Three-dimensional Transient Model Research Articles

An inverse procedure to estimate the heat flux at coated tool-chip interface: a 3D transient thermal model

Technological evolution has contributed to the production of increasingly efficient cutting tools, both from the point of view of the performance of these tools and regarding the increase in their life spans. Coating research and development has certainly played an important role in the advancement of these tools. The coatings facilitate cutting by friction through the action of tribological mechanisms, providing less tool wear and still thermally protecting the base material of the tools, acting as thermal insulators and increasing the tool life. However, because these coatings have a thickness on the order of micrometers, these thermal effects are difficult to prove. The main difficulty lies in identifying the heat delivered to a tool due to the friction at the piece-chip-tool interface. In addition, the complexity of a transient three-dimensional thermal model is added due to the two-layer materials (base-coating) with sizes on the order of centimeters and micrometers. In this sense, this work proposes an analytical solution to a 3D transient thermal problem that can model an orthogonal cutting process carried out by a coated cutting tool. The temperature field is obtained by using an inverse solution technique that estimates the heat flux delivered to the tool due to friction at the tool-piece interface. The inverse problem is solved by combining the analytical solution of the thermal model with the application of the transfer-function-based Green’s function (TFBGF) inverse technique.

Tab Design Based on the Internal Distributed Properties in a Zinc–Nickel Single-Flow Battery

The distribution of physicochemical properties inside the battery, which is difficult to measure using experimental methods, has a significant impact on the performance of the battery. Therefore, based on the numerical simulation method, this paper established a three-dimensional transient model of a zinc–nickel single-flow battery considering the tabs for the first time. The model is based on universal conservation laws (mass, momentum, and charge) coupled with global reaction dynamics. On this basis, the influence of tabs on the physicochemical property distribution in the battery was studied, including the change of ion concentration, current density, overpotential, and local state of charge distribution with time and space. Based on overpotential distribution and ion concentration distribution, the effects of tab size, position, and number on voltage loss and ion concentration distribution were investigated. The results show that the extreme values of various physicochemical properties always appear in the region near the tabs, and the chemical reaction rate in the region near the positive electrode tab decreases significantly in the later period of discharge. The voltage loss of the positive electrode is greater than that of the negative electrode during discharge, especially in the later period of discharge. Also, at the end of discharge, the maximum value of the local charge state of the negative electrode appears in the region near the positive electrode tab. In addition, increasing the length and number of tabs can effectively reduce the voltage loss and improve the uneven distribution of ion concentration; however, when the number of tabs is larger than two sets, this effect is obviously weakened. However, changing the position and width of the tab has little effect on voltage loss and ion concentration distribution.

Modeling of chemical composition in the melt pool during laser welding of Aluminum / Magnesium alloys

Joining dissimilar metals is very difficult due to the formation of brittle intermetallic phases which may be detrimental to mechanical properties. The present work aims to investigate the transport phenomenon in the weld bead and to understand the materials mixing during laser welding process of dissimilar Aluminum-Magnesium alloys. A three-dimensional transient model based on fluid flow, heat and mass transfer has been developed to predict the formation of the weld and to study numerically and experimentally the diffusion of alloying elements in the melted zone. SEM analysis of chemical composition has been realized to map elements distribution in the melted zone. The results of simulation show the formation of a heterogeneous mixture in the melt pool. The elements distribution map and the presence of brittle intermetallic phases in the fusion zone were analysed. The formation of intermetallic compounds, comprising Al3Mg2 and Al12Mg17 phases were predicted by studying the chemical elements distribution in the weld pool. A good tendency between experimental and numerical results is noticed for the weld.

