-ε 湍流模型,对其在不同结构参数下的流场分布进行了数值模拟.考察了分布器外锥对分布器性能的影响,通过改变外锥上导流槽的尺寸和方位,得出了在既定的床径下达到沿分布器内锥外表面压力均布要求时的外锥最优尺寸.通过模拟分布器内锥在不同的开孔率及四个不同锥角时床内的流场分布,考察了气体分布随内锥开孔率及锥角的变化趋势,分析得出使分布器压降低,流场分布最优时的内锥开孔率及锥角分别为0.89%、60°.并与实验测试结果进行了比较,模拟结果与实验结果基本吻合.     

MODELING OF THE PRESSURE DROP AND FLOW FIELD IN A ROTATING FLUIDIZED BED

Rotating fluidized beds (RFB) have found applications as dust filters, dryers, particle coaters, and granulators, and recently as catalytic reactors for the clean up of diesel exhaust. However, successful design and operation of an RFB requires an in-depth understanding of the fundamentals of the fluid dynamics involved. In this study, mechanistic models have been developed to account for the pressure drop relationship with respect to rotating speed, flow rate, properties of the granular particles, and fluidization conditions in the RFB. The models show that the total pressure drop across the bed is quadratically dependent on the rotating speed as well as the flow rate. These quadratic relationships have also been validated experimentally. The pressure drop relationship has further been validated through a full flow field numerical simulation of flow through a rotating bed with a slotted cylindrical distributor but without granular particles in the bed. Using our analytical model together with experimental results from three different types of distributors, a slotted cylinder with a thin metal screen, a perforated cylinder with a thin metal screen, and a sintered metal cylinder, three semi-empirical quadratic equations are obtained to predict the pressure drop across these distributors. A comparison of the distributor pressure drop with that across the fluidized bed (granules only) shows that the pressure drop across the distributor is appreciable and cannot be neglected in RFB applications. The higher the rotating speed, the more significant the pressure drop across the distributor.     

Distributor effects near the bottom region of turbulent fluidized beds

The distributor plate effects on the hydrodynamic characteristics of turbulent fluidized beds are investigated by obtaining measurements of pressure and radial voidage profiles in a column diameter of 0.29 m with Group A particles using bubble bubble-cap or perforated plate distributors. Distributor pressure drop measurements between the two distributors are compared with the theoretical estimations while the influence of the mass inventory is studied. Comparison is established for the transition velocity from bubbling to turbulent regime, U_c, deduced from the pressure fluctuations in the bed using gauge pressure measurements. The effect of the distributor on the flow structure near the bottom region of the bed is studied using differential and gauge pressure transducers located at different axial positions along the bed. The radial voidage profile in the bed is also measured using optical fiber probes, which provide local measurements of the voidage at different heights above the distributor. The distributor plate has a significant effect on the bed hydrodynamics. Owing to the jetting caused by the perforated plate distributor, earlier onset of the transition to the turbulent fluidization flow regime was observed. Moreover, increased carry over for the perforated plate compared with the bubble caps has been confirmed. The results have highlighted the influence of the distributor plate on the fluidized bed hydrodynamics which has consequences in terms of comparing experimental and simulation results between different distributor plates.