Range Of Superficial Gas Velocities Research Articles

Experimental characterization of a random packing with high specific surface area in a small diameter cryogenic distillation column

In present study, comprehensive experimental examination is performed to investigate the characteristics of packing for the separation of light stable isotopes. This work focused on the effect of liquid redistribution on wall flow reduction. In this research work, 0.005 m Dixon ring packing was constructed and characterized. Experimental tests were conducted in a packed column with a diameter of 0.04 m and various heights up to 1 m. Structural characteristics, pressure drop, dynamic hold-up and redistribution spacing were comprehensively investigated. Dry and wet pressure drop charts were plotted for a wide range of gas superficial velocities corresponding to gas loading factor values of 0.2–1.3 Pa0.5 Height of the packed section between two consecutive redistributors was defined at various liquid superficial velocities. Our results show that compared to larger columns, liquid should be redistributed in smaller spacings when the diameter of packed columns is smaller than 0.05 m. In addition, it is found that efficient redistribution spacing is about 0.3 m in a 0.04 m column. According to our findings, this value decreases the wall flow more than 50%.

Study on the natural frequencies of pipes conveying gas-liquid two-phase slug flow

The natural frequencies of pipes conveying gas-liquid two-phase slug flow are explored, considering the significance of the intermittent characteristic of gas-liquid two-phase slug flow particularly. The widely used finite element method is employed to establish the theoretical model. The local flow parameters including local gas and liquid velocities and local liquid holdup varying with time and position along the pipe are calculated to obtain the global matrix equation of motion for the system. An experiment is conducted to verify the theoretical model. The results show that the time domain values of the natural frequency would keep periodicity during the process of slug flow. Root-mean-square of the natural frequency is employed to represent the characteristic of the piping system natural frequency. If the superficial gas velocity is given, root-mean-square of the natural frequency will decrease with the increase of the superficial liquid velocity. Yet if the superficial liquid velocity is given, root-mean-square of the natural frequency will increase firstly and then decrease with the increase of superficial gas velocity when the superficial liquid velocity is relatively large. Thus a critical superficial gas velocity exists for these conditions. The range of superficial gas velocity that could make the system become unstable may be predicted preliminarily by analyzing this critical value. Sufficient analysis of slug parameters and geometrical parameters of the pipes is necessary to obtain the critical superficial gas velocity. Finally, the divergent instability of the piping system is predicted based on the above analysis.

Online measurement of solids motion in fluidized bed reactor with different distributor for Fischer–Tropsch synthesis

In this paper, the distributions of particle velocity in a gas–solid fluidized bed with branched pipe distributor or circle distributor were measured by using a laser Doppler velocimetry. Our results show that, within a certain range of superficial gas velocity, when using circle distributor, the particle velocity is large and the distribution of the particle velocity is even more compared with the branched pipe distributor. On the basis of the amplitude of tangential movement statistics, the amplitude of tangential movement statistics (AVATMS) decreases with increasing the axial height under the appropriate superficial gas velocity.

Experimental study on vertical downward air-water two-phase flow in a large diameter pipe

Downward two-phase flows in large diameter pipes are important in various industrial applications, especially for the safety analysis in nuclear reactors. To address the issue that few data of downward flow in large diameter pipes is available for model evaluation, experiments of air–water downward flow in a pipe with inner diameter of 203.2 mm have been performed. Area-averaged void fraction and pressure measurement, as well as flow visualization, have been conducted at several axial locations. The flow conditions for superficial gas velocity range from 0.05 m/s to 3.00 m/s and for superficial liquid velocity range from 0.1 m/s to 1.5 m/s, which cover cap-bubbly flow, churn-turbulent flow and annular/falling film flow. The flow structure at several axial locations and the transition from churn-turbulent flow to annular/falling film flow have been discussed. Current available drift-flux models developed for downward flow in regular pipes as well as for upward flow in large pipes are evaluated using newly collected data. For churn-turbulent flow, the data indicates a larger drift velocity than the model prediction. Corresponding drift-flux constitutive equations are suggested which can reduce the prediction error from 34.37% to 11.79%.

Hydrodynamic and mass transfer characterization of flat-panel airlift photobioreactors for the cultivation of a photosynthetic microbial consortium

The design and build of industrial photobioreactors are critical steps for the production of photoautotrophic microorganisms. Flat-panel airlift photobioreactors (PBRs) of 50L and 150L were built; hydrodynamics (gas hold-up (ε), mixing time (tm) and Reynolds number (Re)) and mass transfer properties were characterized in the two flat-panel airlift PBRs (50 and 150L). The geometric ratio (illuminated area: operation volume (A/V) ratio) selected for building the 150L PBR was adequate to carry out biomass production of a microbial consortium (MC). A high CO2 utilization efficiency in the PBRs was obtained. Finally, the experimental results of kLa were correlated mathematically to describe the influences of the considered factors (the overall power input and density) on the studied superficial gas velocity range. The predicted kLa values yielded acceptable results compared to the experimental results.