Coupled heat transfer and phase transformations of dual-phase steel in coil cooling

Dual-phase steels are generally used in the car industry due to high tensile strength and good formability, which are obtained by a mixture of bainite and ferrite phases. This microstructure is achieved through slow rate coil cooling. However, the manufacturing of dual-phase steels introduces various challenges such as the instability of the cold rolling process. An important factor affecting this is the non-uniform coil cooling of a hot rolled strip. In coil cooling the cooling rates are not controlled and there are different thermal contacts during coil conveyance causing unequal cooling of the steel coil. Unequal cooling rates lead to non-uniform coil cooling, producing irregular phase transformations on different sides of the coil, which causes periodical variations of the phase fractions in the steel strip. Varying phase fractions cause thickness deviations in the strip during the cold rolling process. A three-dimensional transient heat transfer finite element model was developed and used for modeling the complete coil conveyance chain and coil field cooling of the coil on an industrial scale. A coupled phase transformation model is implemented as a subroutine into the finite element model for calculating the resulting phase fractions. It was found that the different thermal contacts during the coil conveyance produce uneven cooling rates causing length- and widthwise variations in the phase fractions. The heat transfer model is validated by comparing temperature profiles between the simulated and measured coil edges. The phase transformation model is fitted into experimental data and verification is carried out in industrial conditions by comparing the modeled phase fractions and test samples from a cooled and unwound steel coil.

Numerical evaluation of contaminants mixing uniformity in a full-scale test chamber with mixing fan

Most existing models and standards for volatile organic compounds emission assume that contaminants are uniform in the testing devices. In this study, a three-dimensional transient numerical model was proposed to simulate the mass transport process based on a full-scale test chamber with a mixing fan, and the airflow field and contaminants concentration distribution were obtained within the chamber under airtight and ventilated conditions. The model was validated by comparing the numerical results with experimental data. The numerical results show that the contaminant source position and the airflow field characteristics have significant impact on the contaminant mixing, and the fan rotation has an important role in accelerating mixing. In the initial mixing stage, the concentration distribution is obviously uneven; as the mixing progresses, it gradually reaches acceptable uniformity except for some sensitive regions, such as high concentration region at the injection point of the contaminants and low concentration region at the air inlet. To ensure test accuracy, the monitor should avoid above sensitive regions; and some special regions are recommended where contaminant concentration uniformity can be reached sooner. The ventilated chamber results indicate that the mixture of contaminants in the chamber is actually better than the results shown by conventional test method.

Numerical analysis of the heat transfer of radiant tubes and the slab heating characteristics in an industrial heat treatment furnace with pulse combustion

For a heat treatment furnace, the precise study of the flow characteristics, combustion and heat transfer in the furnace is essential to know the temperature distribution in a slab during the heating process. In this context several different three-dimensional CFD (Computational Fluid Dynamics) models have been developed to simulate the combustion and heat transfer process in the furnace. These models were developed based on direct fired reheating furnaces with continuous fuel input. In this paper, a novel three-dimensional transient CFD model used to investigate the slab heating characteristics in the heat treatment furnace with pulse combustion was developed. The transient calculation in the furnace was performed based on the steady-state simulation of the furnace temperature, and the movement of slabs on the rollers in the furnace was simulated using dynamic mesh. By comparison, the results from the EDC with two different reaction mechanisms showed good consistency. However, the EDC with the two-step reaction mechanism required one fifth the calculation time of the EDC with the GRI-Mech3.0, and was thus the preferred model. In contrast to direct fired reheating furnaces, the outer radiant tube walls were treated as the coupled boundary conditions in the model to realize indirect heat transfer between the process gas in the furnace and the combustion gas in the radiant tubes. Furthermore, a pulse combustion method was proposed to control the working states of the burners based on UDF (User-Defined Function), in order to realize the pulse combustion process in the heat treatment furnace. By the validation of “Black Box”, the temperature variation of the slab and the gas temperature in the furnace predicted by the model agreed well with the experimental results. The simulation revealed that the temperature distribution of the radiant tubes and furnace gas was uniform and the maximum temperature difference on the outer radiant tube walls was less than 84 K. During the slab transient heating process, the slab temperature distribution became more uniform in the soaking zone and the maximum temperature difference along the thickness of the slab was below 13 K at discharge.

