Dispersed Gas Phase Research Articles

Investigation of gas-liquid mass transfer in slurry systems driven by the coaxial mixer

The coaxial mixer was applied to the gas-liquid mass transfer process in slurry systems containing up to 8 vol% solids. The effects of impeller type, impeller speed, solid content, and gas flow rate were examined, and a correlation for the volumetric mass transfer coefficient was established. The findings indicate that at identical impeller speeds, the combination of an anchor and Rushton turbine exhibited the highest volumetric mass transfer coefficient and gas hold-up among coaxial mixers. However, when the pitched blade turbine with a down-pumping direction was utilized as the inner impeller, the coaxial mixer demonstrated superior performance under the same power consumption conditions. Additionally, the lower anchor speed was found to improve gas-liquid mass transfer, whereas a higher speed would lead to poor dispersion of gas phase, thereby deteriorating the performance of coaxial mixers. Increasing solid content caused a continuous decline in both the volumetric mass transfer coefficient and gas hold-up, while a rise in gas flow rate had the positive effect. Finally, the correlation developed for the volumetric mass transfer coefficient in slurry systems showed a deviation of less than 20% between predicted and measured values.

Gas/Liquid Operations in the Taylor-Couette Disc Contactor: Continuous Chemisorption of CO2

Gas/liquid contactors are widely used in chemical and biotechnological applications. The selection and design of bubble-column-type gas/liquid contactors requires knowledge about the gas distributor design to provide appropriate gas flow patterns. This study presents the continuous chemisorption of CO2 in 0.1 molar sodium hydroxide solution in a counter currently operated gas/liquid Taylor-Couette disc contactor (TCDC). This vertical-column-type contactor is a multi-stage agitated gas/liquid contactor. The performance of a lab-size TCDC contactor in gas/liquid mass transfer operations was investigated. The apparatus design was adjusted for gas/liquid operations by installing perforated rotor discs to provide a rotational-speed-dependent dispersed gas phase holdup in the column. The parameters of dispersed gas phase holdup, volumetric mass transfer coefficient and residence time distribution were measured. In the first step, hydraulic characterization was performed. Then, the efficiency in gas/liquid operations was investigated by continuous neutralization of 0.1 molar sodium hydroxide with a gas mixture of 30 vol% CO2 and 70 vol% N2. Temperature, rotational speed and gas flow rate were varied. The desired pH value of pH 9 at the column outlet was kept constant by adjusting the sodium hydroxide feed. From the experimental results, the volume-based liquid-side mass transfer coefficient kLa was deduced in order to model the reaction according to the two-film theory over the column height. The CSTR cascade model fitted the experimental data best. The experimental results confirm stable and efficient reactive gas/liquid contact in the Taylor-Couette disc contactor.

Analysis of the Structure of the Dispersed Gas Phase Produced in Turbulent Foam-Concrete Mixers

It was noted that the overall stability of foam concrete mixtures made by single-stage technology depends significantly on the measure of distribution of the dispersed gas phase involved in the mixing. The effect of the gas phase structure on the foam concrete mixture was evaluated by the value of the current consumed by the concrete mixer. The results of the experimental studies have shown the relevance of the scientific justification of mass transfer phenomena, that occur during mixing of raw materials in an industrial turbulent mixer. It was found that the process of dispersion of large-sized gas inclusions formed in the foam concrete mixture in the initial period of high-speed mixing is characterized by achieving the maximum power consumption at the mixer shaft. Then there is a slight decrease in energy consumption, in which there is an additional distribution of the dispersed gas phase, sufficient to attain stability of the foam concrete mixture.

