环隙气提式环流反应器中的气含率和液相循环流动

在筒体直径310mm、高2000mm的环隙气提式环流反应器实验装置中,对上流区的气含率、液相循环流动等流体力学特性作了研究.用漂流通量模型描述了上流区的气含率;通过对体系的能量耗散机理进行分析,基于体系总能耗最小的原理推导出液相循环流动方程,结果表明:用此方程能较好地模拟这种反应器内的液相循环状况.     

喷射环流膜生物反应器水力特性的研究

通过清水试验,确定了喷射环流膜生物反应器的最大吸气量,探讨吸气量、循环水量等因素对气含率、液相循环速度的影响,测定膜组件加入前后的气含率、液相循环速度大小,并与已有的生化反应器进行了比较.结果表明,装置的最大吸气量可达到0.67 m~3·h~(-1)吸气量是影响气含率的主要因素,并且随着吸气量的增加,气含率也随着增加;循环水量是影响液相循环速度的主要因素,随着循环水量的升高循环液速升高;膜组件的加入对气舍率、液相循环速度的影响非常小,与已有的生化反应器比较,JLMBR在水力特性方面具有明显的优势.所得结果可以为该类反应器的放大设计提供借鉴.     

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.     

三相循环流化床中的气液相界面积和传质系数

采用溶氧法测量了三相循环流化床中液相溶氧浓度的轴向分布,并按轴向扩散模型处理实验数据,优化得到气液体积传质系数kLa,同时用光纤探头测量了体系中的气含率和气泡大小分布,计算得到了气液相界面积a和气液传质系数kL,并研究了主要操作条件(表观气速、表观液速和固含率)对气液传质系数的影响规律.     

气升式环流反应器流动特性的数值模拟

应用Fluent计算流体力学软件，通过数值模拟的方法考察了气升式环流反应器内导流简直径、导流筒高度、导流筒安装高度以及液相进口速度对反应器内两相流动的影响。计算结果表明：导流简直径增大。液相循环量和上升段气含率均增大；导流筒高度增大，液相循环速度和循环量均增大，但是当导流筒的高径比增加到6．3后，液相循环速度和循环量反而减小；导流筒安装高度增加．液相循环速度及循环量均增大，升液管气含率降低；增加液相的进口速度，虽然上升段的液速有所增加，但是降液管循环液速及循环量基本不受影响。最后计算了反应器内液相速度随进口气速的变化情况，并与实际测量值进行了比较，模拟值和测氨值都表明随着进口气速的增加，液相循环速度随着进口气速的增加而增加．两者呈现良好的一致性。     

卧式矩形环流反应器中气含率和液相流动研究

针对矩形卧式多级串联环流反应器，在改变结构和气速的情况下，对全系统的气含率、上流区和下流区的气含率、液相循环速度、液相返混等进行了实验考察，并利用漂流模型，最小能耗原理等进行了模拟计算。     

鼓泡塔气液两相流内部流场的流体力学特性

采用计算流体力学CFD软件对鼓泡塔内部4种表观气速下内部流场的流体力学行为进行模拟。分析了鼓泡塔内部整体气含率及轴截面处（X=0）液相速度随时间的变化情况;并且对比了在不同表观气速下局部气含率和液相速度在不同高度处的径向分布情况。模拟结果表明,随着时间的增大,整体气含率增大速度比较快,到达稳定时间,整体气含率不再增大。在同一高度处局部气含率随着表观气速的增大而增大。H/D<3时,液相循环流动表现为单相循环流;当H/D=3时,表现为双循环流,流型较单相复杂。     

