在鼓泡塔中平板电极和扩张金属电极上的质量传递

本文测定了置于鼓泡塔中心处的平板电极和扩张金属电极上的质量传递速率,在电解液物理性质不同和改变气体速度的条件下,对不同类型的扩张金属进行了研究,在有些情况下,得出传质系数的增量超过平板电极值的100%。不同体系、均存在无量纲关系。术语A 平板网眼孔径 D 扩散系数Dc 塔直径 g 重力加速度Ga 加利略数 gl~3/υ~2 Gr 格拉肖夫数 gΔQL~3/QL~2K 传质系数 L 电极高度r 径向位置 R 塔半径Re 雷诺数 RhVs/γ Rh 液压半径ε/(?)Sc 施密特数 L/D Sh 西尔乌得数 KL/DVs 表面速度 C 气泡空隙百分数εM 扩张金属孔隙率υ动态粘度Q 密度 (?)单位体积上的电极面积ψ单位网面积上的电极面积1、绪论多年来,在化学工业中,已经把鼓泡塔用作吸收器、分离器、反应器和电化学电解槽等。尽管它们在经济上和操作都优于机械     

热态下鼓泡浆液反应器的气含率研究

本文在热态条件下，研究了鼓泡浆液反应器的气含率、反应器直径为0.098m，物系组成为氮气－液体石腊－石英砂。考察了气速、压力、温度、静床高及固体引入等因素对气含率的影响。对于53μm粒子的三相浆态体系，气含率与表观气速关系式为εG=0.053uG^1.2。     

鼓泡塔内气液两相湍流实验研究

介绍了研究鼓泡塔气液两相流的实验装置、实验方法。液相用激光多普勒测速技术(LDV)测量,气相用粒子示踪测速技术(PIV)测量。实验表明,轴向液相速度的径向分布呈塔中心峰值、壁面附近倒流形式,且与气相表观速度大小有关,当液相表观速度一定时,随气相表观速度增大而愈加陡峭,返混也剧烈。当表观液速与表观气速之比小于19．6时,返混区总是存在,且返混区大小与高度有关：当表观液遣与表观气速之比大于19．6时,返混消失,含气率分布由塔中心峰值转向壁面峰值。径向液相速度既与气相表现速度有关又与位置高度有关,在塔底部呈现负值,这意味着向塔轴心方向流动。随着塔高增加。流动方向逐渐转变为向塔壁方向,且又有明显的峰值。     

鼓泡填料塔中水与餐厅污水氧传递特征

用不稳定传质模型对鼓泡填料塔中水和污水氧传递进行了理论分析,通过定义表面更新速率和含气率导出了鼓泡填料塔中水和污水中氧传递系数与操作条件和填料特征之间的关系式,并通过实验确定了关系式中特征参数.用关系式计算得到的氧传递系数与实测值基本吻合,最大偏差为20%.结果表明：采用的组合型填料具有优良的氧传递性能;在相同操作条件下餐厅污水中的氧传递系数小于清水中的数值.     

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。     

垂直风冷翅片管中氨水鼓泡吸收特性

详细描述了垂直风冷翅片管吸收器中氨水鼓泡吸收的传热和传质过程。管外侧套用翅片,管内侧中氨水吸收溶液和氨气都从吸收器的底部流入、顶部流出。根据质量守恒方程和能量守恒方程建立了热质传递的微分数学模型。该模型分析了吸收器中两相流(即波动流、弹状流、泡状流)的变化,同时考虑了不同的两相流中气液相之间的热质传递以及两相流与管外空气之间的热量传递。通过解模型的微分方程,得到了一些重要参数(温度、摩尔分数)的局部值以及这些参数在吸收高度方向上的变化趋势。     

