Gas Injection Velocity Research Articles

Pore-scale study of [formula omitted] desublimation in a contact liquid

Cryogenic carbon capture (CCC) designed to operate in a contact liquid is an innovative technology for capturing CO2 from industrial flue gases, helping mitigate climate change. Understanding CO2 desublimation properties in a contact liquid is crucial to optimizing CCC, but is challenging due to the complex physics involved. In this work, a multiphysics lattice Boltzmann (LB) model is developed to investigate CO2 desublimation in a contact liquid for various operating conditions, with the multiple and fully-coupled physics being incorporated (i.e., two-phase flow, heat transfer across three phases, CO2 transport between the gas and liquid, homogeneous and heterogeneous desublimation of CO2, and solid CO2 generation). The CO2 desublimation process in a contact liquid is well reproduced. Moreover, parametric studies and quantitative analyses are set out to identify optimal conditions for CCC. The decreasing liquid temperature (Tl) and flue gas temperature (T0) are found to accelerate the CO2 desublimation rate and enhance the CO2 capture velocity (vc). However, excessively low Tl and T0 values should be avoided. These conditions increase the energy consumption of cooling while only marginally improving vc, due to the limited CO2 supply. The CCC system performs effectively when purifying flue gases with high CO2 content (Y0). This is because the large Y0 accelerates the CO2 desublimation rate and enhances the overall CO2 capture efficiency. A high gas injection velocity (or Pe) is beneficial for amplifying vc by increasing the gas–liquid interfaces and enhancing the CO2 supply. Nevertheless, too high a Pe should be avoided, as it hinders the transport of CO2 to the liquid or solid CO2 surfaces, ultimately restricting the amount of CO2 available for desublimation and inhibiting the enhancement of vc. This study develops a viable LB methodology to investigate CO2 desublimation in a contact liquid for varying conditions, which advances the knowledge base of CCC and facilitates its industrial applications.

Jet injection and spout formation in a fluidized bed

A single jet was studied in a rectangular fluidized bed by analyzing the pressure fluctuations data to characterize the jet hydrodynamics. The bed contained with glass beads of different mean sizes (450, 650, and 920 µm) as well as pharmaceutical pellets (920 µm). The analysis of the pressure fluctuation data was performed using the power spectral density function (PSDF) and discrete wavelet transforms technique. This study investigated how the flow regime changed from a jet in a fluidized bed to a spouted regime as the gas injection velocity was increased. Increasing the mean particle size led to an increase in the minimum spouting velocity. The minimum spouting velocity for 450, 650, and 920 μm glass bead particles and for 920 μm pharmaceutical pellets were determined to be 32.47 m s-1, 38.66 m s-1, 44.78 m s-1, and 44.47 m s-1, respectively. The study also examined how the dominant frequency of the various particles and the energy percentage of scales changed with increasing injection velocities. The ratio of energy percentages of meso-scale changes as the injection velocity increases and these changes were used to estimate the minimum spouting velocity. Wavelet sub-signals analysis revealed that the Daubechies 2 (DB2) wavelet was the most effective at capturing the characteristics of the jet. Based on the Shannon entropy of the approximate coefficients, the wavelet analysis showed that 11 levels of decomposition were required. By combining the wavelet analysis and PSDF, a more detailed analysis of the meso-scale was achieved. This study provided valuable insights into the behavior of jets and spouts in fluidized beds, which can greatly contribute to the optimization of a jet in fluidized beds and spout-fluidized beds by enhancing our understanding of jet behavior in such environments.

Assessment of the coating quality in a top-spray fluidized bed coater: An experimental study

The effects of multiple factors on the coating process in a top-spray fluidized bed coater were systematically investigated. The intra-particle coating variability could be assessed by the SEM measurement. Fluidizing gas temperature (0.5–0.9, normalized by the boiling point of water), injection velocity (0.115–0.397 m/s) and concentration (2.1–5.2 wt%) of the coating liquids, atomizing pressure (1.0–3.0 bar) and nozzle height (378 and 470 mm) were found to impact particle agglomeration, coating efficiency and thickness dramatically. Their impact trends and mechanisms were analyzed in detail. The effect of the particle size (0.22–1.26 mm) on particle agglomeration behavior was highlighted. Critical injection velocities and the corresponding agglomeration ratios were experimentally determined. Finally, it was established that there were no universal optimum conditions for the spray coating process, and they can be experimentally determined according to the attributes of interest.

