Bubble Velocity Research Articles

Bubble departure and sliding in high-pressure flow boiling of water

Bubble growth, departure and sliding in low-pressure flow boiling has received considerable attention in the past. However, most applications of boiling heat transfer rely on high-pressure flow boiling, for which very little is known, as experimental data are scarce and very difficult to obtain. In this work, we conduct an experiment using high-resolution optical techniques. By combining backlit shadowgraphy and phase-detection imaging, we track bubble shape and physical footprint with high spatial ( $6\,\mathrm {\mu }{\rm m}$ ) and temporal ( $33\,\mathrm {\mu }{\rm s}$ ) resolutions, as well as bubble size and position as bubbles nucleate and slide on top of the heated surface. We show that at pressures above 1 MPa bubbles retain a spherical shape throughout the growth and sliding process. We analytically derive non-dimensional numbers to correlate bubble velocity and liquid velocity throughout the turbulent boundary layer and predict the sliding of bubbles on the surface, solely from physical properties and the bubble growth rate. We also show that these non-dimensional solutions can be leveraged to formulate elementary criteria that predict the effect of pressure and flow rate on bubble departure diameter and growth time.

Investigation on the effects of an elliptical wall on the dynamic behaviors of a bubble restricted by two parallel plates

The present paper investigates the dynamic behaviors of a bubble restricted by two parallel plates near an elliptical wall. The typical experimental phenomena of the bubble are recorded employing the high-speed photography and a theoretical Kelvin impulse model is established. The impacts of the spatial position and the curvature of the wall on the bubble collapse behaviors are quantitatively investigated through the theoretical model and verified against the experimental results. The Kelvin impulse intensity and the direction during the bubble collapse process are compared and discussed for different elliptical-shaped walls. The main conclusions include: (1) During the bubble collapse process, the phenomenon of the bubble uneven splitting is discovered. (2) At different spatial positions and wall curvatures, the bubble collapse jet angle, movement distance, and velocity are in good agreement with the theoretical Kelvin impulse predictions. (3) As the short-to-long axis ratio increases, the differences in the distributions of the Kelvin impulse intensity and the direction near the elliptical wall gradually become larger, and the range of the influence of the impulse intensity expands.

Modifications to The Alcubierre Warp Field Metric in Anisotropic Matter and Implications to Detection of Warp Fields

The Alcubierre warp drive concept demonstrates a designed spacetime metric which enables hyperfast travel within the framework of known physics and has become one of the most widely studied spacetimes in the community. However, there has always been a singular issue with practical realization of the “warp drive” in that a large amount of matter with unattainable properties (such as negative or “exotic” matter/energy densities) are required. The negative matter-energy or “exotic” mass-energy density requirements violating the Averaged Weak and Null Energy Conditions mainly arise from solutions to the Einstein equations with little consideration of the matter content and characteristics within the metric. Recent efforts have shown that investigating details of the matter characteristics might offer new insights to practical warp field design and might lead to realizable solutions. This paper gives analysis of an anisotropic matter field solution, hypothetical applied variations to the Einstein coupling constant (via a multiplier function), and a multilayered warp bubble approach to reducing the warp field mass requirements to realizable forms and quantities. A discussion on the detection of such an advanced warp field is also given. Keywords: Alcubierre, Warp Drive, Spacetime Metric, Negative Energy, Einstein Equations, Anisotropic Matter

Machine Learning Assisted Experimental Characterization of Bubble Dynamics in Gas-Solid Fluidized Beds.

This study introduces a machine learning (ML)-assisted image segmentation method for automatic bubble identification in gas-solid quasi-2D fluidized beds, offering enhanced accuracy in bubble recognition. Binary images are segmented by the ML method, and an in-house Lagrangian tracking technique is developed to track bubble evolution. The ML-assisted segmentation method requires few training data, achieves an accuracy of 98.75%, and allows for filtering out common sources of uncertainty in hydrodynamics, such as varying illumination conditions and out-of-focus regions, thus providing an efficient tool to study bubbling in a standard, consistent, and repeatable manner. In this work, the ML-assisted methodology is tested in a particularly challenging case: structured oscillating fluidized beds, where the spatial and time evolution of the bubble position, velocity, and shape are characteristics of the nucleation-propagation-rupture cycle. The new method is validated across various operational conditions and particle sizes, demonstrating versatility and effectiveness. It shows the ability to capture challenging bubbling dynamics and subtle changes in velocity and size distributions observed in beds of varying particle size. New characteristic features of oscillating beds are identified, including the effect of frequency and particle size on the bubble morphology, aspect, and shape factors and their relationship with the stability of the flow, quantified through the rate of coalescence and splitting events. This type of combination of classic analysis with the application of the ML assisted techniques provides a powerful tool to improve standardization and address the reproducibility of hydrodynamic studies, with the potential to be extended from gas-solid fluidization to other multiphase flow systems.

