Gas-liquid Two-phase Flow Field Research Articles

A modified capacitance tomography image reconstruction approach based on iterative shrinkage-thresholding algorithm combined with deep networks

Abstract Due to the ‘soft-field’ effect and the challenges posed by ill-posed and ill-conditioned inverse problems, it is difficult to obtain high quality images from an electrical capacitance tomography (ECT) system. To achieve both high-quality images and fast imaging speed with limited measurement data, an image reconstruction algorithm, which was initially proposed for compressive sensing, is adapted for ECT image reconstruction to optimize the ill-posed nature of its inverse problem. The proposed algorithm leverages deep learning networks inspired by the iterative shrinkage-thresholding algorithm (ISTA), thereby creating a model that is both mathematically interpretable and endowed with trainable parameters. Building upon this foundation, the conventional Landweber iteration is integrated with the ISTA-Net to refine the optimization process for ECT image reconstruction. In order to propose an effective model adapting to the actual multiphase flow characteristics and complex flow pattern changes, the training and test process is driven by a comprehensive dataset generated from dynamic simulations, rather than artificial samples of multiphase distributions. This numerical methodology simulates the dynamic measurement process of a virtual ECT sensor by coupling the gas–liquid two-phase flow field and the ECT electrostatic field. The results of the testing phase indicate that the proposed algorithm outperforms traditional ECT image reconstruction methods. Compared with the linear back projection algorithm, the average image error and gas fraction error have been reduced by 20.44% and 16.74%, respectively, while maintaining a computational speed comparable to that of the Landweber iteration. The accuracy of the new algorithm in reconstructing the two-phase interface and estimating the gas fraction has been validated by static experimental tests, showing its potential for practical application in online gas–liquid two-phase flow measurement scenarios.

Analysis of gas-liquid two-phase flow field with six working teeth spiral incremental cathode for deep special-shaped hole in ECM

Analysis of gas-liquid two-phase flow field with six working teeth spiral incremental cathode for deep special-shaped hole in ECM

Study on the safety of a magnetic strainer at the deaerator outlet under two-phase and large-scale flow fields

Iron oxide corrosion exists in the deaerator, which causes serious damage to the water supply system. To absorb iron oxide impurities for the feed water quality, a magnetic strainer device has been designed at the deaerator outlet. In order to ensure the safe and stable operation of the deaerator, the computational fluid dynamics (CFD) method was used in this work to analyze the impact of complex outlet conditions on the gas-liquid two-phase flow field, pressure field, and structural safety within a deaerator. After the strainer is installed, turbulent kinetic energy (TKE) and turbulence intensity (TI) are not monotonically changing throughout strainer region and depend on the local flow state and geometry. TI relies more on turbulence disturbance and geometry. The overall flow near the strainer is accelerated, and the dimensionless velocity in the shear layer on both sides of the strainer center bracket increases by a maximum of 153.44%. Stable vortices and complex secondary vortices are formed near the strainer. The overall eddy is more fragmented, and eddy dissipation is prone to occur in the outlet region. However, this does not cause additional large turbulence losses. The impact of the strainer on the static pressure loss of the entire deaerator is very limited, and the reduction in static pressure difference does not exceed 0.04%. Finally, suggestions are made for the structural improvement and maintenance of the strainer based on the simulation results, which provide a reference for further safe and stable application of the deaerator magnetic strainer.

Computational Fluid Dynamics Analysis of Wet Dust Removal in High-Gravity Countercurrent Rotating Packed Bed

High-gravity wet dust removal technology has attracted much attention because of its potential to cut liquid into smaller liquid droplets and lower energy consumption. However, the complex structure and the high-speed rotation of the rotating packed bed do not allow us to analyze the flow field using conventional methods, and thus the capture mechanism of fine particles in a high-gravity environment is poorly understood. In this study, a two-dimensional computational fluid dynamics model was established to investigate the distribution of the gas–liquid two-phase flow field inside of a rotating packed bed. The characteristics of the flow field, such as the liquid form, gas–liquid contact time, and gas flow path, were investigated, and the droplet size distribution and gas–liquid slip velocity were quantitatively analyzed. The inertial capture efficiency was calculated using the Stokes number, and the dust removal efficiency distribution in the rotating packed bed was compared. The reason for the high collection efficiency of fine particles by the high-gravity wet dust removal technology was explained by numerical simulations. Two new structures were designed to improve the total dust removal efficiency.

