Bubble Parameters Research Articles

Statistical Analysis Of Bubble Parameters From A Model Bubble Column With And Without Countercurrent Flow

Bubble columns are widely used in numerous industrial processes, because of their advantages in operation, design and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors precise numerical simulations and modelling is needed. These simulations and models have to be validated with experimental data. For this reason experiments were carried out in a laboratory-scale bubble column with shadow imaging technique with and without countercurrent liquid flow. In the experiments two types of gases –relatively badly soluble air and good soluble CO2 – are applied and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates overall 108 different flow conditions were investigated. The gathered data has been statistically evaluated over the whole 1 m measurement area and bubble parameters have been obtained such as bubble diameter, velocity, aspect ratio, bubble motion direction and inclination. The analysis of these parameters shows, that the countercurrent liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO 2 bubbles remarkable bubble shrinkage has been observed at counter-current liquid flow due to the enhanced mass transfer. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the validation of numerical simulations and models.

A deep learning-based image processing method for bubble detection, segmentation, and shape reconstruction in high gas holdup sub-millimeter bubbly flows

The sub-millimeter bubble technique can enhance the gas–liquid inter-phase mass transfer by significantly reducing the bubble size and increasing the gas–liquid interfacial area. To accurately describe the flow and mass transfer characteristics, it is necessary to characterize bubble parameters. High-speed photography followed by image processing is an effective way to characterize the gas bubbles in the multiphase flows. However, the efficient image processing method for the sub-millimeter bubbly flows with high gas holdup and high bubble overlap has not been reported yet. The present work developed a novel deep learning-based image processing method for bubble detection, segmentation, and shape reconstruction in high gas holdup sub-millimeter bubbly flows. In order to segment the highly overlapping sub-millimeter bubbles, our method was built based on Mask R-CNN, with which the pixel-level segmentation masks can be obtained, and the shape of the overlapping bubbles can be accurately described. The feature pyramid architecture was coupled with ResNet101 and Feature Pyramid Network to detect sub-millimeter bubbles with significant size differences. A shape reconstruction module was proposed to restore the real shape of overlapping bubbles and improve prediction accuracy. In order to sufficiently validate the proposed method, adequate images of sub-millimeter bubbly flows were obtained by changing the experimental media (air-tap water, air-sodium dodecyl sulphate aqueous solution, air-diesel, and air-diesel-fine catalyst particles), reactor configurations (3D beds and 2D beds), lenses, and photography (shadowgraphy and front illumination). Our method shows high accuracy under the experimental conditions and can process sub-millimeter bubble images under gas holdup up to 20%.

Experimental and numerical investigation of local bubble parameters for subcooled flow boiling in a pressurized annulus

The wall boiling models adopted in the Computational Multi-Fluid Dynamics (CMFD) tools rely on empirical correlations for closures, which causes considerable uncertainties in their results. Thus, well-defined experimental data for local boiling parameters are essential for the development and validation of the wall boiling constitutive models. This paper presents new experimental data on the local bubble parameters and the wall temperatures along the heated tube for the subcooled flow boiling under high-pressure conditions. The radial distributions of the bubble parameters, namely, void fraction, bubble velocity, interfacial area concentration, and Sauter mean diameter were measured at multiple elevations to evaluate their development along the flow. Furthermore, the experimental data set was utilized to validate physical models for predicting subcooled flow boiling using a CMFD code. The source of discrepancies between the experimental and calculated results were analyzed and possible directions for research in subcooled flow boiling under high-pressure conditions were defined.

Comprehensive analysis of spherical bubble oscillations and shock wave emission in laser-induced cavitation