Numerical investigation of gas-liquid flow hydrodynamics in three-dimensional bottom-blown reactor via LES-VOF coupled model

In this study, a coupled interface-resolved volume of fluid model and large eddy simulation is employed to explore bubble dynamics in a three-dimensional bottom-blown reactor. After the model validation, the bubble plume area, motion characteristics, and force analysis are analyzed. Three distinct stages of bubble rising are quantitatively identified: disengaging nozzle stage, accelerated ascent stage, and stable upward stage. Specifically, an increase in reactor height reduces both the bubble rising velocity and interphase surface tension impact. Moreover, the influence of inlet size on bubble volume frequency distribution surpasses that of gas injection velocity. The gas penetration depth remains relatively unchanged amidst variations in boundary conditions, while the liquid type profoundly influences it. Axial fluid velocity, dynamic pressure, Reynolds number, and turbulent viscosity peak at the reactor center. Liquid back-mixing is found near the bottom blowing wall region, coupled with an enhanced distribution of turbulent viscosity.

Numerical modelling of stirring characteristics of gas−slag−copper matte multiphase flow in bath with top submerged lance

The hydrodynamics and stirring characteristics of the nitrogen−slag−copper matte in a bath with top submerged lance were numerically studied via the volume-of-fluid (VOF) method. The relationship between the bubble behavior and fluid velocity was elucidated. The effects of gas injecting velocity and swirling flow on the fluid vortex structure, gas penetration depth, and fluid velocity were investigated. The results demonstrate that the formation and rising of the bubble increase and reduce the fluid velocity, respectively. The V-shaped and W-shaped temperature distributions of the fluid are observed at the height of 0.43 and 0.52 m, respectively, resulting from the injection of the low-temperature gas phase. Compared to the gas injection velocity of 58 m/s, the time-averaged and maximum penetration depths of the gas phase with the injection velocity of 96 m/s increase by 78.4 % and 31.9 %, respectively. Swirling flow reduces the gas penetration depth, enhances the momentum transfer efficiency between phases, and suppresses the slag splashing, which is attributed to the reduced axial velocity component.

DOPPLER OPTICAL PROBE FOR DROP SIZE, VELOCITY, AND FLUX MEASUREMENTS IN ASSISTED ATOMIZATION

For research as well as for process control, reliable drop size, velocity, and flux measurements are desirable in particular in dense, high-speed flows. A new optical probe has been recently manufactured by A2 Photonic Sensors company that combines an accurate phase detection capability (its latency length is small, about 6 µm) with the collection of a Doppler signal that provides the absolute velocity of an incoming gas-liquid interface. In this article, raw signals acquired over diverse flow conditions in terms of gas velocity and liquid concentration are analyzed. A dedicated signal processing routine is then proposed and optimized. The latter provides statistics on drop velocity and size. It also gives access to local liquid concentration and liquid flux. This Doppler probe combined with its processing has been tested in sprays produced from assisted atomization over a wide range of flow conditions. Transverse profiles of spray characteristics are presented for gas injection velocities ranging from 32 m/s to 283 m/s, for drops Sauter mean diameters D<sub>32</sub> varying from 37 µm to 275 µm, and for number densities-as estimated from liquid concentration and D<sub>32</sub>-comprised between 1 #/mm<sup>3</sup> and 218 #/mm<sup>3</sup>. The Doppler probe happens to be able to consistently detect chords as small as 4 µm, and to ensure a significant (up to 70%) fraction of direct velocity measurements. Besides, the injected liquid flow rate is recovered from the spatial integration of local liquid fluxes within 8% for gas velocities up to 50 m/s and within 17% for gas velocities above 90 m/s. Hence, the new Doppler probe combined with the proposed processing provides reliable statistics on drop velocity, size, and flux, and is a valuable tool for investigating dense, high-velocity, and fine sprays.

