一种新型板翅式换热器气液分配器分配特性的敏感性分析

两相流动分配不均是影响板翅式换热器换热效率的主要因素。传统的"先混合,后分配"方法不能解决在导流翅片中流向突变时气液分离引起的气液两相流体分配不均问题,因此采用"先分配,后混合"的理念提出了一种新型的气液分配器,气体和液体分别从各自的通道进入分配器,在分配器内均匀混合后进入换热器的翅片换热通道进行换热。通过对分配器内部流场的数值模拟,发现:分配器的气液分配不均匀度随流量的增加而增加,且不均匀度受液相流量的影响比气相大。该气液分配器的气液分配不均匀度相比传统封头结构降低了一个数量级,能够有效改善板翅式换热器层间通道的气液分配特性,提高板翅式换热器的换热效率。     

分布板对液固流化床换热器颗粒分布的影响

以三维Navier-Stokes方程为控制方程,结合k-ε二方程湍动模型,以直径为1 mm刚玉球作为颗粒相,水为流动相,采用隐式有限体积法对流化床换热器内的液固二项流动进行数值模拟.研究了换热器下管箱安装分布板与否及分布板板面结构形式对颗粒分布的影响,并通过下管箱内压力分布的实验结果对所采用的数值计算方法进行验证.结果...     

板翅式换热器两相流分配器

两相流体分配不均匀是造成低温换热器传热性能急剧下降的主要原因。在板翅式换热器两相流入口设置分配器是一种广为采用的改善分配特性的工程方法。本文以空气-水实验模拟系统研究了一种两相流分配器的分配特性。研究表明：所研究的气液分配器能够提高气液在板翅式换热器层间翅片通道分配的均匀性。     

预分布管内流场的CFD模拟及实验验证(英文)

Liquid distributor is a very import internal for distillation columns. Pre-distributor is usually set on the top of distributor for initial distribution. Fluid flow in pre-distributor is a complex system of variable mass flow with many orifices and sub-branches. Consequently, the two phase modeling of pre-distributors was carried out and the homogeneous model with free surface model was applied. The numerical method was validated by comparing with experimental data. Using the simulated results for different pre-distributors, the impacts of inflow rate, location and orientation upon the outflow distribution were investigated. Furthermore, influences of the outflow distribution for pre-distributor on liquid uniformity in trough were also analyzed. The conclusions can be adopted for the struc-tural design of liquid distributor and pre-distributor of large scale.     

并行微通道内气液相分配规律

微反应器的集成放大对于微化工技术的工业应用具有重要意义。利用高速摄像仪对4个并行微通道内气液两相流动状况及相分配规律进行了研究,考察了气液两相流量及液相黏度对两相分布均匀性的影响。实验所用液相为含0.3%表面活性剂十二烷基硫酸钠（SDS）的蒸馏水-甘油溶液,气相为氮气（N₂）。实验观察到了6种典型的两相流型。对各支通道均为弹状流情况下气泡长度和气泡速度的分布规律进行了研究。在一定气相流率下,各支通道气泡长度的相对标准偏差随液相流率的增大而增大,气泡速度的相对标准偏差值随液相流率的增大先升高到一定值然后逐渐减小。气相分配不均匀性随液相流率和黏度的增大而增大,液相分配不均匀性随液相黏度的增大而减小,气相流率的变化对于两相分布影响不明显。研究结果有助于并行微通道的结构设计与优化,以实现更为均匀的气液两相流动分配。     

固定床反应器中气液分配器的流体力学性能

设计了一种底部带有碎流板的新型管式气液分配器。以水和空气代替工业上的原油和氢气进行冷模实验。实验过程为:水由水箱经水泵抽出,经液体流量计计量后进入实验塔上部的气液扩散器,气液两相流经急冷箱冷却后同时向下通过分配器。进入到接液装置的液体通过橡胶管导入到放置在地面上的17个标有编号的量筒中,未进入接液装置的液体流入水箱,气体则排放到大气中。最后用U形管差压计测量分配器的压力降。实验研究了该分配器的分配性能、压力降损失、气液相操作弹性和分布不均度,优化并确定该分配器的结构形式和结构参数。结果表明,该分配器的最佳工作条件为:液相量为0.3m³/h左右,气相量为20~30m³/h。     

