In this paper, a three-dimensional numerical model is developed for an anion exchange membrane electrolyser cell (AEMEC) with a double serpentine flow field pattern. The focus on the AEMEC is due to ...its benefits, including the solid membrane, inexpensive catalysts and membrane, and high stability. The effect of important operating parameters, i.e. cell temperature and cathode pressure, on the performance of the electrolyser is numerically modeled by considering different causes of performance degradation. The polarization curve, uniformity index, and the distribution of the hydrogen concentration, current density, temperature, and pressure in different operating conditions are presented. By increasing the operating temperature and decreasing the cathode pressure, the voltage of the elctrolyser decreases. Due to the higher concentration of water at the inlet of the cathode channel, more hydrogen is produced, and the current density is higher. The maximum current density and hydrogen concentrations are 7868Am2 and 0.898molm3, respectively, when the operating condition is set to the temperature of 343 K, the pressure of 1 bar, and the cell voltage of 1.85 V.
•The polarization curve of the anion exchange membrane electrolyser was verified.•Applying a three-dimensional numerical model for anion exchange membrane electrolyser.•The effect of different operation parameters investigated on the polarization curve.•The lowest voltage is for higher temperature and lower cathode pressures.
A numerical model NEWTANK (Numerical Wave TANK) has been developed to study three-dimensional (3-D) non-linear liquid sloshing with broken free surfaces. The numerical model solves the spatially ...averaged Navier–Stokes equations, which are constructed on a non-inertial reference frame having arbitrary six degree-of-freedom (DOF) of motions, for two-phase flows. The large-eddy-simulation (LES) approach is adopted to model the turbulence effect by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. Laboratory experiments are conducted for both 2-D and 3-D non-linear liquid sloshing in a rectangular tank. A linear analytical solution of 3-D liquid sloshing under the coupled surge and sway excitation is also developed in this study. The numerical model is first validated against the available analytical solution and experimental data for 2-D liquid sloshing of both inviscid and viscous fluids. The validation is further extended to 3-D liquid sloshing. The numerical results match with the analytical solution when the excitation amplitude is small. When the excitation amplitude is large where sloshing becomes highly non-linear, large discrepancies are developed between the numerical results and the analytical solutions, the former of which, however, agree well with the experimental data. Finally, as a demonstration, a violent liquid sloshing with broken free surfaces under six DOF excitations is simulated and discussed.
A three dimensional numerical model of oscillating single mode laser-GMA hybrid welding process with lap joint and arc inclination configuration has been developed for the first time. The model is ...used to investigate the temperature field and fluid flow corresponding to the aforesaid welding process and weld configuration. An asymmetric distribution of arc heat and a cylindrical volumetric distribution of laser heat are established to describe the heat transfer from the combined heat source to the workpieces. The droplet with predefined temperature and velocity is impinged on the weld pool at a given fillet weld angle. Arc pressure, electromagnetic force, Marangoni force and buoyancy are also considered in the model with some modifications with respect to the lap joint and arc inclination configuration. Results show that the droplet impingement process has a significant influence on the weld geometry, temperature field and fluid flow pattern due to the transfer of mass, energy and momentum into the weld pool. These unique temperature fields and flow patterns are characteristic to the lap joint and arc inclination configuration. The proposed model exhibits close correspondence with the experimental results with respect to weld geometry.
We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling ...System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection–diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave–current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay.
Previous research of segmental joints are mainly based on experimental and theoretical methods; few studies have focused on refined numerical model. Therefore, a refined numerical model is ...established in which eight‐node solid element and three‐dimensional beam element are adopted to simulate joint structures and reinforcement, respectively, and bolt preload is considered. Then, the numerical model is verified with full‐scale tests and applied to analyze the influence of joint deformation and bolt preload. It is confirmed that (a) the numerical model can reproduce joint deformation process with good accuracy; (b) bolt stress are controlled by tensile action caused by joint opening and bending action caused by joint vertical displacement; (c) the changes of joint deformation with bending moment can be divided into three stages; bolt preload has no effect on the change of joint deformation with bending moment but has significant impact on the value of joint deformation in each stage.
Seasonal circulation of the Yellow Sea (YS) in response to wind and tidal forces is examined using a three‐dimensional numerical model. Wind forcing affects the wintertime circulation of the YS; on ...the other hand, the summer southerly monsoon is weak and therefore has little impact on the circulation, on the basis of comparative experiments with and without wind conditions. Results indicate that the Yellow Sea Warm Current (YSWC) along the YS trough exists regardless of wind forcing. However, strong winter northerly winds intensify the southward coastal flows along both coasts of the YS, and therefore, the northward intrusion of the YSWC becomes stronger. These flows in the YS are substantially weakened when wind forcing is not applied to the model. In addition to wind‐driven circulation, tide‐induced circulation is also dominant in the YS, particularly in summer. In winter, the tidal effect weakens the upwind and downwind flows in response to the strong northerly winds, while in summer, tidal forcing induces a strong southward residual flow along the western slope and a cyclonic gyre with a bottom cold water dome at the central region of the YS. The southward residual current possibly explains the southward movement of the Yellow Sea Bottom Cold Water as observed in summer. Comparison to the effects of parameterized tidal mixing suggests that residual flow driven by explicit tidal forcing plays an important role in the summertime circulation of the YS.
