Bubble Swarm Research Articles

Research and Model Prediction on the Performance of Recycled Brick Powder Foam Concrete

In order to achieve resource conservation, protect the environment and realize the sustainable development of the construction industry, the low energy resource utilization of construction waste was explored. In this paper, the effect of air bubble swarm admixture, recycled brick powder admixture, water to material ratio, and HPMC content on the physical and mechanical properties of recycled brick powder foam concrete was investigated by conducting a 4‐factor, 5‐level orthogonal test with recycled brick powder as fine aggregate, and the effect of each factor on the physical and mechanical properties of recycled brick powder foam concrete was derived, and the optimum ratio of recycled brick powder foam concrete was determined by analysing the specific strength. Five machine learning models, namely, back propagation neural network improved by particle swarm optimization (PSO‐BP), support vector machine (SVM), multiple linear regression (MLR), random forest (RF), and back propagation neural network (BP), were used to predict the compressive strength of recycled brick powder foam concrete, and the PSO‐BP model was found to have obvious advantages in terms of prediction accuracy and model stability. The experimental results and prediction models can provide experimental and theoretical references for the research and application of recycled brick powder foam concrete.

Particle decontamination from elliptical bubbles in scrubbing pools simulated using Eulerian–Lagrangian method

The particle dynamics in the rising bubble swarm is dominant in the scrubbing pools to remove the contaminated aerosol/particles. These gas bubbles occurred in the three shapes, spherical for small bubbles, ellipsoidal for median-size bubbles and spherical cap for large bubbles. In this paper, the aerosol particle decontamination in the median-sized rising bubble in the ellipsoidal shape is simulated using the Eulerian-Lagrangian method. The particle flow is traced by Discrete phase method (DPM). The mechanism of particle coagulation/agglomeration and particle decontamination in the elliptical bubbles are investigated with the effect of the bubble dynamics and particle properties from the simulation. The simulated decontamination factors (DFs) of particles in the elliptical bubbles are compared with the DFs of particles in spherical bubbles in previous research [1].

Direct numerical simulation of deformable rising bubbles at low Reynolds numbers

We investigate numerically the dynamics of freely rising gas bubbles driven by buoyancy at low Reynolds numbers, focusing on two distinct characteristics: the clustering morphology and the probability density functions (p.d.f.) of the velocity fluctuations for bubbles. A modified Volume-of-fluid (VOF) method is implemented in our direct numerical simulations to circumvent the nonphysical coalescence between bubbles. Four values of the gas fraction are studied: 5%, 10%, 15%, and 20%. The Eötvös number and the Galileo number are fixed at Eo = 2 and Ga = 855, respectively. For a single rising bubble, the Reynolds number according to the terminal velocity and the bubble diameter is around 27, displaying an ellipsoidal shape. For a swarm of bubbles, both irregular and regular clustering configurations are observed in our numerical simulations as we vary the gas fraction, which can only be realized at high Reynolds numbers in the previous experiments due to the low gas fraction limit. Moreover, we find that the p.d.f.s for bubble velocity fluctuations exhibit distinctly different behavior from the high Reynolds number experiments. The horizontal components for these p.d.f.s approach Gaussian distributions only when the gas fraction is high, i.e., α=15% and 20%. It suggests that the strong bubble–bubble interaction through their flow wakes is an efficient way to trigger the flow into turbulent states.

Evaluation of models for bubble-induced turbulence by DNS and utilization in two-fluid model computations of an industrial pilot-scale bubble column

This paper presents numerical studies on modeling of bubble induced turbulence at two significantly different scales. On the scale of a bubble swarm, direct numerical simulations are performed with a geometric volume-of-fluid method and the budget equation of liquid phase turbulence kinetic energy is analyzed. By a priori testing of models for the interfacial term in this equation, suitable closure relations are identified. On the scale of an industrial bubble column, simulations with a two-fluid model are performed with water and cumene as liquid phases under elevated pressures. Turbulence is taken into account by a mixture k–ε model, considering two closure relations for the interfacial term identified from the DNS. For both liquids, an influence of the model for the interfacial term on turbulence kinetic energy and gas holdup is found, which is, however, small at elevated pressures. Numerical results for local and overall gas holdup are in reasonable agreement with measurements reported for this industrial pilot-scale bubble column. For the overall gas holdup, an empirical correlation from literature is identified which predicts the present numerical results reasonably well.

