滴流床反应器内脉冲流下动持液量实验

对气液强相互作用下滴流床反应器内的流体动力学进行了分析讨论 .实验测定了脉冲流流型下的床层平均动持液量 .考察了气液流率、液体黏度、填料材料等因素对动持液量的影响 .根据对滴流床反应器内流体流动机理的分析及实验结果 ,提出了关联脉冲流型式下动持液量的关联式 .该关联式能很好地关联实验数据 ,可用于预测温和型脉冲流下的动持液量     

Liquid holdup in wire-mesh pads

The holdup distribution and pressure drop of five different wire-mesh pads have been investigated experimentally. The wire-mesh pad porosities ranged from 93.4 to 98.4 vol% and were tested at 1 bar with air as gas phase and water as the liquid phase. The liquid holdup in the mesh pads was measured at three locations. The results show variations in the holdup profile of the pads depending on geometry, surface area, gas velocity and measuring height. The results show that the Souders–Brown equation is a poor correlation for low pressure mesh pad design and identifies several mechanisms relevant for wire-mesh pad design. The data show that there is a strong correlation between surface area of the mesh pad and the flooding point.     

低含液率多相管路平均持液率

The experimental study on average holdup in multiphase pipelines with low loads of liquids was conducted on a large multiphase flow loop. The average holdup increased with increasing liquid load and decreased with increasing gas velocity, and also depended on the undulation of pipeline and flow patterns in the pipeline. The effects of eight dimensionless parameters on average holdup were seriated with grey relational degree analysis so as to find the most important factors affecting the average holdup in multiphase pipelines with low loads of liquids. An average holdup correlation based on low liquid loads was also developed and the correlation related the most important three factors including superficial gas velocity number (Ngw), superficial liquid velocity number (Nlw) and liquid Reynolds number (Rel) to the average holdup. Finally the correlation was tested with the field data and the result was satisfying.     

Gas holdup in a bubble column with immikible liquid mixtures

Experimental measurement of gas holdup was carried out in a medium-size gas-liquid-liquid bubble column with a multiple nozzle sparger plate using air, water and organic liquids. It was found that the fractional holdup depends on gas velocity, liquid properties, phase inversion in the liquid mixture as well as spreading coefficient of the organic liquid. In the presence of a liquid with a negative spreading coefficient the holdup is a minimum at the phase inversion point. but the reverse is true for a liquid with a positive coefficient of spreading. Observed bubble characteristics have been discussed. Correlations for gas holdup have been developed for different ranges of liquid composition.     

Prediction of dispersed phase holdup in a modified multi‐stage bubble column scrubber

This paper reports on the experimental investigation carried out to evaluate fractional dispersed phase holdup for a gas‐liquid mixture in a modified multi‐stage bubble column (with contraction and expansion disks), which has been conceived, designed and fabricated as a wet scrubber for control of air pollution; in addition it has versatile use as a gas‐liquid contactor in chemical process industries. A correlation developed for predicting fractional dispersed phase holdup has been found to be encouraging and highly significant from statistical analysis.     

Gas holdup in a two‐phase reversed flow jet loop reactor

Experimental investigations have been carried out in Reversed Flow Jet Loop Reactor (RFJLR) to study the influence of liquid flow rate, gas flow rate, immersion height of two‐fluid nozzle in reactor and nozzle diameter on gas holdup without circulation, that is, gas–liquid mixture in draft tube only (E_gd) and gas holdup with circulation loop (E_g). Also critical liquid flow rate required for transition from draft tube to circulation loop has been determined. Gas holdup was measured by isolation valve technique. Gas holdup in draft tube and circulation loop increased with increase in liquid flow rate and gas flow rate. It is observed that the increased flow rate is required for achieving a particular value of gas holdup with larger nozzle diameter. Nozzle at the top edge of draft tube have higher gas holdup as compared to other positions. It has been noted that, no significant recirculation of gas bubbles into the top of draft tube from annulus section has been observed till a particular liquid flow rate is reached. A plot of gas holdup with no circulation and with circulation mode determines minimum liquid flow rate required to achieve complete circulation loop. Critical liquid flow rate required to achieve complete circulation loop increases with increase in gas flow rate and is minimum at lowest immersion height of two‐fluid nozzle.     