Angular momentum Based-Analysis of Gas-Solid fluidized beds in vortex chambers

Gas-solid vortex chambers are a promising alternative for reactive and non-reactive processes requiring enhanced heat and mass transfer rates and order-of-milliseconds contact time. The conservation of angular momentum is instrumental in understanding how the interactions between gas, particulate solids, and chamber walls influence the formation of a rotating solids bed. Therefore, this work applies the conservation of angular momentum to derive a model that gives the average angular velocity of solids in terms of gas injection velocity, wall-solids bed drag coefficient, gas and particle properties, and chamber geometry. Three datasets from published studies, comprising 1 g-Geldart B- and d-type particles in different vortex chambers, validate the model results. Using a sensitivity analysis, we assessed the effect of input variables on the average angular velocity of solids, average void fraction, and average bed height. Results indicate that the top and bottom end-wall boundaries exert the most significant braking effect on the rotating solids bed compared with the cylindrical outer wall and gas injection boundaries. The wall-solids bed drag coefficient appears independent of the gas injection velocity for a wide range of operating conditions. The proposed model is a valuable tool for analyzing and comparing gas–solid vortex typologies, unraveling improvement opportunities, and scale-up.

Numerical study on the release and migration behavior of fission gas in a molten LBE pool

The lead-cooled fast reactor (LFR) is one of the most promising fast neutron reactors using molten lead or the lead–bismuth eutectic (LBE) alloy as a coolant. Under postulated severe accidents, the fuel rod of LFR may be damaged, which would cause the release of fission gas, and the migration of fission gas bubbles in the reactor molten pool will affect the release and absorption of radioactive substances in the reactor. In this paper, a three-dimensional numerical study on the release and migration behavior of fission gas in the molten LBE pool of LFR is carried out based on the volume of fluid method. The bubbles are continuously released by gas injection, and the research mainly focuses on the detachment time, the rising velocity, and the size of the bubble when it detaches at the orifice. The coalescence of bubbles is observed, and the acceleration effect of the bubble wake is confirmed. The distribution of the bubble terminal rising velocity with diameter has no simple or linear relationship. The effects of the gas injection velocity, the release depth, and the gas injection angle are studied. A lower gas injection velocity will delay the detachment and reduce the size of the bubble. The increase of release depth tends to release smaller bubbles. The bubbles released from a vertical surface will attach to the wall. The simulations and theoretical analysis are comparable and have similar tendencies. The distribution of the bubble terminal rising velocity with equivalent diameter may predict the migration behavior of bubbles in molten LBE.

Three-Dimensional Numerical Simulation of Hydrocarbon Production and Reservoir Deformation of Oil Shale In Situ Conversion Processing Using a Downhole Burner.

A three-dimensional numerical simulation of oil shale in situ conversion processing by applying the downhole burner heating technology was conducted. The evolution of the fluid vector and temperature field and the characteristic of kerogen decomposition and oil and gas production were analyzed. The effects of different burning temperatures and gas injection velocities on the thermal evolution processing of oil shale in situ conversion were investigated. The stress–strain and deformation of the oil shale stratum during in situ processing were studied. The results show that kerogen decomposition is a thermo-kinetically controlled mechanism. Both the gas injection velocity and burning temperature can enhance the kerogen decomposition and oil production, especially for the latter one. In addition, the stratum–deformation of oil shale should be considered for oil shale in situ conversion processing, especially for the long-term operational lifetime.

Modeling of Advanced Silicon Nanomaterial Synthesis Approach: From Reactive Thermal Plasma Jet to Nanosized Particles.

A three-dimensional numerical modelling of a time-dependent, turbulent thermal plasma jet was developed to synthetize silicon nanopowder. Computational fluid dynamics and particle models were employed via COMSOL Multiphysics® v. 5.4 (COMSOL AB, Stockholm, Sweden) to simulate fluid and particle motion in the plasma jet, as well as the heat dependency. Plasma flow and particle interactions were exemplified in terms of momentum, energy, and turbulence flow. The transport of nanoparticles through convection, diffusion, and thermophoresis were also considered. The trajectories and heat transfer of both plasma jet fields, and particles are represented. The swirling flow controls the plasma jet and highly affects the dispersion of the nanoparticles. We demonstrate a decrease in both particles’ velocity and temperature distribution at a higher carrier gas injection velocity. The increase in the particle size and number affects the momentum transfer, turbulence modulation, and energy of particles, and also reduces plasma jet parameters. On the other hand, the upstream flame significantly impacts the particle’s behavior under velocity and heat transfer variation. Our findings open the door for examining thermal plasma impact in nanoparticle synthesis, where it plays a major role in optimizing the growth parameters, ensuring high quality with a low-cost technique.

