Liquid Flow Field Research Articles

The evolution of the bubble collapse morphology between two cylinders within a confined space

This work investigates the dynamic bubble behaviors between two cylinders within a confined space using high-speed photographic experiments and Kelvin impulse theory. First, the evolution of the collapse morphologies of bubbles located at the origin and along the y axis between two cylinders is qualitatively investigated. The effects of the cylinder spacing and bubble ordinate on the characteristics of the bubble deformation and the liquid velocity are then explored. The variations of the bubble interface velocities, the roundness of the bubble cross section, and the bubble radius are quantitatively analyzed. The conclusions can be summarized as follows: (1) The experimental bubble collapse phenomena at the origin can be divided into three cases: hourglass-shaped collapse, “8”-shaped collapse, and capsule-shaped collapse. Bubble collapse at the y axis can also be divided into three scenarios: awl-shaped collapse, spindle-shaped collapse, and inverted triangle-shaped collapse. (2) The cylinder spacing and the bubble ordinate significantly affect the experimental bubble collapse behaviors and the theoretical liquid flow field. (3) High-velocity liquid regions are generated around the bubble when it oscillates freely, and the nearby cylinders always lead to low-velocity regions between them and the bubble. The closer the bubble is to the cylinder, the smaller the low-velocity regions and the larger the high-velocity regions.

Hydrodynamic study of gas–liquid-solid mini-fluidization based on fluorescence PIV

The fluorescence-based tracer particle image velocimetry (fluorescence PIV) was used to obtain the flow regimes transition, bubble size and velocity, liquid and particle flow field characteristics of the 1 ∼ 3 mm GLSMFBs and 93 ∼ 195 μm glass beads. When the bed-to-particle diameter ratio increased, the bubble size and velocity distribution tended to be more concentrated. Bubble rose as straight line and S-shaped spiral trajectory. The divergence and vorticity of the flow field were preliminarily quantified. There showed a close relationship between the macroscopic hydromechanical behaviors such as bubble size and velocity and the mesoscopic behaviors such as the movement and development of vortices. The upward drag force of liquid and bubble on particles mainly affected the particle axial velocity, while the particle radial motion was mainly caused by bubble wake and surface force among particles. The results provide theoretical reference for the design and optimization of GLSMFB reactors.

Enhancing Sensitivity And Quantifying Uncertainty Of Volumetric Two-Colour Two-Dye Laser-Induced Fluorescence Thermometry Of Aqueous Solutions

Laser-induced fluorescence (LIF) is a nonintrusive method for temperature field measurement in gaseous and liquid flow fields. There has been attempts to enhance the temperature sensitivity of this method mainly by applying two fluorescent dyes with opposite temperature sensitivity. While there has been advances in enhancing the temperature sensitivity of LIF thermometry in aqueous solutions, there factors that limits the enhancement of the temperature sensitivity. This work explores the factors that restricting the temperature sensitivity in the ratiometric systems using Fluorescein and Kiton red dyes. The uncertainty resources associated to this ratiometric system is also investigated considering the application of this method in both planar and volumetric configurations.

A coupled computational fluid dynamics-discrete element method modeling for the dynamic behavior of the polar detector in a crushed ice environment during polar exploration

Investigating the dynamic behavior of polar detectors holds significance for the polar exploration of clean energy production. This paper uses computational fluid dynamics and the discrete element method, complemented by laboratory experiments, to systematically explore the water entry dynamics of a projectile passing through a zone of crushed ice accumulation. The research analyzes the influence of different crushed ice accumulation heights (ha) and water entry conditions on cavity formation, flow field distribution, and dynamic characteristics as the projectile passes through the crushed ice zone. Moreover, the influence of multi-body coupling on the movement of crushed ice and fluid is analyzed. The findings reveal alterations in the water entry behavior of the projectile due to the presence of the crushed ice accumulation zone. A notable two-way coupling mechanism between crushed ice and fluid is identified: crushed ice particles influence liquid level fluctuations and cavity evolution, while fluid flow impacts the movement of crushed ice particles. As the height of crushed ice accumulation increases, this coupling effect intensifies, leading to changes in the flow field distribution near the cavity and the hydrodynamic behavior of the projectile. While the alteration in water entry Froude number (Fr) may not significantly alter the evolution pattern of the liquid level flow field, it notably affects the distribution range and formation scale of the flow field characteristics. Additionally, the water entry Fr influences the load characteristics of the projectile as it passes through the crushed ice zone.