Numerical study on particle decontamination from spherical bubbles in scrubbing pools by using Eulerian–Lagrangian method

Pool scrubbing is conducted to remove contaminated aerosols/particles released from nuclear power generation systems in severe accidents. Gas-entrained particles pass through the pools in three stages: 1) injection into the pools through a vent, 2) decontamination process in bubbles rising in the pools, and 3) secondary entrainment into the atmosphere at the pool surface. The particle separations in the rising bubble swarm constitute the primary process for aerosol decontamination. The dynamics of the particles contained in the rising bubble swarm are crucial. Numerical modeling of particle transportation in bubbles in three-phase systems is complex and challenging. This study aimed to investigate the particle flow dynamics in scrubbing pools to understand the particle decontamination mechanism, which can guide equipment design to achieve high aerosol separation efficiency. In this study, particle decontamination in bubbles is simulated by using the Eulerian–Lagrangian method. This numerical method is used to investigate the mechanisms of flow dynamics, coagulation, and separation of particles in the bubbles, as well as the particle decontamination affected by the operation parameters such as the bubble velocity, and gas and particle properties. In addition, the decontamination factor is predicted for aerosol particles in the small bubbles of the rising swarm, which agrees with the calculated experimental DF of the bubble swarm.

Hybrid CFD-experimental investigation into the effect of sparger orifice size on the metallurgical response of coal in a pilot-scale flotation column

ABSTRACT Although column flotation cells have been extensively studied in the literature, the hydrodynamic impact of orifice properties has not been adequately addressed yet. This paper initially investigates the effect of sparger orifice diameter on hydrodynamic behavior of coal particles in a pilot-scale column flotation. The metallurgical responses (i.e., ash, yield and recovery contents) were evaluated for four different sparger orifice sizes including 1, 3, 5, and 7 mm under constant operating conditions by experimental measurements associated with computational fluid dynamics (CFD) simulations. A numerical model of a two-phase air-water flow in the column (3 m × 0.5 m) was chosen and the turbulence patterns inside the collection zone and at the pulp-froth interface were simulated by employing the Volume-Of-Fluid (VOF) model. The experimental results indicated that desiring concentrated product i.e., ash content of 8.8% and yield of 57.2% could be obtained using the 3 mm orifice size. Simulation results revealed that as the sparger orifice size decreased to 1 mm, the reduced carrying capacity of the bubbly regime led to the poor flotation performance. In contrast, the turbulence condition intensified as the sparger orifice size was increased to 7 mm. Another negative consequence of the 7 mm orifice was attributed to the exceeded entrainment of high ash fines due to a bubble swarm mechanism. The 7 mm sparger orifice diameter showed a concentrate of 17.1% ash and 12.5% yield. Finally, according to the obtained results in this work and literature studies, several necessary highlights were suggested for future works in this scope.

Bubble cascade may form not only in stout beers.

In a glass of stout beer, a very large number of small dispersed bubbles form a texture motion of a bubble swarm moving downwards. Such a cascading motion is caused by a gravity-driven hydrodynamic instability and depends on the interbubble distance. To estimate these two corresponding indicators, an experimentally measured velocity profile is required and, thus, is obtained a posteriori. However, it is unknown why the bubble cascade is observed only in stout beer with nitrogen, such as Guinness beer. To address this question via a priori estimation, here, we develop a mathematical continuum model of film flow in bubbly liquid, uncovering the essential dynamics among many physical processes occurring simultaneously in a glass. To validate the proposed model, we perform a numerical simulation of the distribution of massless Lagrangian particles in an inclined container. We investigate the effects of particle concentration, inclination angle, particle diameter, and container size on the cascading film flow. The results reveal that the motion and waviness of clear-fluid film can be successfully estimated a priori to experiments or simulations. Moreover, it is found that the continuum behavior of particles in the film flow is analogous to the continuum description of rarefied gas dynamics. These findings explain how the cascading bubbles in a pint glass of stout beer satisfy the continuum assumption and suggest a general condition for the onset of the cascade, for instance, a 200-l drum for carbonated water.