The effect of gas injection velocity and pore morphology on displacement mechanisms in porous media based on CFD approach

Because of the unique advantages such as easy miscibility, high temperature resistance and so on, hydrocarbon gas flooding has proved to be a promising technology for enhanced oil recovery in deep reservoirs. In order to reveal the potential mechanism of miscibility and displacement of crude oil and hydrocarbon gas, an innovative two-dimensional physical field model is constructed by coupling Navier-Stokes equations and mass transfer equation. Accordingly, the effect of gas injection velocity and pore morphology on fluid transport and miscibility properties is investigated based on computational fluid dynamics approach. The simulation results demonstrated that the residual oil (RO) content is lower at low gas injection velocity than that at high gas injection velocity due to the better miscibility of fluids. For pore morphology, the RO content increases with increasing pore throat ratio and pore throat angle, which are not related to the gas injection velocity. The blocked pore structure has a negative effect on hydrocarbon gas flooding, resulting in the higher RO content. In addition, the influence of the pore throat length on the RO content is related to the gas injection velocity, which means the RO content increases at low gas injection velocity and decreases at high gas injection velocity with increasing pore throat length.

Experimental study of the nozzle size effect on aerosol removal by pool scrubbing

Pool scrubbing is the phenomenon of removing contaminants by injecting a contaminated gas into a water pool. In the nuclear industry, this technique is used as a method to reduce the release of radioactive materials into the environment during severe accidents. In this approach, aerosol particles are removed through interactions between the injected gas and water so that properties, such as the pool height, pool temperature, gas flow rate, and steam fraction are important in determining pool scrubbing performance. In particular, since the size of the injection nozzle is a crucial factor when evaluating the velocity, flow regime, and bubble size of the injected gas, experimental studies are needed to observe the bubble behavior and aerosol removal effect due to the size of the nozzle. In this study, visualization experiments were conducted to observe the behavior of the injected gas using a high-speed camera to analyze the effect of nozzle size on pool scrubbing efficiency, and aerosol removal experiments were also performed. Additionally, the experimental results were simulated using a pool scrubbing code. In the visualization experiments, as the nozzle size increased, the gas injection velocity decreased, and the globule size at the nozzle inlet increased. In the aerosol removal experiments, the decontamination factor (DF) decreased from 197 to 6.2 as the nozzle size increased from 5 mm to 30 mm. As a result of the pool scrubbing code simulations, the DF decreased with nozzle size, and the trend was the same as the experimental results.

Effect of gravity segregation on CO2 flooding under various pressure conditions: Application to CO2 sequestration and oil production

This research evaluates the effect of gravity segregation on CO2 sequestration and oil production during CO2 flooding under immiscible, near-miscible, and miscible conditions. The core experiment results show that CO2 flooding recovery was seriously affected by gravity under immiscible conditions, while under miscible conditions, this influence was not apparent. Visual experiments show when immiscible, gravity restricts the oil and gas front’s stability, and different gas injection strategies have evident differences in the swept region; when miscible, gravity has almost no effect on the swept region. These results indicate that when CO2 immiscible flooding is implemented, the reservoir thickness affects the choice of gas injection direction. However, for miscible flooding, the reservoir thickness and gas injection direction are not essential for developing CO2 flooding. In immiscible conditions, gas injection velocity greatly restricts the CO2 gravity flooding recovery; in miscible conditions, the velocity is no longer the main influencing index of CO2 gravity flooding recovery. For CO2 sequestration, gravity segregation is conducive to increasing CO2 sequestration potential. As the pressure increases, the influence of gravity on CO2 sequestration weakens. Regardless of whether there is gravity effect, the best oil recovery and gas sequestration potential of CO2 flooding is obtained under miscible conditions.