Statistical Analysis of Bubble Parameters from a Model Bubble Column with and without Counter-Current 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 are 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 using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.

Synergistic effects of air–liquid flow and electric field on membrane performance

High-level membrane fouling control is required in various membrane processes. Different techniques have been proposed for membrane fouling control, while the synergistic effects of the techniques are less explored. We proposed a novel membrane fouling control approach by applying slug flow and an electric field simultaneously. In contrast to synthetic bulk solutions, surface water containing different particles with various properties was applied. Results showed that transmembrane pressure (TMP) increased from 8 kPa to 10 kPa in 30 min at an optimized air velocity, showing a significant increasing trend. Nevertheless, by applying an electric field with a voltage ranging from 0.5 V to 1.0 V, TMP remained relatively constant over 120 min of filtration with a permeate flux at 100 L/m2.h, showing that a significant membrane fouling control effect was achieved. Particle size and zeta potential of permeate decreased and increased respectively by applying the bubbles, while the effects were enhanced significantly when an electric field was further applied. Furthermore, three-dimensional fluorescence spectrum confirmed that the amount of membrane foulant was reduced significantly by the synergistic effect. This study proved that microparticles were affected by the slug flow and the electric field affected nanoparticles respectively. By this way, the novel approach was effective in enhancing membrane performance by tackling membrane foulants with different properties. This study also contributed to a better understanding of corresponding membrane fouling process in membrane bioreactors.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Baffleless coils can operate as continuous oscillatory flow reactors to produce pharmaceutical products where process intensification is intended. A method to evaluate mixing performance and its impact on reaction conversion is residence time distribution (RTD) analysis. Liquid macromixing in a long baffleless coil reactor (L = 24 m, dt = 4.57 mm) at ranges of oscillation amplitude (11.75–58.75 mm), frequency (0–3.68 Hz), and net flow rate (30–120 g⋅min−1) was investigated based on measured RTDs fitted to the skewed normal distribution model. The impact of operating conditions on the RTD was supported by analyzing the liquid flow field derived from CFD simulations. The RTD variance under different oscillation conditions suggests a near plug flow pattern, although deviations from ideality such as skewness and long tailing were always observed. The model parameters, along with the RTD variance, were correlated to the operating conditions lumped in an oscillatory Dean number that used the flow amplitude as characteristic length (Deox). Values of Deox varied between 150 and 11000, and the RTD variance at the different net flow rates was minimized for 300 < Deox < 600, as also evidenced from the minimum cross-sectional variance of the simulated time-averaged axial velocity profile. Normalizing the data allowed comparison to similar coil studies with different geometrical dimensions and operating conditions, leading to generalized correlations for the RTD model parameters. Finally, chemical conversion was assessed for first- and second-order single phase reactions at different Damköhler numbers using the segregation and maximum mixedness micromixing models combined with the fitted RTDs. The performance of the coil remained consistent with a plug flow reactor despite its departures from ideal flow.

Mass transfer enhancement and flow field simulations for a Venturi bubble generator with multiple inlet tubes

The Venturi device plays a crucial role in the Filtered Containment Venting System (FCVS), effectively preventing the release of radioactive pollutants from nuclear reactor containment during overpressure events. Various configurations of the Venturi device yield different outcomes, with mass transfer efficiency being contingent on bubble size and overall gas holdup. This study examines the impact of varying numbers of inlet tubes on the Venturi device, while keeping the inlet area constant. Specifically looking at the gas–liquid flow field, bubble behavior, and mass transfer capacity in the diverging section. By comparing Single Inlet Tube Venturi Device (SITVD) and Double Inlet Tubes Venturi Device (DITVD), we have reached the following conclusions: (1) In SITVD, the liquid flow field is biased to one side, whereas in DITVD, the liquid flows along the axial direction, resulting in bubbles experiencing stronger shear forces. (2) DITVD exhibits a higher overall gas holdup compared to SITVD, with an average axial gas holdup of 0.0317, which is greater than SITVD's 0.0247. However, SITVD's gas holdup is more evenly distributed. (3) SITVD exhibits a higher turbulence dissipation rate of 545 m2/s3, while the bubble residence time in DITVD is comparatively longer. (4) The average bubble diameter of DITVD is 1.116 mm, which is higher than the 1.011 mm of SITVD. (5) DITVD has better mass transfer than SITVD. The proposed structure of the new Venturi scrubber in this study demonstrates a significant enhancement in mass transfer capacity and filtration efficiency. This discovery provides a solid basis for the design and optimization of FCVS, thereby ensuring the safe operation of nuclear reactors.

