鼓泡塔中液相环流速度分布模型

提出鼓泡塔中液相环流预测的一维流动模型和相应的湍流封闭关系式,并对模型求解方法进行了改进。通过模拟结果和文献数据的对比分析表明,环流速度与塔内液相的流型密切相关。在平稳鼓泡流和剧烈湍流两种流型下,应用本文推荐的涡粘系数关系式可预测液相环流速度的分布,精度令人满意。     

分布器对鼓泡塔中气泡直径分布的影响

采用电导探针测定了冷态鼓泡塔中不同气速下的气泡直径及气含率的轴向分布,考察了分布板对鼓泡塔操作性能的影响.结果表明:随着开孔率的减小,从均匀鼓泡区到过渡区的转变提前;在均匀鼓泡区,开孔率对气泡直径影响较小;在过渡区,开孔率大的分布器形成的稳定气泡直径较小、气含率较大;分布板开孔直径越大,形成的初始气泡直径越大,但对轴向气泡直径分布的影响仅限于分布器区.包含分布器影响的气泡直径经验关联式为d/D=140.2Bo-0.5Ga-0.12Fr0.099(h/D)-0.15T-0.34(0.5 cm/s＜ug＜7 cm/s).     

Bubble size distribution in cyclonic zone of a novel flotation column

In order to investigate bubble size distribution (BSD) in the cyclonic flotation column, a series of tests were conducted to study flow velocity distribution (FVD) and BSD by using the method of particle image velocimetry (PIV). Foaming performance of the n-octyl alcohol is more applicable than both of n-butyl alcohol and terpenic oil. At different circulation volume conditions, BSD range lies in 0–800 μm, and a large number of tiny bubbles (<90 μm) are generated. Besides, the curve presents a normal distribution in 90–180 μm. With the increase in circulation volume, bubble size decreases. BSD determined by cyclonic flow effect plays a crucial role on bubble mineralization with fine particle in cyclonic zone of the flotation column.     

Bubble Size Distribution in Oil‐Based Bubble Columns

A practical population balance model was used to evaluate the bubble size distribution in a bubble column. In addition, the bubble size distribution in the bubble column was measured at different gas velocities by photography and analysis of the pictures. Four types of liquid, i.e., water and three petroleum‐based liquids, were used in the experiments. The gas phase was air. It was found that the existing models in the literature are not able to satisfactorily predict the experimentally measured bubble size distribution. The model can be corrected by applying a correction factor to the energy dissipation rate. The corrected model fits the experimental bubble size distribution considerably better than the existing models. The variation of this correction factor is reported for different systems at different gas velocities.     

搅拌槽内的气泡尺寸分布

在槽径分别为Φ０．２８７ｍ、Φ０．４９５ｍ、Φ１．１００ｍ三个几何相似的搅拌槽内，采用双电导探针法测定了搅拌槽内上、下循环区及叶轮区的气泡尺寸分布，研究了单位液体体积搅拌功率、表现气速及搅拌槽放大过程对气泡尺寸的影响规律以及气泡尺寸的空间分布规律，并得到了相应的经验关联式，为气－液搅拌槽的设计放大提供参考。     

一个用于计算鼓泡塔平均循环速度的模型

A new model without any fitting parameter for estimating the mean liquid recirculating velocity has been derived from previous work direct]y. The prediction agrees with experimental data reasonably well. Accurency of prediction from the new model is comparable with the models reported in the literature. However, the new model has a potential capability to predict the average liquid recirculation velocity at elevated pressure bubble columns since n and c is developed under pressure. However this needs to be further tested experimentally.     

鼓泡塔中气泡尺寸分布和局部气含率研究

在内径为0.38 m的鼓泡塔中采用双电导探针法对不同通气速率下的气泡尺寸分布和局部气含率进行了实验研究,分析了气泡尺寸的概率密度分布。结果表明:气泡尺寸随轴向高度的增加而增大,随径向距离增加而减小;鼓泡塔中气液流动可分为过渡流域和充分发展流域,在过渡流域气含率随轴向高度增加而增大,在充分发展流域气含率趋于均值,径向局部气含率分布呈抛物线型下降。高气速下气泡尺寸概率密度分布比低气速下宽,且随轴向高度的增加分布变宽。     

