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。     

Hydrodynamics of a flowing gas-solids suspension in a tube at high angles of inclination

A study was made of pneumatic transport of particles of sand suspended in air in a 31.8 mm diameter Plexiglas tube inclined at either 72 or 90 degrees with respect to the horizontal plane. The solids holdup, pressure gradient and pressure drop fluctuations over a 4.55 m test section were measured as functions of the air velocity and the solids flux. Previously observed sudden changes in slope of plots of solids holdup versus solids flux at constant gas velocity in a vertical tube (Mok et al., 1989), which were identified as transition points between dilute and dense phases, were confirmed and extended to inclined tubes. Breaks were also found in plots of pressure drop fluctuations versus solids flux at constant gas velocity.     

Gas holdup characteristics in a flotation column with different solids

This paper presents the effect of process variables on gas holdup. It was measured by volume expansion method in a continuously operating flotation column using coal and sphalerite. It was observed that addition of both solids reduced gas holdup. Increase in solid concentration and particle size reduced gas holdup. Also, increase in gas velocity and frother concentration increased the gas holdup as amount of gas increased and bubble surface property favored the formation of small bubbles. An empirical mathematical model was developed to predict gas holdup. The predicted results were in good agreement with the experimental and available published data.     

Size of bubbles and liquid circulation in a bubble column with a draught tube and sieve plate

The size distribution of bubbles and the liquid circulation in a bubble column with a draught tube and sieve plate were studied experimentally. The size of bubbles is well correlated with the previous result of the authors; the size distribution data are fitted reasonably well by a logarithmic normal probability distribution. Gas holdup in the draught tube and annulus and pressure drop were measured and correlations for these parameters are obtained. An energy balance is used to predict liquid circulating velocity using gas holdup and pressure drop correlations. Reasonable agreement is found between the calculated and measured circulating velocity.     

固液分布器中主分布器的实验研究

在不同结构形式的主分布器条件下，研究了表观液速对换热管中固含率、下管箱内床层高度、静压降及平均固含率的影响。利用体积容积法测量了换热管束中的固含率、刻度尺测量了下管箱中的床层高度、U形管测量了下管箱的静压降，并运用差压法测量了下管箱中平均固含率。采用不均匀度函数衡量了不同结构条件下管束间固含率的不均匀程度。实验结果表明：在换热管下方增加优化后的主分布器可以均匀分布固液两相；主分布器直径变化时对下管箱内流动特性的影响大于主分布器轴向位置改变时的影响。     

Gas holdup and overall volumetric mass transfer coefficient in a modified reversed flow jet loop reactor

Experiments were conducted in a modified reversed flow jet loop reactor having the liquid outlet at the top of the reactor to determine the gas holdup and overall volumetric mass transfer coefficient in the air-water system. The influence of gas and liquid flow rates, and the draft tube to reactor diameter ratio were studied. It was observed that both gas holdup and volumetric mass transfer coefficient increased with increased gas and liquid flow rates and were found to be significantly higher in the modified reactor compared to the conventional one. The optimum draft tube to reactor diameter ratio was found to be in the range of 0.4 to 0.5. Empirical correlations are presented to predict gas holdup and overall volumetric mass transfer coefficient in terms of operational and geometrical variables.     

三相环流反应器中的局部相含率

将压差法与气-液相间滑移速度相结合,提出了利用压差法测量三相区局部相含率的新方法,将测得的局部固含率进行轴向平均并与由颗粒装填量计算所得的固含率进行比较,证明了此方法的可靠性. 利用所提出的测量方法,考察了三相环流反应器中气含率和固含率随操作条件的变化规律. 结果表明,气含率随表观气速的升高而增大,且随轴向位置的升高而增大;大颗粒具有破碎气泡的作用,能够增大反应器内的气含率;固含率随表观气速的增加而降低,且沿轴向变化较大. 表观气速较高时,固含率沿轴向近似呈S形分布.     