Research on simulation method of multiple time scales dissolution process in tube electrode pulse electrochemical machining

Tube electrode pulsed electrochemical machining (TE-PECM) has received widespread attention as an electrochemical perforation technique that is widely used for machining deep small holes/oblique small holes such as air film holes in blades. However, the TE-PECM process is characterized by complex multi-physics field coupling relationships and multiple time scales for multi-physics interactions, making the simulation of the pulsed electrolytic processing process computationally huge and difficult to perform. To accurately describe the multi-physical field coupling relationship for pulsed electrochemical processing. In this paper, a k-ε gas-liquid two-phase flow model has been introduced to model the interpolar gas-liquid two-phase flow field variation law, and on this basis, a coupled multi-physics field model for pulsed electrochemical machining processing is established to provide an accurate description of the interpolar multi-physics interaction mechanism. A quasi-steady-state iterative simplification algorithm based on heat source averaging is proposed to solve the problem that the time scale span of the dissolution process leads to a huge amount of simulation calculations. The simulation analyzes the dissolution characteristics at the micro time scale and macro time scale and compares them with the full precision method. The results show that the simulation accuracy of the two methods is the same, but the simulation calculation time of the simplified algorithm is reduced by two-thirds. The experimental platform was designed and built to carry out a series of experiments under different processing times, and the results effectively verified the correctness of the simulation method.

Numerical study on the effect of the vane channel parameters on the performance of gas-water separators for a PEMFC system

In this study, the effects of vane channel parameters on the flow field and separator performance are investigated based on a vane type gas-water separator for a PEMFC (proton exchange membrane fuel cell) system. The Eulerian-Eulerian model combines with the Multi-Fluid VOF (volume of fluid) modeling approach is used to comprehensively investigate the gas-liquid two-phase flow field and performance indexes in the separator, and the sensitivity analysis of the structural parameters is carried out. The results show that the pressure drop of the separator gradually increases with the increase of the vane contraction ratio, while the separation efficiency has a tendency to increase and then decrease with the increase of the vane incidence angle. For the separation efficiency, the most beneficial structural variant results in an increase of 11.63%, while for the pressure drop, almost all structural variants result in a reduction of the pressure drop from the standard structure with a maximum reduction of 36.58%. By analyzing the phase distribution, pressure field and velocity distribution of different structures, it can be obtained that the main factors affecting the performance of the separator are the extreme values of tangential velocity inside the separator and the symmetry of velocity distribution in the internal flow field. The results presented in this study can provide a reference for the PEMFC gas-water separator.

Gas-liquid two-phase flow rates measurement using physics-guided deep learning

Machine learning has been widely used in the gas-liquid two-phase flow field. However, data-driven machine learning methods are often considered black-box methods which may lead to insufficient interpretation and extrapolation abilities. Combining machine learning and physical principles is a promising method to improve the generalization abilities and interpretation of the deep neural network model, which is still a challenge in gas-liquid two-phase flowrates measurement. In this work, we propose a physics-guided deep learning model for gas-liquid two-phase flow rate measurement through the differential pressure meter. The simplified physical constraint term of gas-liquid two-phase flow is established based on the momentum equation and continuity equation of gas-liquid two-phase flow, and then, the physical constraint term is added to the loss function of the deep neural network. Consequently, the predictions of the model not only satisfy the target values but also conform to the physical term. The performance of the physics-guided neural network (PGNN) is tested and compared with an artificial neural network (ANN) model that is trained without the physical constraint term. Results show that the gas and liquid flow rates could be measured simultaneously with satisfactory accuracy using the proposed PGNN model, more importantly, the model also performs well on a wider range of testing conditions (Gas Volume Fraction, GVF>95%). It indicates that this method is possible to improve the generalization and interpretation of the purely data-driven neural network model.

Study on Characteristics of Two Phase Flow Field in Grinding Zone of Large Spiral Angle Groove Wheel

Aiming at the high specific removal energy and heat generation rate in grinding process, and the low heat transfer efficiency in grinding arc zone of ordinary grinding wheel, the problems of local high temperature and grinding burn are easy to occur. In this paper, the plane grinding of grooving wheel with large spiral Angle is taken as the research object, and the numerical analysis model of gas-liquid two-phase flow field in wedge zone and grinding arc zone is established. The enhancement mechanism of heat transfer performance in grinding arc of large spiral Angle groove wheel was investigated. The results show that the flow of grinding fluid into the grinding arc will be hindered by the airflow around the grinding wheel, resulting in backflow and side leakage. Compared with ordinary grinding wheels without grooves, the backflow and side drainage in grinding zone of big spiral Angle grooves grinding wheels are significantly reduced, and a large amount of grinding fluid is transported in the heat exchange channel. The spiral groove has a good conduction effect on the grinding fluid, and the grinding fluid is easier to enter the grinding zone, thus significantly improving the heat transfer performance of the grinding zone and effectively reducing the grinding temperature during the grinding process.