Numerical study of subfreezing temperature cold start of proton exchange membrane fuel cells with zigzag-channeled flow field

An automotive proton exchange membrane fuel cell (PEMFC) engine needs to be capable of surviving from sub-freezing temperatures. Cold starting up a PEMFC engine presents great technical challenge due mainly to the intra-electrode ice formation that is closely related to the involved multi-physical transport. The flow field configuration to some extent dictates the reactants and product transport and is thus of important influence on PEMFC cold start performance. The present work carefully analyzes the cold start process of PEMFCs with zigzag-channeled flow field (ZZFF). A transient three-dimensional numerical model is established and experimentally validated first, and then we make comparisons of cold-start performance between zigzag and straight channel flow-field PEMFCs to reveal the effects of ZZFF. It is found that the ZZFF better distributes the reactants/product and current density in the PEMFC as it enhances the transport along the flow direction in-between the under-land and under-channel regions inside the cell. The process of cold starting the ZZFF PEMFC is found to generate slightly less heat, which is not good to cold start. Therefore, the ZZFF enhances the survivability of PEMFC engine cold starting from subfreezing temperatures, whereas it slightly degrades the quick self-startup ability of PEMFC engine. Case study with PEMFCs of more zigzagged flow fields further corroborates the effects of ZZFF configuration on PEMFC cold start performance.

The investigation of arc fluctuations in thermal plasma torch using 3D modeling approach

Two and three-dimensional transient models of a thermal plasma torch are presented to analyse the effect of operating conditions on arc root fluctuations for various types of anode configuations. The computational fluid dynamics code, OpenFOAM(c), is utilised in a modified form to model the arc and plasma flow inside the argon plasma torch. Modeling a thermal plasma requires a combination of mutually related fluid dynamics and electromagnetic phenomena which dictate the size and stability of the arc column. While the 2D axisymmetric model is effective in depicting the average energy and average velocity profiles of plasma gas, it fails to describe the fluctuations in arc behaviour and its mode of attachment on the anode. In a 3D model, the arc movement is captured in both axial and azimuthal directions wherein the arc-root attachment on anode surface seems to fluctuates in a periodic manner and the voltage fluctuations mirrors the arc-root attachment behaviour within the system. We have here investigated the effect of operating conditions on the frequency of this arc reattachment, finding that the input current and gas flow rate have a significant effect on arc behaviour. We have also reported the effect of arc voltage perturbations on the exit plume properties (velocity and average temperature) and finally the effect of anode nozzle geometry on the fluctuations and plume behavior is presented.

Simulation Study on Weld Formation in Full Penetration Laser + MIG Hybrid Welding of Copper Alloy.

Considering the coupling of a droplet, keyhole, and molten pool, a three-dimensional transient model for the full penetration laser + metal inert gas (MIG) hybrid welding of thin copper alloy plate was established, which is able to simulate the temperature and velocity fields, keyhole behavior, and generation of the welding defect. Based on the experimental and simulation results, the weld formation mechanism for the hybrid butt welding of a 2 mm-thick copper alloy plate was comparatively studied in terms of the fluid dynamic feature of the melt pool. For single laser welding, the dynamic behavior of liquid metal near the rear keyhole wall is complex, and the keyhole has a relatively drastic fluctuation. An obvious spattering phenomenon occurs at the workpiece backside. Meanwhile, the underfill (or undercut) defect is formed at both the top and bottom surfaces of the final weld bead, and the recoil pressure is identified as the main factor. In hybrid welding, a downward fluid flow is strengthened on the rear keyhole wall, and the stability of the keyhole root is enhanced greatly. There are large and small clockwise vortexes emerging in the upper and lower parts of the molten pool, respectively. A relatively stable metal bulge can be produced at the weld pool backside. The formation defects are suppressed effectively, increasing the reliability of full penetration butt welding of the thin copper alloy plate.

Multidimensional and transient modeling of an alkaline water electrolysis cell

A three-dimensional (3-D) transient numerical model of an alkaline water electrolysis (AWE) cell with potassium hydroxide solution is developed by rigorously accounting for the hydrogen and oxygen evolution reactions and resulting species and charge transport through various AWE components. First, the AWE model is experimentally validated against a polarization curve corresponding to a wide range of currents as high as 2.0 A·cm−2. In general, the simulation results compare well with the measured data and further reveal the operating characteristics of AWE cells, showing key distributions of solid/electrolyte potentials and multidimensional contours of reactant and product concentrations at various current densities. In particular, the contribution of hydroxide ion (OH−) diffusion to the ohmic losses through porous electrodes and a porous separator are quantitatively examined at low and high electrolyte flow rates. The present full 3-D AWE model provides a basic understanding of the electrochemical and transport phenomena and can be further applied to practical large-scale AWE cell and stack geometries for grid-scale hydrogen production.

