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Bubble flow can be simulated by the two-fluid model and the multi-fluid model based on the Eulerian method. In this paper, the gas phase was further divided into several groups of dispersed phases according to the diameter by using the Eulerian-Eulerian (E-E) multi-fluid model. The diameters of bubbles in each group were considered to be the same, and their distributions were reorganized according to a specific probability density function. The experimental data of two kinds of bubble flow with different characteristics were used to verify the model. With the help of the open-source CFD software, OpenFOAM-7.x (OpenFOAM-7.0, produced by OpenFOAM foundation, Reading, England), the influences of the group number, the probability distribution function, and the parameters of different bubble diameters on the calculation results were studied. Meanwhile, the numerical simulation results were compared with the two-fluid model and the experimental data. The results show that for the bubble flow with the unimodal distribution, both the multi-fluid model and the two-fluid model can obtain the distribution of gas volume fraction along the pipe radius. The calculation results of the multi-fluid model agree with the experimental data, while those of the two-fluid model differ greatly from the experimental data, which verifies the advantage of the multi-fluid model in calculating the distribution of gas volume fraction in the polydisperse bubble flow. Meanwhile, the multi-fluid model can be used to accurately predict the distribution of the parameters of each phase of the bubble flow if the reasonable bubble diameter distribution is provided and the appropriate interphase force calculation model is determined.

An axial piston pump can produce a serious cavitation phenomenon in the high- and low-pressure ‎transition process. Cavitation bubbles expand, compress, rebound and collapse when they enter the high-‎pressure oil drainage area. This affects the outlet flow ripple as well as the pressure pulsation of the ‎piston pump. However, the effect of the cavitation bubbles is ignored in the current outlet flow ripple ‎model of axial piston pumps. It affects the optimization design of the axial piston pump distribution area ‎structure parameters with the objective of reducing the pressure and flow rate. Therefore, a method of ‎optimizing the fluid dynamic characteristics and the flow distribution area structure parameters of an axial ‎piston pump considering the cavitation bubble evolution is proposed. A single-cavity dynamic model was ‎established to study the bubble evolution as the piston chamber pressure changes. According to the ‎cavitation cloud (group cavitation) characteristics of the axial piston pump, theoretical models of the ‎outlet flow ripple and the pressure pulsation of a piston pump were established considering the cavitation ‎bubble characteristics. The influence of cavitation characteristics on the outlet flow ripples and pressure ‎pulsation of the axial piston pump was analyzed and compared with that without cavitation. Comparison ‎with the experimental results, verified that the outlet flow ripple model becomes more accurate when ‎cavitation bubble characteristics are considered. Based on the multi-agent particle swarm optimization ‎‎(MAPSO) algorithm, an optimization model of the piston pump outlet flow ripple was established ‎considering the cavitation bubble characteristics. The optimized design parameters for the flow ‎distribution area of the axial piston pump were evaluated. The proposed method can provide theoretical ‎guidance for the design of a low flow ripple axial piston pump.‎

To investigate the characteristics of the bubbles trapped in liquid cross flow, air was injected into flowing water circulated in a closed loop. High speed photography was used to record bubble images instantaneously. An image-processing code was specifically developed to identify bubbles in the images and to calculate bubble parameters. Effects of the water velocity and the flow rate of the injected air on bubble patterns were investigated. The results indicate that the inclination of bubble trajectory relative to the nozzle axis is enhanced as the water velocity rises. Meanwhile, bubble size varies inversely with the water velocity. The bubble profile tends to be rounded as the water velocity increases. Fluctuations of the bubble velocity are intensified as the water velocity decreases. As the balance between the external forces exerted on the bubble is reached, an approximately linear relationship between the velocities of the bubble and the water is manifested. For a given equivalent bubble diameter, the bubble terminal velocity is higher than that associated with quiescent water. At small Eötvös number, the consistency of the bubble aspect ratio in the liquid flow and quiescent water is revealed. The range of Eötvös number is extended considerably due to the flowing water. Values of Weber number are accumulated in a range within which high bubble aspect ratio is associated with relatively high water velocity.

Rising bubbles are often encountered in many engineering fields and have diverse applications. A thorough understanding of bubble rising phenomenon is crucial in these engineering applications. In this study, we employ the developed updated Lagrangian particle hydrodynamics (ULPH) multiphase flow model to investigate the dynamic behavior of bubble flow in quiescent liquids, including bubble rise, deformation, fragmentation, and coalescence. First, a comprehensive numerical study of the influences of computational domain dimensions and fluid/bubble density ratios at the multiphase interface on bubble dynamics is conducted. Subsequently, a variety of scenarios featuring single bubble rising in viscous fluid media are examined. The ULPH simulation results are validated against experimental data, the Level-set (LS) method and Lattice Boltzmann Method (LBM) results. Furthermore, results of three calculations are presented, including dynamic characterization of two horizontal coaxial bubbles, three vertical coaxial bubbles and a single bubble in the presence of an obstacle. The results indicate that the established ULPH multiphase flow model is effective in accurately simulating dynamic characteristics of rising bubbles under various conditions, affirming its applicability in engineering analyses.

This study employs a numerical simulation approach to investigate argon bubble flow behavior within a steel continuous casting mold, with a focus on the impact of bubble swarm correction models. Three scenarios are compared: one without any correction and two incorporating drag coefficient corrections, specifically designed for bubble swarm effects. The results demonstrate that incorporating these correction models significantly improves the predictive accuracy of simulations. In particular, the inclusion of a bubble swarm correction model reduces the error in predicted bubble trajectories by 51.7% and 23.0%, respectively, when measured by Hausdorff distances against experimental trajectory data, compared to the scenario without corrections. These findings underline the importance of selecting an appropriate drag correction model for accurate simulations of bubble dynamics and their interaction with the liquid steel in continuous casting molds. This study highlights that drag correction models tailored to the specific conditions of the continuous casting process are essential for achieving realistic predictions.

