Two-dimensional Axisymmetric Model Research Articles

Effects of Diffusion-Induced Nonlinear Local Volume Change on the Structural Stability of NMC Cathode Materials of Lithium-Ion Batteries

Electrochemical stress induced by the charging/discharging of electrode materials strongly affects the lifetime of lithium-ion batteries (LIBs) by regulating mechanical failures. Electrochemical stress is caused by a change in the local volume of the active materials associated with the lithium-ion concentration. The local volume change of certain active materials, such as nickel-rich LiNixMnyCozO2 (NMC), varies nonlinearly with the lithium content, which has not been considered in the stress calculations in previous studies. In this paper, the influence of nonlinear local volume change on the mechanical response of NMC-active materials is investigated numerically. The goal is achieved by using a concentration-dependent partial molar volume calculated from the previously obtained local volume change experimental results. A two-dimensional axisymmetric model was developed to perform finite element simulations by fully coupling lithium diffusion and stress generation at a single particle level. The numerical results demonstrate that (1) the global volume change of the particle evolves nonlinearly, (2) the stress response correlates with the rate of change of the active particle’s volume, and (3) stress–concentration coupling strongly affects the concentration levels inside the particle. We believe this is the first simulation study that highlights the effect of a concentration-dependent partial molar volume on diffusion-induced stresses in NMC materials. The proposed model provides insight into the design of next-generation NMC electrode materials to achieve better structural stability by reducing mechanical cracking issues.

Effect of Positive Bias and Pressure on Plasma Flow Characteristics in a Chemical Vapor Deposition Chamber

To better understand how positive bias and deposition pressure affect the plasma flow properties in the deposition chamber during the bias-enhanced MPCVD process, a two-dimensional axisymmetric model based on the discharge mechanism of pure H2 was constructed. The coupling process between different physical field models of the electromagnetic field, plasma, and temperature field in the MPCVD reactor is realized. We studied the influence of positive bias voltage and deposition pressure variation on microwave plasma flow characteristics in the deposition chamber. There was a bias voltage threshold phenomenon in the case of positive bias, and the suitable value range was narrow. Additionally, with the increase in the deposition pressure, the electron temperature in the deposition chamber tends to increase locally and reaches its maximum value when the pressure is approximately 30 torr. It provides new ideas and guidance for optimizing the process parameter setting of the bias-enhanced MPCVD process.

Numerical Modeling on Dissociation and Transportation of Natural Gas Hydrate Considering the Effects of the Geo-Stress

A deep understanding of the dissociation and transportation mechanism of natural gas hydrate (NGH), taking into account the effects of geo-stress, contributes to optimizing the development strategy and increases the exploitation efficiency of NGH. In this paper, the mathematical model, coupled with fluid heat and mass transfer, multiphase flow mechanics, and reaction kinetics with phase change in the process of hydrate decomposition was established. An axisymmetric two-dimensional model was developed to simulate the depressurization decomposition process of natural gas hydrate in the Berea sandstones. FLUENT software was used to solve the fundamental governing equations of the multi-phase flow, and UDF programming was employed to program the hydrate decomposition model and the modified permeability model in the dissociation and transportation of NGH. The simulation results were then validated by Masuda’s experimental data. The effects of gas saturation, outlet pressure, temperature, absolute permeability and geo-stress on the decomposition of natural gas hydrate were studied. The results indicated that a higher absolute permeability, higher initial gas saturation, lower outlet pressure, and higher initial temperature advance the decomposition rate of hydrate. Thus, an optimized production plan is essential to promote the extraction efficiency of the NGH. The geo-stress causes a decrease in the porosity and permeability of the porous rock, which restricts the efficiency of the heat and mass transfer by the fluid flow, leading to a slower dissociation and transportation rate of the NGH. Thus, it is important to take geo-stress into consideration and balance the extracting efficiency and the well pressure, especially when the NGH is developed by depressurization.

