逆向气流对规整填料表面液膜流体动力学特性的影响

为研究气相流量对规整填料内气液两相逆流流动情况下流场结构及界面行为的影响,建立了基于分离涡模拟(DES)方法与VOF模型相结合的CFD分析模型,VOF控制方程离散采用显示差分格式,体积分数离散采用界面重构方法。计算域整体采用结构化曲线网格(贴体网格)划分,并对局部进行了细化。结果表明,气相F因子较小时(F≤1.354 Pa^0.5),液膜自由表面及其纵向速度分量(v_y)均呈周期性规律分布,波动幅度基本一致,而v_y均为负值。F=3.386 Pa^0.5时,液膜自由表面波动出现紊乱,幅值差异明显增大,而界面液膜v_y值仍基本呈周期性规律分布,在液相波峰下沿出现v_y >0的情况。F=5.418 Pa^0.5时,出现液相返混,气相和液相内均出现大小不等的回流区并随液相返混过程发展演化,同时局部液膜出现整体向上流动特征。F≥6.772 Pa^0.5后,填料下部出现干板区,底部出口不再有液相流出。随气相F因子增大,持液量和有效界面传质面积均先增后减。     

水平管环状流液膜厚度与波动参数分布

环状流是常见的一种气液两相流流型,基于双平行电导探针阵列传感器设计了环状流液膜动态测量系统,以水和空气为介质,进行了气相表观流速15~35 m/s、液相表观流速0.1~0.4 m/s范围内的水平管环状流周向液膜测量实验,分析了水平管环状流的液膜厚度、相界面波动参数的空间分布与发展变化规律。结果表明,水平管环状流底部液膜厚度随气相表观流速的增加而减小,随液相表观流速的增加而增大,但在高液相表观流速时有饱和趋势,对应条件下周向其他位置的液膜厚度持续增大,尤其在45°位置显著增大,下半周液膜分布趋于平缓;由底部到顶部,液膜波速和波频在周向上均呈逐渐减小趋势,与液膜厚度的分布规律一致,大幅度的扰动波主要分布在底部;底部液膜波速和波频随气相表观流速增加而增大,液相表观流速增加时,波速随之增大,但波频无明显变化,对应波长增大。     

管柱式气液旋流分离器液膜厚度的空间分布特性

管柱式气液旋流分离器（GLCC）是一种耦合离心力与重力的分离设备，其上部筒体内旋流液膜的分布特征显著影响其分离性能。液膜厚度作为该旋流液膜的关键参数，掌握其分布规律可为理解液膜的流动机制奠定基础。利用纽扣式电导传感器测量了GLCC上部筒体内的液膜厚度，通过改变入口气液相流量、入口喷嘴尺寸，系统地研究了其空间分布特性。结果表明，操作参数一定时，液膜厚度沿轴向向上趋于减小；在某一轴向位置，液膜厚度随入口气量的增大呈现“S”形分布，随入口液量的增大而近线性增大；此外，入口喷嘴尺寸对液膜厚度的分布影响显著：在不同的轴向位置，不同尺寸喷嘴对应的液膜厚度间的大小存在差异。液膜厚度随气液量的变化规律证明液膜逃逸是GLCC液相分离效率降低的直接原因，而喷嘴尺寸对液膜厚度沿轴向分布的影响则反映了GLCC旋流效应与重力效应间的相互作用。     

液相物性对规整填料内气液二相流的影响

运用商用流体计算软件FLUENT6.3,建立基于Navier-Stokes方程和VOF方法相结合的CFD分析模型,湍流结构模拟采用RNG k-ε模型,研究了液相物性参数对规整填料内气液二相流体动力学特性的影响。采用文献实验测试结果对该模型进行了验证。重点研究了在一定逆向气流速度条件下液相密度和黏度等物性参数对液膜流动的影响。结果表明:在分析的液相物性参数变化范围内,填料表面均能形成一层稳定的液膜流,气相流场分布也基本一致。液相密度增加,界面液相速度均值增大,沿界面速度值波动幅度降低,填料持液量减小。液相黏度增大,界面液相速度均值减小,持液量增加。2个物性参数改变时,有效界面传质面积均保持在一定值范围内波动。     