Bubble characteristics from injected air sheet through slots in a water cross-flow

While air injection has already been widely studied for stagnant water at low air injection rates for circular injectors, limited data is available on gas in liquid cross-flows injected through slots at high air flow rates. The key purpose of this work is to observe the evolution of bubble swarm characteristics for simple geometries such that, by correlation rules, these characteristics can be projected for more complicated geometries and environment. To that effect, an experimental water loop with both controllable water and air flow rates is used to generate bubble clouds with cross-flow air injection.Measurements with an optical probe allow the void fraction, the size and velocity of bubbles to be measured. The findings show that the general size of bubbles increases with an increase in the air flow rate for a constant water flow rate. Furthermore, bubbles pick up speed while moving away from the injection slot. Bigger bubbles travel faster than small ones ; they also tend to rise to the top of bubble plumes while small bubbles stay in the lower portion. Finally, the maps of void fraction indicate that its local values drop while heading away from the injection slot.

Study on the slag-metal interfacial behavior under the impact of bubbles in different sizes

A novel ladle shroud was employed to produce small bubbles to remove inclusions smaller than 50 μm meanwhile inhibiting the formation of slag eye. Both water modeling and industrial tests were carried out to confirm the generation of small bubbles with the ladle shroud. The numerical model was developed to investigate slag-metal interfacial behaviors, considering the effects of bubble sizes and distributions. The gas flux through the surface was employed to evaluate the impact of bubble swarm on slag layer. The results show that reducing bubble sizes can effectively disperse bubbles passing through the slag layer, so as to inhibit the formation of slag eye, under the same gas flow rate. The diameter of slag eye matches well 1.7 times diameter of the region with gas flux higher than 0.0025 m/s. The heat loss of the entire tundish was estimated, considering the convection and radiation heat transfer of slag eye.

Species transport analysis of noble metal fission product transport, deposition, and extraction in the molten salt reactor experiment

This work provides a general overview of the detailed reports of noble metal fission product behavior during the Molten Salt Reactor Experiment (MSRE) and applies a species mass transport analysis to replicate and explain the basic behavior of these fission products in molten salt systems. Specifically, the operational difference between the MSRE experimental runs which used 235U and 233U as the enriched fuel is described and analyzed in light of the different transport behavior of noble metals during these two very different sets of operational runs. The generation of a circulating helium bubble swarm during the MSRE is also analyzed and a helium bubble model is coupled with the noble metal mass transport analysis. This coupled model provides specific insight in how noble metal deposition on the helium bubble swarm affected the reactor behavior and the results are discussed in relation to the general findings of the MSRE.

Experimental study of SRT scrubbing model in water coolant pool

In pool-type nuclear reactors, a postulated fuel pin failure can result in the release of fission products into the coolant pool. While the coolant pool itself tends to scrub the majority of radionuclides, they have the potential to be transported to the cover gas region via entrainment in gaseous bubbles. The SRT source term analysis code includes models to assess this pool scrubbing behavior and calculate the ratio of fission product aerosols that reach the cover gas. This code was developed to model pool-type sodium cooled fast reactors, but underlying models can also be used to predict pool scrubbing in a water coolant pool with dry air bubbles passing through as a test of the physics. The accuracy of this code is analyzed in this paper. A parametric study was conducted to determine the significance of bubble size, aerosol density, pool depth, and aerosol concentration, over a wide range of aerosol sizes, on the pool scrubbing efficiency. The basic tests were run with isolated bubbles as to best match the assumptions within the code. For simulating potentially realistic pool scrubbing conditions, an applied test was run injecting a bubble swarm into the pool to analyze the bubble-to-bubble interactions. From these results, it was found that the SRT code matches the trends found experimentally, but underestimates the actual amount of pool scrubbing. The bubble swarm testing further exemplifies this trend. Furthermore, it was determined that the overall pool scrubbing increases with bubble size, aerosol density, and pool height and is unchanged by aerosol concentrations. Additionally, aerosol sizes ranging from one to 0.01 µm were found to be of particular interest as the lowest amount of scrubbing occur over this range. These tests also inform the design of the experiment which will be conducted in sodium.