The influence of HTS single-pancake coil with double strips winding structure on transmission loss under different self-field conditions

The transport loss generated by a high temperature superconducting coil (HTS) in an AC transmission process will affect the operational stability of the superconducting power equipment. However, under different self-field conditions, the influence of the oscillation waveform parameters and coil structure parameters on the transport loss still needs to be clarified. This article establishes a two-dimensional axisymmetric model with a single-pancake coil with a double strip winding as the research object. For four different oscillation waveforms—sine waves, square waves, triangular waves and sawtooth waves—the influence of four variables, namely, the transmission current amplitude, the coil radius, the number of turns of the coil, and the turn-to-turn spacing of the coil, on the transport loss of HTS coils is studied in detail. The results show that under the exact parameters of the coil, for the generated transport loss, the square wave is the largest, the sine wave is the second largest, and the sawtooth and triangular wave are the smallest. Under the same self-field condition, the transport loss can be reduced by increasing the coil radius, the number of turns of the coil, and the turn-to-turn spacing of the coil, in which if the number of turns of the single-pancake coil with a double strip winding is less than 14, the transport loss can be obviously reduced by increasing the number of turns of the coil. When the number of turns exceeds 14, it does little to reduce the transport loss. Research findings can confirm the investigation of the operational stability and design of HTS coils.

Two-dimensional axisymmetric radiation hydrodynamics model of moderate-intensity nanosecond laser-produced plasmas

A two-dimensional axisymmetric radiation hydrodynamics model has been proposed to simulate nanosecond laser ablation of a solid target in ambient argon, air and helium at different pressures. The heat conduction equation used to simulate the conduction of laser deposition energy in the target and gas dynamic equations to describe the interaction between laser and vapor plasma and the evolution of plasma are coupled through the Knudsen layer relations at the target-vapor interface. A collisional-radiative model including 12 atomic processes is used to calculate the population of atomic energy levels and fractional ion abundance. The internal energy and pressure of the plasma are expressed by the equations of state based on a real gas approximation, which divides the internal energy into the ionization energy, thermal energy, and excitation energy of atoms and ions. The distributions of the temperature, pressure, density and velocity of the target and plasma are calculated by using this model, and the results are analyzed. Experimental results of multiple diagnostic tools including fast photography, shadowgraphy images, spatio-temporally resolved optical emission spectroscopy and laser interferometry, are used to benchmark the simulation results, and satisfactory consistencies are obtained. The model provides a numerical tool to interpret experimental data of a moderate-intensity nanosecond laser ablated solid target when the temperature of the target surface does not reach the critical value.

Research on a novel combined shock control mechanism for thermal protection and drag reduction in hypersonic compressible flow field

Aerodynamic heating and extreme shock drag are major problems faced in hypersonic compressible flow fields. This paper proposes a combined flow control mechanism that combines the advantages of spike, lateral jets and aero-disc. The effects of the combined mechanism in reducing aerodynamic heating and changing the flow field structure were studied by computational fluid dynamics. The physical model is a two-dimensional axisymmetric blunt body model with a novel combination mechanism. The numerical model is the coupling of the two-dimensional axisymmetric Reynolds averaging method and the SST model. The accuracy of the numerical calculation model and calculation method is verified by comparing with the experimental data in the literature. The results show that the new combination mechanism can effectively reduce the heat flow on the surface of the blunt body, and can be used as a new type of hypersonic compressible flow field thermal protection system (TPS). The research results show that appropriately reducing the Mach number of the lateral jet and increasing the total pressure ratio of the lateral jet can further expand the subsonic recirculation zone and reduce the intensity of the reattachment shock wave. This can effectively improve the thermal protection and drag reduction efficiency of the combined structure, but put forward higher requirements on the heat resistance and mechanical strength of the upper spike. At the same time, the influence of different jet angle on thermal protection performance, drag reduction effect and changing shock structure performance is further studied. The results show that the negative jet Angle is more conducive to the effect of cooling gas, while the positive jet Angle is more conducive to the effect of changing the shock structure in hypersonic flow field.

