Non-homogeneous Temperature Field Research Articles

(Best Presentation Award - 1st Place) Cyclic Aging Study of Commercial Li-Ion Batteries Focusing on Temperature

It is well known that temperature significantly impacts the cyclic aging behavior of Lithium-ion batteries. Temperatures outside the recommended optimum range promote different aging mechanisms. However, the temperature dependency of these aging mechanisms might also vary for different cell chemistries used in commercial Li-ion battery cells. Additionally, due to heat generation inside the cell and the cooling strategies in the applications the temperature field inside the cell is most likely inhomogeneous. This has led to several cyclic aging studies looking into these non-homogeneous temperature fields [1–4]. Hunt et al.[4] observed more pronounced aging for surface cooled cells, which they attributed to through-plane thermal gradients. Werner et al.[1,2] found no acceleration of the aging behavior for the applied in-plane thermal gradients compared to homogeneously aged cells. For thermal transients both Werner et al.[1,2] and Carter et al.[3] found faster aging in some cases.Few cyclic aging studies have been done on the impact of more complex temperature boundary conditions. These studies involved very few cell chemistries and more research is needed. A test was set up and preliminary results of a cyclic aging study on commercial Lithium-ion battery cells can be presented. Multiple parameters, such as capacity and resistance, are evaluated and compared to reference cells, which are cycled at a standard, homogeneous temperature. Werner et al. (2020) Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part I: Experimental Investigation. Batteries 6:13. https://doi.org/10.3390/batteries6010013Werner et al. (2020) Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part II: Analysis and Correlation. Batteries 6:12. https://doi.org/10.3390/batteries6010012Carter et al. (2019) Detection of Lithium Plating During Thermally Transient Charging of Li-Ion Batteries. Front Energy Res 7. https://doi.org/10.3389/fenrg.2019.00144Hunt et al. (2016) Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells. J Electrochem Soc 163:A1846-A1852. https://doi.org/10.1149/2.0361609jes

Effect of the supporting disks shape on nonlinear flow dynamics in a liquid bridge

The stability of convective flows in a non-homogeneous temperature field is affected by the shape of the container hosting the fluid. We present a nonlinear two-phase computational study of convection in a liquid bridge that develops under the action of buoyancy and Marangoni forces. The hydrothermal instability is examined for three shapes of disks supporting liquid bridge: both disks flat, the upper (hot) disk tapered, and the lower (cold) disk tapered. Steady flow is also analyzed for the case that both disks are tapered. In all the cases of instability, the flow pattern comprises, but is not limited to, a hydrothermal wave with an azimuthal wavenumber m = 2. An intriguing flow pattern is observed in the case of flat disks when the nonlinear interaction between the modes m = 0 and m = 2 leads to quasiperiodic motion forming a torus in the phase space. The torus originates from two traveling waves (TW) with the same mode m = 2 but with distinct (close) frequencies. Note that this was not observed in the one-phase model. The case with a tapered cold disk reveals an oscillatory state with a single TW wave associated with m = 2 mode. In the case of a tapered hot disk, an axially symmetric TW with m = 0 is observed first and, at later times, is accompanied by a TW with m = 2.

Thermal stresses in a functionally graded rotating disk: An approximate closed form solution

The purpose of this study is to analyze a circular annulus made of a functionally graded material (FGM) subjected to thermomechanical loading. The governing nonlinear differential equation for heat transfer, comprising of all the modes of heat transfer, such as conduction, convection, radiation, and internal heat generation, was formulated and then solved using the homotopy perturbation method (HPM). The stress field in the circular annulus due to thermomechanical loading was obtained using a HPM based approximate closed-form solution for a steady-state nonhomogeneous temperature field coupled with the solution of the classical theory of elasticity. The present work considered both Dirichlet and Neumann boundary conditions. A rigorous study on the effect of various thermomechanical parameters and grading parameters on temperature as well as the stress field is presented. The present approximate closed-form solution was validated with the finite element method (FEM) based solution. The close agreement between HPM based solutions of this work with the results of the ANSYS based FEM confirms the effectiveness and the viability of the present solution method for a FGM rotating disk with multiple variable nonlinearities. The present closed-form solution is more rational and computationally efficient over FEM and other numerical solutions.