Research on the characteristics of multiphysics coupling fields in the electrochemical trepanning of an inward facing blisk

As an effective method of electrochemical machining (ECM), electrochemical trepanning (ECTr) is used in the machining of the outward facing blisks in aero-engines such as the integral blisk and the diffuser. However, as a special type of blisk, the inward facing blisk has dense blades, narrow spaces in the disc and poor tool accessibility. To date the research on the ECTr of the inward facing blisk is lacking. In this study, a cambered cathode structure is proposed for ECTr of the inward facing blade, since this can improve the distribution of the multiphysics coupling fields in the machining gap and result in an improvement in the quality of machining for the inward facing blade. To progress this idea, a multiphysics coupling fields model for ECTr of inward facing blade based on electric field, gas-liquid two-phase flow field and temperature field is established. Then through simulation of the multiphysics coupling fields, the distribution laws for the flow velocity, the current density, the gas bubbles volume fraction, the temperature and the electrolyte conductivity in the machining gap are obtained. Compared with a conventional planar cathode structure, in the transition section, the uniformity of the flow field of a cambered cathode is improved, and the formation time of the blade is shorter, such that the machining quality and efficiency of the inward facing blade is enhanced. Subsequently, a series of ECTr experiments is conducted on the inward facing blade, and the simulation prediction is found to be in good agreement with the experimental results. As a result of using a cambered cathode, the cathode feed rate is increased from 1.6 mm/min to 2.2 mm/min, with the result that the machining efficiency is increased by 37.5 %. The width and surface quality of the blade improved with increase of the feed rate, the width increasing from 11.506 mm to 12.413 mm, and the surface roughness increasing from Ra 1.372 μm to Ra 0.953 μm. Use of a cambered cathode as the inward facing blade is demonstrated, and the feasibility of a novel ECTr method is verified.

Research on Multi-Physical Field Coupling Simulation of Local Electrochemical Machining

Casing is one of the most important components of an aircraft engine. However, due to its thin wall thickness and difficult-to-cut materials, it is difficult to process with a conventional mechanical method. Counter-rotating electrochemical machining (CRECM) is a special electrochemical machining method, which is very suitable for machining aircraft engine casing parts. However, for the convex structure with large surface height and a complex shape of the casing, is sometimes difficult for CRECM to obtain the desired design accuracy. Local electrochemical machining is proposed under this background, which is used for after-machining of the pre-shaped convex structure by CRECM. In order to predict the local electrochemical machining result accurately and improve the machining precision, this paper establishes a multi-physical field coupling simulation model of the local electrochemical machining considering the influence of gas–liquid two-phase flow and temperature field. The influence of a gas–liquid two-phase flow field and temperature field on the conductivity distribution were simulated and analyzed, the reason for simulation error with pure electric field and the influence of cathode end width L on machining accuracy was analyzed, and it was found that the gas–liquid two-phase flow field played a major role in the simulation results of local electrochemical machining. The experimental results show that there is a significant error between the pure electric field simulation results and the experimental results, and the multi-physical field coupling simulation results are basically consistent with the experimental results. The multi-physical field coupling simulation can predict the results of local electrochemical machining with high accuracy and has important significance for improving the precision of local electrochemical machining.

Load Characteristics and Extreme Response of Straight-Bladed Floating VAWT Using a Fully Coupled Model

Operating Offshore Floating Vertical Axis Wind Turbines (OF-VAWT) have the potential to perform well in the deep-sea area. Some researchers gave performance prediction by developing simplified computing models. However, these models have imperfections in considering load and motion nonlinearity, especially in extreme environments. In this work, a numerical model is developed composed of Computational Fluid Dynamics (CFD) and Dynamic Fluid Body Interaction (DFBI) to acquire the aero-hydrodynamic load and performance of OF-VAWT in general and extreme environments. Unsteady Reynolds-Averaged Navier-Stokes (URANS), SST k-ω and Eulerian Multi-Phase (EMP) models are combined to generate a gas-liquid two-phase flow field; the Volume of Fluid (VOF) model is employed to capture free-surface and make numerical wind-wave. DFBI superposition motion technology is proposed for local motion definition and motion solution, and overset with sliding meshes is introduced to achieve the grid motion. The numerical approach is verified by the tunnel and tank experimental data from the available literature. Simulation results of general cases, such as variable wind speed, wave height and wave length, are compared to discuss the effect of environmental parameters on load and performance. Comparison shows that this straight-bladed OF-VAWT is more susceptible to wind speed. Furthermore, the aerodynamic load generated by the shut-down rotor is still significant in extreme environment, which has implications for the development of OF-VAWT controller.

