Correlations For Gas Holdup Research Articles

Data-Driven Gas Holdup Correlation in Bubble Column Reactors Considering Alcohol Concentration and Carbon Number

Due to the complex relationship between various parameters affecting gas holdup in bubble column reactors, a unique correlation for gas holdup does not exist. The available correlations proposed in the literature for gas holdup prediction in aqueous alcohol solutions in bubble columns fail to predict gas holdup over a wide range of conditions. Therefore, based on around 1000 data points from the previous studies, an empirical correlation and a trained model were derived using the dimensionless numbers Reynolds, Froude, Eötvös to Morton ratio, and alcohol carbon number. The predictions were compared to experiments with different water–alcohol mediums at various concentrations to validate the correlation and trained model, and a good agreement was observed. However, the ML model was predicting more accurately, and it was indicated that the Reynolds number had the most significant impact on gas holdup, followed by the Eötvös to Morton ratio.

Prediction of intensity of dispersion in surfactant solutions in vertical sparged bubble column

AbstractDispersion of liquid in bubble column is an important process in chemical and allied industries. In the present work, the dispersion characteristics of liquid phase in a bubble column is studied in three different surfactant solutions. A comparative analysis on the dispersion characteristics of liquid phase in different surfactants has been carried out. The gas holdup and mixing time are also analysed. The effect of different physiochemical properties and operating variables on the dispersion coefficient and gas holdup is examined. A novel model for the estimation of dispersion due to bubble motion has been developed which incorporates the effect of gas holdup, liquid viscosity and circulation velocity. The contribution of dispersion coefficient due to the bubble motion in overall dispersion is also examined. The value of velocity distribution parameter in three different surfactant solutions is also compared. Generalised correlations for gas holdup, dispersion coefficient and mixing time are also developed based on the physicochemical properties of liquid. This research may be useful for the selection and application of these three surfactants in industries. This article will also help researchers for designing multiphase flow system where role of dispersion due to the motion of bubbles is significant.

Hydrodynamics, mixing and mass transfer in a pilot-scale bubble column with dense internals

Bubble column reactors with exothermic reactions are often equipped with dense tube bundle heat exchangers. While there is some knowledge about the impact of such internals on hydrodynamics and mass transfer for narrow columns, its role in pilot-scale columns is less clear. In this paper we report on a study of hydrodynamics and mass transfer in a BCR of 4.2 m height and 0.392 m diameter. We investigated different tube arrangements with triangular and square pitch and tube diameters of 32 × 10−3 m and 45 × 10−3 m at the same cross-sectional coverage (∼25%). The column was operated at homogeneous and heterogeneous flow conditions. A customized three-layer wire-mesh sensor was utilized to visualize gas phase dynamics and liquid mixing characteristics in the column’s cross-section. We found that sub-channel size is the most crucial geometric design parameter. Tracer mixing experiments revealed that internals reduce the mixing time due to the induction of large-scale liquid circulation. Mass transfer was studied with the oxygen stripping method. Here we found, that the effect of the internals on the gas-liquid mass transfer is almost negligible. Eventually, correlations for gas holdup, axial liquid dispersion and the volumetric gas-liquid mass transfer coefficient are given, which take the internals’ geometry into account.

Gas distribution characteristics for heterogeneous flows in the slender particle-containing scrubbing–cooling chamber of an entrained-flow gasifier

Dual-tip conductivity probes and a high-speed camera were used to study the gas distribution characteristics in a cold model apparatus of the slender particle-containing scrubbing–cooling chamber. The three-dimension column was 200mm in internal diameter and 1353mm in height. The effects of superficial gas velocities, fiber volume fractions and fiber aspect ratios on global gas holdups were determined. The results showed that under the influence of reverse buoyancy and negative pressure gradients, plume gas flow went up along the outside of the downcomer in downcomer spout region. Local radial gas holdup which was closely related with the internals and flow patterns presented obviously proximate core peak distribution in bubble-breaking plate region. The foam region consisted of bubble coalescence and breakup as well as droplets formation and splashing. At higher gas velocities, the increasing rate of global gas holdup gradually reduced. With the increase of fiber volume fraction, global gas holdup slightly increased at low gas velocities due to suppressed bed turbulence and bubble loading, but decreased at high velocities for increased liquid viscosity and vortex-shedding. Due to suppressed small-scale velocity fluctuation, global gas holdup increased with increased fiber aspect ratio. A modified drift-flux model containing crowding factor and fiber number density for global gas holdup correlations was proposed and all of the data could be calculated with a relative deviation less than 10%.