液相物性对规整填料内气液二相流的影响

运用商用流体计算软件FLUENT6.3,建立基于Navier-Stokes方程和VOF方法相结合的CFD分析模型,湍流结构模拟采用RNG k-ε模型,研究了液相物性参数对规整填料内气液二相流体动力学特性的影响。采用文献实验测试结果对该模型进行了验证。重点研究了在一定逆向气流速度条件下液相密度和黏度等物性参数对液膜流动的影响。结果表明:在分析的液相物性参数变化范围内,填料表面均能形成一层稳定的液膜流,气相流场分布也基本一致。液相密度增加,界面液相速度均值增大,沿界面速度值波动幅度降低,填料持液量减小。液相黏度增大,界面液相速度均值减小,持液量增加。2个物性参数改变时,有效界面传质面积均保持在一定值范围内波动。     

水平管环状流液膜厚度与波动参数分布

环状流是常见的一种气液两相流流型,基于双平行电导探针阵列传感器设计了环状流液膜动态测量系统,以水和空气为介质,进行了气相表观流速15～35 m/s、液相表观流速0.1～0.4 m/s范围内的水平管环状流周向液膜测量实验,分析了水平管环状流的液膜厚度、相界面波动参数的空间分布与发展变化规律。结果表明,水平管环状流底部液膜厚度随气相表观流速的增加而减小,随液相表观流速的增加而增大,但在高液相表观流速时有饱和趋势,对应条件下周向其他位置的液膜厚度持续增大,尤其在45°位置显著增大,下半周液膜分布趋于平缓;由底部到顶部,液膜波速和波频在周向上均呈逐渐减小趋势,与液膜厚度的分布规律一致,大幅度的扰动波主要分布在底部;底部液膜波速和波频随气相表观流速增加而增大,液相表观流速增加时,波速随之增大,但波频无明显变化,对应波长增大。     

水平烧结管降膜蒸发器管外流动分析

烧结管由光滑圆管外表面烧结铝合金或铜合金粉末制备，用于水平管蒸发器传热元件，实现高效传热。模拟分析烧结层材质、喷淋孔流量和烧结层孔隙率对烧结管管外液膜分布的影响。结果表明：比较液柱截面及波峰截面的平均液膜厚度，铝合金烧结层减薄了52.22%,而铜合金烧结层减薄了56.12%,故铝合金烧结层液膜流动较稳定。当烧结层为铝合金时，在喷淋孔流量Q_v=140—200 L/h,液膜厚度随着流量增大而增大，增大幅度达到了16.52%。当Q_v=160 L/h时，流速随着液膜厚度增大逐渐减小；随着孔隙率增大，液膜厚度在周向角度θ=0°—160°时增大，在θ=160°—170°时减小。当孔隙率n=50%时，平均液膜厚度减薄率较小，表明液膜厚度均匀性较好。2种烧结管表面均可形成连续的流动液膜，烧结层增大了工质接触管壁的传热面积。     

R32在水平微细圆管内凝结换热的数值模拟

采用VOF模型对R32在内径为1 mm水平圆管内的凝结换热进行了数值模拟.圆管进口饱和蒸气和壁面温度分别为40℃和30℃.假设气相为湍流、液相为层流,考虑重力和表面张力的影响,模拟分析了干度、液膜厚度和轴向速度沿管长的变化.结果表明,沿管轴向顶部液膜先增厚后基本保持不变,管底部液膜持续增厚.表明当量直径在1 mm时重力作用仍不可忽略.传热系数的模拟值随干度的增大而增大;与实验结果相比,模拟值小于实验值,但二者差别在实验误差范围内.     

管内垂直下降液膜速度与厚度分布特性

对洗涤冷却管内垂直降膜的流动特性进行研究,采用超声波多普勒测速仪对管内不同周向以及轴向位置的液膜厚度和速度进行了无接触式的测量,液膜Reynolds数范围为1.0×10⁴~3.1×10⁴。结果表明:在0°周向位置上液膜厚度与速度均达到最大值,导致该位置局部液膜厚度过大而不能保持稳定,部分液体脱离液膜表面,此外还造成了8°和16°位置的液膜厚度激增。在轴向上,当Reynolds数小于2.0×10⁴时,液膜速度在重力作用下随流动距离增加而增加,反之,液膜速度因为流动阻力会随距离增加而减小。随着Reynolds数的增大,液膜平均厚度和速度呈增大趋势。此外,Reynolds数的增大还会使得液膜更加不稳定。     