Local magnetic flux density measurements for temperature control of transient and non-homogeneous processing of steels

Measuring temperatures during high-temperature processing of steels is usually limited to surface measurements that cannot directly assess the internal temperature distribution. Here, we demonstrate the feasibility of using a magnetic flux density measurement system to assess transient and non-homogeneous temperature fields in a modern high-strength steel, within the intercritical temperature range where microstructural evolution defines their key mechanical properties. The system accurately detects the Curie temperature and distinguishes temperature change rates within the processed volume. The magnetic measurements are also sensitive to the volume above Curie temperature and its shape, as revealed when integrated with thermal computational simulations. The electromagnetic signal provides real-time qualitative and quantitative information relevant to the metallurgical conditions enabling future intelligent control systems for the production and processing of steels. Contactless measurements of temperature-dependent electromagnetic properties can enable through-thickness temperature monitoring solutions, opening up opportunities for non-destructive full-field imaging of steels during thermal and thermomechanical processing.

Analysis of Mine Ventilation Network by 1D FEM: Simulation of Fans and Natural Draught

The version of simulating fans in mine ventilation network analysis by using the combination of FEM with the laminar solution method is considered. Two ways of fan insertion are discussed: in the form of a separate active element and in the form of combined element (an active element inserted into a passive element). The latter approach allows changing a position of the fan in a design stage without renumbering of a grid. The method of chords is used to linearize in general nonlinear fan characteristic. It is shown that the dependence of air discharge on the upstream-downstream pressure difference is an ascending curve for the fan. This provides a convergence for the iterative procedure of solving the FEM nonlinear equations system. A method of calculation of convective heat transfer between the air flow and the rock wall based on Lyon’s solution for a pipe with the constant density of boundary heat flow is described. As the density of heat flow and the air properties are slowly varying functions along a mine working (a branch of a network), then discretizing each branch into small segments permits to consider these parameters as constant along segments. Calculation of nonhomogeneous temperature field and treatment of gravity allow modelling the natural draught effect. The results of solution of the test problems validating used algorithms are given. Calculation results of flow mass rate in a mine network within the year are also represented which make it possible to estimate the influence of natural draught on venting capability.

Assessment of the Fluctuations in the Microstructural Parameters of Cellulose in Wood in an Inhomogeneous Temperature Field

The possibility of assessing the average crystallite size of cellulose in wood by formalised modelling from the magnitude of the potential difference arising in the wood specimen owing to polarisation in a non-homogeneous temperature field is considered.

Creep of t-joint of pipeline under joint action of temperature-force and radiation fields

The mathematical statement of three-dimensional problem of creep, which is running under the action of temperature, force and radiation fields, is presented in a paper. The total strain is considered as a sum of elastic, temperature, creep and swelling parts. The nonhomogeneous temperature fields are considered for determining the strain distribution as well as for obtaining the value of the neutron fluence function. The case of long term deformation under the creep with isotropic properties was analyzed by use of Norton law. The Finite Element Method, which is used jointly with finite differences method for time integration, was accepted for the problem’s solution. The volume finite element with eight nodes is used in numerical analysis. The approach uses the algorithm of parallel computing for the system of linear algebraic equations, which is solved by Choletski method. The program complex in C++ programing language was developed in order to realize the method and algorithms. It has been applied for numerical analysis. The influence of creep and radiation swelling on the stress-strain state of the cooling system fragment from nuclear reactor was investigated. The von Mises stress distributions are presented for different cases of nonlinearities both for tube’s volume and for the place of stress concentration. It was established that obtained solutions for the separate problems of creep under irregular temperature field and inner pressure as well as for problem of radiation swelling significantly differ from the solution of complex problem with consideration of both effects. It was found by numerical simulation that influence of radiation swelling significantly decreases the stress relaxation in creep conditions and increases the stress level in the place of tubes joint.

Planar laser-induced fluorescence diagnostics of water droplets heating and evaporation at high-temperature