Hydrodynamics and bubble behaviour in a three-phase two-stage internal loop airlift reactor

Abstract Local hydrodynamics of a gas–liquid–solid system, such as bubble circulation regime, gas holdup, liquid velocity and axial profile of solid concentration, are studied in a two-stage internal loop airlift reactor. Empirical correlations for gas holdup and liquid velocity are proposed to ease the reactor design and scale-up. Different bubble circulation regimes were displayed in the first (lower) and second (upper) stages. Increasing superficial gas velocity and solid loading can promote regime transition of the second stage, and the gas holdup of the second stage is higher than that of the lower stage. In addition, the effects of solid loading on bubble behaviour are experimentally investigated for each stage. It is found that bubble size in the downcomer decreases with the presence of solid particles, and bubble size distribution widens under higher superficial gas velocity and lower solid loading.

Novel gas holdup and regime transition correlation for two-phase bubble columns

The gas holdup is dimensionless parameter of fundamental and practical importance in the operation, design and scale-up of bubble columns. Unfortunately, the many relationships between the bubble column fluid dynamic parameters and the various variables characterizing the system make it difficult to find general correlations for the precise estimation of the gas holdup. Wilkinson et al. (1992), in their pioneering paper, proposed a correlation to predict the gas holdup in industrial-scale bubble columns, based on the physical properties of the phases and the operating conditions. However, this correlation lacks in generality, as it does not take in account the bubble column design. In this paper, we propose a generalization of the Wilkinson et al. (1992) gas holdup correlation to take into also the bubble column design parameters. Starting from considerations concerning the flow regime transition, corrective parameters are included to account for the effects introduced by the gas sparger openings, the bubble column aspect ratio and the bubble column diameter. The proposed correlation has been found to predict fairly well previously published gas holdup and flow regime transition data.

A review on empirical correlations estimating gas holdup for shear-thinning non-Newtonian fluids in bubble column systems with future perspectives

AbstractGas holdup is one of the most important parameters for characterizing the hydrodynamics of bubble columns. Modeling and design of bubble columns require empirical correlations for precise estimation of gas holdup. Empirical correlations available for prediction of gas holdup (εG) in various non-Newtonian systems for both gas-liquid and gas-liquid-solid bubble columns have been presented in this review. Critical analysis of correlations presented by different researchers has been made considering the findings and pitfalls. As the magnitude of gas holdup depends on many factors, such as physicochemical properties of gas and/or liquid, column geometry, type and design of gas distributors, operating conditions, phase properties, and rheological properties, etc., all of these have been discussed and examined. In order to emphasize the significance, relative importance of parameters such as flow behavior index, consistency index, column diameter, gas flow rate, and density of aqueous carboxymethylcellulose (CMC) solution on gas holdup has been quantified using artificial neural network and Garson’s algorithm for an experimental data set of air-CMC solution from the literature. Besides, potential areas for research encompassing operating conditions, column geometry, physical properties, modeling and simulation, rheological properties, flow regime, etc., have been underlined, and the need for developing newer correlations for gas holdup has been outlined. The review may be useful for the modeling and design of bubble columns.

COD reduction of textile effluent in three-phase fluidized bed bioreactor using Pseudomonas aureofaciens and Escherichia coli