错流碟片旋转超重力场中液膜体积分率的实验研究

错流碟片旋转填充床反应器可有效脱除燃煤烟道气中的二氧化碳和其它有害成分,但液体分布状态对反应速率有很大影响,研究液膜的体积分率可为该类型反应器的设计提供有效的依据参数;实验研究了碟片转速、液体流量、气体流量、碟片间距和碟片开孔率与液膜体积分率的关系,用每张碟片底部对应液体收集器储存并测量碟片表面液膜的体积流量,用高速摄像机记录不同条件下液膜的存在状态和变化规律.研究表明随碟片转速增加液膜分率降低,增强的离心力促使液膜破裂,但液滴的甩出速率增加,促使液滴二次聚并,有不连续液丝产生.增大入口液体流量,液膜分率减小,液膜厚度变化缓慢,空间液滴增大.增大气体流量,液膜分率减小,厚度变薄,碟片表面附着液膜被吹散,促使液体雾化.液膜分率随碟片间距增加减小,提高碟片间距可有效减少液滴二次聚并;碟片开孔率增大液膜分率减小,提高碟片开孔率可有效降低碟片表面液膜的连续性,促使液膜分裂.     

液相流动方式对波纹规整填料性能的影响

根据液相在波纹规整填料片上呈现渗流、膜状流等不同的流动方式,选择5种不同的波纹规整填料对其流体力学和传质性能进行研究,以探究液相在波纹片上的流动方式对波纹规整填料性能的影响.研究结果表明,液相呈渗流流动的泡沫碳化硅波纹规整填料(SCFP型)有利于液体横向扩散和液膜均匀分布,当液相喷淋密度和气相F因子均较小时,其压降最低,传质效率最高;液相主要呈渗流流动、兼有膜状流动的双层错孔丝网填料(DMⅢ型)有利于波纹片两侧液体交换,强化液体在流动过程中的扰动,其压降及传质性能略逊于SCFP型填料;液相主要呈膜状流动的BX型、DMⅠ型及DMⅡ型填料波纹片表面液膜较厚,横向扩散能力差,其传质效率低于SCFP型和DMⅢ型填料.研究揭示了依靠渗流作用的波纹规整填料具有较好的应用性能,为波纹规整填料的进一步发展开拓了新思路.     

规整填料塔内两相流动的三维计算流体力学建模(英文)

Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.     

激光诱导荧光技术观测填料表面非等温降膜流动形态变化

非等温降膜流动在精馏过程中较为常见,其流动特性较为特殊,对填料表面的质量和热量传递有重要影响。本文搭建了可视化的实验装置,在保证液相室温进料的前提下升高填料温度,在规整填料表面构造液相被加热的非等温降膜流动,运用激光诱导荧光技术对液膜形态变化进行观测分析,对液体润湿面积、液膜厚度等参数进行比较。结果表明,随着填料温度的升高,液体润湿面积显著减小,波谷处液膜厚度显著增加,液膜逐渐收缩为沟流,填料表面的不规则液滴数目增多,干板现象越发严重。液体的聚并和分散轨迹消失,液相再分布及表面更新能力降低。因此,填料表面的非等温降膜流动液膜收缩现象十分明显,降低传热传质能力,需在工业生产中引起足够重视。     

大流量下倾斜管气液两相流实验研究

在较高的气液范围内,以水和空气为实验介质,在多相流实验平台上进行了倾斜向上的高产量气液两相流模拟实验研究。实验采用内径为40 mm、长8 m的透明有机玻璃管,并利用高速摄像仪记录实验过程中的流型。对实验流型进行分析,发现了倾斜管中低气流速下的一种新的流型-振荡冲击流,并研究了表观气、液流速和倾斜角对气液两相流动中压降的影响,建立气/液膜流动模型来分析表观气、液流速对压降梯度的影响作用,实验研究结果表明:在高气液量范围内,倾斜管中观察到的气液两相流型主要为振荡冲击流、过渡流和环状流,并且倾角对流型转变边界的影响不显著;振荡冲击流压降随气流速的增加而降低,环状流压降随气流速的增加而增加,过渡流压降梯度最小;倾斜管压降梯度随着倾斜角度的增加而增大。     