The dynamics of spherical laser-induced cavitation bubbles in water is investigated by plasma photography, time-resolved shadowgraphs and sensitive single-shot probe beam scattering that portrays the transition from initial nonlinear to late linear oscillations. The frequency of late oscillations yields the bubble's gas content. Numerical simulations with an extended Gilmore model using plasma size as input and oscillation times as fit parameter provide insights into experimentally not accessible bubble parameters and shock wave emission. Model extensions include a term covering the initial shock-driven acceleration of the bubble wall, an automated method determining shock front position and pressure decay and a complete energy balance for the partitioning of absorbed laser energy into vaporization, bubble and shock wave energy and dissipation through viscosity and condensation. These tools are used for analysing a scattering signal covering 102 oscillation cycles from a bubble with 36 μm maximum radius produced by a plasma with 1550 K average temperature. Predicted bubble wall velocities during expansion agree well with experimental data. Upon first collapse, most energy was stored in the compressed liquid around the bubble and radiated away acoustically. The collapsed bubble contained more vapour than gas and had a pressure of 13.5 GPa. The decay of the rebound shock wave pressure with radius r was initially $\mathrm{\ \propto }{r^{ - 1.8}}$ , and energy dissipation at the shock front heated the liquid near the bubble wall to temperatures above the superheat limit. The shock-induced temperature rise reduces damping during late bubble oscillations. Damping in first collapse increases significantly for small bubbles with less than 10 μm radius.

Evaluation of the multiple sensor optical fiber probe methods for the measurement of local bubble parameters accordng to bubble shape

Abstract It is necessary to evaluate a multiple sensor probe methods according to the bubble shape for the measurement of local bubble parameters. For this, numerical simulation and air-water benchmark experiments were performed with the double-sensor and four-sensor probes. It was found that the velocity measurement errors of the probes were 5.3% and 4.2%, respectively. In terms of Sauter mean diameter (D 32), its measurement performance is affected by the type of the probe and bubble shape. The double-sensor probe showed reasonable measurement accurancy of the D 32 for the spherical shape bubble. However, as the bubble shape is distorted from the sphere, the D32 measurement error increases. The four-sensor probe has a relatively large error compared to that of the double sensor probe under the bubbly flow with small size. While, when the D 32 is larger than 2 mm, the four sensor probe shows excellent measurement performance regardless of the bubble shape.

Assessment of wall heat flux partitioning model for two-phase CFD

The Eulerian-Eulerian two-phase flow (EETF) model coupled with the Wall Heat Flux Partitioning (WHFP) model is slowly becoming an effective tool for two-phase hydrothermal analysis in nuclear applications, with prediction accuracy highly dependent on sub-models for three bubble parameters, namely nucleation site density (N), bubble departure diameter (Dw) and bubble departure frequency (f). In this study, the preformance of different sub-models combinations is evaluated under a wide range of conditions, especially focusing on the prediction of void fraction. The four most commonly used or investigator-recommended combinations are identified by a literature review. A large database of flow boiling experiments covering 52 sets of experiments is developed for the assessment, rather than the popular case-by-case adjustment for a limited number of experiments. One of the combinations is distinguished to be the optimal combination, with an overall 44.2% mean absolute error (MAE). A nearly fixed relationship between void fraction and steam quality is predicted by this combination. It suggests that there is an ‘optimal’ range of operating conditions for which the combination can accurately predict the results. Based on the current assessment, for water, this range is between 17 and 97 K for subcooling and a mass flux larger than 770 kg/(m2s). However, the prediction of bubble diameter and gas velocity are not accurate, since the Kurul and Podowski model simply assumes the bubble diameter as the function of liquid temperature. Models considering bubble coalescence and breakup are desired to predict the bubble diameter and gas velocity more accurately. It is also shown that the performance of combinations, which are genreally considered to be applicable to a broader range, is not satisfactory. Experimental measurements of bubble departure diameter and nucleation site density under a wider range of conditions are desired to evaluate those sub-models.

Experimental investigation on the steam condensation dynamic characteristics at low steam mass flux

An experimental study has been performed to investigate the dynamic characteristics of steam direct contact condensation at low steam mass flux. Visible steam bubble parameters can be identified through the image processing algorithm. The maximum dimensionless diameter of steam bubble is calculated and the analysis model of identifying condensation regime is developed to predict transition boundaries of steam chugging and oscillatory bubble regimes. The pressure oscillation waveforms in pipe and in pool are distinguished. In chugging regime, the pressure pulse wave transforms to continuous wave in pool as water temperature increasing, however, in oscillatory bubble regime, continuous wave becomes pulse wave because of increased bubble pulsation volume. The oscillation frequencies are obtained from four different methods of bubble dynamic parameters, pressure pulse periods, pressure frequency spectrums in pipe and in pool to reveal the oscillation mechanism. The low-frequency component in chugging regime increases with water temperature increasing, while the intermediate-frequency component in chugging regime and the frequency in bubble regime decreases.