The hydrophilicity of the porous transport layer (PTL) critically influences the mass transport overpotential and overall efficiency of a proton exchange membrane water electrolyzer (PEMWE). In this study, titanium felts with three distinct levels of hydrophilicity are systematically characterized and evaluated electrochemically. A novel bilayer gradient hydrophilic titanium felt structure is designed, resulting in notable performance improvements: the average cell voltage decreases by 12.92%, and the overpotential is reduced by 9.94–18.03% across a current density range of 0.1–1.6 A·cm[sup.−2]. High-speed imaging reveals that the gradient hydrophilic structure effectively regulates bubble dynamics, nearly eliminating annular flow bubbles, reducing the proportion of slug flow bubbles by 40.78%, decreasing the bubble detachment diameter by 28.26%, and enhancing bubble displacement by 51.03% compared to that of untreated titanium felt. These results demonstrate that gradient hydrophilic structures can significantly enhance PEMWE performance, offering a promising strategy and a theoretical foundation for optimizing mass transfer in electrolytic systems.

To address the unclear coupling mechanism between bubble detachment behavior and acoustic characteristics in gas–liquid two-phase flow, this paper systematically studied bubble behavior and acoustic characteristics under different conditions by building a high-precision synchronous measurement system, combining acoustic signal analysis and bubble dynamics observation. The influence mechanism of liquid surface tension, dynamic viscosity, and orifice diameter on the critical gas flow velocity of bubble flow transition was analyzed, and a flow pattern classification criterion system was established. The experimental results showed that the bubble flow state could be divided into three states according to the characteristics of the acoustic signals: discrete bubble flow, single-chain bubble flow, and dual-stage chain bubble flow. The liquid surface tension and dynamic viscosity had no significant effect on the critical gas flow velocity of the transition from discrete bubble flow to single-chain bubble flow, but significantly increased the critical gas flow velocity of the transition from single-chain bubble flow to dual-stage chain bubble flow. The increase in the orifice diameter reduced the critical gas flow velocity of the two types of flow transition. In addition, the Weber number (We) and Galileo number (Ga) were introduced to construct a quantitative classification system of flow pattern, which provided theoretical support for the optimization of industrial gas–liquid two-phase flow.

Regulating valves are a key component in coal liquefaction systems, whose control precision and service life are affected by cavitation phenomena. The flow pattern matching relationship of this regulating valve is complicated, where local optimization of structure and size cannot inhibit the cavitation phenomenon effectively. Thus, an innovative valve seat structure with biomimetic drainage function is designed based on Bio-TRIZ bionic theory to inhibit cavitation inside the regulating valve. The distribution characteristics of cavitation in this bionic valve have been studied by numerical simulation, experimental measurement, and theoretical analysis. The influence of the bionic drainage valve seat on the internal cavitation development and the distribution of 3D cavitation morphology were also fully discussed. Results show that the bionic drainage hole structure destroyed the distribution law of the cavitation ring in the flow channel and accelerated the collapse of the cavitation flow, which mainly concentrates on the inner surface of the valve seat. When the inlet pressure is 4.0 MPa, the maximum average cavitation vapor volume fraction of the bionic valve seat section was reduced by 17.3%, and the cavitation area at the cross section was reduced by 3.02 mm 2 , compared with the original valve seat. Furthermore, the bionic drainage hole structure causes the vortex structure to break into smaller vortices during the cavitation collapse stage, and the cavitation bubble is dissipated in the form of smaller vortex and then disappear finally. The research could inhibit the cavitation inside the regulating valve effectively and extend the service life of the regulating valve.

The article explores the impact of various factors on the determination of gas bubble equivalent diameters using optical shadowgraphy. The experimental setup involves a liquid-gas system. The results indicate that the distance between the camera and the bubble rise-up plane has negligible influence on measurement precision as long as the area captured is constant. Increasing the number of analyzed frames significantly reduces uncertainties, while higher image magnification leads to increased uncertainties due to a reduced number of frames and smaller area captured. Image distortion correction minimally affects results and precision. The study concludes that factors such as resolution, frame rate, and elongated flow path captured contribute to more accurate determination of equivalent bubble diameters, essential for the determination of mass and heat transfer coefficients in liquid-gas flows. The results indicate that a sufficiently high number of video frames may be more important than indiscriminately increasing the resolution.

Oxygen bubble accumulation on the anodic side of a polymer exchange membrane water electrolyzer (PEMWE) may cause a decrease in performance. To understand the behavior of these bubbles, a deep-learning-based bubble flow recognition tool dedicated to a PEMWE is developed. Combining the transparent side of a single PEMWE cell with a high-resolution high-speed camera allows us to acquire images of the two-phase flow in the channels. From these images, a deep learning vision system using a fine-tuned YOLO V7 model is applied to detect oxygen bubbles. The tool achieved a high mean average precision of 70%, confirmed the main observations in the literature, and provided exciting insights into the characteristics of two-phase flow regimes. In fact, increasing the water flow rate from 0.05 to 0.4 L/min decreases the bubble coverage (by around 32%) and the mean single-bubble area. In addition, increasing the current density from 0.3 to 1.4 A/cm2 leads to an increase in bubble coverage (by around 40%) and bubble amount.