鼓泡浆态反应器的传热研究

在内径为98 mm 的鼓泡浆态反应器内,研究了浸没表面与浆液之间的传热特性。在实验的条件下,模拟了浆态床 F—T 合成的操作。三相体系为氮气-液体石腊-石英砂所组成。实验中考察了不同因素对传热模系数的影响。采用95组实验数据进行关联,建立了新的传热模系数关联式:h/u_GρC_P=0.179[(u_G)~3ρ/ug]~(-0.25)(C_Pu/k)~(-0.66)该方程适用于气—液两相体系及小粒子三相浆态体系。     

多级鼓泡塔内液体速度分布的实验研究

液体循环流动是多级鼓泡塔重要流体力学特征之一,文中在内径为282 mm,高2000 mm的鼓泡塔内,采用不同类型的筛板将普通鼓泡塔分割成双级气液鼓泡塔.采用Pavlov管测液速的方法考察了不同筛板、不同表观气速下该鼓泡塔中上下二侧的液体速度分布.根据实验结果得出了液体速度在塔中心处最大,且与表观气速有关,随着表观气速的...     

超声场中鼓泡塔内气泡直径分布特征研究

利用自主研发的超声鼓泡塔和双电导探针气泡特征参数测量仪测定了不同频率组合下超声场辐射对鼓泡塔内气泡Sauter直径随表观气速和鼓泡塔径向及轴向位置的分布情况。实验结果表明,在距气体分布板轴向距离250 mm、塔中心处气泡Sauter直径由于超声作用而显著减小,最大减幅达55%;在超声场作用下随着表观气速增大,气泡Sauter直径呈增大趋势,当表观气速大于0.06 m/s时,气泡Sauter直径趋于不变;大气泡在塔中心区域聚集倾向明显,小气泡分布在塔壁面附近,气泡Sauter直径(在径向位置)呈现中心峰分布趋势;随着距气体分布板轴向距离增加,气泡Sauter直径增大,在多频混响声场中,气泡Sauter直径增速小于单频声场中增速,即在多频混响超声场中易形成小气泡。实验结果证实,超声场有利于减小气泡体积,增大气泡比表面积,这对于加强气液相间传质、提高传质效果会有显著作用。     

Gas hold-up and mass transfer in a bubble column with viscoelastic fluids

The influence of viscoelasticity on gas hold-up and the volumetric mass transfer coefficient in a bubble column is discussed and examined experimentally. It was found that the gas hold-up increased due to an increase in the number of entrapped very small bubbles formed because of the elasticity of the liquid. On the other hand, a decrease in volumetric mass transfer coefficient due to the fluid elasticity was observed. Qualitative effects of an antifoam agent and a draft tube on the performance of the bubble column with viscoelastic fluids were also examined.     

Heat transfer in a continuous bubble column

The effective thermal conductivity k_e was measured for a continuous bubble column operating within the bubbly flow regime. k_e was found to be independent of liquid flow rate but strongly dependent on gas flow rate and physical properties of the liquid phase over the ranges 0.1>u_G>4 cm/s, 0>u_L>3.4 cm/s, 0.00096> μ >0.0028 kg/m μ s and 0.047 >σ>0.072 N/m.     

Heat transfer and gas holdup studies in a bubble column: Air-water-sand system

Air-holdup and heat transfer coefficient data are reported for the air-water and air-water-sand system as a function of air velocity in the temperature range 297-343 K as measured in a 0.305 m diameter bubble column operating in semi-batch mode and equipped with either a five- or seven-tube bundle. A 65 μm average size sand powder is used at concentrations of 5 and 10 mass percent in the slurry. Available correlations of gas holdup and heat transfer coefficients are examined on the basis of these data. These are found inappropriate and inadequate for representing these experimental data. Gas holdup data are well represented by an approach based on Nicklin's (1962) work, and heat transfer data are adequately represented by a simple semi-empirical expression. Accurate experimental data on additional systems are needed to develop a reliable heat transfer theory particularly for process representation at temperatures higher than ambient.     