Bubble dynamics in high-pressure flow boiling conditions

High resolution measurements of key parameters relevant to bubble departure processes in high-pressure water systems has been a major challenge over the past several decades due to the small size and fast motion of vapor bubbles, making conventional optical measurements unreliable. Addressing this difficulty is critical, as accurate bubble departure data and computationally inexpensive models are needed for future two-phase heat transfer models. To close this gap, we use high-speed imaging to track bubble size and velocity in high-pressure flow boiling conditions (10 – 40 bar). It is observed that bubbles are almost always perfectly spherical in shape and slide along the boiling surface immediately after nucleating. To predict sliding, we conduct a force balance on the bubble and derive an equation of motion in the direction of the bulk flow. Interestingly, we find that at high pressure conditions, the equation of motion can be significantly simplified, resulting in an analytical expression for the bubble motion, growth time and departure diameter, allowing us to develop simple and computationally efficient equations. The applicability of the model and departure criterion across a broader range of high-pressure conditions is discussed, and recommendations for further characterization of bubble departure processes are made.

Numerical study of bubble rise in plunging breaking waves

During the occurrence of plunging wave breaking, a substantial number of multi-scale bubbles are generated. These submerged bubbles persist for extended periods and contribute to the distinct acoustic and optical characteristics of the wake. In this study, we utilize high-fidelity simulations, combined with the adaptive refinement strategy to accurately track bubbles of multi-scales during the entire rising stage. Unlike previous studies, our emphasis is specifically on investigating the process of bubble rising during plunging wave breaking. Comprehensive statistical analyses are performed and characteristics of bubbles across various scales are also provided. Our findings reveal that most bubbles are concentrated in small scales, while larger bubbles rapidly ascend to the surface or undergo fragmentation into smaller bubbles through breaking cascades eventually. A distinct stratification of bubble size distribution along the depth direction is observed. Bubble velocity distributions are also important characteristics that are frequently neglected in studies of plunging wave breaking. Bubbles primarily spread along the spanwise direction, with a uniform distribution of velocity in this dimension. The velocity distribution of bubbles displays asymmetric tails that extend to higher velocities, and within this high-velocity regime, a power law behavior is observed, similar to the size distributions. Ultimately, the flow field is left with only a few small bubbles, moving at an exceedingly low speed. Furthermore, dynamical evolution of bubble rise in plunging wave breaking is described in detail and we analyze the intricate interactions between bubbles and turbulent flows. We observe that vortices are predominantly generated in close proximity to the bubbles, and bubble motion plays a crucial role in initiating turbulent flows. Simultaneously, these vortices contribute to the fragmentation of large-scale bubbles, transforming them into smaller counterparts due to turbulent fluctuations.

Cross-sectional analysis of initially curved composite beams with rectangular and circular sections using an asymptotic meshless method

An analytical meshless cross-sectional dimensional reduction method is developed to perform structural analysis of initially curved composite beams. By introducing the Pascal polynomials in the Cartesian coordinates system for beams with rectangular cross-sections and in the polar coordinates system for the beams with circular cross-sections to the warping field, a three-dimensional beam problem can be split into a two-dimensional cross-sectional analysis and a one-dimensional along the reference line of the beam. The obtained cross-sectional stiffness matrix based on higher-order of the strain energy can be incorporated into a one-dimensional finite element solution for initially curved composite beams, for the purpose of strain and stress analysis. Finally, the three-dimensional strain through the thickness of the beam can be achieved by the recovery analysis. The present method takes advantage of Pascal polynomials so that the solution procedure will be more simplified and computationally more efficient compared to three-dimensional finite element (3D FE) method. The proposed method for different isotropic and anisotropic beams is examined and compared with the literature, 3D FE, and Variational Asymptotic Beam Sectional (VABS) package which is a finite element based cross-sectional analysis tool for composite beams.