Simultaneous effect of particle size and solid concentration on the hydrodynamics of slurry bubble column reactors

The simultaneous effect of particle size and concentration on the total gas holdup of slurry bubble column reactors was investigated in this work. The total gas holdup was measured for air–water–glass beads systems. Three solid concentrations and three particle diameters were used. It was found that increasing particle size at high constant concentration decreases gas holdup. Moreover, increasing solid concentration decreases gas holdup and this decreasing effect is higher for larger particles. Also, solid particles have two effects on hydrodynamics, namely, changing the viscosity and density of the liquid phase as well as hindering the bubbles from rising within the column by the collision phenomenon. Therefore, a novel correcting factor was introduced to correct the gas holdup. The hindering factor considers both the collision efficiency affected by the particle size as well as the solid concentration. A novel correlation was developed to predict the experimental data of the three-phase gas holdup.     

倾斜管柱气液两相流持液率计算方法研究

倾斜管柱气液两相流持液率的计算方法在石油工业中具有重要地位。采用Beggs-Brill相关式、Mukherjee-Brill相关式、Eaton相关式和杜克勒Ⅱ相关式计算了倾斜管柱的持液率,通过实验手段测量相同气液体积流量下,不同角度的持液率数据,分析了上述4种计算式的准确性,发现Beggs-Brill相关式比较准确。对Beggs-Brill相关式进行了分析,发现当其他条件一定时,其计算的持液率关于管柱倾斜角度具有一定的对称性,对称轴为50°,倾斜角度为90°时和10°时计算的持液率相等,结合所测量的实验数据,做出曲线发现在倾斜角度在45°到60°之间持液率最大,倾斜角度为90°的持液率与为10°的持液率比较接近,同时持液率随角度的变化具有一定的对称性。     

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.     

Hydrodynamics of a mobile bed contactor with ‘Low’ density packing particles of different shapes

Experimental studies have been reported on pressure drop, liquid holdup, bed expansion and minimum fluidization velocity in a 0.15 m ID mobile bed of relatively low density (53–183 kg m^?3) spherical and irregular shaped particles. The Kito-Tabei-Murata correlation has been adapted to fit the data on the liquid holdup and the pressure drop. The bed expansion was found to depend on the shape and density of the particles. It is shown that, in general, only a part of the liquid holdup in the bed is supported by the upward flow of gas. It was observed that in some regions the particles congregated at the wall, leaving a particle free core. The maps depicting these regions are presented.     

CFD analysis of two‐phase turbulent flow in internal airlift reactors

The hydrodynamic performance of three internal airlift reactor configurations was studied by the Eulerian–Eulerian k–ε model for a two‐phase turbulent flow. Comparative evaluation of different drag and lift force coefficient models in terms of liquid velocity in the riser and downcomer and gas holdup in the riser was highlighted. Drag correlations as a function of Eötvös number performed better results in comparison to the drag expressions related to Reynolds number. However, the drag correlation as a function of both Reynolds and Eötvös numbers fitted well with experimental results for the riser gas holdup and downcomer liquid velocity in configurations I and II. Positive lift coefficients increase the liquid velocity and decrease the riser gas holdup, while opposite results were obtained for negative values. By studying the effects of bubble size and their shape, the smaller bubbles provide a lower liquid velocity and a gas holdup. The effects of bubble‐induced turbulence and other non‐drag closure models such as turbulent dispersion and added mass forces were analysed. The gas velocity and gas holdup distributions, liquid velocity in the riser and downcomer, vectors of velocity magnitude and streamlines for liquid phase, the dynamics of gas holdup distribution and turbulent viscosity at different superficial gas velocities for different reactor configurations were computed. The effects of various geometrical parameters such as the draft tube clearance and the ratio of the riser to the downcomer cross‐sectional area on liquid velocities in the riser and the downcomer, the gas velocity and the gas holdup were explored. © 2011 Canadian Society for Chemical Engineering     

变径鼓泡浆液反应器的气含率特性

本文研究了变径鼓泡浆液反应器的平均气含率特性,考察了气体速度、静液床高、固体颗粒浓度以及颗粒直径的影响,并提出了变径鼓泡浆液反应器平均气含率的计算方法。     

Local gas holdup in a draft tube airlift bioreactor

Airlift column bioreactors are gas–liquid contact devices characterized by a rising channel and a down flow channel due to gas holdup differences in these two channels. Local gas holdup distribution strongly affects the overall gas–liquid flow dynamics in airlift columns. In this work, local gas holdup distributions in a draft tube airlift column covering both bubbly flow and churn–turbulent flow regimes have been studied using computed tomography (CT) technique as well as conventional techniques. The radial and axial evolutions of the gas holdup distribution will be discussed, together with the effects of superficial gas velocity and geometry parameters. The obtained gas holdup results will also be used to verify various empirical and semi-empirical correlations in the literature. Moreover, the obtained gas holdup information, combined with liquid flow dynamic information reported in Luo and Al-Dahhan, 2008a, Luo and Al-Dahhan, 2008b, forms a benchmark database for the design and scale-up of airlift column bioreactors and for computational fluid dynamic (CFD) modeling validations.     