Gas-liquid mass transfer in the bubble column with viscoelastic liquid

The effects of liquid-phase viscosity, pseudoplasticity, and viscoelasticity on gas-liquid mass transfer in a bubble column have been investigated using aqueous solutions of sucrose, xanthan, polyacrylamide, and mixtures of xanthan and polyacrylamide. The elastic properties, considered in the form of the Weissenberg number, decreased the volumetric mass transfer coefficient by a factor of up to 5. The effect was strong even at low Weissenberg numbers encountered in many liquids, the elasticity of which is usually neglected.     

Survey of heat transfer mechanisms in a slurry bubble column

Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil‐free compressed air, tap water and 35 μm glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time‐averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model.     

Liquid-Solid mass transfer in a slurry bubble column and a gas-liquid-solid three-phase fluidized bed

Mass transfer coefficients between particles and liquids in a slurry bubble column and a three-phase fluidized bed containing small size particles were obtained with two mass transfer systems: (1) K⁺ –Na⁺ ion-exchange in cation-exchange resin bead beds, including anion-exchange resin beads as inert particles; (2) zinc dissolution by HCl in zinc-plated glass bead beds, and in beds of non-plated glass beads. Operating parameters were gas velocity, liquid velocity, particle diameter, and particle concentration. The dependence of mass transfer coefficients on these parameters is discussed from the viewpoint of the energy supplied into the systems. Correlations of the experimental data using dimensionless groups are compared to previous correlations.     

分散颗粒和超声场对鼓泡塔内传质性能的影响

用双电导探针气泡特征参数测量系统实时测定超声场与分散颗粒(活性炭)对鼓泡塔水+CO₂体系气泡Sauter直径和体积传质系数影响的变化规律。实验结果表明:无活性炭颗粒添加时,多频超声场比单频超声场更有利于提高体积传质系数,输入功率为100 W、组合超声频率为20-50-100 kHz时,体积传质系数增幅达40%~64%;加入活性炭颗粒后,体积传质系数随加入活性炭固含量的增大呈现先增大后逐渐减少的趋势,气泡Sauter直径变化规律相反,当体系中活性炭固含量为1.0 kg·m^-3时,传质增强最明显。体积传质系数随加入活性炭粒径的减小呈现增大的趋势。与无活性炭颗粒(d_s=0)比较,活性炭(固含率1.0 kg·m^-3)粒径d_s=38 μm时,液相体积传质系数在扣除吸附传质效果后仍增大1.58倍,同时引入超声场后,当组合超声频率为20-50-100 kHz,超声功率100 W时,液相体积传质系数增大2.02倍,可见超声场和分散颗粒对气液传质有显著的协同强化作用。     

Correlations for liquid-phase mass transfer coefficients in bubble column reactors with newtonian and non-newtonian fluids

The earlier work of Calderbank and Moo-Young (1961) dealing with the liquid-phase mass transfer coefficient in gas-liquid dispersions is examined. Their well-known empirical correlations for small and large bubbles which are free to move under gravity are theoretically derived. The analyses are based on the approach for natural convection mass transfer, and include the case where the fluid is non-Newtonian. The predictions of the models are compared with reported experimental data and correlations.     

Flow regimes and mass transfer in counter-current bubble columns

Counter current bubble columns have the feature that specific gas-liquid interfacial area and gas holdup are larger than those for standard and cocurrent bubble columns. In this study, three different flow regimes, churn-turbulent flow, bubble flow and bubble down-flow, have been observed in a counter-current bubble column and correlations of gas holdup and volumetric liquid-phase mass transfer coefficient have been proposed as functions of operating variables such as the superficial velocities of gas and liquid, the gas-liquid slip velocity and the liquid properties.     

Heat transfer in bubble column and airlift bioreactors: Newtonian and non-Newtonian fermentation broths

A theoretical model has been developed for heat transfer in bubble column and airlift bioreactors, which is applicable for Newtonian and non-Newtonian fermentation media. The proposed model is based on a similarity between heat transfer in gas-sparged pneumatic reactors and turbulent natural convection. The applicability of the proposed model was discussed using a wide range of experimental data, and good agreement was obtained.