This paper investigated the effect of mixed cultures of Pseudomonas aureofaciens and Escherichia coli and air as gas on degradation of chemical oxygen demand (COD) in three-phase inverse fluidized beds (TPIFBs) for textile effluents with initial COD of 1200 ppm (effluent 1) and 640 ppm (effluent 2). Investigators focused on the importance of different design of gas spargers of the TPIFB for checking its effect on COD reduction performance. For this purpose, four different gas spargers were fabricated for gas flow entry into bioreactor with different % open area: Gas sparger 1 (18% open area), sparger 2 (10.42% open area), sparger 3 (8.077% open area) and sparger 4 (1.53% open area). These percentage open area decided the amount of gas flow in a unit time in batch studies, which in turn rely mainly on superficial gas velocity. The reduction in COD was measured at two different superficial gas velocity (0.00343 and 0.004068 m/s) and at two ratio of static bed height to diameter (H/D) of 0.5 and 0.25 in an aerobic mode. Textile effluent 1 resulted in 98.07% COD reduction with sparger 3 and discharged at 23.14 ppm in 28 h. Textile effluent 2 resulted in 96.5% COD reduction with sparger 2 and discharged at 22.4 ppm in 22 h. The resulting COD values of Effluent 1 and effluent 2 were in range of discharge limit and resulted at a low gas velocity of 0.00343 m/s and low H/D ratio of 0.25. The gas holdup correlation was found to be εg = 0.0064 Ug0.98.

The effect of aspect ratio in counter-current gas-liquid bubble columns: Experimental results and gas holdup correlations

It is generally admitted that the gas holdup is independent of the column dimensions and gas sparger design if three criteria are satisfied: the diameter of the bubble column is larger than 0.15m, gas sparger openings are larger than 1–2mm and the aspect ratio is larger than 5. This paper contributes to the existing discussion; in particular, the effect of the aspect ratio (within the range 1–15) in a counter-current gas-liquid bubble column has been experimentally studied and a new gas holdup correlation to estimate the influence of aspect ratio, operation mode and working fluid on the gas holdup has been proposed. The bubble column, equipped with a spider gas sparger, is 5.3m in height, has an inner diameter of 0.24m; gas superficial velocities in the range of 0.004–0.23m/s have been considered, and, for the runs with water moving counter-currently to the gas phase, the liquid has been recirculated at a superficial velocity of −0.0846m/s. Filtered air has been used as the gaseous phase in all the experiments, while the liquid phase has included tap water and different aqueous solutions of sodium chloride as electrolyte. Gas holdup measurements have been used to investigate the flow regime transitions and the global bubble column hydrodynamics. The counter-current mode has turned out to increase the gas holdup and destabilize the homogeneous flow regime; the presence of electrolytes has resulted in increasing the gas holdup and stabilizing the homogeneous flow regime; the aspect ratio, up to a critical value, has turned out to decrease the gas holdup and destabilize the homogeneous flow regime. The critical value of the aspect ratio ranged between 5 and 10, depending on the bubble column operation (i.e., batch or counter-current modes) and liquid phase properties. Since no correlation has been found in the literature that can correctly predict the gas holdup under the investigated conditions, a new scheme of gas holdup correlation has been proposed. Starting from considerations concerning the flow regime transition, corrective parameters are included in the gas holdup correlation to account for the effect of the changes introduced by the aspect ratio, operation mode and working fluid. The proposed correlation has been found to predict fairly well the present experimental data as well as previously published gas holdup data.

Large scale preparation of microbubbles by multi‐channel ceramic membranes: Hydrodynamics and mass transfer characteristics

AbstractMicrobubbles have potential applications in chemical engineering, water treatment, and medicine. By designing multi‐channel ceramic membrane distributors, large scale preparation of microbubbles is achieved in a co‐current bubble column. Oxygen and water are used as interacting gas‐liquid phases. Gas holdup, bubble size distribution, and mass transfer rate are influenced by the membrane pore size, superficial gas velocity, and cross flow velocity. The empirical correlations for gas holdup and volumetric mass transfer coefficient are formulated and good agreement with experimental data is obtained. The multi‐channel ceramic membranes can successfully produce a lot of microbubbles, resulting in larger values of gas holdup, volumetric mass transfer coefficient, and equilibrium dissolved oxygen concentrations as compared to the conventional gas sparger. These findings will aid the development of gas‐liquid reactors with high performances.