Magnetic particle tracking for nonspherical particles in a cylindrical fluidized bed.

In granular flow operations, often particles are nonspherical. This has inspired a vast amount of research in understanding the behavior of these particles. Various models are being developed to study the hydrodynamics involving nonspherical particles. Experiments however are often limited to obtain data on the translational motion only. This paper focusses on the unique capability of Magnetic Particle Tracking to track the orientation of a marker in a full 3‐D cylindrical fluidized bed. Stainless steel particles with the same volume and different aspect ratios are fluidized at a range of superficial gas velocities. Spherical and rod‐like particles show distinctly different fluidization behavior. Also, the distribution of angles for rod‐like particles changes with position in the fluidized bed as well as with the superficial velocity. Magnetic Particle Tracking shows its unique capability to study both spatial distribution and orientation of the particles allowing more in‐depth validation of Discrete Particle Models. © 2017 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 63: 5335–5342, 2017

Prediction of the gas hold-up in a large-diameter bubble column with liquid mixtures and electrolytes

Many correlations are available in the literature for computing the gas hold-up in bubble columns, mainly in pure liquids. Contrarily, very few works deal with the gas hold-up in liquid mixtures, giving different opinions about the successful application of Andrew’s dynamic surface tension model. This work further investigates this topic using more recent gas hold-up data presented in a previous work for the binary mixture comprising monoethylene glycol and water and measured for a large-diameter bubble column, which differs from the equipment used in the other few works that have pointed out the unusual behavior of the gas hold-up in binary liquid mixtures. The correlation proposed for representing the experimental data on the basis of the dynamic surface tension theory has been applied in the entire range of gas superficial velocities (0.004–0.20m/s) and it has been also generalized to predict the gas hold-up enhancement due to the presence of electrolytes. The results suggest that the dynamic surface tension model allows to reproduce the experimental gas hold-up data in a qualitative way, but a quantitative agreement is still lacking since the maximum frothing ability has been experimentally observed for a monoethylene glycol concentration lower than that predicted by Andrew’s theory.

Hydrodynamics and mass transfer coefficients in a bubble column photo-bioreactor

The present study compares typical measurements of bubble dynamics obtained with a 4-point optical probe over the same range of superficial gas velocity in the same size gas–liquid contactor in two different systems. The classical bubble column (BC) arrangement employed air bubbled through water. The photo-bioreactor (PBR) used a growing algae in appropriate culture solution. Local gas holdup distribution across the vessel was monitored, as well as the local distribution of bubble velocity, bubble chord length, bubble frequency and interfacial area per unit volume for both systems. It was observed these parameters were significantly different in the photo-bioreactor. This information coupled with the tracer absorption studies with oxygen provided the needed information to evaluate the gas liquid volumetric mass transfer coefficients from an appropriate model for both systems. The development of such a model is described. It was concluded that the difference in hydrodynamics of the two systems was due to difference in physicochemical properties.

Comparative analysis of liquid hydrodynamics in a co-current flow-through bubble column with densely packed internals via radiotracing and Radioactive Particle Tracking (RPT)

Bubble column reactors are widely used for gas-liquid operations and most often are fitted with vertical internals for appropriate heat transfer. Apart from these applications, cylindrical vessels with concentrically installed vertical tube bundles find major use in boiling water reactors. Most often, heat removal takes place in boiling water reactors by phase change of the flowing water, which results in a complex, axially developing and highly dynamic two-phase flow pattern. Though the hydrodynamics in a bubble column with vertical internals have been addressed in few publications, the characteristics of liquid phase mixing and turbulence over a wide range of operating conditions and dense configuration of the internals have not been reported thus far. The present communication addresses the hydrodynamic characteristics in bubble column equipped with dense internals over a wide range of superficial gas and liquid velocities. Experiments were performed using the air-water system in a 120mm I.D. bubble column with, and without internals, by varying the percent cross-sectional area covered by the internals. A non-invasive Radioactive Particle Tracking (RPT) method has been employed for estimating the hydrodynamic parameters and mixing characteristics have also been investigated using residence time distribution (RTD) studies with radiotracers. The experimental results obtained in this work indicates that the configuration of the heat exchanger internals, superficial gas, and liquid velocities have a strong effect on liquid phase hydrodynamics and mixing characteristics.