Bubble columns with fine pore sparger operating in the pseudo-homogeneous regime: Gas hold up prediction and a criterion for the transition to the heterogeneous regime

New experimental data concerning the gas holdup in bubble columns equipped with porous sparger were acquired. The effect of liquid properties and sparger characteristic (i.e., pore size, dimensions) on gas holdup at the pseudo-homogeneous regime has been studied and a correlation regarding the prediction of the transition point from the pseudo-homogeneous to the heterogeneous regime has been proposed and found to be in good agreement with available data. Moreover, a previously proposed correlation [Mouza, A.A., Dalakoglou, G.K., Paras, S.V., 2005. Effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Chemical Engineering Science 60(5), 1465-1475], for the prediction of gas holdup at the homogeneous regime for this type of equipment, has been modified to take into account the effect of the mean pore diameter and it is also found to be in good agreement with published data.     

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.     

Prediction of Pressure Drop and Holdup for Homogeneous Ternary Mixtures of Spherical Glass Bead Particles in a Three-Phase Fluidized Bed

Hydrodynamic characteristics, viz. bed pressure drop and gas holdup, have been studied for ternary mixtures of homogeneous regular particles in a co-current three-phase fluidized bed. For this, a series of experiments have been carried out in a 5-cm diameter column with air as the gas phase, water as the liquid phase, and ternary mixtures of glass beads (1.54, 1.3, and 1.1 mm) as the solid phase. The dependence of bed pressure drop on the average particle diameter, superficial gas velocity, and initial static bed height has been discussed. Based on the dimensional and statistical analyses, correlations have been developed with the system parameters, for both bed pressure drop and gas holdup. Experimental values of bed pressure drop and gas holdup have been found to agree well with those calculated from developed correlations.     

Gas-holdup distribution and energy dissipation in an ejector-induced downflow bubble column: the case of non-Newtonian liquid

A precise knowledge of gas-holdup distribution and energy dissipation is essential for designing gas-liquid contactors. A semi-theoretical approach has been presented to obtain the axial distribution of gas holdup through the column for gas-non-Newtonian liquid two-phase flow system. The whole column is distinguished to have three zones based on gas holdup, viz. top, middle and bottom. The middle section where significant accumulation of bubbles takes place, contributes higher gas holdup towards the total compared to the other two sections. Energy dissipation in the column have been calculated from two-phase gas-liquid frictional losses. A comparative study shows that substantial gas holdup are observed in the present system with considerably lower energy losses. The experimental data of gas holdup have been correlated in terms of pressure drop by the modified Lockhart-Martinelli equation.     

OXYGEN TRANSFER IN THE WATER-JET VESSEL

This is an investigation of the gas holdup and the volumetric mass transfer coefficient of a plunging water jet in an air-water system. We sound k_La to be directly proportional to gas holdup in two regions. For the first time, this has been clarified in the plunging liquid jet system. The volumetric mass transfer coefficient and the gas holdup have been well correlated in terms of the Froude number, liquid jet length, nozzle diameter and vessel diameter.     

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.     

Experimental analysis and development of correlations for gas holdup in high pressure slurry co-current bubble columns

The effect of liquid and gas velocities, solid concentrations, and operating pressure has been studied experimentally in a 15 cm diameter air-water-glass beads bubble column. The superficial gas and liquid velocities varied from 1.0 to 40.00 cm/s and 0 to 16.04 cm/s, respectively, while the solid loading varied from 1 to 9%. The gas holdup in the column was reduced sharply as we switched from batch to co-current mode of operation. At low gas velocity, the effect of liquid velocity was insignificant; while at high gas velocity, increasing liquid velocity decreased the gas holdup. Drift flux approach was applied to quantify the combined effect of liquid and gas velocities over gas holdup. For co-current three phase flows, the gas holdup decreased with increase in solid loading for all pressures. But for batch operations, when solid loading was 5% or more, settling started leading to higher gas holdup. Increasing pressure from atmospheric conditions increased the gas holdup significantly, flattening asymptotically.