Dynamics of interaction of components during mixing

The effect of mechanical action on the mixing and whipping of the mixture of components contributes to the formation of a three-dimensional spongy-reticulate continuous structure of the gluten frame, because it determines the elastic and elastic properties of the medium and is relevant in dispersing gas in a liquid. That is why, the objective of the research was to establish the relationship between the gas-holding capacity of the medium and the energy spent on the hydration of the components. The research solved the problem of determining the gas-holding capacity of the medium with variable parameters of the height of the liquid phase depending on the intensity of mixing, time of the transient processes of formation of the full volume of the gas-liquid medium, time of the transient process of the output of the dispersed gas phase. The difference in levels before the formation of the gas phase and in the mode of mixing (aeration) determines the value of the gas-holding capacity. In this regard, we came to the conclusion about the expediency of the complete destabilization of the established regimes due to the change in the modes of action of the working body in the flow system. At the same time, one more feature should be mentioned. Part of the gas phase that existed and continues to exist in a new regime after mixing enters the regime of the transition process. Therefore, the most effective mixing occurs in case of compliance with the shifted mode of dosing of components in a suspended state and the mechanical influence of the working body. Considering the problems and conditions for mixing the scam, the requirements for the design of the mixer are determined, and also it is established that feeding of components should last at least 45 seconds. During this period, hydration occurs and energy consumption is reduced. This approach of the formation of pulsed flows of surface contours during the interaction in a suspended state of the dosing components, under the rotating action of the disc-shaped working body and the forces of gravity, creates the conditions for intensification of transferring the mass and biochemical processes under conditions of thermodynamic equilibrium with the corresponding desorption bonds of the dissolved part of the gaseous phase and liquid, which reveals a new method of mixing and allows further use of cylindrical working chambers in structural calculations.

Dynamics of interfacial interaction between components during mixing

. The effect of mechanical action on the mixing and whipping of a mixture of components contributes to the establishment of a three-dimensional sponge-mesh continuous structure of the gluten framework, as it determines the elastic and elastic properties of the medium and is relevant in the dispersion of gas in a liquid. The purpose of the work was to establish the relationship between the gas retention capacity of the medium and the energy consumed for the hydration of the components. The experiments performed the task of determining the gas retention capacity of the medium with variable parameters of the height of the liquid phase from the intensity of mixing, the time of the transient processes of the formation of the full volume of the gas-liquid medium, the time of the transient process of the dispersed gas phase. The difference in levels before the gas phase generation and the stirring mode determines the value of gas retention capacity. Therefore, it was concluded that it is expedient to completely destabilise the steady-state regimes by changing the modes of action of the working body in the flow system. An additional impact on the system is the change of hydrodynamic regimes due to the unstable dynamics of the dispersed gas phase generation. The generation of this phase means the presence of energy costs for the interfacial surface establishment, which must be considered in the overall energy balance. In addition, a part of the gas phase, which existed and continues to exist in the new regime after mixing, enters the transient regime. Therefore, the most effective mixing occurs in case of compliance with the shifted mode of dosing components in a suspended state and the mechanical impact of the working body. Considering the tasks and conditions for mixing the dough, the requirements for the design of the mixer are determined, and it is established that the supply of components should last at least 45 seconds. During this period, there is hydration and a reduction in energy consumption. Such an approach intensifies mass transfer and biochemical processes under conditions of thermodynamic equilibrium with appropriate desorption bonds of the dissolved part of the gas phase and liquid, which covers a new method of mixing and allows further use in the design calculations of working chambers

Experimental evidence of a transition from a sponge-like to a foam-like nanostructure in water-rich L3 phases

HypothesisThe micrometer-sized gas bubbles of a liquid foam with a dispersed gas phase of > 74 vol% are polyhedral and surrounded by a continuous aqueous phase. The structure of a water-rich microemulsion with a water phase of > 74 vol% normally consists of oil droplets in water or is bicontinuous. We hypothesize that at these high water contents polyhedral water droplets in oil can also exist. ExperimentsWe (a) carried out phase studies on the water-rich side of the phase diagram of the quaternary system water/NaCl – hexyl methacrylate – AOT, because AOT is known for its propensity to form water-in-oil structures and hexyl methacrylate can be polymerized, (b) measured the electrical conductivities and viscosities, and (c) visualized the nanostructure with freeze-fracture electron microscopy (FFEM). FindingsWe found narrow 1-phase regions emanating from the L3 phase of the oil-free water/NaCl – AOT system by adding small amounts of oil. In these regions the conductivities become extremely low and the viscosities are extremely high. In addition, FFEM images clearly show the foam-like nanostructure.