Multiphysics Coupled Simulation of Electrolytic Machining of Toothed Grooves of Contrate Gear

In the field of aviation, the contrate gear is an important component, the material of the contrate gear is the basis for ensuring the reliability and high performance of the aircraft engine, the commonly used material for contrate gear is 20Cr2Ni4A. In order to fully understand the electrolytic machining of the toothed groove of the contrate gear, a multiphysics coupling model of the electric field, the gas-liquid two-phase flow field and the temperature field was established to study the distribution of bubble rate, temperature, conductivity and current density in the processing gap. Simulation results show that the temperature and bubble rate gradually increase along the process direction in the processing gap, the conductivity and current density of the electrolyte gradually decrease.

Research on Multi-physics Field Coupling Dynamic Process in Forward Flow Electrochemical Trepanning Blades

In this work, a multi-physics field coupling model based on electric field, gas-liquid two-phase flow field and temperature field of the forward flow electrochemical trepanning (FFECT) blades was established, and the distribution law of hydrogen bubble volume fraction, electrolyte temperature and electrolyte conductivity in machining gap was obtained. Based on the simulation results, the time-varying process of electrolyte flow velocity distribution was divided into three stages according to the change in machining gap corresponding to different blade machining heights H, and the effects of the machining voltage U and the cathode feed rate v on the side gap Δ s and the end gap Δ e were investigated. The simulation analysis and experimental results show that both side gap and end gap increase as machining voltage increases while decrease with the increase in cathode feed rate. The model predictions are in good agreement with the experimental results, and the maximum errors of side gap and end gap are 10.6% and 17.7% respectively. In addition, the effects of machining voltage and cathode feed rate on the surface quality were studied experimentally. Results reveal that surface roughness can be reduced by appropriately decreasing the machining voltage and increasing the cathode feed rate.

Numerical study on flue gas–liquid flow with side-entering mixing

Abstract In this article, the side-entry agitator commonly used in the wet desulfurization absorption tower of a 300 MW thermal power unit was taken as the research object, and the gas–liquid two-phase flow field in the stirring tank was numerically simulated by using the two-fluid model based on Euler–Euler method. The vertical and horizontal velocity field distribution and gas phase distribution in the stirring tank were studied. The results showed that the side-entry agitator formed a “fountain” circulating flow in the stirring tank. The high-speed region of the liquid flow was mainly concentrated near the mixing blade and the bottom banded region. The range of large changes in the fluid velocity was mainly concentrated from the bottom of the mixing tank to 2–3 m from the bottom. The distribution of the oxidizing air was concentrated in the middle of the stirring tank. The mixing effect of two phases in the stirred tank was good, and the oxidizing air was fully diffused. The numerical study in this article has reference significance for in-depth understanding of the flow field and mixing effect of the side-entry agitator.

Most Suitable Blade Inclination Angle for Multiphase Flow in Soybean Milk Machine

The blade inclination angle of soybean milk machine is a key geometric parameter for efficient crushing. For the purpose of obtaining optimal design, the gas-liquid two-phase flow field inside a soybean milk machine is simulated. The gas holdup from simulation is in agreement with the experiment. The simulation result shows that the lower blade A has a great influence on the internal flow field of soybean milk machine, while the upper blade B has a small influence on the flow field. As the angle l αA l increases, the peak value of radial velocity decreases and moves to the interior of the cavity, so does the total pressure. When αA changes from -24° to -26°, the velocity vector at the bottom of the cavity changes from the connected state to the separated state, and the pressure difference between the up and the bottom surface of blade A becomes large. When αA = 24°, the flow field has the strongest turbulent kinetic energy and dissipation. When αB =28°, the pressure difference reaches the maximum. In summary, the best inclination angles are αAopt =-24° ∼ -26° and αBopt =28°, respectively.