入口流速对间断微通道内流型演变及流量分配特性影响

微通道内气液两相流动规律是影响微通道换热器换热系数和流场温度均匀性的主要因素。以N2和H2O为工质，对间断、并联矩形微通道换热器内气液两相流型的起始、发展、稳定过程的演化以及并联通道内流量分配不均匀特性进行了数值模拟研究。结果表明，不同的进口Re对微通道内流型的演变过程和流动周期有重要影响，当进口Re为450时，气相工质在均流腔内以离散的散团状形态脉动扩散至微通道中，并联通道内气相工质从弹状流型态逐渐转变为泡状流型态；当进口Re增至为1600时，气相工质在均流腔内以较连续的椭圆状型态扩散至微通道中，并联通道内气相工质从环状流型态逐渐转变为泡状流型态。通道结构还将影响并联通道间的流量分配的均匀性，间断微腔的存在使微通道内工质质量流量分布均匀性提升38.7%，通过研究通道内压力分布规律，发现通道内静压的分布不均匀是导致两相工质从均流腔进入微通道时发生不均匀分配的重要原因。     

Design of an Efficient Gas Distribution System for a Fluidized Bed Dryer

Fluid bed dryers are commonly used to process granular solids. The design of the gas distributor has a significant impact on the performance of heat and mass transfer with or without chemical reactions in fluidized beds because it affects the quality of the fluidization obtained. In this work, an extensive study was carried out to design an optimal gas distribution system for a fluidized bed dryer. The air distribution chamber, also called a plenum chamber or gas chamber, was modified to obtain uniform air distribution across the bed cross section. Percentage maldistribution of the flow is considered as the basic evaluation parameter to quantify uniformity of the fluidizing gas distribution. Effects of various relevant design parameters such as the ratio of the orifice diameter to plate thickness (d_o/t), percentage free area, superficial gas velocity, etc., were examined experimentally and via modeling. The gas chamber was redesigned by inserting different types of packings in the chamber. In addition, the effect of height-to-diameter ratio (H/D) of the chamber on flow distribution was studied. Chambers of different H/D ratios and different air inlet nozzle diameters at various positions were examined to evaluate their effect on flow uniformity across the distributor. Three-dimensional computational fluid dynamic studies were carried out to evaluate the effects of pertinent parameters on flow uniformity, which has a direct bearing on the quality of fluidization and hence heat and mass transfer rates obtained.     

大型塔进料分布器二相流场数值分析

以大型塔器常用的双切向环流进料分布器为例,通过数值分析研究了气液二相流体在分布器中的分布规律。选用k-ε湍流模型和Lagrange二相流模型,模拟计算气液二相混合进料时,通过改变液气质量流量比,研究气液二相流动规律、分布器的压降及雾沫夹带,同时与只模拟气相流场的结果进行比较。结果显示,气液混合进料比气相进料时的气体分布不均匀度小,压降和平均湍动能则偏大,气液二相流场的计算更接近实际工况,这为大型塔分布器的设计及确定适宜操作条件提供了理论指导。     

A new streamlined bubble-cap distributor for high gas–liquid ratio and the liquid distribution mechanisms

The bubble-cap distributor is the most commonly used and critical internal for trickle bed reactors but holds the inherited disadvantage of liquid central aggregation when operating at a high gas–liquid ratio. A new bubble-cap distributor with a streamlined downcomer was developed in this paper to counter back the liquid aggregation and improve its comprehensive performance. The effect of the streamline parameters of the new distributor on liquid distribution was systematically explored by the coupled Euler–Euler-population balance equation (PBE) model. Compared with the classical and polyline converging–diverging structures, the results showed that the streamlined downcomer was a key to generating radial velocity of two-phase flow and reducing the liquid central aggregation for the bubble-cap distributor. The mechanism of well-distribution was explored for the new distributor. Lower converging and diverging angles enhance the distribution performance. A downcomer with a small converging angle and a 30° diverging angle was recommended for dispersing the central aggregated liquid column and acquiring the high distribution uniformity and spray covering circle. These data would be helpful to the optimal design and scale-up of the bubble-cap distributor in further industrial applications.     

THE EFFECT OF DISTRIBUTORS ON TWO-PHASE AND THREE-PHASE FLOWS IN VERTICAL COLUMNS

Two-phase air-water and three-phase air-water-solids flows have been investigated in a 0.152 m internal diameter vertical column. Pressure drop across the distributor and average phase hold-up were measured for two-phase and three-phase flows over flow ranges of superficial gas velocity from 0 to 259 m/s and superficial liquid velocity from 0 to 0.0346 m/s. Gas hold-up/pressure-drop ratios were obtained as a function of superficial gas velocity and liquid flow rate. It was found that the bubble cap was better at gas distribution than that of the Koch static mixer in two-phase and three-phase vertical flows. Drift flux to gas hold-up and drift flux to gas flow rate correlations were obtained for two-phase and three-phase vertical flows. Three flow patterns, churn-turbulent, transition and ideal bubble flows, were observed for vertical upflow.     