Comparative Analysis of the Parameters of the Normal and Abnormal DC Glow Discharges

A comparative numerical study of the parameters of normal and abnormal direct current glow discharges between two flat disk electrodes with a radius of 3 cm in a 1-cm-high electric discharge gap is performed. A two-dimensional axisymmetric drift-diffusion model of the glow discharge is used for the numerical simulation, including equations for the transfer of electrons and molecular nitrogen ions, and the Poisson equation for finding the electric potential in the discharge gap taking into account the regions of the space charge and the positive column. Abnormal discharges are obtained when the radius of the cathode decreases. A numerical procedure is proposed for smoothing local maxima of the electric field strength near the boundaries of the abnormal glow discharge cathode, which ensures the stability of the solution and the weak effect on the calculated data. The numerical simulation results of the electrodynamic structure of normal and abnormal glow discharges are presented.

Laser Beam Machining of Tungsten Alloy: Experimental and Numerical Analysis

Laser beam machining of various materials has found wide applications in the industry due to its advantages of high-speed machining, no tool wear and no vibration, precision and accuracy, low cost of machining, etc. Investigations into the laser beam machining of uncommon alloy are still limited and more research is needed in this field. In this paper, an analysis of the laser beam machining of tungsten alloy was performed, for cutting and drilling machining processes. First, an experimental analysis of microhardness and microstructure on the laser-cut samples was performed, and then the numerical simulation of the laser beam drilling process and its experimental validation was carried out. The experiments were carried out on a tungsten alloy plate of two different thicknesses, 0.5 and 1 mm. No significant changes in the microhardness, nor in the microstructure characteristics in the heat-affected zone (HAZ), were observed for the cutting conditions considered. A two-dimensional axisymmetric mathematical model for the simulation of the laser beam drilling process is solved by a finite volume method. The model was validated by comparing numerical and experimental results in terms of the size of HAZ and the size and shape of the drilled hole. Experimental and numerical results showed that HAZ is larger in the 0.5-mm-thick plate than in the 1-mm-thick plate under the same drilling conditions. Good agreement was observed between the experimental and numerical results. The developed model improves the understanding of the physical phenomena of laser beam machining and allows the optimization of laser and process parameters.

Thermal Characteristics of Gaseous-Helium-Cooled HTS Cables With Practical Operating Conditions

High temperature superconducting (HTS) cables have the advantages of low loss and large capacity transmission. The cryogen used for HTS cable cooling is mainly liquid nitrogen. In some applications, using gaseous helium (GHe) as a cryogen has advantages. For example, it can reduce the weight of the system, remove the risk of frostbite of surrounding equipment and people caused by leakage of liquid nitrogen, and avoid suffocation due to evaporation of liquid nitrogen in confined spaces. Temperature is closely related to the performance of superconducting tapes. Therefore, it is of great significance to study the thermal characteristics of cables using GHe as cryogen under several important operating conditions. These conditions include cooling, carrying rated current, cryocooler fails, both cryocooler and cryogenic gas circulation pump fail, and local hot spot. In this article, a two-dimensional axisymmetric simulation model of a 50-m 4 kA HTS cable was built in COMSOL to study the thermal characteristics of GHe-cooled HTS cables. The range of mass flow rates of GHe suitable for operation of this cable was calculated considering different operating conditions.

Loading-Unloading Behavior of a Spherical Contact for Varying Tangent Modulus and Yield Strength

Abstract Understanding the elastoplastic contact loading-unloading behavior between a sphere and a rigid plane is a problem in the field of contact mechanics. In this study, a bilinear strain-hardening material model was used to study the frictionless elastoplastic contact loading-unloading behavior of a sphere in contact with a rigid plane across a large range of interference. A two-dimensional axisymmetric finite element model was established. The effects of the tangent modulus (Et) and the ratio of the reduced elastic modulus to the yield strength (E/Y) on the contact load, residual interference, and contact area of the spherical contact model during loading-unloading were analyzed for a series of different interferences. The effects of Et and E/Y on the elastoplastic contact loading-unloading behavior were amplified with increasing interference. With an increase in Et, the effect of E/Y on the contact behavior was diminished. A new constitutive model for elastoplastic contact loading-unloading is presented. The model accommodates the calculation of the contact load, contact area, and residual interference of the spherical contact model across a large range of interference. The proposed model was verified by comparing its predictions with those of previous models. In the range of material properties considered in this work, the current research results can be applied to particle and contact mechanics.