Bubble Parameters in an Inclined Rectangular Channel with Downward-Facing Heated Wall Under the Subcooled Boiling Flow Condition

Bubble Parameters in an Inclined Rectangular Channel with Downward-Facing Heated Wall Under the Subcooled Boiling Flow Condition

Interaction of two out-of-phase underwater explosion bubbles

This study presents an experimental investigation of the dynamic properties of underwater explosion (UNDEX) bubble pairs produced with a range of phase differences Δθ, defined as 2π(t1−t2)/Tosc, where ti (i = 1,2) represents the bubble inception moment and Tosc is the experimentally obtained first period of a single UNDEX bubble. Each bubble was generated by a spherical hexogen explosive charge detonated in a cubical tank and observed via high-speed photography. The phase difference was adjusted by setting different delays between the two detonations, with an accuracy of 1.0 ms. Experiments were conducted with both horizontally and vertically positioned bubble pairs and with single bubbles as well. UNDEX bubble pairs are subject to a larger buoyancy effect than cavitation or spark-generated bubble pairs. The resultant bubble behavior in the bubble–bubble interaction is more complex and is yet to be understood. In our experiments, various bubble parameters, including bubble pulsation periods, bubble elongation ratios, and collapse-induced shock wave pressures bubble, were measured and studied. Dependence of the bubble dynamics on Δθ was found, demonstrating the significant influence of Δθ on the morphology and shock wave pressure of bubble pairs. The findings suggest a method of strengthening or weakening the damage potential of an UNDEX bubble pair based on the proper adjustment of the delay between two detonations. It may also lead to a better understanding of the dynamics of interacting bubbles with buoyancy effects.

Tomoscopy: Time-Resolved Tomography for Dynamic Processes in Materials.

The structure and constitution of opaque materials can be studied with X-ray imaging methods such as 3D tomography. To observe the dynamic evolution of their structure and the distribution of constituents, for example, during processing, heating, mechanical loading, etc., 3D imaging has to be fast enough. In this paper, the recent developments of time-resolved X-ray tomography that have led to what one now calls "tomoscopy" are briefly reviewed A novel setup is presented and applied that pushes temporal resolution down to just 1ms, that is, 1000tomograms per second (tps) are acquired, while maintaining spatial resolutions of micrometers and running experiments for minutes without interruption. Applications recorded at different acquisition rates ranging from 50 to 1000tps are presented. The authors observe and quantify the immiscible hypermonotectic reaction of AlBi10 (in wt%) alloy and dendrite evolution in AlGe10 (in wt%) casting alloy during fast solidification. The combustion process and the evolution of the constituents are analyzed in a burning sparkler. Finally, the authors follow the structure and density of two metal foams over a long period of time and derive details of bubble formation and bubble ageing including quantitative analyses of bubble parameters with millisecond temporal resolution.

A flexible image processing technique for measuring bubble parameters based on a neural network

The main parameters in a liquid-gas system are the size, shape, and kinetic parameters of bubbles, which affect the mass transfer process. To describe the mass transfer process accurately, it is necessary to characterize bubble parameters such as bubble volume and surface area under different experimental conditions. However, these bubble parameters are not accurately assessable by conventional methods, which are limited by poor robustness and flexibility, including numerical methods and conventional neural networks. Based on the neural network technique, we propose a flexible method for measuring bubble parameters in three steps: segmentation of bubble images, segmentation of overlapping bubbles, and extraction of bubble feature parameters. This technique combines geometric, optical, and topological information. To verify the effectiveness of our method, we considered a gas-liquid reactor and microbubble radiosensitizer for brachytherapy as testing scenarios and used several groups of experimental images and synthetic images as testing sets. In the first step, the accuracy of the segmentation of bubble images was greater than 90% in all scenes and reached 99% in some scenes. In the second step, the proposed method was capable of segmenting overlapping bubbles and avoiding excessive segmentation. In the final step, our approach considers the geometric shape and deflection angle of bubbles. Therefore, the bubble parameters of largely deformed and deflected bubbles were obtained with high flexibility. Our method is a powerful tool with robustness and flexibility for the study of gas-liquid interface measurements in chemical and biochemical processes.