Preliminary Analysis and Optimization via CFD of a Liquid Hydrogen Pressure Regulating Piston Valve

Due to their high reliability and precision, piston valves are frequently used for pressure regulating applications. Particularly in the aerospace industry, where cryogenic fluids such as liquid hydrogen are frequently used, the design and operation of piston valves become crucial. The current state of advancement of this technology in the cryogenic field is still in its early stages, owing to the difficulties in designing such complex systems in harsh environments. This justifies the need for further in-depth studies and analysis using CFDs tools and predictive models. In order to ensure an optimal and efficient use of a piston pressure regulating valve in cryogenic environment, it is necessary to understand the strengths and limitations of this technology in an extreme thermal and mechanical condition. The presented work concentrates therefore on a preliminary analysis and optimization of a piston valve operating in liquid hydrogen flow field, for pressure regulating applications. Particular focus will be dedicated to the overall dynamics of the main body of the piston, in terms of robustness and controllability of the desired response of the system. The dynamics of the piston within an extremely low-viscous flow, as well as the thermodynamic and fluid dynamic aspects of the valve system, will be discussed. Simulations of the flow field will be performed through CFD tool, crossing the results with the dynamics of the simulated system response through and implemented Simulink model. The obtained results will be then critically analysed in order to suggest possible optimization of the valve in the locations where the system is most affected from a thermal and mechanical standpoint.

Liquid Flow Patterns and Particle Settling Velocity in a Taylor-Couette Cell Using Particle Image Velocimetry and Particle Tracking Velocimetry

Summary Controlling the downhole pressure is an important parameter for successful and safe drilling operations. Several types of weighting agents (i.e., high-density particles), traditionally barite particles, are added to maintain the desired density of the drilling fluid (DF). The DF density is an important design parameter for preventing multiple drilling complications. These issues are caused by the settling of the dense particles, an undesired phenomenon also referred to as sagging. Therefore, there is a need to understand the settling characteristics of heavy particles in such scenarios. To this end, simultaneous measurements of liquid phase flow patterns and particle settling velocities have been conducted in a Taylor-Couette (TC) cell with a rotating inner cylinder and stationary outer cylinder separated by an annular gap of 9.0 mm. Liquid flow patterns and particle settling velocities have been measured using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) techniques, respectively. Experiments have been performed by varying the rotational speed of the inner cylinder up to 200 rev/min, which is used in normal drilling operations. Spherical particles with diameters of 3.0 mm or 4.0 mm and densities between 1.2 g/cm3 and 3.95 g/cm3 were used. The liquid phases studied included deionized (DI) water and mineral oil, which are the basic components of a non-Newtonian DF with a shear-thinning viscosity. The DF is a mud-like emulsion of opaque appearance, which impedes the ability to observe the liquid flow field and particle settling in the TC cell. To address this issue, a solution of carboxymethyl cellulose (CMC) with a 6% weight concentration in DI water was used. This non-Newtonian solution displays shear-thinning rheological behavior and was used as a transparent alternative to the opaque DF. For water, PIV results have shown wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTVF), which agrees with the flow patterns reported in the literature. For mineral oil, circular Couette flow (CCF) was observed at up to 100 rev/min and vortex formation at 200 rev/min. For CMC, no vortex formation was observed up to 200 rev/min, only CCF. The settling velocities for all particles in water matched with the particle settling velocities predicted using the Basset-Boussinesq-Oseen (BBO) equation of motion. For mineral oil and CMC, the results did not match well with the predicted settling velocities, especially for heavy particles due possibly to the radial particle migration and interactions with the outer cylinder wall.