Gas-steam-droplet technologies are widely used in systems operating at high temperatures ranging between 400 and 2000°C, namely: fire-fighting systems, thermal fluid cleaning, fuel compounding, industrial waste gasification and evaporation systems for advanced fuel components, cleaning of thermally loaded surfaces of power equipment, etc. System parameters are usually selected empirically via multiple tests and continuous trial operation of appropriate units, aggregates, assemblies, and installations. This situation is caused by insufficient basic knowledge of conditions and parameters of high-temperature (over 500°C) heating and evaporation of water and water-based emulsions, solutions, and slurries. Limited information is available regarding the evaporation rates dependent on the temperature of gaseous medium. Consequently, the up-to-date evaporation models allow the researchers to achieve adequate values (in good agreement with the experiment) of evaporation rates at air temperatures not exceeding 300–400°C. The paper presents a set of experiments on water droplets with the size ranging from 1 to 2mm, which is used to create the information database on high-temperature evaporation parameters. The approach to measuring the evaporation rate involves observation of the droplet size or more exactly its mean radius, and recording the time of its existence. A high-speed video camera and Tema Automotive software with different tracking algorithms are used for experimental observations. During gas heating, the distribution of highly non-homogeneous and non-steady temperature field in evaporating water droplets is detected by the hardware and software cross-correlation system and Planar Laser-induced Fluorescence optical diagnostics. Instantaneous and medium evaporation rates are computed for the whole period of the droplet lifetime. Highly nonlinear evaporation rate dependences are suggested for gas temperatures and the water droplet surface, size, and time of gas heating. Approximate relationships are described for the prediction of evaporation rates depending on the basic parameters. The evaporation rate is shown to increase several-fold during the heating of a water droplet in a high-temperature gaseous medium. The experimental data are described most accurately by exponential dependences of water evaporation rate versus the airflow temperature and velocity. This result makes it possible to predict the corresponding highly nonlinear dependences of evaporation rate versus the density of convective heat flux and the overall thermal conditions in the industrial chambers, evaporators, heat exchangers, etc. The mathematical expressions obtained can be used to identify the effective conditions of water droplet heating in a large group of high-temperatures applications as well as for developing high-temperature liquid evaporation models.

Analytical closed-form expressions for the structural response of helical constructions to thermal loads

In the current work, we present an analytical model for the characterization of the mechanical response of helical constructions to thermal loads. In particular, we elaborate closed-form expressions to compute the forces and moments induced by homogeneous and non-homogeneous temperature fields. We numerically verify the validity of the formulas over a wide range of geometric configurations, while we apply them to evaluate the mechanical response of two single layer cable configurations upon combined axial and thermal strains. Finally, we demarcate the range of angles for which the thermal structural response to homogeneous and non-homogeneous temperature fields considerably differs.

Darcy Scale Modeling of Smoldering: Impact of Heat Loss

ABSTRACTModeling the propagation of smoldering fronts with forced air feeding in a porous medium remains a challenge to science. One of the main difficulties is to describe the carbon oxidation reaction that supports this self-sustained process. Pore scale approaches are required to tackle this complex coupled heat and mass transfer problem with chemistry. They, nevertheless, require high computation effort and still miss experimental validation. Furthermore, the heat loss at the walls of the cells inherent to every laboratory scale system adds another level of complexity in the understanding of the coupling between the phenomena at stake. Indeed, it induces a nonhomogeneous temperature field throughout the system. In this article, a 2D Darcy scale model is developed and validated by confrontation with experimental results from the literature, covering wide ranges of carbon content of the medium and forced air velocity. A reasonable description of the front temperature, velocity, and non-consumption oxygen amount is reached. The model finally enables understanding of the impact of heat loss, which controls the front shape and stability near the system walls.

MODELOVÁ CIRKULACE FLUID V EXPERIMENTÁLNÍ NÁDOBĚ MOCK-UP-CZ

Experiment simulating the storage of spent nuclear fuel in the canister filled by bentonite mixture took place in the Center of experimental Geotechnics (CEG) on the Faculty of Civil engineering of the Czech Technical University in Prague during the years 2002–2006. After the realisation of the experiment it was shown, that both non-homogeneous geochemical and temperature fields were established. The main aim of the work was focused on the evaluation of the fluid flow characteristics inside the container, especially on the direction and flow velocities influenced by the increased temperature. Numerical modelling using the SHEMAT computer code was used to simulate the fluid flow.Mathematical modelling confirmed the probable formation of the convection cells along the heater with variable velocities depending on the hydraulic and thermal properties of the bentonite mixture and on the physical properties of the saturating fuid. The generated flow field could be the driving force for the geochemical non-homogeneities.

Tomographic laser absorption spectroscopy using Tikhonov regularization.

The application of tunable diode laser absorption spectroscopy (TDLAS) to flames with nonhomogeneous temperature and concentration fields is an area where only few studies exist. Experimental work explores the performance of tomographic reconstructions of species concentration and temperature profiles from wavelength-modulated TDLAS measurements within the plume of an axisymmetric McKenna burner. Water vapor transitions at 1391.67 and 1442.67nm are probed using calibration-free wavelength modulation spectroscopy with second harmonic detection (WMS-2f). A single collimated laser beam is swept parallel to the burner surface, where scans yield pairs of line-of-sight (LOS) data at multiple radial locations. Radial profiles of absorption data are reconstructed using Tikhonov regularized Abel inversion, which suppresses the amplification of experimental noise that is typically observed for reconstructions with high spatial resolution. Based on spectral data reconstructions, temperatures and mole fractions are calculated point-by-point. Here, a least-squares approach addresses difficulties due to modulation depths that cannot be universally optimized due to a nonuniform domain. Experimental results show successful reconstructions of temperature and mole fraction profiles based on two-transition, nonoptimally modulated WMS-2f and Tikhonov regularized Abel inversion, and thus validate the technique as a viable diagnostic tool for flame measurements.