Analysis of Theoretical and Experimental Research on Bubble Parameters and Gas-liquid Interaction in Bubble Flow

Bubble flow is a phenomenon in which gas flows with liquid in the form of bubbles, which widely exists in production and life. As an important part of fluid mechanics, bubble flow also has a certain impact on the actual production process. This work briefly summarizes the development of research on bubble flow in recent years. Firstly, a brief introduction to the development process and current situation of bubble flow in chronological order is presented, and the main difficulties related to the research and development of bubble flow are also pointed out, including the complicated gas-liquid distribution pattern and the exchange of materials and energy between gas and liquid phases, which slow down scholars’ research progress. Then, several theoretical models for bubble flow research are introduced. These models take bubble parameters into account, including the ultimate velocity of bubble rising, the transfer of energy and matter in the coalescence, and rupture of the bubble, the phase distribution of the bubble in the tube, and the interaction between the bubble and the liquid (the shear stress produced by bubbles affecting the turbulence field). This work briefly explains the ideas of each model and the results obtained, compares and analyzes their advantages, disadvantages and limitations, and predicts the theoretical and technical means required for subsequent theoretical model construction. Finally, part of the experimental research is summarized, along with the process and technical means of each experiment as well as the relationship between the experimental results and the theoretical research. It is hoped that this work could help to have a preliminary understanding of the research process and research methods of bubble flow, and provide some perspectives for incorporating bubble flow hydrodynamic theory into industrial applications and real life.

Investigation of bubble parameters and interfacial heat transfer correlations based on radial void fraction profiles of R-134a subcooled boiling flows

Investigation of bubble parameters and interfacial heat transfer correlations based on radial void fraction profiles of R-134a subcooled boiling flows

Improving the Performance of Surface Flow Generated by Bubble Plumes

Gas–liquid two-phase flow is widely used in many engineering fields, and bubble dynamics is of vital importance in optimizing the engineering design and operating parameters of various adsorptive bubble systems. The characteristics of gas–liquid two-phase (e.g., bubble size, shape, velocity, and trajectory) remain of interest because they give insight into the dynamics of the system. Bubble plumes are a transport phenomenon caused by the buoyancy of bubbles and are capable of generating large-scale convection. The surface flow generated by bubble plumes has been proposed to collect surface-floating substances (in particular, oil layers formed during large oil spills) to protect marine systems, rivers, and lakes. Furthermore, the surface flows generated by bubble plumes are important in various types of reactors, engineering processes, and industrial processes involving a free surface. The bubble parameters play an important role in generating the surface flow and eventually improving the flow performance. This paper studies the effects of temperature on bubble parameters and bubble motion to better understand the relationship between the various bubble parameters that control bubble motion and how they impact the formation of surface flow, with the ultimate goal of improving the efficiency of the generation of surface flow (i.e., rapidly generate a strong, high, and wide surface flow over the bubble-generation system), and to control the parameters of the surface flow, such as thickness, width, and velocity. Such flow depends on the gas flow rate, bubble size (mean bubble diameter), void fraction, bubble velocity, the distance between bubble generator and free surface (i.e., water height), and water temperature. The experiments were carried out to measure bubble parameters in a water column using the image visualization technique to determine their inter-relationships and improve the characteristics of surface flow. The data were obtained by processing visualized images of bubble flow structure for the different sections of the bubble regions, and the results confirm that temperature, bubble size, and gas flow rate significantly affect the flow structure and bubble parameters.

Neutron Matter and Interactions for Ni nuclei in a Supernova 1987A

Structure of neutron matter and neutron-interactions in a Supernova (SN) are investigated by the theoretical model approach. For that purpose, we calculate the neutron skin thicknesses, neutron-proton interactions, density distributions, central depletions in nuclei using Skyrme Hartree-Fock (SHF) model. The neutron skin thickness (NST) properties are obtained by bulk and surface contributions, based on two-parameter Fermi (2pF) distributions, as a function of the relative neutron excess I = (N− Z)/A. For the central depletion in the nucleus, the depletion fraction (DF) of nuclei is calculated by bubble parameters b and b′. To demonstrate the accuracy of the mass model in the theoretical model, calculated binding energies are compared with the theoretical and experimental data in the literature, namely the relativistic mean-field theory (RMFT), atomic mass evaluation (AME), and finite-range droplet model (FRDM). The fluctuations in the mass model are shown for average neutron-proton interactions δ,V1n−1p and the residual neutron-proton interaction δnp for both odd-A and even-A nuclei. Additionally, the single-particle energy levels and charge form factors for some nuclei are presented for the contribution experimental processes. The based on the theoretical and experimental data, the importance and relevance of results of the calculated results are discussed.