Numerical Simulation of the Interaction between a Planar Shock Wave and a Cylindrical Bubble

Three-dimensional (3D) computational fluid dynamics (CFD) simulations have been carried out to investigate the complex interaction of a planar shock wave (Ma = 1.22) with a cylindrical bubble. The unsteady Reynolds-averaged Navier–Stokes (URANS) approach with a level set coupled with volume of fluid (LSVOF) method has been applied in the present study. The predicted velocities of refracted wave, transmitted wave, upstream interface, downstream interface, jet, and vortex filaments are in very good agreement with the experimental data. The predicted non-dimensional bubble and vortex velocities also have great concordance with the experimental data compared with a simple model of shock-induced Rayleigh–Taylor instability (i.e., Richtmyer–Meshkov instability) and other theoretical models. The simulated changes in the bubble shape and size (length and width) against time agree very well with the experimental results. Comprehensive flow analysis has shown the shock–bubble interaction (SBI) process clearly from the onset of bubble compression up to the formation of vortex filaments, especially elucidating the mechanism on the air–jet formation and its development. It is demonstrated for the first time that turbulence is generated at the early phase of the shock cylindrical bubble interaction process, with the maximum turbulence intensity reaching about 20% around the vortex filament regions at the later phase of the interaction process.

Effect of surfactant on dynamics and gas-liquid mass transfer for single carbon dioxide bubbles

In carbonation reaction, the impact of surfactants on the movement and mass transfer behavior of carbon dioxide bubbles were crucial for the production of high-quality silicon dioxide products. The study employed the Matlab image processing system to investigate the shapes, motion velocities, and rise path of single carbon dioxide bubbles within varying concentrations of cetyltrimethyl ammonium bromide (CTAB) solutions. This exploration aimed to elucidate the effect of CTAB on the movement and mass transfer coefficient (MTRC) of single carbon dioxide bubbles. Alterations in the CTAB solution concentration and bubble sizes significantly influenced the mass transfer and movement characteristics of single carbon dioxide bubbles. The conclusion was drawn through the computation of the MTRC of single carbon dioxide bubbles in deionized water and CTAB solutions: the addition of CTAB significantly reduced the mass transfer efficiency of carbon dioxide in deionized water, with the MTRC of CTAB solutions decreasing as the solution concentration increased. Utilizing the stagnant cap model, it can be concluded that CTAB's reduction of the MTRC of carbon dioxide was attributed to the high viscosity of the medium, low bubble velocity, stable flow conditions, and intensified adsorption degree of CTAB molecules at the gas-liquid interface. According to the significant periodic trajectories of single carbon dioxide bubbles in the stable range, the correlation between the trajectories of compressible bubbles in surfactant solution and mass transfer in liquid phase was established, and the previous method based on rigid sphere model was modified. The paper proposed the mechanism of CTAB's influence on single carbon dioxide bubbles, offering crucial theoretical insights into the industrial application of surfactants in the carbonation process for producing silicon dioxide.

Directional vapor mobility from asymmetric microstructured surfaces in an adverse gravity orientation

Stagnant vapor growth on a downward-facing flat surface leads to increased surface temperature and dryout at relatively low heat fluxes. The current study investigates boiling from a surface with periodic 60°-30° or 75°-15° asymmetric sawtooth microstructures to passively remove vapor slugs in adverse gravity. Bubble dynamics is experimentally investigated in an 8-mm square borosilicate glass tube and visualized using a high-speed camera to measure vapor bubble morphology and velocity in the FC-72 dielectric liquid. The vapor bubble's morphology is observed to change based on its relative size to the ratchets. This change manifests as a decrease in the curvature ratio between the crest and trough of the microstructure as the vapor bubble gets larger. The pattern of vapor slugs nucleating from intended, engineered sites, coalescing to form larger slugs that slide across the microstructure, is observed at different frequencies at different heat fluxes. The microstructure supports increased vapor volume at higher heat fluxes, suggesting that a passive and self-regulating thermal management solution for adverse gravity applications is feasible. An empirical force balance model is developed based on the curvature-induced Young-Laplace pressure difference and retarding forces due to drag and buoyancy. The interplay between these forces is analyzed at different liquid film thicknesses, and the force balance is compared with a 75°-15° sawtooth structure. For a vapor slug spanning four sawteeth, the 75°-15° structure supported a 54 % increase in the feasible liquid film thickness range due to the increased long slope area.