基于能量最小多尺度曳力模型的搅拌槽内气液两相流计算液体力学模拟及实验研究

采用双电导探针和欧拉-欧拉双流体模型对涡轮桨搅拌槽内局部气液分散特性分别进行了实验和三维计算流体力学(CFD)数值模拟研究。重点研究了转速对搅拌槽上下循环区局部气含率分布、全槽液相流场和湍动动能的影响。实验表明,转速对上循环区气含率分布的影响大于下循环区,且上循环区气含率随转速的增大而增大。CFD模拟比较了TOMIYAMA曳力模型和基于能量最小多尺度理论(EMMS)的DBS-Local曳力模型对局部气含率的预测结果。结果显示DBS-Local曳力模型能够较好地预测出不同搅拌转速下搅拌槽循环区气含率径向分布;TOMIYAMA曳力模型只能定量预测出低搅拌转速下(140r/min,280r/min)循环区的气含率分布,高转速下(420r/min,560r/min)该曳力模型不能模拟出下循环区壁面附近的气体,且低估了上循环区气含率。     

气液固三相环流反应器的研究进展

综述了气液固三相环流反应器的类型及工作原理、气液固三相环流反应器的特性参数(气含率、固含率、循环液速、液相体积传质系数、轴向分散系数)的测量方法和影响因素，介绍了特性参数的数学模型。并对现有模型进行了评述。对今后的研究提出一些建议。     

喷淋散射塔鼓泡区域的气液两相流动特性

为了探究喷淋散射脱硫塔鼓泡区域的气液两相流动特性,搭建了鼓泡塔实验台,在不同表观气速和气体分布器浸没深度的条件下进行了实验。实验结果表明:气体分布器表面形成的气泡直径约12 mm;气泡溢出液面时有小气泡形成,并随着返混的液相运动,且液相的返混剧烈程度与表观气速和气体分布器浸没深度正相关;液相在散射管管壁和鼓泡池壁面间形成大尺度循环;随着表观气速增大,气泡直径和气泡运动速度均增大,使得气含率增大,气液两相湍动加剧;随着气体分布器浸没深度增大,鼓泡床床层气含率降低,表观气速对气含率的影响效果减弱。实验结果对喷淋散射脱硫塔的设计和运行有一定参考价值。     

高长径比三相内环流反应器中细颗粒相含率和循环液速的分布研究

在高径比为22的三相内环流反应器中,在常温常压下以空气-水-石英砂为物系,研究了在不同粒径下上升区固含率、下降区固含率和上升区循环液速随表观气速的变化规律和不同粒径下轴向固含率的分布情况,以及在固体体积分数不同的条件下,平均气含率和上升区气含率随表观气速的变化情况。结果表明:当粒径(ds)≤0.3 mm时,上升区固含率随表观气速的增加呈平缓变化趋势,下降区固含率随表观气速的增加而增加;当0.3 mm相似文献   

Phase distributions in a gas–liquid–solid circulating fluidized bed riser

The distributions of the three phases in gas–liquid–solid circulating fluidized beds (GLSCFB) were studied using a novel measurement technique that combines electrical resistance tomography (ERT) and optical fibre probe. The introduction of gas into a liquid–solid circulating fluidized bed (LSCFB), thus forming a GLSCFB, caused the increase of solids holdup due to the significantly decreased available buoyancy with the lower density of the gas, even with a somewhat increased liquid velocity due to the decreased liquid holdup giving space for the gas holdup. The gas passed through the riser in the form of bubbles, which tended to flow more through the central region of the riser, leading to more radial non‐uniformity in radial holdup of the phases. The gas velocity has the most significant effect on the gas phase holdup. While the gas velocity also has an obvious effect to the solids holdups, the liquid flow rate had a much more considerable effect on the phase holdups. The solids circulation rate also had a significant effect on the phase holdups, with increasing solids circulation rate causing much more increased solids holdup in the central region than close to the wall. A correlation was developed for the relative radial distributions of solids holdup in GLSCFB, as such radial profiles were found similar over a wide range of operating conditions, like those in a typical gas–solid circulating fluidized beds (GSCFB). Finally, the axial solids profiles in a GLSCFB was found to be much closer to those in an LSCFB which are very uniform, than those found in a GSCFB which are less uniform and sometime having a S shape. Water was used as the continuous and conductive phase, air was the gas phase and glass bead and lava rock particles were used as the solid and non‐conductive phase.     