Influence of Electro-Emulsification on Desulfurization of Rejected Electrolytic Manganese Metal in Electroslag Remelting Process

A transient three-dimensional comprehensive numerical model was developed to clarify the effect of electro-emulsification on sulfur mass transfer during the electroslag remelting process of rejected electrolytic manganese metal scrap. The magnetohydrodynamic thermal two-phase flow and solidification behavior were numerically clarified. The kinetics module was established to assess the sulfur mass transfer rate between molten manganese metal and molten slag. Furthermore, variations of the alternating current (AC) magnitude and direction were taken into account. A reasonable agreement between the experimental and simulated results was observed. The surface area of molten droplets was shown to enlarge and it regularly fluctuates under the Lorentz force action. At the constant frequency of 50 Hz, the desulfurization rate rises from 54.7 to 71.0 pct when the AC root mean square (RMS) value of the AC is increased from 3000 to 4000 A, while at the constant AC RMS value of 3500 A, it dropped from 63.4 to 58.5 pct with the frequency increases from 5 to 500 Hz.

Thermal performance analysis on steady-state and dynamic response characteristic in solar tower power plant based on supercritical carbon dioxide Brayton cycle

ABSTRACT Supercritical Carbon Dioxide (S-CO2) Brayton cycles and Concentrating Solar Power (CSP) plants are gaining increasing attention due to environment pollution problems and their higher efficiencies. At present, there is a lack of researches on the dynamic thermal analysis of CSP plants based on S-CO2 Brayton cycle, which needs to be resolved urgently. Therefore, a one-dimensional dynamic model of the printed circuit heat exchanger (PCHE) is developed, which is incorporated into transient model of the solar tower power plant. And the Modified Euler or Fully-implicit Runge-Kutta Method is used to complete the dynamic solution. The results indicate that the pressure ratio equaling to 3.5 and the zigzag PCHE regenerator with a diameter of 2 mm will be the best choice for our designed power plant to achieve the balance between larger net output work and power efficiency improvement, which provides the reasonable design parameter for more complicated three-dimensional transient models. By taking the binary nitrate working temperature limitation and common influences of temperature and pressure on S-CO2 thermophysical properties into consideration, as the direct normal irradiance (DNI) decreases, the S-CO2 heat transfer coefficient will increase. When DNI value changes between 780 W/m2 and 970 W/m2, the cold side S-CO2 outlet temperature of PCHE regenerator and S-CO2 Brayton cycle power efficiency will produce 114.65 K and 8% fluctuation in no more than 15 minutes.

Influence of material constitutive models on thermomechanical behaviors in the laser powder bed fusion of Ti-6Al-4V

A transient three-dimensional thermomechanical model was developed to examine the evolution of thermal and mechanical fields in the laser powder bed fusion of Ti-6Al-4V alloy, particularly with respect to the development of plastic strain. A primary focus was to evaluate the influence of material constitutive models on predicted mechanical behaviors. Johnson-Cook (JC) constitutive material models were chosen to account for the contribution of strain, strain rate, and temperature on material responses. Three different modifications of the JC models were applied to assess the sensitivity of rate hardening and temperature-dependent strain hardening on mechanical prediction. Numerical results revealed that predicted stress and strain fields were highly sensitive to the rate-dependent term but minimally affected by the temperature-dependent strain hardening. The maximum differences in average stresses and plastic strains were 23% and 13% when comparing results between the JC model and the JC model without strain rate hardening, respectively. Moreover, it was found that strain rate hardening mostly occurred at intermediate temperatures, ≈ 1000 – 1600 K, during the continuous cooling phase. Finally, the present study emphasizes the importance of material constitutive models on mechanical behavior in laser powder bed fusion as well as providing insight for further exploration of process parameter optimization.