3D simulation of gas-laden liquid flows in centrifugal pumps and the assessment of two-fluid CFD methods

An assessment of a two-fluid model assuming a continuous liquid and a dispersed gas phase for 3D computational fluid dynamics (CFD) simulations of gas/liquid flow in a centrifugal research pump is performed. A monodisperse two-fluid model, in conjunction with a statistical eddy-viscosity turbulence model, is utilized. By a comprehensive measurement database, a thorough assessment of model inaccuracies is enabled. The results on a horizontal diffuser flow reveal that the turbulence model is one main limitation of simulation accuracy for gas/liquid flows. Regarding pump flows, distinctions of single-phase and two-phase flow in a closed and semi-open impeller are figured out. Even single-phase flow simulations reveal challenging requirements on a high spatial resolution, e.g., of the rounded blade trailing edge and the tip clearance gap flow. In two-phase pump operation, gas accumulations lead to coherent gas pockets that are predicted partly at wrong locations within the blade channel. At best, a qualitative prediction of gas accumulations and the head drop towards increasing inlet gas volume fractions (IGVF) can be obtained. One main limitation of two-fluid methods for pump flow is figured out in terms of the violation of the dilute, disperse phase assumption due to locally high disperse phase loading within coherent gas accumulations. In these circumstances, bubble population models do not appear beneficial compared to a monodisperse bubble distribution. Volume-of-Fluid (VOF) methods may be utilized to capture the phase interface at large accumulated gas cavities, requiring a high spatial resolution. Thus, a hybrid model, i.e., a dispersed phase two-fluid model including polydispersity for flow regions with a dilute gas phase, should be combined with an interphase capturing model, e.g., in terms of VOF. This hybrid model, together with scale-resolving turbulence models, seems to be indispensable for a quantitative two-phase pump performance prediction.

Computational fluid dynamics of rectangular external loop airlift reactor

AbstractThe novel design of a rectangular external loop airlift reactor is at present the most used large-scale reactor for microalgae culture. It has a unique future for a large surface to volume ratio for exposure of light radiation for photosynthesis reaction. The 3D simulations have been performed in rectangular EL-ALR. The Eulerian–Eulerian approach has been used with a dispersed gas phase for different turbulent models. The performance and applicability of different turbulent model’s i.e., K-epsilon standard, K-epsilon realizable, K-omega, and Reynolds stress model are used and compared with experimental results. All drag forces and non-drag forces (turbulent dispersion, virtual mass, and lift coefficient) are included in the model. The experimental values of overall gas hold-up and average liquid circulation velocity have been compared with simulation and literature results. It is seemed to give good agreements. For the different elevations in the downcomer section, liquid axial velocity, turbulent kinetic energy, and turbulent eddy dissipation experimental have been compared with different turbulent models. The K-epsilon Realizable model gives better prediction with experimental results.

Technical support of aerobic fermentation processes

The article shows that aerobic fermentation of sugar-containing media requires the presence of dissolved oxygen in them. In most cases, the latter condition is fulfilled by the introduction and dispersion in the liquid phase of the air, which is compressed to levels corresponding to hydrostatic pressures with some exaggeration. The formation of the dispersed gas phase is accompanied by the interaction of the inlet air and the liquid phase, the efficiency of which is determined by the formed contact surface. The study presents generalizations that relate to the dynamics of biomass growth and correlate with the amount of oxygen introduced into the system. It is important that oxygen refers to gases with limited solubility, and therefore the hydrodynamic state and the interfacial surface are among the factors of intensification of mass transfer processes. It is also shown that the nominal estimation of the hydrodynamic state of gas-liquid media should begin with an assessment of the aeration intensity and it is proposed to take the reduced gas phase velocity as the ratio of the volume air flow to the cross-sectional area of the apparatus. Turning to the indicator of the reduced speed negates the influence of geometrical parameters in the form of the ratio of height and diameter. The results of the process and the efficiency of the equipment used are determined by the performance indicators in the form of concentrations of microorganisms and the output rate of the input power supply. The combination of these requirements leads to the need to combine the maximum achievable concentrations of dissolved oxygen and the minimum concentrations of sugars. The features of the double influence of ambient temperatures in the manifestations of the optimal for microorganisms and for the solubility of gases in accordance with Henry's law are shown, the values of Henry constants are given. The list of factors of influence includes such physical parameters of the environment as viscosity, surface tension, osmotic pressure, hydrostatic pressure, temperature. It is determined that the presence of dissolved nitrogen has an influence on the hydrodynamics of gas-liquid media due to changes in hydrostatic pressure in the circulation circuits.