G-LISR不同气相入口流速对流场特性的影响

为了提高气液撞击流反应器(G-LISR)的混合性能,找到合适气相入口速度的操作参数,采用ANSYS Workbench中的Geometry模块,基于欧拉·拉格朗日法建立G-LISR气液两相流动数学模型。在加速管对置距离为400mm,液相入口速度为5m/s,三种不同的气相入口速度(10,15,20m/s)条件下,用数值模拟软件Fluent分析模拟出了不同气相入口流速下反应器内流场的分布特征。模拟结果表明:随着气相入口初始流速的增大,反应器内湍流强度有所增加,在压力波动最为剧烈的撞击面中心点处,压力急剧增大。增大气相初始流速,将降低反应器中的液滴的浓度分布,减少了液相在反应器中的停留时间。从能量损耗和气液两相在反应器中的混合效果来看,气相初始流速不宜过大,10m/s为较佳。     

Local mass transfer for tube banks in two-phase flow

The local mass transfer rate to tubes immersed in gas-liquid two-phase systems was studied using the electrochemical method. It was found that the mass transfer distribution around the tube perimeter is not uniform and depends on the geometry of the system, the properties of the liquid phase and the superficial gas velocity. Taking into account the analogy between heat and mass transfer, these results may be useful in both fields.     

基于临界分流理论的气液两相流均匀分配器

提出了一种新型气液两相流分配器,主要由旋流叶片、整流器、分流喷嘴以及分配腔室组成。通过采用“流型调整”与“临界分流”控制相分离。为研究不同分流比下的分配特征,设计了2喷嘴和4喷嘴两种分配结构。建立了气液两相流数值模型,模拟了气液两相流在分配器内流动特性。在气液两相流实验环道上进行了测试,气相折算速度范围为5.0～25.0 m·s^-1,液相折算速度范围为0.012～0.14 m·s^-1,实验中出现的流型包括波浪流、段塞流以及环状流。结果表明,在临界分流条件下,气液相分流系数主要取决于与侧支管相连通的分流喷嘴数目与总喷嘴数目的比值,不受流型、气液流速等参数波动的影响。对于2喷嘴分配器分流系数接近理论值0.5,对于4喷嘴气液分流系数约为0.25。     

文丘里型气液分布器的实验与数值研究

以一种文丘里型气液分布器为对象,在直径为28 cm的冷模装置中考察了其流体力学性能。气、液流量分别在5~25 m³·h^-1、0.2~0.6 m³·h^-1范围内,使用激光粒度仪测量了液滴Sauter平均粒径（D₃₂）,并测定了其分布均匀性和抗塔板倾斜性能。结果表明：文丘里结构加强了气液混合,与泡罩型分布器相比,此分布器具有更好的液滴破碎性能;气速增大会使出口液体从伞状流变为喷射流,但仍能在直径约为出口直径10倍的区域内均匀分布;在气、液相负荷分别为10~20 m³·h^-1、0.4~0.6 m³·h^-1时,液位在进液口和进气口之间,此时分布器具有优异的抗塔板倾斜性能。采用计算流体力学软件模拟了分布器内部气液流动过程,得到了相含率和速度矢量图,所得结果有利于分布器的分析与改进。     

对称分支并行微通道中气液两相流的均匀性规律

采用高速摄像系统研究了对称分支形并行微通道内气液两相流及弹状气泡均匀性规律。实验中分别采用含0.3% SDS的甘油-水溶液与氮气作为液相和气相。观察到弹状流和泡状流两种流型,作出了由两相操作条件构成的流型图及流型转变线。结果表明,气泡非均匀性主要由两微通道内流体之间的相互作用、下游通道中流体动力学的反馈作用以及通道制造误差造成。随液相黏度增大,气泡均匀性变好;在高液相流量以及低气相压力下操作,气泡尺寸分布更易达到均匀。基于压力降守恒原理和微通道内气液两相流阻力模型,构建了两通道中气泡尺寸的预测模型。     

Comparison of two-phase upflow and downflow fixed bed reactors performance: Catalytic SO2 oxidation