Axial hydrodynamic studies in a gas-liquid-solid circulating fluidized bed riser

Axial distribution of phase holdups was studied in the riser of a gas-liquid-solid circulating fluidized bed (GLSCFB). The effects of gas and liquid superficial velocities as well as solids circulation rate on radial distribution of phase holdups at different axial locations were investigated. Electrical resistance tomography (ERT) and optical fiber probe were employed online in the experiments for a precise determination of phase holdups. An empirical model was developed for the determination of gas bubbles in analysis of data obtained by fiber optic sensor. Gas holdup was higher at the central region of the riser and increased axially due to coalescence of small bubbles and decrease of hydrostatic pressure at higher levels in the riser. This led to an increase in solids holdup in regions close to the wall which was slightly higher than the solids holdup at the wall. Both solids and liquid holdups were lower in the central region and increased radially towards the wall. Gas holdup decreased with increasing solids circulation rate but opposite trend was observed for solids holdup. Solids circulation rate had negligible effect on liquid holdup at lower axial locations compared to top of the riser. Cross-sectional average of solids, gas and liquid holdups did not change significantly at higher liquid superficial velocities.     

Gas Holdup and Solid‐Liquid Mass Transfer in Newtonian and non‐Newtonian Fluids in Bubble Columns

Gas holdup and surface‐liquid mass transfer rate in a bubble column have been experimentally investigated. De‐mineralized water, 0.5 and 1.0% aqueous solutions of carboxy methyl cellulose (CMC), and 60% aqueous propylene glycol have been used as the test liquids. Effects of column diameter, liquid height to column diameter ratio, superficial gas velocity and liquid phase viscosity on gas holdup and mass transfer rate are studied. Generalized correlations for the average gas holdup and wall to liquid heat and mass transfer coefficients are proposed. These are valid for both Newtonian and pseudoplastic non‐Newtonian fluids.     

Hydrodynamic behaviour of a draft tube gas-liquid-solid spouted bed

Experiments were conducted using various types of solid particles to investigate the hydrodynamic properties of a gas-liquid-solid spouted bed with a draft tube. The hydrodynamic properties under study include flow modes, pressure profile and pressure drop, bubble penetration depth, overall gas holdup, apparent liquid circulation rate and bubble size distribution. Three flow modes were classified: a packed bed mode, a fluidized bed mode and a circulated bed mode. It was found that the friction factor accounting for the friction loss in the bed varies linearly on a logarithmic scale with the Reynolds number defined based on the apparent liquid circulation rate. The bubble penetration depth in the annular region, overall gas holdup and apparent liquid circulation rate increase with an increase in gas or liquid velocity. At high gas flow conditions an optimal solids loading exists which yields a maximum apparent liquid circulation rate. A model was proposed to describe the liquid circulation behaviour in the draft tube three-phas spouted bed. The average bubble size in the draft tube region is higher than that in the annular region for both the dispersed bubble regime and the coalesced bubble regime in the draft tube region.     

Macroscopic properties of liquid-solid circulating fluidized bed with viscous liquid medium

Experiments were conducted in a liquid-solid circulating fluidized bed to study the effect of liquid viscosity and solids inventory on pressure gradient, critical transitional liquid velocity, onset average solids holdup, axial solids holdup distribution, average solids holdup and solids circulation rate in circulating fluidization regime with riser operated in fixed inventory mode. The results indicate that critical transitional liquid velocity decreases with increase in liquid viscosity. The onset average solids holdup, on the other hand, increases with increase in either auxiliary liquid velocity or solids inventory. The variation of axial solids holdup distribution, average solids holdup and solids circulation rate with liquid viscosity when solid inventory was 0.15 m was dissimilar with either 0.25 m or 0.35 m solid inventory. Correlations were proposed for estimating the average solids holdup and are satisfactorily compared with experimental values.     