Comprehensive performance study on reflux solar methanol steam reforming reactor for hydrogen production

In this paper, a reflux solar methanol steam reforming reactor (SMSRR) system is proposed for efficient solar thermal hydrogen produced. A two-dimensional (2D) axisymmetric model is used to compare the comprehensive performance of three different SMSRRs: no reflux tube (SMSRR0), flow from the inside of the reflux tube to the outside (SMSRR1) and flow from the outside of the reflux tube to the inside (SMSRR2). The results showed that the reflux SMSRR uses the heat of the fluid at the outlet to further provide the reaction heat, which greatly reduces the outlet temperature, thereby improving the overall performance of the SMORE. By optimizing the diameter of the reflux tube and the operating conditions, the energy conversion rate can be increased by 19.5%, and the temperature distribution coefficients can be increased by 1.89% while the methanol conversion is increased by 6.43%, and the hydrogen yield is increased by 5.96%.

Minimizing Risk of Failure from Ceramic-on-Ceramic Total Hip Prosthesis by Selecting Ceramic Materials Based on Tresca Stress

The choice of ceramic-on-ceramic coupling in total hip prosthesis has advantages over couplings with other combinations of materials that use polyethylene and metal materials in terms of high hardness, scratch resistance, low wear rate, and increased lubrication performance. To reduce the risk of primary postoperative failure, the selection of ceramic materials for ceramic-on-ceramic coupling is a strategic step that needs to be taken. The current study aims to analyze ceramic-on-ceramic coupling with commonly used ceramic materials, namely zirconium dioxide (ZrO2), silicon nitride (Si3N4), and aluminium oxide (Al2O3), according to Tressa failure criterion for the investigation of the stress distribution. A two-dimensional axisymmetric finite element-based computational model has been used to evaluate the Tresca stress on ceramic-on-ceramic coupling under gait cycle. The results show that the use of ZrO2-on-ZrO2 couplings can reduce Tresca stress by about 17.34% and 27.23% for Si3N4-on-Si3N4 and Al2O3-on-Al2O3 couplings, respectively.

The influence of the thermal expansion on the magnetic fluid sealing performance

Magnetic fluid seal is the most mature application of magnetic fluid at present. However, some deficiencies limit the application of magnetic liquid seals at high rotation speeds, including the thermal expansion under different temperatures. The sealing gap width is affected by thermal expansion significantly, which leads to a change in the sealing performance. This paper proposes a new numerical simulation method to obtain the magnetic fluid boundary and the thermal deformation of the sealing gap. The dynamic mesh and thermo-hydro-mechanical coupling methods are used to calculate the thermal deformation in the two-dimensional axisymmetric model. Numerical results show the fluid temperature and sealing gap change under different rotation speeds, which influences the sealing performance.

Inversion of thermal properties of lunar soil from penetration heat of projectile using a 2D axisymmetric model and optimized PSO algorithm

The thermophysical parameters of lunar soil can be inferred from the temperature field during the invasion process of reconnaissance projectile. This paper adopts a two-dimensional axisymmetric model to reconstruct the projectile invasion process. An optimized particle swarm optimization method is then used to retrieve the thermophysical parameters of lunar soil. When the reconnaissance projectile penetrates the lunar interior, it rubs against the lunar soil and generates heat, which diffuses between the projectile body and the lunar soil. The sensors inside the reconnaissance projectile measure the temperature variation of the projectile body to inverse the thermophysical parameters. This paper carried out physical modeling of the penetration process of reconnaissance projectile. A two-dimensional axisymmetric simulation model is constructed for the physical process, and the adaptive inertial weight particle swarm algorithm is adopted. The inversion experiment of lunar soil thermophysical parameters based on the simulation model shows that the inversion error is less than 10%, which verifies the feasibility of this method.