Evolution and Physical Characteristics of a Raceway Based on a Transient Eulerian Multiphase Flow Model

In industrial processes, a semi-cavity area formed by airflow wherein the particles circulate is called a “raceway”. In a blast furnace, the role of the raceway is particularly important. To understand and predict the evolution and physical characteristics of the raceway, a three-dimensional transient Eulerian multiphase flow model in a packed particle bed was developed. In the model, it was assumed that the gas and solid (particle) phases constitute an interpenetrating continuum. The gas-phase turbulence was described as a k–ε dispersed model. The gas-phase stress was considered in terms of the effective viscosity of the gas. The solid-phase constitutive relationship was expressed in terms of solid stress. It was found that the evolution process of the raceway can be divided into three stages: (1) rapid expansion, (2) slow contraction, and (3) gradual stabilization. When the blast velocity was increased from 150 m/s to 300 m/s, the surface area of the raceway increased from 0.194 m2 to 1.644 m2. The depth and height of the raceway increased considerably with velocity, while the width slightly increased.

Laser-induced softening analysis of a hardened aluminum alloy by physical simulation

The study focuses on the analysis of the softening effects of the work-hardened aluminum alloy sheets EN AW 5754 H32 1.5 mm thick, through the physical simulation of thermal cycles induced in the material by laser heat treatments (LHTs). A numerical-experimental approach was implemented to define the laser thermal cycles and to subsequently reproduce them on the GleebleTM 3180 physical simulator. The obtained softening was measured by microhardness and metallographic analysis tests. For the definition of laser thermal cycles, preliminary tests with a 2.5 kW CO2 laser source have been realized, and a three-dimensional transient finite element thermal models were developed and calibrated with the experimental results. The investigated laser heat treatment parameters explored thermal cycles with different shape, interaction time, and peak temperature. Physical simulation tests were performed using laser thermal cycles that showed the maximum softening of the aluminum alloy. A three-dimensional transient finite element thermoelectric model was developed to design the shape of the Gleeble specimens, which satisfy the heating and cooling rate required by laser thermal cycles. Results obtained show that it is possible to physically simulate the investigated laser thermal cycles, reducing the cross section of the shaped part of the specimen. Softening effects depend on the thermal cycle shape. Greater softening is observed by increasing the interaction time and the peak temperature, but beyond a peak temperature threshold value, negligible effects are detected.

High-throughput laser fabrication of Ti-6Al-4V alloy: Part I. Numerical investigation of dynamic behavior in molten Pool

In the present work, an innovative high-throughput method was developed to fabricate a Ti-6Al-4V alloy via pulsed laser melting with water-cooled copper mold. Moreover, a three-dimensional transient model was established via numerical simulation to reveal the dynamic mechanism of heat transfer and fluid flow of the molten pool during high-throughput laser fabrication processes. Different laser powers, laser pulse durations and Marangoni coefficients were adopted to perform the numerical simulations, revealing the underlying physics of the heat transfer and fluid flow during the melting and solidification process. Special attention was paid to the cooling rate of the molten pool affected by cooling water velocity. Numerical results indicated that a “button” sample can be prepared in a short time of 200 ms by adjusting the processing parameters in this high-throughput preparation process. The maximum temperature of the molten pool was attained at the center underneath the laser beam and decreased radially outward. There was vigorous fluid flow mainly driven by thermal-capillary force in the molten pool. With increases in laser power and laser pulse duration, both the peak temperature and velocity of the molten pool increased. Accordingly, a high cooling rate was obtained under high cooling water velocity. Furthermore, the Marangoni effect fully changed the flow direction of the molten pool fluid, and the Marangoni convection flow influenced the temperature distribution of the molten pool. A new principle of the metallurgical dynamic behavior for the high-throughput laser fabrication process was established in this study and can provide technical guidance for high-throughput preparation experiments, such as laser parameter selection, structural control, and performance optimization.