•We numerically find best protrusive GDL arrangement to enhance cell performance.•We use Taguchi method to find the optimal combined factors at the best arrangement.•Stoichiometric flow ratio at ...cathode inlet contributes to power the most by 70%.•Stoichiometric flow ratio at anode contributes most to pressure drop at anode side.•Optimal combined factors upgrade cell power 12% but decrease pressure drop 35%.
The proton exchange membrane (PEM) fuel cell is regarded as the best choice in the next power generation source in recent years due to its high fuel conversion efficiency, low noise, no emissions, and so on. The performance of the PEM fuel cell is dominated by the flow field design. The authors first numerically explore how the changed flow field design by the arrangement pattern of the protrusive gas diffusion layer (GDL) affects the cell performance for a full-scale serpentine channel. The best arrangement pattern of the protrusive GDL is then used to find the optimal combined factors by Taguchi design of experiments. The optimal energy conversion and conservation for this arrangement can upgrade the PEM fuel cell performance about 12% while decreasing pressure drop is approximately 35%. In addition, employing experimental data validates the calculation results of the flow channel design. Both the numerical and the experimental results can contribute to a better comprehension of the flow phenomenon that occurs in the energy process device.
In this paper, a finite volume numerical method is developed to investigate a high temperature polymer exchange membrane (PEM) electrolyzer cell using a three-dimensional and non-isothermal model. ...The results that are obtained for the single cell are generalized to a full stack of electrolyzer and an exergoeconomic analysis is performed based on the numerical data. The effects of operating temperature, the pressure of cathode, gas diffusion layer (GDL) thickness, and membrane thickness on the energy and exergy efficiencies and exergy cost of the electrolyzer are examined. This study reveals that by increasing the working temperature from 363 K to 393 K, the exergy cost of hydrogen decreases from 23.16 $/GJ to 22.39 $/GJ, and the exergy efficiency of PEM electrolyzer stack at current density of 10,000 A/m2 increases from 0.56 to 0.59. The results indicate that increase of pressure deteriorates the system performance at voltages below 1.4 V. It is concluded that operation of the electrolyzer at higher pressures results in decrease of the exergy cost of hydrogen. Increase of membrane thickness from 50 μm to 183 μm leads to increase of the exergy cost of hydrogen from 23.24 $/GJ to 35.99 $/GJ.
•A non-isothermal and three dimensional CFD model is developed for PEMEC.•Exergo-economic analysis of PEMEC is presented based on numerical data.•The exergy cost of hydrogen is determined under different working conditions.•The effects of various operating and geometrical conditions are determined.
At present, the development of some oil and gas fields has gradually shifted from vertical to highly deviated wells. To improve the intensity of reservoir reconstruction, highly deviated wells mostly ...adopt staged fracturing for reservoir reconstruction. The fracture interference law of multiple fractures in highly deviated wells is not clear, and the fracture steering and stress interference problems in the fracturing process are obviously different from those in horizontal wells, resulting in a lack of a theoretical basis for fracture spacing design. Therefore, it is necessary to study the stresses induced by multiple fractures in highly deviated wells. To reproduce the spatial distribution of multiple fractures in highly deviated wells and analyze the changes in induced stress more accurately, a three-dimensional numerical model of the fracture-induced stress field in highly deviated wells was established based on the finite element method and elasticity theory, which can simulate a fracture-induced stress field under different angles of inclination. The results indicate that the key to mutual exclusion or proximity of the two fractures is whether the fractures overlap in the plane parallel to the fracture height direction. Based on the analysis of the control variables, the first fracturing fracture height is the key factor affecting the induced stress, and the fracturing fracture height has slight effect on the induced stress. As the angle of inclination increases, the probability of the two fractures overlapping in space increases and the critical distance from the induced tensile stress to the induced tensile stress decreases. The influence of the fracture half-length, net pressure, and stress difference on the induced stress is related to whether the spatial projection of the two fractures overlaps. The research results provide a theoretical basis for the optimal design of staged fracturing in highly deviated wells.
A numerical model has been developed to study three-dimensional (3D) liquid sloshing in a tank with baffles. The numerical model solves the spatially averaged Navier–Stokes equations, which are ...constructed on a non-inertial reference frame having six degree-of-freedom (DOF) of motions. The large-eddy-simulation (LES) approach is employed to model turbulence by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. The baffles in the tank are modeled by the concept of virtual boundary force (VBF) method. The numerical model is first validated against the available analytical solution and experimental data for two-dimensional (2D) liquid sloshing in a tank without baffles. The 2D liquid sloshing in tanks with baffles is then investigated. The numerical results are compared with other results from available literatures. Good agreement is obtained. Finally, the model is used to study 3D liquid sloshing in a tank with vertical baffles. The effect of the baffle is investigated and discussed.