Influence of Geometrical Parameters on Supersonic Steam-Ejector Performance

Geometrical parameters such as the nozzle exit position (NXP) and the diameter ratio (DR) considerably influence the performance of steam ejectors. An axisymmetric two-dimensional model for a supersonic steam ejector is developed to investigate the steam-ejector performance with the aim of simultaneously optimizing the NXP (-10 < NXP < 10) and DR (6 < DR < 10), and the simulation results are in good agreement (relative error was merely 7%) with the experimental results. At the optimum value of the NXP, the supersonic steam ejector acquires the optimal entrainment ratio (ER) under the given conditions. Deviation from the optimal NXP value may result in a 12.4% decrease in ER. With optimized NXP, the optimization of DR is more significant; however, a deviation from the optimal DR weakens the ER and the supersonic steam ejector eventually breaks down. Therefore, the NXP should be approximately close to its optimum value, and the DR must be designed at its optimum value to ensure effective operation of the supersonic steam ejector.

Countercurrent flame propagation inside vertical PMMA cylinders against pure oxygen flow

The countercurrent flame propagation against pure oxygen flow inside a vertical polymethyl methacrylate (PMMA) cylinder under oxygen-limited conditions was systematically investigated experimentally and numerically, with a particular attention given to the effect of the inner diameter (di = 6, 5, and 4 mm) of the cylinder. Metered pure oxygen was flowed through the cylinder from the bottom and, when ignition was initiated at the top, a blue flame was formed and propagated downwards in a quasi-steady state. The flame propagation velocity (Sf) was determined by analysing the digital video record of the entire flame propagation process. The flame was apparently fuelled by the volatiles from the pyrolysis of the inner surface the PMMA cylinder. The rate of pyrolysis (mpy) was estimated by measuring the initial and remaining masses of the PMMA cylinder. A transient two-dimensional axisymmetric numerical model considering one-step finite-rate PMMA pyrolysis and gaseous phase oxidation reactions was developed and applied to simulate the flame structure and propagation process. By comparing the measured and predicted Sf and mpy, the validity of the numerical model was confirmed. The flame structure was depicted and the role of the gas – solid heat transfer was quantified. A decrease in di leads to an increase in the heat flux that preheats the unburnt PMMA ahead of the flame front. This results in a greater pyrolysis rate of the unburnt PMMA and a faster flame propagation velocity. Effects of thickness of the PMMA cylinder and radiative heat transfer from the flame to the inner PMMA surface were also discussed.

CFD analysis on flow through nozzle of conical type and truncated conical plug type

Conical type nozzle and truncated conical plug type nozzles have been recently developed rocket nozzles appropriate as elevation compensating nozzles. This research work focuses on the analysis of flow through nozzle types of conical plug type and truncated plug type nozzles. It is statistically simulated and validated with the values of experimental data. Also, it is aimed to relate the performance while a base bleed is being introduced. Two-dimensional axisymmetric model is being considered for statistical analysis. Reynolds Averaged Navier Stokes (RANS) equations are resolved with two-equation shear stress transport k-ɛ turbulence kind model. Along with the flow patterns, the wall pressure of conical plug type nozzle and base pressures of truncated plug type nozzle were evaluated at a range of pressure ratios of the nozzle. Mathematical models about these in two-equation flow have been solved using CFD software ANSYS fluent. Three-dimensional simulation has also been performed to explore the flow in the turbulent RANS and models in two-equation flow. Suitable boundary conditions are adopted during the analysis to predict the flow characteristics. Form the results obtained, it is understood that the flow separation region prolongs with the increase in nozzle pressure ratio for 40% truncated conical plug type nozzle. It is also observed that, the 40% conical plug type contributed to a higher thrust, flow velocity and Mach number. Increase in nozzle pressure ratio increases the length of flow pattern for a truncated plug type nozzle.