Overall stability analysis of oversized steel‐framed buildings in a fire

SummaryOur present paper summarizes the shortcomings in the current fire‐resistant design of oversized steel structures and proposes a method for overall stability analysis of steel structures in the event of fire. The Fire Dynamics Simulator (FDS) software platform–based large‐eddy simulation technology can accurately reflect the environment in a fire scenario and correctly predict the spatial–temporal change in the smoke temperature field within an oversized space. Adopting the FDS software and finite element structural analysis (ANSYS) coupling can fundamentally overcome the natural defect of adopting the International Organization for Standardization (ISO) standard curve (or other indoor homogeneous temperature increase curves) that substitutes a point for the overview of a field. They reflect the structural additional internal force and internal force redistribution incurred by the gradient temperature difference of the spatial–temporal changing nonhomogeneous temperature field and both theoretically and technically realize the analysis of structural heat transfer and mechanical properties in a natural fire. Furthermore, a modified model to predict the steel temperature curve in localized fire is also proposed. The localized fire in large spaces can be treated as a point fire source to evaluate the flame thermal radiation to steel members in the modified model. Copyright © 2014 John Wiley & Sons, Ltd.

Numerical analysis of Nd:YAG pulsed laser polishing CVD self-standing diamond film

Chemical vapor deposited (CVD) diamond film has broad application foreground in high-tech fields. But polycrystalline CVD self-standing diamond thick film has rough surface and non-uniform thickness that adversely affect its extensive applications. Laser polishing is a useful method to smooth self-standing diamond film. At present, attentions have been focused on experimental research on laser polishing, but the revealing of theoretical model and the forecast of polishing process are vacant. The paper presents a finite element model to simulate and analyze the mechanism of laser polishing diamond based on laser thermal conduction theory. The experimental investigation is also carried out on Nd:YAG pulsed laser smoothing diamond thick film. The simulation results have good accordance with the results of experimental results. The temperature and thermal stress fields are investigated at different incidence angles and parameters of Nd:YAG pulsed laser. The pyramidal-like roughness of diamond thick film leads to the non-homogeneous temperature fields. The temperature at the peak of diamond film is much higher than that in the valley, which leads to the smoothing of diamond thick film. The effect of laser parameters on the surface roughness and thickness of graphite transition layer is also carried out. The results show that high power density laser makes the diamond surface rapid heating, evaporation and sublimation after its graphitization. It is also found that the good polish quality of diamond thick film can be obtained by a combination of large incident angle, moderate laser pulsed energy, large repetition rate and moderate laser pulse width. The results obtained here provide the theoretical basis for laser polishing diamond film with high efficiency and high quality.

Non-linear failure analysis of HCPB Test Blanket Module

For the European Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) the reduced activation ferritic martensitic (RAFM) steel EUROFER 97 is selected as a structural material. During operation the TBM will be subjected to complex thermo-mechanical loadings which yield at certain positions of the structure to stresses beyond the design limits of the structural material. Preliminary structural analyses of the TBM have shown critical behavior in several key points of the structure. An improved design has been proposed and in order to identify and assess the problematic positions in the improved version of the TBM a non-linear failure analysis is performed, for which a coupled deformation damage model developed at KIT for RAFM steels and recently implemented in the finite element code ABAQUS is used. The thermal loads in the form of non-homogeneous temperature fields distributions are obtained from a thermal analysis performed using the finite element code ANSYS on the same structure. Importing the temperature fields into the finite element code ABAQUS and applying the remaining loads – coolant internal pressure and structural boundary conditions – non-linear simulations are conducted taking into account the ITER-typical cyclic nature of the loading. The simulation results are evaluated and discussed considering ratcheting and damage at most critical highly loaded areas of the structure.