Bubble characteristics in shallow bubble column reactors

The bubble characteristics have been investigated in an air–water bubble column with shallow bed heights. The effect of bed height, location and the presence of solids on the bubble size, bubble rise velocity and overall and sectional gas holdup are studied over a range of superficial gas velocities. Optimal shallow bed operation relies on the combined entrance and exit effects at the distributor and the liquid bed surface. The gas holdup is found to decrease with an increase in H/D ratio but the effect is diminishing at high H/D ratios. A H/D ratio of 2–4 is found to be suitable for shallow bed operation. The presence of solids causes the formation of larger bubbles at the distributor and the effect is diminishing as the gas velocity is increased.     

鼓泡床反应器内流动与传质行为的研究进展

总结了有关浆态鼓泡床反应器内流动、混合用气液传质特性的研究成果,详细地介绍了鼓泡床反应器内气含率、液速、液体轴向扩散系数、传质系数的测量方法,阐述了鼓泡床反应器性能的主要影响因素,如系统压力、温度、气体表观气速、液体性质及固含率等对流动、液相混合和传质特性的影响,并对鼓泡床反应器的应用前景进行了详述.     

用人工神经网络方法预测鼓泡塔气含率

A new correlation for the prediction of gas hod up in bubble columns was proposed based on an extensive experimental database set up from the literature published over last 30 years .The updated estimation method relying on artificial neural network,dimensional analysis and phenomenological approaches was used and the model prediction agreed with the experimental data with average relative error less than 10%.     

用神经网络法预测鼓泡塔内的气含率

在 2 0 0 0多组公开发表的鼓泡塔实验数据组成的数据库基础上 ,提出了一个预测鼓泡塔内气含率的关联式 ,介绍了一种新的神经网络回归方法。将该方法与受力分析结合起来得到 4个对鼓泡塔内气含率影响较大的无因次准数 ,对所得到的模型作出评价     

Artificial Neural Networks Modeling of Ozone Bubble Columns: Mass Transfer Coefficient,Gas Hold-Up,and Bubble Size

This study aims at applying artificial neural network (ANN) modeling approach in designing ozone bubble columns. Three multi-layer perceptron (MLP) ANN models were developed to predict the overall mass transfer coefficient (k_La, s^?1), the gas hold-up (? _G , dimensionless), and the Sauter mean bubble diameter (d_S , m) in different ozone bubble columns using simple inputs such as bubble column's geometry and operating conditions. The obtained results showed excellent prediction of k_La, ? _G , and d_S values as the coefficient of multiple determination (R² ) values for all ANN models exceeded 0.98. The ANN models were then used to determine the local mass transfer coefficient (k_L , m.s^?1). A very good agreement between the modeled and the measured k_L values was observed (R² ?=?0.85).     

Experimental Study on Bubble Rising and Descending Velocity Distribution in a Slurry Bubble Column Reactor

To determine bubble rising and descending velocity simultaneously, a BVW‐2 four‐channel conductivity probe bubble parameters apparatus and its analysis are used in gas‐liquid and gas‐liquid‐solid bubble columns. The column is 100 mm in internal diameter and 1500 mm in height. The solid particles used are glass beads with an average diameter of 17.82 μm, representing typical particle size for catalytic slurry reactors. The effects of superficial gas velocity (1.0 cm/s ≤ U_g ≤ 6.4 cm/s), solid holdup (0 % ≤ ?_s ≤ 30 %), and radial location (r/R = 0, 0.4, and 0.7) on bubble velocity distributions are determined. It is found that increasing U_g can increase the velocity of bubbles but do not exert much influence on bubble velocity distribution. Solid holdup mainly affects the distribution of bubble velocity while the radial direction affects bubble velocity distribution only slightly. The ratio of descending bubbles to rising bubbles increases from the bubble column center to the wall. It can be proved experimentally that large bubbles do not always rise faster than small bubbles at higher U_g (for example 6.4 cm/s).     