Interaction of energy-material flows in gas-liquid environments

The article deals with the features of the flow of energy-material transformations in sugar-containing environments of anaerobic fermentation. Endogenous processes - the synthesis of carbon dioxide, the synthesis of ethyl alcohol and the allocation of thermal energy - are estimated as primary with appropriate support based on the chemical energy of sugars. These three processes are accompanied by secondary energy-material manifestations in the following list: mass transfer between yeast cells and the medium; heat transfer between the medium and the cooling surface; creation of local cooled zones with a convective circulating contour; synthesis of the dispersed gas phase with the corresponding component of the circulating circuit; creation of a concentration gradient based on СО 2 by hydrostatic pressure; creation of a driving factor in the form of Archimedes forces in action on the dispersed gas phase and, accordingly, on the liquid phase; vertical mixing of the environment in conjunction with the processes of its saturation and desaturation in local areas at the level of gravity processes. The mathematical formalizations concerning the named secondary energy-material processes with suggestions on improvement and organization of their flow are offered. The basis of the phenomenological analysis of the physical nature of the formation and existence of secondary energy material flows is the laws of thermodynamics, mechanics, hydromechanics, solubility of gases in their flow in a gravitational field under conditions of alternating pressures. It is shown that the natural course of transition processes should be strengthened by additional organized influences.

Gas Phase Back-Mixing in a Mimicked Fischer-Tropsch Slurry Bubble Column Using an Advanced Gaseous Tracer Technique

Abstract An advanced gaseous tracer technique and procedures were developed and executed to study for the first time the axial dispersion of the gas phase in a slurry bubble column reactor (SBCR) using air-C9C11-FT catalyst. Residence time distribution (RTD) curves were obtained by measuring the pulse-input’s response of the gaseous tracer. The gas phase axial dispersion coefficient (Dg) was obtained from minimum square error fit of the one-dimensional axial dispersion model to the measured tracer response data. The effects of solids loading on the axial dispersion of gas phase and the overall gas holdup have been studied. It was demonstrated that increasing solids loading improves the gas axial dispersion while decreasing the overall gas holdup. This work suggests that gas phase axial dispersion is significant in reactor performance evaluation of bubble columns or slurry bubble columns.

The Formation of a Dispersed Gas System in the Flotation Cells

The use of flotation methods for wastewater treatment is due to their advantages in comparison with other methods of gravity separation, for example, sedimentation. The advantages of flotation water treatment methods include the high speed of the separation process, the ability to extract impurities that are close in density to water, environmental friendliness. Flotation methods are based on adsorptive bubble separation processes. Accordingly, the performance of a particular flotator directly depends on the conditions for the implementation of these processes in a particular flotation cell. The aim of the research was to study the relationship between the dispersed gas phase (DGP) and the ratio of the geometric dimensions of the flotation cells based on the proposed shape indicator of the flotation cell. Studies performed on the experimental model of the flotator have established a significant influence of theshape indicator of the flotation cell on such important indicators of the adsorptive bubble separation processes as gas-filling and the DGP floating speed. The evaluation of different forms of flotation cells, in relation to the properties of extracted bubble-particle complexes is given.

Моделирование процесса ректификации с учетом продольной диффузии на уравнения рабочих линий

Analytically, on the basis of the differential equations of material balance, the equations of working lines and mass transfer in the distillation column for binary mixtures for the strengthening and exhaustive parts of the packed distillation column with a diffusion structure of the flow in a continuous liquid phase are derived. Comparative examples of the calculation for typical structures of the flow of ideal displacement are given using the derived equations that take into account the longitudinal diffusion for a “ethanol – ethyl alcohol” binary mixture. A calculation algorithm is proposed and technological and geometrical parameters are compared with similar parameters of the same column, calculated according to a typical algorithm, when the dispersed gas phase has the structure of an ideal displacement flow, and the continuous liquid phase is an ideal mixing. The scheme of material flows and their concentrations is presented in the exhaustive part of the rectification column taking into account the longitudinal diffusion.