Experimental study of interfacial characteristics of vertical upward air-water two-phase flow in 25.4 mm ID round pipe

An adiabatic upward air-water flow experiment was performed on a vertical pipe with 25.4mm inner diameter to investigate the interface structure and characteristics. Local experiment parameters, including time-averaged void fraction, interfacial area concentration, bubble interfacial velocity and Sauter mean diameter were measured using a four-sensor conductivity probe with a data acquisition frequency of 100kHz. Experiment data for 19 flow conditions was collected at 3 axial locations (z/D=15, 78, and 141) and 13 radial positions from r/R=−0.84 to 0.7. In the experimental study, the measuring range of superficial liquid and gas velocity were from 0.3 to 1.0m/s and 0.03 to 11.0m/s, respectively. The flow regimes ranged from bubbly flow to the transition of churn-turbulent to annular flow. The local measurement result agreed well with the drift flux model by Ishii (1977) and Kataoka (1987). The different interfacial structures in different flow regimes and two group bubble interfacial transfer were observed from the experiment result. This data will be used for the evaluation and extension of the current interfacial area transport equation.

CFD simulation of gas-liquid-solid flow in slurry bubble columns with EMMS drag model

The drag models reflecting the complex phase interactions are of critical importance in the CFD simulation of gas-liquid or gas-liquid-solid flows. In this study, we demonstrate that the Dual-Bubble-Size (DBS) drag model based on the Energy-Minimization Multi-Scale (EMMS) concept, is capable of effectively predicting the distribution of gas holdup in slurry bubble columns. For solid-free or low solid loading systems, a thorough comparison of the DBS-Global and other drag models indicates that, without any fitting parameters, the DBS-Global drag model prediction on the radial distribution of gas holdup and solid hydrodynamics is in conformity with experiments over a wide range of superficial gas velocities. The three-fluid and two-fluid models are also compared in this work, indicating that the three-fluid model in combination with the DBS-Global drag model gives the best prediction. Previous experiments show that the effects of solid presence on hydrodynamics become pronounced at high solid loading conditions. The prediction of the original DBS-Global drag model deviates from the experiments at high solid loading conditions, and the solid effects need to be taken into account. This work then proposes a modified drag model for simulating three-phase systems at high solid concentration. The new model is capable of accurately predicting the local gas holdup for the systems of solid loading of 25% or 40%. Further fundamental study of the solid effect on the change of flow structure and dominant mechanisms in gas-liquid flow is required.

Experimental characterization of dense gas–liquid flow in a bubble column using voidage probes

Gas–liquid flow in bubble columns under dilute flow condition has been investigated widely. In the present work, we have characterized gas–liquid flow in a pseudo 2D bubble column for a wide range of superficial gas velocities (UG=1–30cm·s-1) that cover dilute to dense flow conditions. In-house developed voidage probes were used to measure local gas volume fraction fluctuations, which in turn were used to characterize dynamics of column-scale re-circulatory flow and bubble-scale flow processes, under dilute-to-dense conditions. Importantly, the spatial distribution of internal composition of gas volume fraction, i.e. gas volume fraction contained in different bubble size groups, was measured. Further, the spatial distribution of chord length and bubble size was measured for a wide range of UG. With increase in UG, the low frequency oscillations caused by meandering bubble plume at lower UG were found to diminish and the fluctuations caused by bubble swarms were found to dominate under the dense flow conditions. Using the time spent by the probe in each bubble, the bubble population was classified into different size groups and the gas volume fraction for each size group was measured. Under dense flow conditions, small bubbles were seen to accumulate near column walls, as exhibited by wall peaking in gas volume fraction profiles and that large bubbles were found to flow through the column centre. The results presented in this work are important to improve the understanding of dense gas–liquid flow and also for rigorous validation of CFD models.