Space numerical simulation of full oxygen combustion flame in glass melting furnace based on flue gas preheating

This study explores the innovative design of a glass-melting furnace, which incorporates a combustion lance and a flue on one side. The research validates the simulation that the high-temperature flue gas, produced by the pure oxygen combustion of natural gas, can utilize residual heat in a multi-stage process to preheat and burn the fuel natural gas via a jet heat pump. This process significantly reduces energy consumption, thereby decreasing construction costs and energy usage in industries related to glass furnace production. The research focuses on the flame space of a 600 t/day natural gas flat glass all-oxygen combustion furnace. Utilizing numerical calculation methods, a three-dimensional mathematical model of the all-oxygen lance flame space was developed. Numerical simulation methods were employed to examine the temperature field, airflow field, and the distribution pattern of the liquid flow field within the glass space in the furnace. The simulation results reveal that incorporating high-temperature flue gas into the fuel can markedly enhance the performance of the spray gun flame. Additionally, choosing spray gun outlet designs of varying widths can tailor the flame width to better meet the requirements of the glass melting system, thereby significantly improving the waste heat utilization rate of the flue gas. This offers more alternatives for the direct utilization of flue gas. When compared to traditional oxy-combustion glass melting furnaces, this innovative design substantially reduces construction costs and is more energy-efficient and environmentally friendly.

Hydrodynamics and shape reconstruction of single rising air bubbles in water using high-speed tomographic particle tracking velocimetry and 3D geometric reconstruction

Time-resolved tomographic particle tracking velocimetry (TR-3D-PTV), also called 4D-PTV, is used here to obtain the instantaneous 3D liquid flow field information in the wake of a single rising bubble in water. Simultaneously, the bubble shape, size and velocity are determined by tomographic reconstruction of the 3D bubble shape. Both, tracer particles for PTV and bubbles, are imaged in a shadow mode with background illumination. The Lagrangian method used in this paper, especially combined with the shake the box algorithm, has big advantages compared to particle image velocimetry, in situations, where only low particle per pixel values can be obtained. In this research, single air bubbles of different sizes, with diameters of around 2.4 mm, 4.0 mm, 6.0 mm and 9.6 mm, were injected into stagnant de-ionized water. Their shape was reconstructed in 3D, and an equivalent bubble diameter was determined from this reconstruction. Compared to conventionally used 2D shadow imaging, this diameter is about 13% smaller. The 3D bubble trajectory can be analysed and decomposed into a sinusoidal function curve lateral projection and an ellipsoidal shape vertical projection. As the bubble diameter increases, the radius of the spiral trajectory is decreasing as well as the amplitude of vertical sinusoidal oscillation. The wake structure in the liquid behind the bubbles is also changing with bubble size: from simple vortex pairs for smaller bubbles to an intertwined structure of several twisted vortices for the bigger ones.Graphical abstractThree-dimensional bubble reconstruction (grey surface) and liquid stream lines coloured with velocity magnitude around an ascending air bubble in de-ionized water.

Experimental and numerical investigation of a counter-current flow bubble column

Bubble columns are gas–liquid contactors that are used in many process-engineering applications. A counter-current liquid flow is frequently imposed to adjust the bubbles’ residence-time and thus optimize mixing and mass-transfer. The present work describes measurements in such a device together with corresponding computational fluid dynamics simulations based on the Eulerian two-fluid framework. Bubble-size and -velocity are measured by shadow-imaging for a large range of gas and counter-current liquid flow rates, as well as different nozzle sizes. The corresponding liquid flow-fields are characterized by Particle Image Velocimetry. From the large experimental database, a few cases are selected to analyze the flow structure and effects of the bubble-size. In the simulations, different models for the drag- and lift-force acting on the bubbles are evaluated. While good agreement between experiments and simulations could be achieved for the gas-fraction and gas-velocity, differences are found for the liquid-velocity, which is generally overestimated in the calculations.

Modeling and simulation of cryogenic propellant tank pressurization in normal gravity

The self-pressurization process of cryogenic propellant storage under a normal gravity condition often involves turbulent mixing in the liquid region and complex flow fields in the vapor region caused by heat leak into a cryogenic tank. Over time, the cryogenic tank pressurizes due to a temperature increase in the vapor phase and the heat and mass transfer across the liquid–vapor interface. A nodal simulation approach was employed to study the long term transients of tank self-pressurization. In this paper, mechanistic models and correlations were implemented to simulate the self-pressurization of Multipurpose Hydrogen Test Bed experiments with a commercial nodal code, namely, Systems Improved Numerical Differencing Analyzer with Fluid Integrator (SINDA/FLUINT). A lump number sensitivity study on the prediction of tank pressure and temperature was performed to determine the number of lumps appropriate for a 50% initial liquid fill level. Uniform heat flux boundary conditions were implemented on both phases during the tank self-pressurization with an estimated heat leak provided by NASA. Numerical simulation showed that the predicted pressure profiles of the 50% and 90% fill level cases agreed well with experimental data. In the liquid region, temperatures were primarily uniform and close to saturation due to turbulent natural convection mixing. Findings showed the current model overestimated the temperature profiles in the vapor region when assuming heat conduction transfer.