A time- and space-dependent model based on the piston-dispersion-exchange model for liquid flow was developed to analyze the performance of two-phase upflow and downflow fixed bed reactors and was applied to the catalytic SO₂ oxidation. The hydrodynamic parameters were determined from residence time distribution measurements, using an imperfect pulse method for time-domain analysis of nonideal pulse tracer response. A transient diffusion model of the tracer in the porous particle coupled with the PDE model was used to interpret the obtained RTD curves. Gas-liquid mass transfer parameters were determined by a stationary method based on the least square fit of the calculated concentration profiles in gas phase to the experimental values. It is shown that two-phase downflow fixed bed reactor performs better at low liquid flow rates, while two-phase downflow fixed bed reactor performs better at low liquid flow rates, while two-phase upflow performs better at high liquid flow rates.     

Numerical study of the effect of the gas and solids distributors on the uniformity of the radial solids concentration distribution in CFB risers

The non-uniform radial solids distribution usually has a negative effect on the performance of the circulating fluidized bed (CFB) riser since it may greatly decrease the reactor efficiency and controllability. In order to improve the performance of industrial CFB risers, the numerical study of the effects of the gas distributor and solids distributor at the CFB riser inlet on the uniformity of the radial solids distribution was carried out in this study. Two potential approaches to improve the uniformity of radial solids concentration profile were proposed: (1) the use of the center-sparse side-dense air jets arrangement for the gas distributor and (2) the use of the side-covered arrangement for the solids distributor. The Eulerian-Eulerian computational fluid dynamics (CFD) model with kinetic theory of granular flow was adopted to simulate the gas-solids two-phase flow in a CFB riser with FCC particles. The numerical results show that the patterns of the inlet gas distributor and solids distributor have significant effect on the flow structure in both the entrance region and the fully-developed region in the riser. The gas distributor with center-sparse side-dense air jet arrangement improves the uniformity of the radial solids distribution, while the center-dense side-sparse air jet arrangement steepens the non-uniformity of the solids radial profile. The core-annulus structure can be greatly flattened by applying a side-covered solids distributor, while it can be heavily steepened by employing the center-covered solids distributor.     

新型布浆器的布浆机理及流动特性

在分析了方锥管布浆器的设计方法的基础上,利用方锥管布浆器不均匀的布浆特性,提出一种新型布浆器,把两个结构完全相同的方锥管布浆器对称地上下叠放在一起,由于两个方锥管布浆器的支管束的质量流量分布趋势相反,在混合室内形成互补的混合状态,使混合室出口支管束的质量流量分布更接近期望值,提高了布浆器的布浆性能。采用数值分析方法研究了新型布浆器内浆料的流动特性和布浆机理。结果表明,新型布浆器的浆料在混合室内进行了互补式的充分混合,有效地消除了方锥管支管束出浆的不均匀性。混合室支管束的质量流量分布趋势接近于理论曲线,降低了与期望值的偏差,布浆效果更好,证明了新型布浆器的布浆机理和结构设计是合理的。     

Comparison of hydrodynamic and mass transfer performances of an emulsion loop-venturi reactor in cocurrent downflow and upflow configurations

Hydrodynamic parameters (gas-induced flow rate and gas hold-up) and mass transfer characteristics (k_La, k_L and a) have been investigated in a gas–liquid reactor denoted “Emulsair” in which the distributor is an emulsion-venturi and the gas phase is self-aspired by action of the kinetic energy of the liquid phase at the venturi throat. Two configurations, respectively cocurrent downflow and cocurrent upflow were compared. A chemical method involving the dispersion of a CO₂–air mixture in a monoethanolamine (MEA) aqueous solution was used to measure mass transfer parameters. Experimental results showed that only the homogeneous bubbling regime prevailed in the upward configuration, while an annular regime could also be observed for cocurrent downflow at low liquid flow rate. Gas-induced flow rate and gas hold-up were usually smaller for cocurrent upflow, both at constant liquid flow rate and specific power input. The same stood for mass transfer properties. Conversely, specific power requirements were lower at constant liquid flow rate and mass transfer characteristics were enhanced at constant gas-induced flow rate for cocurrent upflow. A comparison with other gas–liquid contacting devices showed that the Emulsair reactor is a versatile tool avoiding the presence of mechanically moving parts when high and quickly adaptable dissolved gas supply is required. The cocurrent upflow configuration can be preferred when high gas flow rates are desired because the evolutions of gas-induced flow rate and mass transfer characteristics exhibit a stronger dependence on specific power input in the homogeneous bubbling regime for this configuration.