Velocity characteristics of microjets generated by double bubbles near a rigid wall under ultrasound

The cavitation bubble collapse and associated microjets are widely used in ultrasound and chemical engineering. However, much remains to be known about the interplay of double bubbles and their microjets. The dynamic models for the single-bubble and double-bubble near the rigid wall under ultrasound were constructed and numerically solved to reveal the bubble collapse behavior. Results indicates that compared to a free wall, rigid walls have a strong inhibitory effect on the collapse of a single bubble, but have a certain promoting effect on the collapse of double bubbles. The double bubbles have a higher velocity and smaller range of initial bubble radii than a single bubble to produce microjets. When the bubble is close to the stiff wall, the microjet of a single bubble is always stronger than that of double bubbles. But when bubbles move away from rigid walls, the microjet velocity of double bubbles may be greater than that of a single bubble. Compared with the single bubble, the double bubbles can generate microjets with a narrower range of the ultrasound pressure amplitude and a smaller ultrasound frequency. The study will give new insights into the velocity of microjets in ultrasonic related processing applications.

Sex matters: The MouseX DW-ALLEN Atlas for mice diffusion-weighted MR imaging

Overcoming sex bias in preclinical research requires not only including animals of both sexes in the experiments, but also developing proper tools to handle such data. Recent work revealed sensitivity of diffusion-weighted MRI to glia morphological changes in response to inflammatory stimuli, opening up exciting possibilities to characterize inflammation in a variety of preclinical models of pathologies, the great majority of them available in mice. However, there are limited resources dedicated to mouse imaging, like those required for the data processing and analysis. To fill this gap, we build a mouse MRI template of both structural and diffusion contrasts, with anatomical annotation according to the Allen Mouse Brain Atlas, the most detailed public resource for mouse brain investigation. To achieve a standardized resource, we use a large cohort of animals in vivo, and include animals of both sexes. To prove the utility of this resource to integrate imaging and molecular data, we demonstrate significant association between the mean diffusivity from MRI and gene expression-based glia density. To demonstrate the need of equitable sex representation, we compared across sexes the warp fields needed to match a male-based template, and our template built with both sexes. Then, we use both templates for analysing mice imaging data obtained in animals of different ages, demonstrating that using a male-based template creates spurious significant sex effects, not present otherwise. All in all, our MouseX DW-ALLEN Atlas will be a widely useful resource getting us one step closer to equitable healthcare.

Dynamic bubble tracking in fluidized beds via electrical capacitance volume tomography

This work sets forth the development of a novel, dynamic bubble detection algorithm for use with electrical capacitance volume tomography (ECVT) sensors for bubbling fluidized beds. Starting with an in-depth review of existing bubble detection methods, the novel phase detection method was developed to address the shortcomings of the other published methods by more fully utilizing the three-dimensional capability of the sensors. After the sensor parameters were optimized to verify capability of bubble detection, measurements were made with glass beads and quartz sand. A range of air velocities in a 10 cm diameter bubbling fluidized bed were used. The results largely agree with the fundamentals of bubbling fluidization and results from publications with similar experimental setups. Within each measurement the bubble dimensions, velocities and frequencies over the axial and radial position could be evaluated. Due to the three-dimensional nature of the novel bubble detection technique, insight into the directional tendencies of detected bubbles was gained. For example, bubble migration toward the radial center of the bed, radial and axial bubble coalescence, and splitting are more evident from the trends that are producible with this method.

Study on Non-Spherical Deformation Velocity of a Single Cavitation Bubble

Cavitation bubbles commonly exist in shipbuilding engineering, ocean engineering, mechanical engineering, chemical industry, and aerospace. Asymmetric deformation of the bubble occurs near the boundary and then has strong destructiveness, such as high amplitude loading. Therefore, the research on non-spherical deformation is of great significance, and the objective of this paper is to investigate the non-spherical collapse dynamics of laser-induced cavitation bubbles when near different boundaries. In this study, experimental data, such as the bubble pulsation process and bubble surface velocity distribution, were obtained by high-speed camera techniques and full-field velocity calculations. Near the different boundaries, the results show that the bubbles appeared to have different collapse shapes, such as near-hemispherical, near-ellipsoidal, near-cone, and near-pea shapes, and the surface velocity distribution is extremely non-uniform. When the bubble near the free surface or rigid boundary collapses, the smaller the stand-off r is, the more obvious the repulsive effect of the free surface or the attractive effect of the rigid boundary is. As the stand-off r decreases, the larger the Bjerknes force and the bubble surface velocity difference and the more pronounced the non-spherical shape becomes.