A Mathematical Model of Intermittent Gas Lift in Elevation-Production Operation with Line-Pack and Line-Drafting Phenomena in a Gas Line

This paper discusses a transient model of the intermittent gas lift technique in an oil well. The model is developed in the gas line, in the tubing-casing annulus, and the tubing. The line-pack and line-drafting phenomena in the gas line are considered in the model. A numerical approach will be used to solve the mathematical model that represents fluid flow during intermittent gas lift injection. The dynamics of important variables in the intermittent gas lift are investigated and analyzed to determine the best production strategy for intermittent gas lift. The variables are film thickness and velocity, slug height and velocity, and gas height and velocity. The relationships between surface injection control parameters (gas injection pressure and gas injection rate) and the velocity and height of film, gas, and liquid are shown in one cycle of the gas lift intermittent process. The higher the gas injection pressure, the faster the gas injection velocity, and the thinner the film thickness in the tubing. In order to obtain clean tubing from film thickness, the gas injection pressure needs to be optimized, which will lead to maintaining compressor discharge pressure availability. Detailed observation of the dynamic performance inside the tubing production well will give the optimum oil production rate for oil wells under a gas lift intermittent production strategy for field application.

Experimental investigation on stable displacement mechanism and oil recovery enhancement of oxygen-reduced air assisted gravity drainage

The effects of gravity, capillary force, and viscous force on the migration characteristics of oil and gas interface in oxygen-reduced air-assisted gravity drainage (OAGD) were studied through a two-dimensional visualization model. The effects of bond number, capillary number and low-temperature oxidation on OAGD recovery were studied by long core displacement experiments. On this basis, the low-temperature oxidation number was introduced and its relationship with the OAGD recovery was established. The results show that the shape and changing law of oil and gas front are mainly influenced by gravity, capillary force and viscous force. When the bond number is constant (4.52×10 −4 ), the shape of oil-gas front is controlled by capillary number. When the capillary number is less than 1.68×10 −3 , the oil and gas interface is stable. When the capillary number is greater than 2.69×10 −2 , the oil and gas interface shows viscous fingering. When the capillary number is between 1.68×10 −3 and 2.69×10 −2 , the oil and gas interface becomes capillary fingering. The core flooding experiments results show that for OAGD stable flooding, before the gas breakthrough, higher recovery is obtained in higher gravity number and lower capillary number. In this stage, gravity is predominant in controlling OAGD recovery and the oil recovery could be improved by reducing injection velocity. After gas breakthrough, higher recovery was obtained in lower gravity and higher capillary numbers, which means that the viscous force had a significant influence on the recovery. Increasing gas injection velocity in this stage is an effective measure to improve oil recovery. The low-temperature oxidation number has a good correlation with the recovery and can be used to predict the OAGD recovery.

Evaluation of drag force around bubble in an incipiently fluidized bed via a coupled CFD-DEM approach

Detailed micromechanical analysis of an individual bubble injected into a three-dimensional incipiently fluidized bed is carried out by means of a coupled CFD-DEM approach. The distribution of interphase drag force vectors is consistent with the gas flow pattern based on the potential flow theory. The non-uniformity of drag force caused by bubbles is quantitatively analyzed. Moreover, a bubble-induced inhomogeneous coefficient is presented to assess the ensemble bubble impact. The effects of particle diameter and gas injection velocity are evaluated. The results reveal that the bubble negative effect on interphase drag force is strengthened by increasing the particle diameter and gas injection velocity.

Sparger design as key parameter to define shear conditions in pneumatic bioreactors

The average shear rate (γ˙av) is a parameter used to characterize the shear environment in bioreactors, enabling comparison of the performances of different bioreactor models in terms of microorganism morphology and viability, and consequently bioproduct formation. Based on this approach, pneumatic bioreactors have been classified as low shear devices. However, the shear behavior cannot be generalized over a wide range of operating conditions, suggesting that the maximum shear rate (γ˙max) may be more suitable for the purpose of bioreactor performance comparison. Therefore, the aim of this work was to evaluate average and maximum shear rates in pneumatic bioreactors (bubble column and airlift), based on computational fluid dynamics (CFD) simulations. Concentric-duct and split airlift bioreactors exhibited higher γ˙av values, compared to the bubble column design, due to the nature of the liquid circulation patterns. The pneumatic bioreactors exhibited a significant (order of magnitude) difference between γ˙av (11.0–27.3 s−1) and γ˙max 4555 to 25,040 s−1), reflecting a non-uniform spatial distribution. The γ˙max values occurred close to the sparger holes and presented a linear relationship with gas injection velocity, which is dependent on the sparger geometry. In this way, sparger characteristics (number and diameter of sparger holes) defined γ˙max values in pneumatic bioreactors, showing that sparger should be properly designed in order to avoid excessive local shear rates.