Simulation of Grain Growing Process of Zinc-Aluminium Alloy under High Pressure

Under high pressure of more than 1GPa, the grain growing process of Zinc-Aluminium (ZA) alloy is difficult observed by experimental method, therefore numerical simulation method is used to observe grain growing process of ZA alloy. Pressure as a important variable is leading-in thermodynamic parameters of ZA alloy, then solute diffusion and redistribution model, grain nucleating and growing model are present, and dendrite growth module is applied to describe grain growth. The simulation results of grain growth process under high pressure are demonstrated: In the initially solidification stage, grains are equiaxed growing process, after 15s solidification time, dendrite arm size are not equal, the reason is there are nonhomogeneous temperature fields around grains, which make some grains appear fast growing velocity, even it can be observed that dendrite arm of different grains are meet each other at 25s solidification time. Comparing simulated microstructure with experimental microstructure under 2GPa high pressure, it shows both grain size and grain distribution are similar, proving that the grain growing process can be well observed by simulation method.

Numerical analysis of acoustic characteristics in gas turbine combustor with spatial non-homogeneity

Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by a linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analyses are conducted in the combustors without and with acoustic resonator, which is one of the acoustic-damping devices or combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in good agreement with the measurement data. In this regard, the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. From the numerical results for the combustor with present acoustic resonators installed, the acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity. It is found that the resonators with present specifications are not optimized and thus, the improved specification or design is required.

Effect of material non-homogeneity on the inhomogeneous shearing deformation of a Gent slab subjected to a temperature gradient

It is well known that most rubber-like materials are non-homogeneous due to either imperfect manufacturing conditions or the action of severe thermo-oxidative environments in many practical applications. In this study, within the context of finite thermoelasticity, we theoretically analyze the inhomogeneous shearing deformation of a non-homogeneous rubber-like slab subjected to a thermal gradient across its thickness. The major objective of this study is to investigate the effect of the material non-homogeneity, which is the material-coordinate dependence of the material response functions, on the stress–strain fields for a given temperature gradient. First, we show the existence of a simple shearing deformation from which the generalized shear modulus and the generalized thermal conductivity of the slab could be obtained. Based on this information, the Gent material model is generalized to take the material non-homogeneity and the temperature dependence of the stress into account. To analyze the inhomogeneous shearing deformation of the non-homogeneous slab, deformation and temperature fields are postulated; then the decoupled temperature field is obtained analytically by solving the local energy balance equation. Finally, the static equilibrium equations are solved considering the linear temperature field. Our results show that the spatial pattern and the degree of the material non-homogeneity have profound effects on the stress–strain fields. The shear strain becomes nearly homogeneous and the stresses are relatively small for a certain spatial variation of the material non-homogeneity. This result suggests the possibility of designing a novel class of materials: functionally graded rubber-elastic materials (FGREMs).

Functionally graded materials produced by laser cladding

AlSi40 functionally graded materials (FGMs) were produced by a one-step laser cladding process on cast Al-alloy substrate as a possible solution for interfacial problems often present in laser coatings. The microstructure of the FGMs consists of a large amount of silicon primary particles surrounded by α-Al dendritic halos and by Al/Si eutectic. The Si particles exhibit a continuous increase in both size and volume fraction, from 8.5 μm and 22.7% at the bottom to 52 μm and 31.4% at the top of the FGM layer, respectively. The morphology of the Si particles changes accordingly from a small polygonal shape to a coarsely branched equi-axial shape. The α-Al halos and eutectic areas show less change over the same distance. From an analysis of the temperature field of the laser pool, Si particles heterogeneously nucleate on incompletely melted Si particles. The number density of Si particles is most likely being controlled by the non-homogeneous temperature field of the pool that determines the decomposition of the original Si phase in the AlSi40 powder. The growth rate and time available at different depths of the laser pool mainly affect the final size of Si particles.

Some Remarks on Interpolation of Nonstationary Oceanographic Fields

Abstract The performance of four methods for interpolating anisotropic, spatially nonstationary fields is examined. The methods are optimal interpolation (OI, also known as objective analysis), spline interpolation, multiquadric–biharmonic method (MQ–B), and the inverse distance weighted method. The tests were performed using multiple realizations of random bivariate fields with known underlying statistics, as well as highly anisotropic and nonhomogeneous temperature and salinity fields across the Antarctic Circumpolar Current (ACC). The results of tests using homogeneous random fields show that all methods except the inverse distance method have similar performance in the accuracy. When the interpolated field is sampled adequately and data distributions are dense, the presence of spatial deviations of the field statistics from the field average will limit the interpolation skill of OI to be gained from an increase in data density. In contrast, interpolation methods such as spline and MQ–B, which adjust t...