Effect of vertical vibration and particle size on the solids hold-up and mean bubble behavior in a pseudo-2D fluidized bed

The solids hold-up and mean bubble behavior in a vertically-vibrated fluidized bed are experimentally studied in the present work by means of Digital Image Analysis (DIA) for four different powders with Geldart classifications A, B and A/B. The bed has a small thickness (i.e. pseudo-2D bed) and operates in bubbling regime subject to a wide range of gas superficial velocities, vibration frequencies and vibration amplitudes. Mean parameters of the bed and the bubbles, such as solids hold-up, bubble fraction, bubble number density and bubble diameter and velocity, are characterized here by averaging the results over time and space. The results reveal that vibration of the bed promotes a confinement of the bubble path to the central section of the bed. This bubble confinement is more intense for the smallest particles tested and for high vibration strengths and creates two different bubble regimes in the bed. In particular, close to the distributor, the bubble velocity decreases when increasing the vibration amplitude of the bed vessel because bubbles are smaller and less confined, and they behave like isolated bubbles. The behavior of bubbles changes when they are far from the distributor, where the interaction between bubbles becomes greater due to their bigger size and the confinement of bubbles induced by vibration. This confinement promotes coalescence of bubbles. It is shown that consideration of these two different regimes of bubble dynamics allows to shed light on understanding the apparently contradictory results encountered in the literature regarding bubble behavior in bubbling vibrated fluidized beds.

Online measurement of gas and liquid flow rate in wet gas through one V-Cone throttle device

In the present study, an accurate cost-effective online system for metering both the gas flow rate and the liquid flow rate in wet gas with only one V-Cone throttle device is developed. The two-phase mass flow coefficient is employed to correct the measurement deviation of the V-Cone throttle device. The effects of the liquid densiometric Froude number, the gas densiometric Froude number and the ratio of gas density to liquid density on the two-phase mass flow coefficient are experimentally investigated. The equivalent diameter ratio of the V-Cone throttle device is 0.55. The experimental fluids are air and tap water. The operating pressure, the superficial gas velocity and superficial liquid velocity range from 0.1MPa to 0.3MPa, 4.87m/s to 25.26m/s and 0 to 0.38m/s, respectively. The results show that the two-phase mass flow coefficient linearly increases with the liquid densiometric Froude number and is affected by the gas densiometric Froude number and the ratio of gas density to liquid density. On the basis of the two-phase mass flow coefficient, the correlation for measuring the gas flow rate of the wet gas is developed. To reflect the influences of the liquid on the measurement, the pressure loss ratio of the V-Cone throttle is proposed. By incorporating the gas measurement correlation of the wet gas, the wet gas correlations to simultaneously meter the gas and liquid flow rate are concluded. In the present cases, the relative error of the gas mass flow rate predicted by the correlations is within ±5.0% and the mean absolute percentage error is 2.52%; the full scale relative error of the liquid mass flow rate is within ±5.0% and the mean absolute percentage error is 7.03%. The method proposed in this study creates a simple inexpensive wet gas metering system that can operate well in a significant range of industrial applications.

Experimental study of gas–solid overall heat transfer coefficient in vertical tank for sinter waste heat recovery

This work experimentally investigates the gas–solid heat transfer behavior in vertical tank for sinter waste heat recovery. With the purpose of predicting the heat transfer Nusselt number, a homemade experimental setup is built to obtain the temperatures of cooling air and sinter particles over time. Sinter particles of average diameter d = 18, 27 and 36 mm with a range of sphericity of 0.68 ≤ Φ ≤ 0.89 are used in the experiments. The experiments are performed in the range of gas superficial velocity of 1.04~1.75 m/s and the sinter temperature in bed layer from 100 to 750 °C. The influences of gas superficial velocity and sinter particle diameter on the gas–solid overall heat transfer coefficient are analyzed in detail for the covered test cases. The heat transfer Nusselt number is obtained according to the regression analysis of experimental data, and the reliability of the heat transfer Nusselt number is also verified. It is found that the gas–solid overall heat transfer coefficient increases with the increase of gas superficial velocity, and decreases with increasing sinter particle diameter. A small increase in gas–solid overall heat transfer coefficient with the temperature of sinter particles is also observed in the experiments. Compared with the previous literature correlations, the experimental correlation for gas–solid heat transfer in the form of Nusselt number best fits the experimental data. The mean deviation between the experimental data of Nusselt number obtained from this work and the values calculated by the experimental heat transfer correlation is 4.37%, showing good prediction.

The effect of the fluid properties on the wave velocity and wave frequency of gas–liquid annular two-phase flow in a horizontal pipe

The effects of fluid properties on the wave velocity and frequency of gas–liquid annular two-phase flow were investigated in 26 and 16-mm inner pipe diameters. The liquid viscosity was varied from 1.02 to 6.57mPas using water and glycerol solution and the surface tension was varied from 34.0 to 71.7mN/m using water and butanol solution. The range of superficial liquid and gas velocities were set to 0.05–0.2m/s and 12–40m/s, respectively.In general, the wave frequency decreases with increasing liquid viscosity and decreasing surface tension. The wave velocity decreases with increasing liquid viscosity for all range of superficial gas and liquid velocities. The lower surface tension gives the lower wave velocity for low superficial liquid velocity. For high superficial liquid velocity, however, the wave velocity increases with decreasing surface tension. The wave frequency decreases with the increase of liquid viscosity and the decrease of surface tension, with more significant effects are found at the higher superficial gas and liquid velocities. Comparisons of experimental data with the existing correlations for wave velocity and wave frequency have been carried out and new correlations have been developed with a considerably good agreement with the experimental data.