Novel gas holdup correlation for slurry bubble column reactors operated in the homogeneous regime

Abstract The gas holdup is an important parameter for the design of slurry bubble columns. However, there is no correlation in literature to calculate the gas holdup of such reactors for industrially relevant conditions if the reactor is operated in the homogeneous regime. In this article, a novel correlation for calculating the gas holdup in the homogeneous and in the pseudo-homogeneous regimes is proposed. The correlation takes the relevant parameters into account: gas, liquid, and solid properties, sparger design, reactor diameter, and gas velocity. The correlation is also applicable for systems operated at elevated pressure and temperature. The correlation is based on 1199 data points, and it was developed by using the method of least squares. About two thirds of the data used were taken from literature (more than 20 research papers). The data from literature were carefully checked for confidence before using them for the correlation. > 90 % of the data points are covered by the new correlation with a relative error of less than 30 %, the standard deviation is 17.8 % and the averaged relative error is 9.5 %. Finally, the correlation was successfully validated with measurements which were not used to fit the correlation. An Excel file for using the developed correlation can be found in the Supplementary material.

On the single and two-bubble class models for bubble column reactors

A number of bubble column reactor models have been developed in literature on the basis of single-bubble class (SBC) or two-bubble class (TBC) concepts. While some researchers claimed that there was no significant difference between the two models, others believed that the TBC model was in better agreement with experimental data. A systematic and comparative analysis is carried out in this study to evaluate the model performance. We find that the dispute is relevant to the different sub-models used in these studies for hydrodynamics, mass transfer, and reaction kinetics as well as gas contraction. There are basically two aspects dominating the model calculation. The first is the hydrodynamic model for gas holdup, and the second is whether the system is limited by reaction or mass transfer. Then a new reactor model is developed to replace the empirical correlations for gas holdup with the dual-bubble-size (DBS) model, and the empirical contraction factor is eliminated by introducing the gas state equation and overall mass balance. The exchange between the small and large bubbles is also taken into account in the species transport equations. The model calculation indicates that the exchange can be neglected for reaction limited systems but becomes important for mass transfer limited systems. The new reactor model is in reasonable agreement with CFD simulation.

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.

Pressure drop and gas holdup in air–water flow in 180° return bends

Gas–liquid flows in curved tubes are found in a number of applications, such as heat exchangers and transport pipes. The present work deals with air–water flow in 180° tube bends (curvatures of 6.1, 8.7, and 12.2) that connect two 5-m long 26-mm ID horizontal tubes. The bend lies in the vertical position and the two-phase flow can be set as upward or downward. The straight and curved segments of test section were made from borosilicate glass to enable visual access to the two-phase flow. The behavior of the static pressure upstream and downstream of the bend was measured for a wide range of flow conditions, covering the stratified, intermittent and annular flow patterns. The pressure drop and gas holdup change associated with the bend were measured for both upward and downward flows, enabling the calculation of the frictional, accelarational and gravitational components of the total pressure drop in the bend. The distribution of the phases in the bend was investigated with a high-speed camera, revealing several two-phase phenomena responsible for large variations in gas holdup between the inlet and outlet of the bend for both upward and downward flows. An assessment of the prediction methods currently available in the literature showed that correlations for gas holdup in straight tubes give inaccurate predictions of the average gas holdup in the bend for both flow orientations. Frictional pressure drop correlations for gas–liquid flows in return bends also failed to describe with reasonable accuracy the behavior of the experimental data at low gas superficial velocities for both flow orientations. The performance of the correlations improved at high mixture velocities.

Hydrodynamics and mass transfer study of aliphatic alcohols in airlift reactors

Gas holdup and gas–liquid mass transfer coefficient were considered in an external airlift reactor. Air was sparged through some aliphatic alcohols (methanol, ethanol, n-propanol, and n-butanol) with different concentrations (0–1%, v/v). It was observed that gas holdup and mass transfer coefficient increased with increasing the number of carbons in alcohols. Furthermore, an increment in alcohols concentration increased gas holdup and mass transfer coefficient. The same behavior was observed in external and internal loop airlift reactors although gas holdup and mass transfer coefficient values were less than those of internal airlift reactor. According to the experiments, two correlations for gas holdup and mass transfer were developed.