Studies on cocurrent gas-liquid flow in helically coiled tubes. I. Flow patterns,pressure drop and holdup

The effects of tube diameter, coil diameter, helix angle and liquid viscosity on flow patterns, pressure drop and holdup for cocurrent gas-liquid flow in helically coiled tubes have been investigated. Nine coils of varying coil diameter and helix angle have been used with liquids of three different viscosities and air at varying pressures. The effect of tube diameter on pressure drop and holdup was determined by using tubes of diameters up to 2-in. Flow patterns were adequately predicted for all the systems by Baker's plot. Small helix angles were found to have no effect on pressure drop or holdup in coiled tubes. Both pressure drop and holdup could be adequately correlated using the Lockhart-Martinelli approach with modified correlating parameters.     

HYDRODYNAMIC CHARACTERISTICS AND GAS-LIQUID MASS TRANSFER IN A DRAFT TUBE SLURRY REACTOR

Fundamental characteristics of hydrodynamics and mass transfer have been measured in an air lift slurry reactor with a draft tube. The solid suspension capacity, i.e., the critical solid holdup, the gas holdup and the volumetric gas-liquid mass transfer coefficient were measured in the two draft tube columns of 0.1485 and 0.10?m in diameter. Four activated carbon beads ranging in size from 0.25 to 2.19?mm in average diameter were utilized as suspended solids in the experiments.

The critical solid holdup in the draft tube slurry column is found to be much greater than that in the conventional bubble column. An empirical correlation is developed to account for the critical solid holdup behavior in the draft tube column. The gas holdup in the draft tube column agrees well with that in the bubble column. The overall gas-liquid mass transfer coefficient, k₁awas measured by the oxygen probe method. The effect of solid holdup on k₁a is found to be negligible in the present system. The empirical equation is developed to correlate k₁a in the draft tube slurry reactor.     

气升式环流反应器在不同体系下的循环液速和局部气含率

在气升式环流反应器中,分别研究了空气—水、空气-0．1％乙醇水溶液和空气-水-活性污泥体系中的循环液速以及气含率随操作条件的变化规律。实验结果表明,循环液速随着表观气速的增加而增大,不同体系中的循环液速差别不大;导流筒内、外不同高度处的局部气含率均呈自下向上增大的趋势,且导流筒内部气含率高于导流筒外部的气含率。体系的聚并特性对平均气含率和局部气含率有较大影响。     

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.     

反应器类型对流动影响的数值模拟

在油-氢气体系中使用欧拉-欧拉双流体模型考察了温度703.15 K和压力11 MPa下气升式环流反应器和鼓泡床反应器对气液两相流动的影响. 结果表明,环流反应器中气含率和轴向液速沿导流筒径向存在突增现象,环流反应器中气含率在径向0~0.5和0.75~1时明显大于鼓泡床反应器,在径向0.5~0.75处前者的平均气含率比后者高约6%;环流反应器中上升管内环流液速明显大于鼓泡床反应器,且在下降区有所增强,环流反应器平均轴向液速比鼓泡床反应器高约21%;反应器尺寸较小时环流反应器和鼓泡床反应器的流动特性相差不大,反应器体积放大过程中前者的流动特性优于后者的趋势逐渐明显.     

Gas holdup and bubble dynamics in a three-phase internal loop reactor with external slurry circulation

As modified three-phase fluidized reactors, loop reactors have been widely used in the area of chemical and energy processes. An external slurry circulation is introduced into a traditional internal loop reactor to improve the transfer between gas and slurry phases. Gas holdup and bubble dynamics are investigated by using the double-sensor conductivity probe technique in the present work. The results show that gas holdup inside the draft tube is greatly affected by the geometrical configuration and is much higher than that in the corresponding section of the annular region. Local, section-averaged, and overall gas holdups increase with increasing superficial gas velocity, while the effects of solid loading and external slurry circulation velocity are less significant than that of superficial gas velocity. Both local bubble size and bubble rise velocity vary significantly in different regions.     

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.     

采用间接膨胀法研究鼓泡床内气含率特性

引言 鼓泡床反应器凭借其相际接触面大、传递效率高、结构简单和操作稳定等优势而成为气液两相进行质量、动量和能量传递及化学反应的重要设备,在化工及相关领域应用广泛[1-2].尽管前人采用不同测量方法对鼓泡床内气含率特性进行了大量的实验研究,并推导出了相应的经验关联式[3-5],但这些实验大多是针对室温和常压的透明鼓泡床,难以直接应用于非透明的高温或高压实际工业过程中.     