Effect of plate thickness on weld pool dynamics and keyhole-induced porosity formation in laser welding of Al alloy

A three-dimensional (3D) transient numerical model is developed to simulate the keyhole dynamics, melt flow, and keyhole-induced porosity formation. The influence of the plate thickness on keyhole-induced porosity size and number is thoroughly investigated. The simulation results show that the average keyhole depth in plate thickness of 3, 6, and 10 mm is 2.07 mm, 1.89 mm, and 1.77 mm, respectively, and the value of keyhole depth reaching the quasi-steady state is 34 ms, 28 ms, and 14 ms, respectively. Compared to the thinner thickness plate, it is not easy to see the phenomenon of bubble amalgamation in the thickness of 10 mm under the parameter of low laser power and high welding speed. The less porosity in thicker plate laser welding is attributed to lower frequency of keyhole collapse, higher ratio of keyhole open after keyhole collapse to total keyhole collapse number, lower ratio of bubble number to total keyhole collapse number, higher ratio of bubble escape to the total bubbles number, and lower ratio of bubble amalgamation to the total.

Modeling of electromagnetically excited noise and vibration of induction motor

For electric vehicles, acoustic noise of traction motor excited by electromagnetic force is one of the main sources of noise, especially when automobiles are driven at low speed where noise from other sources are comparatively low. To analyze the characteristics of the noise and propose noise reduction suggestions, an accurate noise prediction model is needed. In this paper, a multi-physics model to predict the electromagnetic force excited acoustic noise of induction motor is presented. First, a three-dimensional (3-D) transient electromagnetic model of the motor was established using finite-element method (FEM). The uneven distributed time-varying magnetic force was calculated, and the current harmonics due to pulse width modulation (PWM) supply were considered. Then, a structural model was built, in which the anisotropy characteristic of silicon sheets stacked stator core, as well as the influence of windings, were considered through the assignment of orthotropic parameters to the stator core. Through mesh mapping, the FEM calculated magnetic force was transferred onto the structural model and the forced vibration was calculated using mode superposition method. Base on that, the acoustic noise was further obtained using boundary-element method (BEM). Finally, the noise and vibration of the studied induction motor were tested in a semi-anechoic room. As the simulated results show a good accordance to the measured data, the accuracy of the model was verified.

Modeling of buoyancy-driven thermal convection in immersed granular beds

For the first time, Eulerian three-dimensional transient modeling of thermal convection in immersed granular beds (IGB) has been developed. The modeling accounts for the destabilization of the IGB and the granular boundary upper layer deformation induced by thermal heating element. As observed in the recent experiments, the developed 3D CFD model predicts well the local phenomena: destabilization onset, particles removal or ejection, and the dynamic granular boundary upper layer deformation. The model predicts with good accuracy the two destabilization times td,onset, and td,total as function of the IGB initial height hi. Innovatively, a new critical Rayleigh number Racr* was introduced as function of a locally measured critical temperature Tcr at t=tcr>td,onset. The critical time tcr corresponds to a critical temperature drop observed inside the IGB near the heating element that was locally measured. The CFD model predicts correctly the thermal phase stability diagram, based on Racr* versus hi, as observed experimentally.

Influence of hatch spacing and laser spot overlapping on heat transfer during laser powder bed fusion of aluminum alloy

Direct metal laser sintering is a kind of laser powder bed fusion process that emerged as an advanced manufacturing process in the recent era of industry 4.0. This is a rapid manufacturing process where repeated melting and solidification takes place during scanning of the powder bed. The characteristics of the as-built component depend on the melting and solidification behavior which is directly influenced by the processing conditions. Intending to make a superior part in this process, it is indispensable to comprehend the impact of process parameters on temperature distribution, melting and solidification behavior, etc. In the present study, the authors developed an improved three-dimensional transient heat transfer model and studied the influence of hatching space and laser spot overlapping on temperature distribution with molten pool behavior on the AlSi10Mg powder bed. From this investigation, it was observed that the temperature on the AlSi10Mg powder bed decreases with an increase in hatch spaces and conversely with increasing the laser spot overlapping the temperature increases. Also, the molten pool dimension changes with variation of hatch spacing and laser spot overlapping. By combining these studies, the manufactures can able to optimize the hatch space and laser spot overlap along with other processing parameters to fabricate quality components.