Experimental studies on bubble aspect ratio and corresponding correlations under bubble swarm condition

The bubble shape affects the gas–liquid interface momentum, heat and mass transfer, as well as the flow field around the bubble. Correctly predicting the bubble shape is challenging but indispensable under bubble swarm conditions. In this work, the bubble aspect ratio, which is adopted for the characterization of the bubble shape, is obtained through high-speed photography combined with an image processing algorithm from several experiments with an oscillating bubble plume. The results show that the bubble aspect ratio tends to be a constant value with increasing the bubble diameter, rather than decreasing as predicted by various empirical correlations developed in single bubble experiments. None of the available empirical correlations can accurately correlate the bubble aspect ratio with Weber number or Tadaki number. Among the available correlations in literature, Eo based correlation proposed by Besagni and Inzoli (2016) and Eo-Re based correlation proposed by Besagni and Deen (2020) show a better performance. The predicted values of Eo-Re based correlation developed in this work are the closest to the experimental data compared with others.

Kinematics of droplets and bubbles flowing in a liquid stream

The effect of the insertion of a bubble swarm in the separation of finely dispersed oil droplets in a liquid flow was investigated experimentally. The generation of gas bubbles and oil droplets in a liquid stream allowed the analysis of the efficiency of offshore separation processes, which has shown to be strongly dependent on hydrodynamic forces and physical interactions of the dispersed phases in flows governed by viscous dissipation as well as hydrodynamic effects when inertia forces dominate. Despite its importance, studies in this field are scarce and a lack of information about the physics of the problem persists. The goal of this study is to ascertain which of these phenomena govern the separation kinematics. To achieve this objective, the high-speed shadowgraph technique allowed the determination of the trajectories of the dispersed phases, equivalent diameters and their rising velocity. The experiments suggested that the presence of the bubble swarm enhances the separation of the oil droplets from the liquid because of the increased gravitational effects associated to the liquid-induced flow, where the droplets may rise along the wake of the bubbles, in addition to the observed momentum exchange that arises from a bouncing effect. Furthermore, the insertion of the bubbles reduced the random circulation of the droplets inside the bubble column. Buoyancy effects were increased, leading to a smaller retention time of the droplets. Thence, the hydrodynamic interactions promoted by the insertion of the bubbles govern the separation of droplets from the liquid stream, leading to an enhanced separation process.

CFD-PBM simulation of hydrodynamics of microbubble column with shear-thinning fluid

Abstract A numerical simulation was performed to study the hydrodynamics of micro-bubble swarm in bubble column with polyacrylamide (PAM) aqueous solution by using computational fluid dynamics coupled with population balance models (CFD-PBM). By considering rheological characteristics of fluid, this approach was able to accurately predict the features of bubble swarm, and validated by comparing with the experimental results. The gas holdup, turbulent kinetic energy and liquid velocity of bubble column have been elucidated by considering the influences of superficial gas velocity and gas distributor size respectively. The results show that with the rise of the superficial gas velocity, the gas holdup and its peak width increase significantly. Especially, the curve peak corresponding to high gas velocity tends to drift obviously toward the right side. Except for the occurrence of a smooth holdup peak at the column center under the condition of the moderate distributor size, the gas holdups for the small and large distributor sizes become flat in the radial direction respectively. The distribution of turbulent kinetic energy presents an increasingly asymmetrical feature in the radial direction and also its variation amplitude enhances obviously with the rise of gas velocity. The increase in gas distributor size can enhance markedly turbulent kinetic energy as well as its overall influenced width. At the low and moderate superficial gas velocity, the curves of the liquid velocity in radial direction present the Gaussian distributions, whereas the perfect distribution always is broken in the symmetry for high gas velocity. Both liquid velocities around the bubble column center and the ones near both column walls go up consistently with the gas distributor size, especially near the walls at the large distributor size condition.

Bubble formation in a step-emulsification microdevice: hydrodynamic effects in the cavity

This study focuses on the generation of bubbles in a step-emulsification microdevice via a two-angle photography method. It's found that the bubble generation mechanism is controlled by the interfacial tension, below a critical capillary number; while controlled by viscous force, inertial force and the disturbance induced by the bubble swarm, above the critical capillary number. From the two-angle photography method, a model is established for predicting the bubble size, by taking into account of the dynamic contact angle between gas-liquid interface and wall, and the hydrodynamic feedback of the cavity on bubble formation via the quantification of resistance by the volume fraction of gas in the cavity.