Смена винтовых мод возмущений закрученного течения жидкости при подаче дисперсной газовой фазы

Смена винтовых мод возмущений закрученного течения жидкости при подаче дисперсной газовой фазы

Hydrodynamic and energy parameters of gas-liquid media

The paper presents the results of studies related to determining the interconnections between hydrodynamic and energy parameters of gas-liquid media. The whole scope of information about them taken together allows evaluating the prospects of searching for new technologies and their improvement. In the studies, phenomenological generalizations of theories that comply with Archimedes’, Henry’s, Pascal’s laws and the superposition principle have been used to determine the driving and resistance factors when circulation circuits of media appear.
 It is shown that the energy potential of the latter results from the dissolution of the gas phase and the synthesis of the dispersed gas phase during self-organized or forced processes. These two causes are interrelated, but their manifestations are different. The presence of a dispersed gas phase, regardless of the form it appears in, a priori means the presence of a driving factor in the creation of circulation circuits, whereas the presence of a dissolved gas phase is only the root cause of the formation of the dispersed gas phase. In anaerobic processes, gas phase is represented by carbon dioxide, and in aerobic, by air or nitrogen from the composition of air and CO2. The total driving potential of circulation circuits is determined by the gas-holding capacity that, in turn, depends on the intensity of the synthesis of the dispersed gas phase, on the geometry of the media volumes, and on the physical properties of the phases. The gradient by the level of saturation of the liquid phase by the gas phase is determined basing on their physical and chemical properties and by the hydrostatic pressures of the liquid phase. The boundary saturation depends on the gas phase pressure in the supraliquid volume and the hydrostatic pressure. It is shown that a factor that intensifies mass-exchange processes is the relative rate of emergence of the bubbles in the gas phase. Calculation formulae are developed to estimate the gas-holding capacity and driving factors in the form of Archimedes’ buoyant forces. It is pointed out how important circulation circuits are in creating desaturation and saturation zones of media in order to improve the living conditions for microorganisms.

A T-junction device allowing for two simultaneous orthogonal views: application to bubble formation and break-up

A novel design for the classical microfluidic device known as T-junction is proposed with the purpose of obtaining a simultaneous measurement of the in-plane velocity components in two orthogonal planes. A crucial feature of the proposed configuration is that all three velocity components are available along the intersection of the two planes. A dedicated optical set-up is developed to convey the two simultaneous views from the orthogonal planes into the sensor of a single camera, where a compound image is formed showing on either half one of the two views. A commercial micro-particle image velocimetry system is used to measure the velocity in the two planes. Feeding the T-junction with a liquid continuous phase and a dispersed gas phase, the velocity is measured by phase averaging along the bubble formation and break-up process showing the potentialities of the new design. The accuracy analysis shows that the error is dominated by a systematic component due to the thickness of the measurement slice. The error can be reduced by applying confocal microscopy to the present system with no further modifications so as to reduce the thickness of the measurement slab thereby reducing the error. Moreover, by sweeping the planes across the region of interest, a full three-dimensional reconstruction of the velocity field can be readily obtained. Finally, the simultaneous views offer the possibility to extract the principal curvatures of the bubble meniscus thereby providing access to the Laplace pressure.

Peculiarities of Pyrolysis of Hydrolytic Lignin in Dispersed Gas Phase and in Solid State

The unique decomposition pathways of hydrolytic lignin (HL) dissolved in an acetone/water mixture (9:1) and dispersed by a droplet evaporation technique under nitrogen gas flow has been investigated in a conventional reactor at atmospheric condition, a temperature region of 400–550 °C, and a residence time of 0.12 s. The results validate the fact that dispersion of the lignin into the gas phase by decreasing the sample size (as well as “minimizing the char area to avoid catalytic contact” of molecular products/radicals with the surface) may open new perspectives in understanding the chemistry of the depolymerization of lignin. Using Laser Desorption Ionization-Time of Flight-Mass Spectrometry (LDI-TOF-MS) the intrinsic ion m/z = 550, as the major MS peak from fresh HL dissolved in an acetone/water mixture before pyrolysis, was detected. Surprisingly, the expected phenolic compounds after pyrolysis were in trace amounts at less than 15% conversion of lignin. Instead, oligomeric intermediate substances with...