(Invited) In-Situ Optical Diagnostics of Plasma Electrochemical Reactors

Many methods for synthesizing nanomaterials are complex and can require high temperature, acids, bases, or reducing agents. The plasma electrochemical reactor (PEC), composed of an atmospheric-pressure low-temperature plasma in contact with an aqueous electrode, may provide unique physico-chemical conditions that sidestep these disadvantages because non-equilibrium electrochemistry and nucleation are initiated in solution without additional heating or strong/toxic reagents. Indeed, PECs have successfully synthesized graphene quantum dots (GQD) [1,2].The precise mechanism of GQD growth is likely to be complex, involving non-equilibrium plasma chemistry and interactions near the plasma-liquid interface. Up to now, investigations of the liquid-phase chemistry have relied principally on ex situ measurements with little or no spatially-resolved information. In addition, conventional experimental techniques can suffer from a lack of selectivity and/or degradation of dyes, chemical probes, or spin traps introduced into the liquid.To extend the scope of diagnostics, we employ an in situ approach using multiple diagnostic techniques to study a wide range of physical and chemical properties at the plasma-water interface. The centrepiece of this platform is in situ spontaneous Raman microspectroscopy, which is advantageous because of its non-intrusiveness, selectivity, versatility, and straightforward calibration. Shaping the laser beam into a light sheet enables probing of the interfacial region with micron-scale spatial resolution. To observe the effect of the plasma on the solvent, we tracked the Raman spectrum of water. Analysis of the –OH stretch band reveals that the plasma weakens the hydrogen bonding network of water. This effect becomes especially pronounced near the interface, at a depth of a few tens of microns. Likewise, at a similar depth, the concentrations of aqueous H2O2 and NO3 - both exceed those of the bulk liquid [3]. Similar interfacial layers have been modeled in past studies for radical species such as OH but not for long-lived species such as NO3 -.Concerning GQDs, we tracked their production via in situ photoluminescence (PL) and UV-VIS absorption spectroscopies. Both the PL and absorption intensities reached a maximum not at the interface but rather at a depth of a few millimeters. This observation corroborates with liquid flow field measurements by particle image velocimetry, which revealed a low-velocity zone at this depth. Under certain conditions, we could observe the consumption of the carbon precursor over the course of plasma treatment using in situ Raman spectroscopy. Finally, we characterized plasma properties near the interface, such as the electron number density, using optical emission spectroscopy. Together, these results provide the fullest description to date of the reaction environment during GQD synthesis. Acknowledgments Financial support: ANR grants ANR-15-CE06-0007-01 and ANR-11-LABX-0017-01, PHC Orchid 40938YL, CNRS-IEA “GRAFMET”, Fédération Plas@Par, EUR PLASMAScience, Poitou-Charentes region (CPER program) References [1] Orrière, T., Kurniawan, D., Chang, Y. C., Pai, D. Z., & Chiang, W. H. (2020). Nanotechnology 31 (485001).[2] Yang, J. S., Pai, D. Z., & Chiang, W. H. (2019). Carbon 153, 315-319.[3] Pai, D. Z. (2021) J. Phys. D. : Appl. Phys. 54, 355201

Bulk Cavitation in Model Gasoline Injectors and Their Correlation with the Instantaneous Liquid Flow Field

It is well established that spray characteristics from automotive injectors depend on, among other factors, whether cavitation arises in the injector nozzle. Bulk cavitation, which refers to the cavitation development distant from walls and thus far from the streamline curvature associated with salient points on a wall, has not been thoroughly investigated experimentally in injector nozzles. Consequently, it is not clear what is causing this phenomenon. The research objective of this study was to visualize cavitation in three different injector models (designated as Type A, Type B, and Type C) and quantify the liquid flow field in relation to the bulk cavitation phenomenon. In all models, bulk cavitation was present. We expected this bulk cavitation to be associated with a swirling flow with its axis parallel to that of the nozzle. However, liquid velocity measurements obtained through particle image velocimetry (PIV) demonstrated the absence of a swirling flow structure in the mean flow field just upstream of the nozzle exit, at a plane normal to the hypothetical axis of the injector. Consequently, we applied proper orthogonal decomposition (POD) to analyze the instantaneous liquid velocity data records in order to capture the dominant coherent structures potentially related to cavitation. It was found that the most energetic mode of the liquid flow field corresponded to the expected instantaneous swirling flow structure when bulk cavitation was present in the flow.