Excitation of strongly nonlinear plasma wakefield by electron bunches

We propose a new method for analytical self-consistent description of the excitation of a strongly nonlinear wakefield (a bubble) excited by an electron bunch. This method makes it possible to calculate the shape of the bubble and the distribution of the electric field in it based only on the properties of the driver, without relying on any additional parameters. The analytical results are verified by particle-in-cell simulations and show good correspondence. A complete analytical solution for cylindrical drivers and scaling laws for the properties of the bubble and other plasma accelerator parameters depending on the bunch charge and length are derived.

Shock wave and bubble characteristics of underwater array explosion of charges

In this study, we focused on the effect of the underwater explosion parameters of multi-point array explosion. The shock wave and bubble parameters of aggregate charge, two charges, and four charges were measured through an underwater explosion test, and their influence on the explosion power field of charge quantity and array distance was analyzed. Results show that the multi-shock wave collision of array explosion can be approximated to a linear superposition, and the interaction of delayed shock wave can be deemed as the increase of the shock wave baseline. Shock wave focusing and delayed superposition increase the shock wave peak pressure. Compared with the aggregate charge, the greater the number of array explosion points is, the higher the impulse and the gain of the bubble peak pressure are. At the same array distance, the smaller the charge quantity is, the higher the bubble impulse will be. At the same charge quantity, the smaller the array distance is, the higher the bubble impulse will be. The bubble period decreases gradually with the increase of the charge quantity, but the test orientation has little effect on the bubble period.

Characteristics of a separated flow past a semicircular leading-edge airfoil model under different imposed pressure gradient

The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

Force balance model predictions of sliding bubbles velocity in vertical subcooled boiling flow

In flow boiling systems, bubbles tend to slide along the wall as they depart from nucleation sites where they originate. This behavior has a profound impact on the wall heat transfer as evidenced in previous experiments. As a result, the heat transfer modeling associated with sliding bubbles has gained great attention within the CFD boiling heat transfer community. The modeling efforts are primarily aimed at improving the Heat Flux Partitioning (HFP) model by accounting for the heat transfer mechanisms introduced by sliding bubbles. The performance of the HFP model depends inherently on the accuracy of sub-models to predict the fundamental bubble parameters, such as bubble departure and lift-off diameters. Similarly, the accurate prediction of sliding bubble parameters, such as sliding bubble growth and sliding bubble velocity, is critical to improving the HFP model when taking into account the effect of sliding bubbles. Of the many sliding bubble parameters, this paper deals with the sliding bubble velocity. Specifically, a force balance model is presented and assessed in view of the sliding bubble velocity prediction. The experimental results from Maity (2000)[1] and Yoo et al. (2016)[2] are used to demonstrate the force balance model accuracy under various subcooled boiling conditions of both, water and refrigerant (NOVEC-7000) flowing upward in vertical channels. We performed a parametric study of the key sub-models (e.g., drag force, bubble growth) used in the force balance equation, together with a direct comparison with proposed models from other researchers. Then, a new force balance model is proposed which outperforms previous models and consistently well-predicts both sliding bubble velocity and growth.

Stability analysis and sliding mode control of a single spherical bubble described by Keller–Miksis equation

This paper transforms the Keller–Miksis (KM) model, which is the main equation describing the bubble behavior, into a state space representation and presents a stability condition for the system using the linearized form of the KM equation. The dynamic of the cavitation bubble is analyzed for different gases, and its burst time is measured. Then, a sliding mode controller (SMC) is designed for the nonlinear system to regulate the radius of a single spherical bubble and prevent collapse occurrence, which has a great importance in some industrial applications. The system's robustness in the presence of uncertainties in bubble parameters is one of its most significant control objectives obtained in the controller designed in this paper. A comparison is also made between this controller and the controller previously designed for the simpler bubble model (Rayleigh–Plesset (RP) model). Also, the chattering created by SMC is eliminated by two methods. Simulation results are presented to show the effectiveness of the proposed method.