Principle-based design of distributed multiphase segmented flow

The design of systems incorporating multiphase flows remains a significant challenge for applications including lab-on-chip and microreactors. Segmented two-phase flow is used for the purpose of distributing biological samples from one site to many, enhancing heat and mass transport over laminar single phase flow and rapid chemical synthesis. This paper examines hierarchical designs, regularly utilised in such applications, that transport a segmented gas–liquid flow over an area with maximal thermodynamic performance. Fundamental design rules, predicted using the constructal method, minimize flow resistance of elemental bifurcations. The predicted geometric configuration follows an alternative to the established Murray’s law (or Hess–Murray law) when the global pressure difference is dominated by short liquid slugs and dispersed gas phase. Breakup of phases in the junction region was examined numerically with a volume-of-fluid approach to develop a general criteria where junction losses are non-negligible. Although this loss is periodic, the interfacial pressure during the necking stage of the dispersed phase dominates. Using the findings for an elemental bifurcation, multiple scale hierarchical configurations for combined fluid and heat transport were assessed. The multiple scale tree-shaped design can be advantageous for low thermal resistance and pumping power requirements compared to a single scale serpentine layout. The principle-based method and results can reduce the design space in high-fidelity investigations of microscale segmented flows.

Dispersed two-phase flow in a gas–liquid cylindrical cyclone separator

The performance of a gas–liquid cylindrical cyclone separator for the separation of air bubbles from hydraulic fluid has been analyzed numerically using the commercial computational fluid dynamics flow solver CFX. Two-phase flow behavior is modeled based on an Eulerian–Eulerian approach, representing both liquid and dispersed gas phase as interpenetrating media with interphase momentum transfer captured based on existing bubble drag models. Only a single bubble size is considered for the dispersed phase and bubble coalescence is ignored. At the tangential inlet, a homogeneous gas– liquid mixture is assumed with specified mass flow and air/liquid volume fractions. Pressure conditions were imposed at both the upper gas outlet and the lower liquid outlet boundaries. Effect of changes in turbulence model and bubble drag model on analysis predictions was analyzed for selected operating conditions, that is, bubble sizes, air/liquid volume fractions and flow rates. Separation efficiency was high only for larger bubble sizes (100 mm) and high flow rates (250 L/min). For bubble sizes below 35 mm, the cyclone was ineffective. At high flow rates, cyclone performance suffers due to liquid carry over in the form of a swirling liquid wall film carried with the gas (bubble) phase through the top outlet. The Explicit Algebraic Reynolds Stress Turbulence Model together with the Grace Drag Model was found to be effective in exploring changes to the cyclone geometry. Here, improvements in separation efficiency were only achieved with significantly increased tangential velocities as a consequences of a reduced inlet port cross section. Predicted bubble size separation limits as a function of Reynolds number and axial-to-tangential velocity ratios were found to compare favorably with existing literature.

Uncertainty Quantification of the RELAP5 Interfacial Friction Model in the Rod Bundle Geometry

Interfacial friction in the core affects the two-phase mixture level and the distribution of the dispersed gas phase during a small-break loss-of-coolant accident (LOCA). The RELAP5/MOD3.2 code uses the drift flux model to describe the interfacial friction force in vertical dispersed flow, and the Chexal–Lellouche drift flux correlation is used for the rod bundle geometry. In the present study, the RELAP5 model uncertainty was quantified for the bubbly–slug interfacial friction model in the rod bundle geometry by conducting numerical analyses of void profile tests in the Thermal Hydraulic Test Facility (THTF) of the Oak Ridge National Laboratory (ORNL). The model uncertainty parameter was defined as a multiplier for the interfacial friction coefficient. Numerical analyses were performed by adjusting the multiplier so that the predicted void fractions agreed with the measured test data. The resultant distribution of the multipliers represented the interfacial friction model uncertainty.