Numerical Investigations of Heat Transfer and Fluid Flow Characteristics in Microchannels with Bionic Fish-Shaped Ribs

Microchannel cooling technology is an effective method to solve local thermal stacking. In this paper, four innovative microchannels with bionic fish-shaped rib arrangements (CM-O, CM-R, CM-H, and CM-G) are designed by imitating geese and fish clusters. The heat transfer and flow characteristics of the microchannels are simulated numerically at different Reynold’s numbers (Re = 200 − 1600). The liquid water temperature and flow field in the four innovative microchannels with bionic ribs are analyzed. The results show that the ribs’ arrangement has an influence on the thermal performance of microchannels. Compared to the smooth microchannel (CM), the of the Nu microchannels with the bionic fish-shaped ribs increases by 33.00–53.26% while the fave increases by 28.63–34.93% at Re = 1200. The vortices around the ribs are clearly observed which improves the temperature gradient. The performance evaluation criterion (PEC) of CM-H is higher than that of the others. This indicates that the rib arrangement of CM-H is superior for heat dissipation application.

Periodic large-scale structural characteristics of two-phase flow in tight lattice bundles

This paper investigated the two-phase flow characteristics in a double sub-channel tight lattice (P/D = 1.06). Compared to the prototype, the test channel was magnified by 2.7 times. A self-developed 16 × 32 wire-mesh sensor was utilized to measure the phase distribution at two fully developed positions of the test channel (Z/Dh = 86.86, 115.8). The flow conditions are 0.036 m/s < jg < 1.04 m/s and 0.93 m/s < jl <1.86 m/s at Z/Dh = 115.8, including the bubbly flow (B), the cap-bubbly flow (CB), and the slug flow (S). Combined with the pseudo-side view of the flow pattern and the power spectrum, the coherent structure of the gas phase under the bubbly flow and the cap-bubbly flow was confirmed. For the bubbly flow, the coherent structure is in the form of bubble clusters consisting of discrete bubbles. These bubble clusters are staggered on both sides of the gap but do not traverse across the gap, which is speculated to be caused by the large-scale vortex of the liquid flow field. For the cap-bubbly flow, the coherent structure is in the form of cap-shaped bubbles. In this study, the cap-shaped bubbles are confined in the center of the subchannels and staggered in adjacent subchannels, which is attributed to the compact arrangement of rod bundles and the inter-subchannel liquid cross-flow caused by the cap-shaped bubbles. The characteristic parameters, including the pulsation frequency f, convection velocity v, wavelength λ, and amplitude A were defined to characterize the coherent structure. Data analysis results show that the coherent structure frequency under the bubbly flow increases with the increase of the liquid-phase velocity and the coherent structure frequency under the cap-bubbly flow increases with the increase of the gas-phase velocity. In addition, the coherent structure is suppressed under three flow conditions, including the bubbly flow with low liquid velocity (jl < 1.3 m/s), the B-CB transition, and the slug flow.

Numerical Simulation of the Coupled Magnetic and Liquid Flow Fields in a Spherical Magnetohydrodynamic Attitude Control Device

Numerical Simulation of the Coupled Magnetic and Liquid Flow Fields in a Spherical Magnetohydrodynamic Attitude Control Device

Cattaneo-Christov double diffusive and model development for entropy optimized flow of Reiner-Rivlin material in thermal system and environmental effect

Here we analyze magnetohydrodynamic flow of Reiner-Rivlin material. Thermal and solutal fluxes are discussed through Cattaneo-Christov flux models. Variable mass diffusivity and thermal conductivity characteristics are incorporated. Entropy rate is calculated. Non-linear differential systems are reduced to non-dimensional system through appropriate transformations. The obtained non-linear dimensionless system are analytically computed through optimal homotopy analysis method (OHAM). Graphical aspects of liquid flow, entropy optimization, concentration and thermal field versus influential variables are explored. It is found that fluid flow reduces against magnetic field variation. Temperature boosts against higher thermal relaxation time. An increment in thermal field is witnessed versus thermal conductivity variable. Clearly concentration enhances against higher solutal relaxation time. Augmentation in entropy generation occurs versus magnetic field. Higher diffusion variable result in entropy optimization enhancement. Higher thermal conductivity variable lead to boost of entropy rate. An enhancement in entropy rate is detected for mass diffusivity parameter.