浆态床内固含率轴向分布的数值模拟

采用DBS曳力模型计算气液相间作用,分别采用Gidaspow曳力模型、经Brucato修正的Gidaspow曳力模型和Schiller?Naumann曳力模型计算液固相间作用,忽略气固间的直接作用,对比了浆态床内不同颗粒粒径体系轴向固含率的模拟和实验结果. 结果表明,不同液固相间曳力模型对气含率的预测影响不大;在颗粒粒径较大(140 ?m)的体系中,较低表观气速下气液DBS与液固Schiller?Naumann曳力模型组合模拟的固含率随床高度增加而减小,与实验结果吻合,而其它曳力模型组合的模拟结果较差,轴向分布较均匀;在颗粒粒径较小(35 ?m)的体系中,几种曳力模型组合的模拟结果均与实验结果吻合较好,轴向分布较均匀.     

鼓泡塔中气含量分布与液体循环流动模型

考察了气-液鼓泡塔中气泡流和液流的运动规律,提出了将分散的气泡流连续介质化的假设和基于容积通量的流体力学表达方式,建立了气含率分布与液体内循环流动结构的连续介质流模型,较好地揭示了液体循环流动规律. 模型计算与实验结果吻合.     

Bubble size distribution in a flotation column

The bubbles that were generated in a flotation column were measured. The bubble size distributions were obtained both for air-water and air-water-coal systems. The size distribution pattern was fitted to different equations. It was found that the bubble size distribution in both the flotation and cleaning zones follows the Rosin-Rommler equation used to describe the particle size distribution in crushing. This study indicates that bubbles in the cleaning zone are always larger than those of the flotation zone and finer bubbles are generated when a mixture of frothers is used instead of individual frothers.     

Bubble size distribution in a bubble column with vertical tube internals: Experiments and CFD-PBM simulations

Knowledge of bubble size distribution (BSD) is critical for controlling mass transfer and reaction in bubble column reactors. Installation of internals further complicates this issue. The effects of internals on BSD were systematically investigated through experiments and computational fluid dynamics-population balance model simulations. The experiments show a bimodal distribution of the volume-based BSD except at low superficial gas velocity of 0.01 m/s. Addition of 20% internals increases the small-bubbles fraction, making the first BSD peak more evident. Correspondingly, the simulation reveals a prominent decrease of turbulent dissipation rate and turbulent kinetic energy. Moreover, while the unresolved turbulent kinetic energy dominates in the empty columns, the resolved portion becomes the major component in the presence of internals. This suggests that internals may redistribute turbulent kinetic energy in each scale, which provides more insights into the complex flow characteristics in the presence of internals and process intensification.     

Relationship between Riser and Downcomer Gas Holdups in Semi‐batch Circulating Bubble Columns

Gas holdups were measured in a circulating bubble column (CBC) using air‐water system with various additives. The liquid volume in the gas separator affected downcomer gas holdup up to volume ratio equal to 6%. Presence of surface active agents, alcohols, solid particles had little effects on the gas holdups ?_gd — a?_gr relationships. The gas holdups relationships are theoretically related by a single parameter model ?_gd = a?_gr — a + 1, and empirically by two parameter model ?_gd = a?_gr — constant. The theoretical model yielded a values ? 0.45, while the empirical model yielded a values ? 1.16. Analogy between the two models (Contreras et al., 1998) will lead to incorrect conclusions.     

Simulation of Liquid Velocity Field in a Gas-Liquid Bubble Column

A simplified turbulent model and a modified k-Σ two equation model are proposed todescribe the liquid velocity profiles in a bubble column taking into consideration of the effect of gasdrag force and gas hold-up.In the simplified mode1 the Reynolds equation of motion was adoptedand the turbulent viscosity was calculated from an empirical correlation which was deduced fromour experimental data.The calculated liquid velocity profiles were compared between the proposedmodel and the standard k-Σ two equation model as well as experimental data.The result shows thatthe proposed model simulates and predicts the liquid velocity field most satisfactorily and in goodagreement with the experimental measurement.     

气液鼓泡塔内液体速度分布的测定

鼓泡塔作为一种常见的多相反应器,其中液体速度分布的研究一直是热点。本次实验选用用鼓泡塔高约5.5m,塔径0.5m。利用Pavlov管技术,在不同的操作条件下,我们对于塔不同截面处的液体速度分布进行了测定。实验表明,塔内液速分布呈半抛物线状。在无因次径向位置0.6-0.8左右处,液体速度方向发生改变。而影响转折点位置的主要因素是气相表观速度。