Taylor bubble splitting, flow and coalescence in branching microchannels: An experimental and numerical simulation study

Two novel branching microchannels were proposed for achieving efficient bubble splitting and precise control of their size. A combined numerical simulation and experimental approach was adopted to study the splitting behavior of mother bubbles and the hydrodynamic and coalescence properties of daughter bubbles in two branching microchannels. The research results indicate that the bubble-splitting process in channels BMC-2 and BMC-3 is the same, undergoing three stages: squeezing, neck break and pinching-off. The neck break stage in the BMC-3 channel significantly slows down due to changes in the stress point of the bubbles and the enhanced interfacial tension at the bubble tail. In the symmetrically splitting channel, the daughter bubbles exhibit a notable uniformity, characterized by a length deviation of less than 2.82%. A calculation method for predicting the volume of daughter bubbles in the BMC-3 channel has been developed based on the ideal bubble shape characteristics. The method's accuracy has been validated through experiments and numerical simulations with an error of less than 8.3%. Controlled non-uniform splitting of bubbles was achieved through the BMC-3 channel, and the correlation between the volume fraction of daughter bubbles (φd) in the BMC-3 channel and the Re number was determined. It was observed that φd-subII gradually decreases with increasing Re number and converges to 40%, whereas both φd-subI and φd-subII exhibit gradual increments and tend to approximate 30%. Void fraction significantly influences the velocity of daughter bubbles in the BMC-3 channel, but the bubble velocity in the subⅡ channel is always notably higher than the other two subchannels. The necessary conditions for preventing the coalescence of daughter bubbles in the branching channels were elucidated.

Exploring flow boiling characteristics on surfaces with various micro-pillars using the lattice Boltzmann method

In this study, the lattice Boltzmann method is utilized to simulate flow boiling within a microchannel featuring a micro-pillar surface. This investigation aims to explore the impacts of micro-pillar shape and quantity on the flow boiling characteristics across various superheats and Reynolds numbers (Re). A systematic examination is conducted on three types of micro-pillars, five quantities of micro-pillars, four Re values, and 18 superheat levels. The mechanisms contributing to enhanced heat transfer in flow boiling are elucidated through a comprehensive analysis of bubble dynamics, temperature and velocity fields, local and transient heat fluxes, and boiling curves. Moreover, the critical heat fluxes (CHF) of all surfaces are evaluated to identify the superior micro-pillar configurations. The findings revealed that microchannels with micro-pillar surfaces induce more vortices compared to those with smooth surfaces, attributable to the combined effects of bubble dynamics and micro-pillars. Bubble patterns and boiling curves demonstrated the significant impact of micro-pillar geometrical shapes on the boiling regime and heat transfer performance. As flow boiling progressed, an increase in micro-pillar quantity and Re can mitigate the fluctuation and decline rate in transient heat flux, respectively. Among the three types of micro-pillar surfaces, the circular shape exhibited the highest flow boiling performance, followed by the triangular and rectangular shapes. For all surfaces, the CHF increased with Re, and each micro-pillar type displayed an optimal quantity for achieving maximum CHF, with the highest increase reaching 45.2%. These findings are crucial for optimizing microchannel designs to enhance flow boiling heat transfer efficiency.

Dynamics of Taylor bubble under chemical reaction enhanced mass transfer in minichannel

Taylor bubble dynamic characteristics of CO2 chemical absorption into MEA aqueous solution in a vertical minichannel were systematically investigated in this study. The generation, movement, and shrinkage of bubbles in the minichannel were visualized and monitored using a high-speed camera, and their dynamic behaviors were characterized by image analysis method. The effects of gas and liquid Re numbers and absorbent concentration on two-phase flow patterns, bubble generation frequency, initial bubble length, bubble length decrease rate, and bubble velocity were examined and analyzed. Results showed that chemical reaction-enhanced mass transfer hindered the bubble cap penetration into the main channel, and alleviated the bubble neck thinning, both effects inhibiting the bubble generation. A new Damköhler number (Da)-based correlation has been proposed to predict the initial Taylor bubble length, showing good prediction accuracy for experimental data in the literature using different absorbents. Results also showed that before the formation of sphere bubble at the end of absorption, an approximate linear relationship exists between bubble length decrease rate and bubble velocity, with the slop decided by chemical reaction rate that could be characterized by the Da number. Finally, a simple model has been developed to determine the effective channel length at a given operating condition, providing design guidelines for microchannel-based miniaturized CO2 absorbers.