Experimental study on the flow and heat transfer behavior of polymer solutions in the closed liquid ring vacuum pump system

The closed liquid ring vacuum pump system, which mainly includes the liquid ring vacuum pump and the heat exchanger, is widely used for gas pumping in various industries. In this paper, the energy saving effect in the liquid ring vacuum pump and the flow and heat transfer behavior in the shell-and-tube heat exchanger are investigated for aqueous solutions of rigid xanthan gum (XG) and flexible Polyacrylamide (PAM), and the effects of the concentration, Reynolds number, polymer conformation and flow geometry on the flow behavior of polymer solutions are studied. Results show that, despite the significant differences in molecular conformation and rheological properties between XG and PAM, the similar energy saving rate, about 1.5 ∼ 17.5%, is obtained in the liquid ring vacuum pump. However, in the shell-and-tube heat exchanger, XG solutions exhibit the more obvious pressure drop enhancement and heat transfer reduction than that of PAM solutions for the same concentration. Furthermore, due to the polymer shear degradation, the shaft power in the liquid ring vacuum pump decreases first and then stabilizes, conversely, the flow resistance decreases and the flow rate increases in the heat exchanger. The great difference in the flow condition between the intense rotating gas–liquid two-phase flow field and the gentle liquid pipe flow causes the different flow behavior for XG and PAM solutions.

Comprehensive particle image velocimetry measurement and numerical model validations on the gas–liquid flow field in a lab-scale cyclonic flotation column

The investigation of flow field can provide strong theoretical support for improving the flotation performance of fine particles in a cyclonic flotation column. In this study, particle image velocimetry (PIV) is combined with endoscopic measurement and phase discrimination technique to measure the cross section and axial section of gas–liquid two-phase flow field in a lab-scale cyclonic flotation column. The axial, radial, and tangential velocity of both gas and liquid phases are obtained. Based on the PIV experimental data, computational fluid dynamics (CFD)-based numerical models are validated. The results show the good prediction ability of Eulerian–Eulerian multiphase model, Reynolds stress model (RSM), and Tomiyama drag model. Then the simulated results with validated models are displayed to indicate the flow characteristics of the flotation column. The gas concentration is observed to be higher in the center and low on the sides. The gas phase always moves upward, while the liquid phase moves upward at the axis, downward between the axis and the wall, and upward again near the wall. Overall, this study provides an innovative approach for PIV measurement of complex multiphase flow field, and a useful reference for appropriate numerical models selection.

Experimental Study on the Performance of the Gas Centrifugal Seal with Continuous Injection and Discharge of Sealing Fluid

The centrifugal seal has the advantages of simple structure, long service life and the cost is far lower than the dry gas seal. But under high-speed gas conditions, the temperature of the sealing fluid rises too high and low sealing pressure. This paper studies the gas centrifugal seal with continuous injection and discharge of sealing fluid, establishes a numerical model, simulates the gas-liquid two-phase flow field and temperature field in the sealing chamber. Revealing the effects of the speed and the sealing fluid flux on the sealing performance by comparing the changes in the sealing fluid pressure, temperature, and sealing capacity under different operating conditions. And the reliability of its application to gas mechanical seals is verified through experiments. The results show that at high speeds, the pumping compression effect of the sealing fluid is enhanced, and the sealing capability is improved. Within a certain range, increasing the flux of the sealing fluid can effectively reduce the temperature and prevent the sealing fluid from vaporizing, the continuous injection and discharge structure has a significant effect.

Study on critical speed of vortex rupture and gas-liquid two-phase flow in rotating soybean milk machine

Abstract The gas-liquid two-phase flow field inside a soybean milk machine is simulated with the Navier–Stokes equations, Renormalization group (RNG) k-ɛ turbulence model and the particle two-phase flow model. The critical speed of vortex breakdown in the container and the influence of the characteristics of the two-phase flow on the soybean crushing effect at different speeds are investigated. The results show that there is a critical value of rotating speed of 1500 rpm for the vortex breakdown in the studied machine. At this rotational speed, the turbulent eddy dissipation (TED) reaches the maximum, and the position where the vortex first rupture is near the central axis and with a distance of 0.01 m from the central axis. It is also found that with the increase of rotating speed, the pressure difference around the blade varies significantly. The research in this study has important implication for the design of the soybean milk machine.

Numerical simulation of micro-nano bubble central intake aeration

In this paper, ANSYS FLUENT was used to simulate the gas-liquid two-phase flow in the process of micro-nano bubble aeration and optimized the central air intake aeration conditions. The particle size of microbubbles was 2 μm, the Eulerian model was used in multiphase flow model, and the standard k - ε model was used in turbulence model. The gas-liquid two-phase flow field with different aeration velocity was simulated. The effects of aeration time on gas holdup were studied. The results showed that the aeration effect was better with the increase of aeration speed, stronger turbulence, two-phase mixing and oxygen mass transfer.