Liquid Flow on Structured Packing: CFD Simulation and Experimental Study

A CFD model of the two‐phase countercurrent flow in the geometry of the plate‐type structured packing Mellapak 250.Y was built, tested and verified. The model was applied to determine the effect of liquid and gas flow rates and physicochemical properties of the flowing liquids on the interfacial area formed on structured packing. The CFD model allowed us to determine the minimum liquid flow rate at which an unbroken liquid film was observed on the packing surface. The simulations confirmed that with an increase of the wetting rate the surface of the packing covered with a liquid film increased until the surface was totally covered up, while further slight changes of an interfacial area were the result of wave formation. The effect of gas load (F factor) on the film surface was in the range of a calculation error. Results of the CFD simulation allow us to predict the stages of film formation during liquid flow, to follow local velocity oscillations, film thickness and velocity profiles of phases.     

波纹板填料表面液体降膜流动的特性分析

基于降膜流动实验台,结合计算流体力学方法(Computational Fluid Dynamics, CFD)研究了波纹板表面液体的平均液膜厚度和有效润湿面积等定量信息,并通过三维模拟进一步分析了喷淋密度和波纹倾斜角度β对降膜流动特性的影响。结果表明,液体在波纹板表面的流动并非均匀,分为沟流和溪流两种形式;当喷淋密度较小时,液体在波谷内形成沟流,当喷淋密度达到400 m3/(m2?h),液体跨越相邻波纹进行溪流流动;两种形式波纹板整体的润湿性能均较差,且液膜厚度分布不均;波纹倾斜角度对降膜流动特性影响较大,90°时更有利于提高有效润湿面积。     

Pressure drop hysteresis in trickle bed reactors

An understanding of the hydrodynamics of trickle bed reactors (TBR) is essential for their design and prediction of their performance. Flow variables, packing characteristics, physical properties of fluids and operation modes influence the behavior of the TBR. The existence of multiple hydrodynamic states or hysteresis (pressure drop, liquid holdup, catalyst wetting, gas-liquid mass transfer) is due to the different flow structures in the packed bed and can be attained by a set of different operating procedures. Experiments were performed to study the effect of liquid and gas velocity, liquid surface tension, liquid viscosity and the particle diameter of the packing on two-phase pressure drop hysteresis. The parallel zone model for pressure drop hysteresis in the trickling flow was used for analysis of experimental data and flow structure. Theoretically predicted pressure drop hysteresis loop is in satisfactory agreement with experimental data.     

A new approach to fluid separation modelling in the columns equipped with structured packings

An analogy between the flow patterns in real separation columns equipped with structured packing and film flow is used to develop a new modelling approach. The packing is represented as a bundle of channels with identical triangular cross section. The dimensions of the channels as well as their number are derived from the packing geometry. The channel inner surface is wetted by a liquid flowing downwards, whereas the rest of the volume is occupied by a countercurrent vapour flow. Both phases are assumed to be totally mixed at regular intervals, determined by the corrugation geometry of the packing. The mathematical model is based on a set of partial differential equations describing hydrodynamics and mass and heat transport phenomena. These equations are complemented by the conjugate boundary conditions at the phase interface. A numerical solution of the model yields velocity profiles as well as concentration and temperature fields throughout the column. The model is verified using experimental data for a binary distillation in a column equipped with Montz-Pak A3-500.     

Experimental study of liquid distribution in a column with a structured packing

Reflective fiber optic sensors are used to measure the thickness of a liquid film on geometrically complex surfaces inside a distillation column with a structured packing and countercurrent flow of gas and liquid. Distributions of the liquid-film thickness as a function of flow-rate parameters for an elementary region (cell) of a geometrically repeated pattern in a structured packing consisted of Koch 1Y corrugated plates and for the column cross section are presented. It is shown that the flow conditions characterized by the detachment of liquid films from the plate by air flow (until the complete column “flooding”) is accompanied by a sharp increase in the pressure drop in the column. Inside the cell, the liquid forms menisci in the zone of plate contact points. The countercurrent air flow reduces the fluctuations of the film thickness by 1.5 to 2 times on the edge and side downslopes of the corrugation.