Subcooled forced convection boiling flow measured using high-resolution techniques at the COSMOS-L facility and accompanying CFD simulation employing an interface-tracking scheme

This paper describes state-of-the-art experimental measurement techniques and computational fluid dynamics methods applied to subcooled forced convection boiling flow at 2-3 bar, both featuring high spatial- and time-resolution measurements. The objectives are: (i) to provide the measured boiling flow data, e.g. average and RMS profiles of axial and radial velocities and bubble size distributions, and (ii) to evaluate the capabilities of state-of-the-art numerical simulation techniques to model the observed phenomena, by comparison between measured data and numerical prediction. In the experiment, the bubble velocities in the axial and radial directions were measured using laser Doppler anemometry, and the bubble size was estimated by a shadowgraphy method. The simulation results, incorporating an interface capturing technique, showed good agreement with measurement in terms of the wall temperature and axial velocity, but underestimation of the radial velocity, and overestimation of bubble sizes. The paper shows that the discrepancies between measurement and simulation may be traced to: (i) the uncertainties in the nucleation site density model; (ii) too coarse a grid being adopted, which is not able to resolve the thermal boundary layer around the bubbles; and (iii) spurious numerical bubble coalescence, a feature not seen in the experiment. The mechanism of bubble lift-off from the hot surface, without any sliding motion, as observed in the experiment, is discussed in detail, based on the simulation results, and the condensation on the bubble cap as the bubble is ‘sucked’ into the bulk flow is also examined.

Application of a simplified model for assessing particle removal in dissolved air flotation (DAF) systems: Experimental verification at laboratory and full-scale level

Particle-bubble collisions in dissolved air flotation (DAF) systems play a crucial role in the removal of total suspended solids (TSS). DAF particle-bubble collision models incorporate factors such as particle diameters, charge and density, bubble diameters, and collision factors. The challenge lies in accounting for the wide range of particle and bubble sizes and obtaining complex model inputs. To address this, a simplified model for TSS removal in DAF units was established using low-cost laboratory measurements, including particle size distribution and density. Additionally, microbubble diameter profiles were derived from bubble velocities using particle image velocimetry software (PIV). Six independent variables, encompassing influent particle characteristics (such as particle size distribution and density) and DAF running characteristics (temperature, contact zone detention time, inflow and recycle flows), were employed in the simplified model. The model's accuracy was evaluated using a laboratory-scale DAF system with two different influents: Delft canal water and anaerobic sludge. The predicted TSS removal from the simplified model aligned well with the laboratory-scale DAF results, yielding removal efficiencies of 68 ± 1 % and 77 ± 3 % for Delft canal water and anaerobic sludge, respectively. Furthermore, when the simplified model was applied to two full-scale DAF systems, it successfully identified an underperforming system (DAF2) with a TSS removal efficiency of 91 %, contrasting with the theoretical removal model-predicted efficiency of 98 %. This study highlights the utility of combining bubble size distribution measured by PIVlab and particle size distribution obtained using FIJI-ImageJ as an economical and efficient approach to acquiring the necessary inputs for predicting TSS removal in DAF systems.

Investigation of flow characteristics in a rectangular spouted fluidized bed using electrical capacitance volume tomography

The characterization of gas-solid flow behavior in rectangular spouted fluidized bed (RSFB) poses significant challenges due to the presence of complex gas-phase vortex flow within the bed. The flow characteristics of gas-solid two-phase flow in RSFB were investigated by using a self-developed 32-electrode electrical capacitance volume tomography (ECVT) system with an imaging speed of 105 frames per second when the spouting gas velocity Uf increased from 0.97 m/s to 1.78 m/s. Experimental results demonstrate that with increasing Uf, the flow transitions from weak bubbling/bubble fluidization to turbulent fluidization in the RSFB. The amplitude peak difference of particles in different planes of the fluidized bed gradually decreases, and the rising velocity of bubbles initially decreases and then increases. The gas-particle backmixing effect strengthens, while the entrainment effect during bubble rupture weakens. The research findings can provide valuable insights for understanding the flow behavior in RSFB and offer guidance for optimizing the process operation of fluidized bed reactors.