TRIPHASIC EXTERNAL-LOOP AIRLIFT REACTORS. HYDRODYNAMIC AND DISPERSION STUDIES

Considering that three-phase dispersions are common in chemical engineering and biotechnology, and with increasing airlift reactor applications to chemical and biotechnological processes, a experimental study was undertaken in order to investigate the liquid phase hydrodynamics and dispersion in an external-loop airlift reactor on laboratory scale. Experiments were conducted in order to find a relationship between relevant hydrodynamic and mixing parameters of a solid-suspended external-loop airlift reactor of laboratory scale, and operating variables such as gas velocity, solids loading and solids density, which should be the basis for extending the study to larger scale contactors. It was found that these parameters affect the hydrodynamic characteristics of the investigated external-loop airlift reactor and empirical correlations for gas holdup and liquid circulation velocity were obtained as functions on the above-mentioned operating variables. The lateral and axial mixing of dispersed particles in a circulating fluidized bed were measured by using the phosphor tracer technique. The dispersion model satisfactorily described the measured residence time distribution.

Hydrodynamics, mass transfer and rheological studies of gibberellic acid production in an airlift bioreactor

Although a lot of research has been done into modelling microbial processes, the applicability of these concepts to problems specific for bioreactor design and optimization of process conditions is limited. This is partly due to the tendency to separate the two essential factors of bioreactor modelling, i.e. physical transport processes and microbial kinetics. The deficiencies of these models become especially evident in industrial production processes where O2 supply is likely to become the limiting factor, e.g. production of gibberellic acid and other organic acids. Hydrodynamics, mass transfer and rheology of gibberellic acid production by Gibberella fujikuroi in an airlift bioreactor is presented in this work. Important hydrodynamic parameters such as gas holdup, liquid velocity in the riser and in the downcomer, and mixing time were determined and correlated with superficial gas velocity in the riser. Mass transfer was studied evaluating the volumetric mass transfer coefficient, which was determined as a function of superficial gas velocity in the riser and as a function of fermentation time. Culture medium rheology was studied through fermentation time and allowed to explain the volumetric mass transfer coefficient behaviour. Rheological behaviour was explained in terms of changes in the morphology of the fungus. Finally, rheological studies let us obtain correlations for gas holdup and volumetric mass transfer coefficient estimation using the superficial gas velocity in the riser and the culture medium apparent viscosity.

INFLUENCE OF DIFFERENT CLOSURES ON THE HYDRODYNAMICS OF BUBBLE COLUMN FLOWS

ABSTRACT Computational fluid dynamic (CFD) simulations are performed for two-dimensional bubble columns to examine the effect of different interfacial force closures on the computed liquid velocity and gas holdup profiles. In this regard, six different drag closure relationships and three different virtual mass formulations are incorporated in the framework of the Los Alamos National Laboratory's code CFDLIB. The Eulerian-Eulerian two-fluid model is used. The results are compared with the experimental results of Mudde et al. (1997), the gas holdup correlation of Anabtawi et al., (2003), and CFD simulations of Pan et al. (2000). With the exception of one, all the correlations studied give good agreement (within engineering accuracy) between the computed results and the experimental data.

Novel correlations for gas holdup in large-scale slurry bubble column reactors operating under elevated pressures and temperatures

A comprehensive literature search was conducted to obtain the holdup data for different gases in various liquids and slurries using bubble and slurry bubble column reactors operating under wide ranges of conditions in different size reactors provided with a variety of gas spargers. The data were used to develop two novel correlations, one for the total gas holdup and the other for the holdup of large gas bubbles. The total gas holdup correlation is capable of predicting the experimental data within an absolute average relative error (AARE) and standard deviation ( σ ) of 20%, whereas the correlation of the holdup of large bubbles is capable of predicting the experimental values within AARE and σ of about 25 and 27%, respectively. The novel correlations were used to predict the effects of pressure, temperature, gas velocity, solid concentration, rector size, and distributor type on the holdup of syngas (H 2 /CO = 2) in various slurry bubble column reactors (SBCRs) operating under typical Fischer–Tropsch conditions.

Direct-contact evaporation in the homogeneous and heterogeneous bubbling regimes. Part II: dynamic simulation

Considering the bimodal feature of the bubble size distribution in the heterogeneous regime, a recently developed model for simulating direct-contact evaporators operating in the homogeneous regime was extended to the heterogeneous bubbling regime, enabling, thereby, the simulation of a direct-contact evaporator for any bubbling regime. The proposed model includes a correction factor for isothermal gas hold-up correlations to account for heat and mass transfer effects which arise in non-isothermal bubbling. The model predictions were shown to be in good agreement with literature experimental data for the air–water system, considering four different gas superficial velocities.