Numerical investigation on the drag force of a single bubble and bubble swarm

The bubble drag force correlation plays an important role in the numerical simulation accuracy of gas/liquid flows. In order to systematically investigate the interphase drag force of non-buoyancy driven bubbly flows, a dynamic-positioning body force (DPBF) method is developed in this study. It is proved that this method has an enough computation precision. Using this method, a series of direct numerical simulation (DNS) cases of a single bubble with low-intermediate Re (1 ≤ Re ≤ 200) and a bubble swarm with low Re(5.6 ≤ Re ≤ 45) are carried out and the bubble drag coefficients are calculated. Based on all the DNS data, the drag correlations with dimensionless parameters (Re, We for a single bubble and Re, We, gas fraction for bubble swarm) are systematically investigated and reported in this paper, which can provide a reference to the development of drag force closure model for non-buoyancy driven bubbly flows.

Numerical investigation on the drag force of a single bubble and bubble swarm

Numerical investigation on the drag force of a single bubble and bubble swarm

Wall shear stress modified by bubbles in a horizontal channel flow of silicone oil in the transition region

We performed laboratory experiments on bubbly channel flows using silicone oil, which has a low surface tension and clean interface to bubbles, as a test fluid to evaluate the wall shear stress modification for different regimes of bubble migration status. The channel Reynolds numbers of the flow ranged from 1000 to 5000, covering laminar, transition and turbulent flow regimes. The bubble deformation and swarms were classified as packing, film, foam, dispersed, and stretched states based on visualization of bubbles as a bulk void fraction changed. In the dispersed and film states, the wall shear stress reduced by 9% from that in the single-phase condition; by contrast, the wall shear stress increased in the stretched, packing, and foam states. We carried out statistical analysis of the time-series of the wall shear stress in the transition and turbulent-flow regimes. Variations of the PDF of the shear stress and the higher order moments in the statistic indicated that the injection of bubbles generated pseudo-turbulence in the transition regime and suppressed drag-inducing events in the turbulent regime. Bubble images and measurements of shear stress revealed a correlated wave with a time lag, for which we discuss associated to the bubble dynamics and effective viscosity of the bubble mixture in wall proximity.

Hydrodynamics of air–kerosene bubble column under elevated pressure in homogeneous flow regime

A multiphase computational fluid dynamics (CFD) model coupled with the population balance equation (PBE) was developed in a homogeneous air–kerosene bubble column under elevated pressure ( P ). The specific pressure drop (Δ P / L ), gas holdup ( α G ), and Sauter mean diameter ( d 32 ) were experimentally measured in the bubble column with 1.8 m height and 0.1 m inner diameter, which was operated at a superficial gas velocity of 12.3 mm·s −1 , and P = 1–35 bar (1 bar = 10 5 Pa). A modified drag coefficient model was proposed to consider the effect of bubble swarm and pressure on hydrodynamics of the bubble column. The Luo breakage model was modified to account for liquid density, viscosity, surface tension and gas density. The Δ P / L , α G , and d 32 obtained from the CFD model were compared with experimental data, and the gas density-dependent parameters of the CFD model were identified. With increasing P from 1 to 35 bar, the α G varied from 5.4% to 7.2% and the d 32 decreased from 2.3 to 1.5 mm. The CFD-PBE model is applicable to predict hydrodynamics of pressurized bubble columns for gas–organic liquid in the homogeneous regime.

Labelled Object Velocimetry: Simultaneous Measurements of Bubble Size and Velocity

This paper presents labelled-object velocimetry (LOV) – a technique to determine the velocities of labelled objects in multiphase flow. LOV is based on spatial correlations similar to those used in particle-image velocimetry (PIV) but employs grey-level shadowgraph images to determine object velocities. Object detection and labelling are performed using a classical image-processing algorithm. In contrast to PIV, interrogation areas in LOV are not uniformly distributed. Instead, these areas surround objects, and therefore, depend on object positions and sizes. Additionally, the proposed technique recalls a previously developed algorithm (Laupsien et al., 2019) to distinguish between single bubbles and complex situations, such as overlays, breakups and coalescences. This algorithm-based object selection (ABOS) provides a statistically reliable sample of the entire bubble swarm in terms of size and shape. Although both techniques are completely independent, they can be combined to link object velocities to their geometrical characteristics. Thus, the LOV technique can be used to ascertain velocity-object-diameter histograms.