Measurement of local gas holdup in bubble columns via a non-isokinetic withdrawal method

An inexpensive method was developed to measure local gas holdup based on withdrawal of the air–liquid dispersion in bioreactors under non-isokinetic conditions. The method was tested with several suction probe designs and withdrawal pressures using coalescing and non-coalescing model media as well as during yeast fermentations. Simultaneously, gas holdup was measured manometrically. With a straight end probe and vacuum pressure of 3 kPa, local gas holdup measurements presented a relative error <6% compared to the manometric method, independently of the media composition. This method was used to characterize local gas holdup in a bubble column. Two new parameters are proposed to characterize non-gassed volume and gas holdup homogeneity.     

THE INVERSE FLUIDIZATION AIRLIFT BIOREACTOR, PART I: HYDRODYNAMIC STUDIES

The inverse fiuidization airlift bioreactor offers a simple solution to the problem of handling shear sensitive cultures and/or systems requiring biofilm growth control. This unit combines in a single vessel the hydrodynamic behavior of concentric tube airlift aerators or contactors and liquid-solid fluidized beds. The effects of the diameter of the concentric tubes, liquid level, bed properties and gas flow rate on gas holdup, bed expansion and liquid circulation velocity were investigated in this study. The Zuber and Findlay relation (1965) gives satisfactory results for gas holdup. The inverse bed expansion can be predicted by the Richardson and Zaki correlation (1953). The liquid circulation velocity can be calculated using a mechanical energy balance     

Ultrasonic method for measuring the gas holdup of gas-liquid bubbly flow in a small-diameter pipe

Based on ultrasonic sound pressure attenuation, the ultrasonic pulse transmission method is proposed for measuring gas holdup in gas-liquid two-phase bubbly flows. Two ultrasonic transducers are positioned on opposite sides of a vertical upward pipe with an inner diameter of 20 mm. To obtain the relationship between ultrasonic attenuation and gas holdup, the mean value of the first pulse sequence of ultrasonic signals is first extracted as the measured signal. We used the quick closing valve method to obtain the gas holdup as the set value. Second, the relationship between the gas holdup and measured ultrasonic signals was established. The experiment result shows that the ultrasonic attenuation rate is significantly different at low and high gas holdups, as indicated by the bubble size images with a high-speed camera. We also investigated the ultrasonic field distribution using numerical simulation. The bubble size has an important effect on the ultrasonic attenuation coefficient, which provides a further physical explanation and reference for the experimental phenomena.     

Development of airlift bubble column dispersed with micro‐bubbles

Micro‐bubbles were dispersed in the bubble column with draft tube, and the length and diameter of draft tube were changed. The flow characteristics in air–water system were measured. Ozone gas and methylene‐blue aqueous solution were used, and the decomposition performance was examined. With increasing draft tube length, both the gas holdup and liquid velocity in the annular section increased. When the diameter ratio of draft tube to column was about 0.5, both the gas holdup and liquid circulation flow rate had maxima. For the decomposition by using ozone, the installation of draft tube enhanced the mass transfer and decomposition performance.     

Phase Distribution in a High Pressure Slurry Bubble Column via a Single Source Computed Tomography

Due to their numerous advantages, Slurry Bubble Column Reactors (SBCR) are gaining wide importance in the petroleum, petrochemical, chemical, and biochemical industries. Most previous literature studies on the fluid dynamics and the phase holdup distribution in SBCR are limited to low superficial gas velocity, low solids loading, and the atmospheric pressure. Moreover, the presence of a solids phase poses difficulties in probe measurement techniques such as pitot tube and optical probe and see through measurement techniques such as particle image velocimetry (PIV), Laser Doppler Velocimetry (LDV). Single source γ‐ray Computed Tomography (CT) has been used to measure cross‐sectional phase holdup distribution in two‐phase systems. In the present study, a new methodology has been developed that combines a single source CT with overall gas holdup measurement, along with valid assumptions, to measure the cross‐sectional holdup distribution of the three phases in a slurry bubble column. The implementation of developed methodology has been demonstrated using air‐water‐glass beads (150 µm) at selected conditions of superficial gas velocity and operating pressure.