Analysis of the effect of pyrolytic coking on the flow and heat transfer performance of n-decane in cooling channels at supercritical pressure

• Coking deposition of n -decane on the inner surface of the cooling channel was simulated. • This model is capable of making reasonably accurate predictions in pyrolytic coking. • The effects of pyrolytic coking on flow, heat transfer, and pyrolysis performance were investigated. The formation and deposition of coke in cooling channels is the main factor that limits the application of regenerative cooling. To study the effects of coking deposition on regenerative cooling performance under heavy-cracking conditions, we established a two-dimensional axisymmetric numerical model based on the dynamic mesh model. A detailed pyrolytic chemical reaction model, which contains 16 species and 26 step reactions, and a modified coking deposition kinetic model are incorporated in the numerical model. The numerical model is validated by comparing the temperature, mass fraction, and coking thickness between simulation and experimental results. The transient numerical simulation of n -decane flow, heat transfer, pyrolysis, and pyrolytic coking within 20min was carried out. The results reveal that coking deposition has a significant effect on the flow and heat transfer performance of the cooling channel, while having minimal effect on the pyrolytic performance. The conductive heat transfer resistance will be greater than the convection when the coking layer thickness is more than 110 µm. The research methodology adopted in this study can be used to estimate and manage coke deposition in the regenerative cooling systems, and the quantitative results obtained can provide guidance for the design of cooling channels under heavy-cracking conditions.

Study on Loss and Thermal Properties of a Superconducting Pancake Coil under Self-Field and Analysis of Its Influencing Factors

High-temperature superconducting (HTS) coils generate local heat during the transmission of alternating current (AC), resulting in a decrease in thermal stability. The influence of relevant factors on the local heating location and temperature of the coil is still unclear. In order to strengthen the protection and operation monitoring of the superconducting coil, it is necessary to research this. Based on the H-formulation, the paper uses the electromagnetic–thermal coupling finite element method (FEM) to establish a two-dimensional (2D) axisymmetric model of the YBCO coil. The AC loss and temperature when the coil transmits alternating currents of power frequency are analyzed. Firstly, the internal temperature distribution of the coil is analyzed, and the influence of the turn number on the location of the highest temperature is discussed. For a 16-turn coil, the effects of the convective heat transfer coefficient and the thickness of the insulating layer between two turns on the magneto-caloric properties of the coil are discussed, respectively. The results show that, below 100 turns, the highest temperature of the coil occurs near the inner side; improving the heat transfer efficiency and appropriately reducing the thickness of the inter-turn insulating layer is beneficial to suppress the temperature rise and reduce the temperature difference inside the coil. The research conclusions provide a reference for the design and protection monitoring of HTS coils.

SPATIAL MATHEMATICAL MODELING OF STATIC COMPOST PILES WITH HEAT RECOVERY

Composting experiments with heat recovery reveal spatial non-uniformity in parameters such as temperature, oxygen concentration and substrate degradation. In order to recover heat from static compost piles via integrated heat exchanger there is the need to investigate the temperature distribution for placing the heat exchangers and the interaction between heat recovery, substrate degradation and oxygen concentration to ensure quality of composting process. This study introduces a spatial model to predict the variation in controlling parameters such as temperature, oxygen concentration, substrate degradation and airflow patterns in static compost piles with heat recovery using Finite element method (FEM) in COMSOL Multiphysics ® Version 5.3. The developed two-dimensional axisymmetric numerical model considers the compaction effects and is validated to real case pilot-scale compost pile experiments with passive aeration. Strong matching with the real case experiment was achieved. The spatial model demonstrated that the compaction effect is extremely important for realistic modeling because it affects airflow, temperature distribution, oxygen consumption and substrate degradation in a compost pile. Heat recovery did not disrupt the composting process. Case studies revealed strong influence of convective heat loss through the edges and a 10 % improvement of heat recovery rate with ground insulation. The simulation indicates that an optimized placing of heat recovery pipes could increase the average heat extraction by 10-40 %.