Extraction of aroma compounds of fruit juices by air stripping using a bubble column operating with antifoam and its effect on juice properties

The objective of this work was to evaluate the effect of air bubbling on the physicochemical properties and ascorbic acid concentration of fruit juices during the extraction of their volatile aroma compounds using a bubble column operated with antifoam. The ideal concentration of a commercial antifoam agent was also evaluated to ensure a non-foaming operation during air bubbling in the fruit juice for the range of gas superficial velocity between 1 and 2cm/s. Besides, aroma extraction from a surrogate solution was evaluated, being the best extraction efficiency obtained for ethyl butyrate (97%), followed by hexanal (93%), ethyl acetate (81%) and linalool (32%). However, there was no significant variation of these efficiencies for the gas superficial velocities employed. Finally, after 4h of air bubbling in fresh fruit juice, there were no changes of pH, total soluble solids, titratable total acidity and color of the juice and just a 15% reduction in the concentration of the ascorbic acid. Thus, the use of air stripping in a bubble column was proved to be an interesting alternative to extract aroma compounds from fruit juice without causing any appreciable change in its properties.

Heat transfer between a packed bed and a larger immersed spherical particle

In this paper, heat transfer coefficients between the hot packed beds of particles and the larger cold immersed sphere were experimentally determined. The packed beds consisted of mono-sized spherical glass particles of dp=1.2, 1.94 and 2.98mm. The aluminum test spheres of Dp=6, 12 and 20mm with K-type (Ni/Al) thermocouples inserted in them were immersed into the bed. The temperatures of the test spheres were recorded until the thermal equilibrium was reached. From these recordings, heat transfer coefficients were determined. The experiments were performed in the range of gas superficial velocity of ∼0.3–0.8m/s and the bed temperature from 90 to 320°C. It was found that the measured heat transfer coefficients increased with the increase in gas superficial velocity, while only a slight increase with temperature was observed for test spheres Dp=6 and 12mm in the investigated temperature interval. The heat transfer coefficients were generally larger for smaller test spheres, while they did not show significant dependence on the size of the bed particles.The literature correlations for heat transfer coefficients in packed beds in form of Nusselt number and heat transfer factor jH were compared to experimental data from this work. The correlations proposed by Collier et al. (2004) [18] and Handley and Heggs (1968) [2] fit our experimental data best. The mean error between the experimentally determined heat transfer coefficients and the ones calculated from Collier et al. (2004) [18] correlation was 12.7%.

Effects of superficial gas velocity on process dynamics in bioreactors

Present work analyzes the flow hydrodynamics and mass transfer mechanisms in double Rushton and CD-6 impeller on wide range (0.0075–0.25 m/s) of superficial gas velocity (vg) in a gas-liquid phase bioreactor by employing computational fluid dynamics (CFD) technique. The volume averaged velocity magnitude and dissipation rate are found higher with increasing superficial gas velocity. Higher relative power draw (Pg/P0) is predicted in CD-6 than the Rushton impeller but no significant difference in volume averaged mass transfer coefficient (kLa) observed between these two types of impeller. The ratio of power draw with mass transfer coefficient has been found higher in CD-6 impeller (25–50 %) than the Rushton impeller.

Two-Phase Upward Flow in a Slightly Deviated Pipe

This study was undertaken to look at the effect of a slight inclination of pipe on upward flow characteristics especially at 10 deg from vertical position. Air-silicone oil flows in a 67 mm diameter pipe have been investigated using a capacitance wire mesh sensor (WMS) and electrical capacitance tomography (ECT). They provide time and cross-sectionally resolved data on void fraction. Superficial gas and liquid velocities of 0.05–1.9 and 0.05–0.5 were studied. Statistical methods and visual observation methods were used to characterize the fluid flows obtained into different flow patterns. From the output results from the tomography instruments, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability density function (PDF) plots of the time series of cross-sectionally averaged void fraction. Bubbly, cap bubble, slug, and churn flows were observed when the pipe was deviated by 10 deg from vertical pipe for the range of superficial gas velocities considered.