A parametric study of the drying process of polypropylene particles in a pilot-scale fluidized bed dryer using Computational Fluid Dynamics

Fluidized Bed Dryer (FBD) is one of the efficient methods for drying moist particulate products. At the same time, the design and optimization of a full industrial scale FDB requires extensive studies. Using a pilot-scale dryer can be deemed as an efficient tool to obtain essential information on the drying phenomenon. Although these kinds of experimental analyses can provide valuable insight, there are still some operational limitations, including high-pressure or high-temperature conditions, which make the use of a computational procedure highly desirable. In this study, Computational Fluid Dynamics (CFD) approach has been employed to investigate a dryer. The results of numerical simulations were verified using the experimental data obtained from a pilot-scale dryer. The present investigation aims to study the effects of different operating conditions. It was observed that the impacts of gas inlet temperature were negligible, as the dryer was equipped with a thermal jacket, while the gas injection velocity had significant effects on the dryer’s performance. Moreover, the efficiencies of the conical and horizontal gas distributors were compared and it was concluded that the conical configuration results in better performance. The numerical and experimental investigation from this study can facilitate the design and scale-up of an industrial dryer plant.

Investigation of dust dispersion in a modified Hartmann tube using positron emission particle tracking and simulations

An important research tool that is used for assessing fundamental dust explosion characteristics is the Hartmann apparatus, where dust is dispersed by a pressure wave. Nevertheless, it is questionable as to whether the formed dust cloud is uniformly dispersed as well as how the solid particles behave as they flow. In this study we used two research tools. The first one is the novel experimental technique Positron Emission Particle Tracking (PEPT). It derives from Positron Emission Tomography (PET) technique that is normally used in the medical environment. PEPT is a technique of tracking individual particles and can be used for studying multiphase flows. Thus the main objective of this paper is to demonstrate how this method can be used for studying such systems. The second tool we used in this research is numerical simulations in which the Eulerian-Lagrangian approach was adopted. Therefore the second main objective of the paper is to investigate the flow of a single particle in the Hartmann apparatus and show the complexity of the problem. According to the experimental results the process is highly stochastic and influenced not only by the injection pressure but also by the initial conditions and geometry. High injection pressures lead to frequent particle collisions with the walls resulting in a potential loss of kinetic energy. The simulations showed that the vertical velocity profile of the fluid flow distribution was non-symmetric even though the previous numerical studies showed the opposite. This may have influenced the dust dispersion process. The influence of the gas injection velocity is only important in the beginning of the dispersion process but not further into the process. During this period we observed frequent collisions that counteracted the acceleration of the particle, and the value of the coefficient of restitution influenced the rate of deceleration.

Investigation on jet scrubbing in nuclear reactor accidents: From experimental data to an empirical correlation

The Fukushima accident stressed the significance of suppression pools as passive systems for fission product trapping. Even though pool scrubbing was extensively investigated in the past, there are gaps in the existing data base and modeling that need to be addressed, particularly those relative to high gas injection velocities in the pool. In this paper, the main results of an experimental campaign (PSP tests) on particles scrubbing at the pool inlet region when the carrier gas forms a submerged jet (“jet scrubbing”), are presented and discussed. The tests have been conducted in the PECA-PS facility of the Laboratory for Analysis of Safety Systems (LASS) and the experimental conditions have been based on two non-dimensional variables: the Weber non-dimensional number, which has been set to values over the threshold from globule to jet regime; and the gas saturation ratio, which has ranged from under saturation to over-saturation. Jet scrubbing efficiency at the pool inlet has been measured to be over 90% whenever the gas enters the pool within the jet regime (Wetest ≥ Wec), regardless thermal boundary conditions. Analysis of gas steam content, though, has not shown any clear trend. Based on the PSP experiments and some others gathered from the open literature, a tentative correlation dependent on non-dimensional Stokes number (Stk), which accounts for inertial impaction, and saturation ratio (S), which captures diffusiophoretic deposition, has been proposed as a first step to empirically model jet scrubbing. Finally, some lessons learned for forthcoming experiments have been withdrawn, particularly concerning the high impact of hydrodynamics.This work has been done within the framework of the 7th FWP of EURATOM through the EU-PASSAM project (Grant agreement No. 323217 – Euratom 7FP).