Heat transfer in three-phase (G/L/S) circulating fluidized beds with low surface tension media

Characteristics of heat transfer were investigated in a three-phase circulating fluidized bed whose diameter and height were 0.102 m (ID) and 2.5 m, respectively. Effects of gas and liquid velocities, particle size (0.5–3.0 mm), solid circulation rate (2.0–6.5 kg/m² s), and surface tension (47.53–72.75×10⁻³ N/m) of liquid phase on the heat transfer coefficient were examined. It was found that the heat transfer coefficient (h) between the immersed vertical heater and the riser proper of the three-phase circulating fluidized bed increased with increase in gas and liquid velocities, but did not change considerably with a further increase in liquid velocity, even in the higher range. The value of heat transfer coefficient increased gradually with increase in the size of fluidized solid particles without exhibiting the local minimum, which represented that there was no bed contraction in three-phase circulating fluidized beds due to the higher liquid velocity. The heat transfer system could attain a stabilized condition more easily with increase in particle size. The value of heat transfer coefficient increased with increase in solid circulation rate in all the cases studied due to the increase of solid holdup in the riser. The value of heat transfer coefficient decreased with increase in surface tension of liquid phase, due to the decrease of bubbling phenomena and bubble holdup. The decrease in liquid surface tension could lead to an increase in elapsed time from which the temperature difference between the heater surface and the riser became an almost constant value. The experimentally obtained values of heat transfer coefficient were well correlated in terms of dimensionless groups as well as operating variables.     

垂直管中零净液流量气液两相流的持液率研究

Zero net-liquid flow (ZNLF) is a special case of upward gas-liquid two-phase flow. It is a phenomenon observed as a gas-liquid mixture flows in a conduit but the net liquid flow rate is zero. Investigation on the liquid holdup of ZNLF is conducted in a vertical ten-meter tube with diameter of 76 mm, both for Newtonian and nonNewtonian fluids. The gas phase is air. The Newtonian fluid is water and the non-Newtonian fluids are water-based guar gel solutions. The correlations developed for predicting liquid holdup on the basis of Lockhart-Martinelli parameter are not suitable to ZNLF. A constitutive correlation for the liquid holdup of vertical ZNLF was put forward by using the mass balance. It is found that the liquid holdup in ZNLF is dependent on both the gas flow rate and the flow distribution coefficient.     

两级气液内环流反应器内气含率和循环液速

基于多釜串联可以有效减小返混的原理,通过引入特殊设计的级间构件构建了一种新型的两级内环流反应器。实验研究了级间构件形式、表观气速、表观液速和气液分离器对每一级内气含率和循环液速的影响。实验结果表明,表观气速对反应器二级(上一级)中上升管与下降管气含率之差和循环液速影响较大,而对一级(下一级)的影响较小;各级内上升管和下降管的气含率均随表观液速的增大而减小,但影响程度较小。基于推动力和阻力平衡建立了预测反应器中每一级的气含率和循环液速的流体力学模型,模型预测值与实验结果吻合较好。     

电导探针法测量高固含体系循环液速和气含率

基于电导探针和示踪法,开发了一种利用电导探针同时测量环流反应器中高固含体系下循环液速和局部气含率的方法. 利用2个单针电导探头测量脉冲注入KCl饱和溶液后两路电导信号的先后响应,测得两路液体的停留时间分布曲线. 通过对单路信号进行幅值分析可以得到气含率,与压差法相比测量值误差小于5%;通过对过滤气泡信号后的液体的停留时间分布曲线进行相关处理可得到循环液速,测量值与超声多普勒(UDV)的测量结果一致. 实验研究了外环流反应器中操作条件对气含率和循环液速的影响. 结果表明,低表观气速下气含率沿径向分布较均匀,高于0.1 m/s后逐渐呈抛物线型分布,整体随表观气速增加而增大;循环液速随表观气速增加近似线性增大,随固含率增加而减小.