Time Evolution Of Temperature Research Articles

Investigation on fire resistance of steel-reinforced concrete-filled steel tubular columns subjected to non-uniform fire

The fire performance of steel-reinforced concrete-filled steel tubular (SRCFST) columns under non-uniform fire exposure is analytically and experimentally examined. Four SRCFST columns are methodically tested under 3-, 2-opposite-, 2-adjacent-, and 1-face heating to achieve the failure modes, temperature evolution in time, axial and lateral deformations, and fire resistance. Finite element (FE) analysis models were used to verify and assess the test results. The obtained results reveal that profiled steel benefits the integrity and fire resistance of SRCFST columns. The temperature distribution of the cross-section is substantially affected by uneven temperature distribution, resulting in shifting the stiffness center toward the unexposed side at the elevated temperature. The parametric studies are also conducted over various influential factors to analyze their effects on the fire resistance of SRCFST columns subjected to non-uniform fire. A modified calculation methodology based on the extended Rankine approach is developed to predict the fire resistance of SRCFST columns under various fire conditions, covering uniform fire, 3-, 2-opposite-, 2- adjacent-, and 1-face heating. Based on the quantitative comparisons between the experimentally observed data and the numerically predicted results, the simplified method generally yields accurate predictions on the ultimate load capacity of SRCFST columns under non-uniform fire.

Investigation of the Heat Storage Capacity and Storage Dynamics of a Novel Polymeric Macro-Encapsulated Core-Shell Particle Using a Paraffinic Core

Thermal energy storages represent important devices for the decarbonisation of heat; hence, enabling a circular economy. Hereby, important tasks are the optimisation of thermal losses and providing a tuneable storage capacity, as well as tuneable storage dynamics for thermal energy storage modules which are composed of either sensible or phase change-based heat storage materials. The thermal storage capacity and the storage dynamics behaviour are crucial for fulfilling certain application requirements. In this work, a novel macro-encapsulated and spherical heat storage core-shell structure is presented and embedded in a supercritical ammonia working fluid flow field. The core of the macro-capsule is built by an organic low molecular weight substance showing a solid–liquid phase transition in a respective temperature zone, where the shell structure is made of polyvinylidene fluoride. Due to the direct coupling of computational fluid dynamics and the simulation of the phase transition of the core material, the influence of the working fluid flow field and shell thickness on the time evolution of temperature, heat transfer coefficients, and accumulated heat storage is investigated for this newly designed material system. It is shown that due to the mixed sensible and phase change storage character, the shell architecture and the working fluid flow field, the heat storage capacity and the storage dynamics can be systematically tuned.

Fully analytical solution in time and space domains on temperature in multi-barrier nuclear waste repository

Temperature evolution is one of the crucial factors in safe operation and geometric design of high-level radioactive waste disposal repositories. A three-dimensional two-layer axisymmetric heat transfer model was established to study the temperature evolution of the repository in the case of single canister. Applying a series of mathematical tools such as the finite Fourier sine transform, separation of variables and Duhamel's theorem, a fully analytical solution was obtained, which can visually and quickly represent the temperature evolution in both time and space. The validity of the model and solution was confirmed by comparing it with the existing line heat source solution, semi-analytical solution and finite element simulation results. The canister surface temperature was obtained by superimposing the temperature difference between the internal and external surfaces of buffer layer on the rock wall temperature. A single-panel calculation model was established, and dimensional and parameter analysis were carried out using the obtained fully analytical solution. According to the quantitative analysis using the obtained solution, increasing the canister spacing has a better effect on reducing the peak temperature than increasing the tunnel spacing. The effect of the two ways in reducing the peak temperature weakens with increasing the spacings.

The Great Flare of 2021 November 19 on AD Leonis

We present a detailed analysis of a superflare on the active M dwarf star AD Leonis. The event presents a rare case of a stellar flare that was simultaneously observed in X-rays (with XMM-Newton) and in the optical (with the Transiting Exoplanet Survey Satellite, TESS). The radiated energy in the 0.2 − 12 keV X-ray band (1.26 ± 0.01 × 1033 erg) and the bolometric value (EF, bol = 5.57 ± 0.03 × 1033 erg) place this event at the lower end of the superflare class. The exceptional photon statistics deriving from the proximity of AD Leo has enabled measurements in the 1 − 8 Å GOES band for the peak flux (X1445 class) and integrated energy (EF, GOES = 4.30 ± 0.05 × 1032 erg), which enables a direct comparison with data on flares from our Sun. From extrapolations of empirical relations for solar flares, we estimate that a proton flux of at least 105 cm−2 s−1 sr−1 accompanied the radiative output. With a time lag of 300 s between the peak of the TESS white-light flare and the GOES band flare peak as well as a clear Neupert effect, this event follows the standard (solar) flare scenario very closely. Time-resolved spectroscopy during the X-ray flare reveals, in addition to the time evolution of plasma temperature and emission measure, a temporary increase in electron density and elemental abundances, and a loop that extends into the corona by 13% of the stellar radius (4 × 109 cm). Independent estimates of the footprint area of the flare from TESS and XMM-Newton data suggest a high temperature of the optical flare (25 000 K), but we consider it more likely that the optical and X-ray flare areas represent physically distinct regions in the atmosphere of AD Leo.

Fire performance on steel-reinforced concrete-filled steel tubular columns with fire protection

Steel-reinforced concrete-filled steel tube (SRCFST) is widely used as an innovative composite structure to provide better performance in construction. This study focuses on comprehensive experimental and numerical investigations of the fire performance of SRCFST columns with fire protection under the ISO-834 standard fire test procedures. The fire resistance tests were conducted on eight SRCFST columns with various thicknesses of fire resistive coating. The fire test results, including the thermal conductivity of protection material, failure modes, temperature evolution in time, axial and lateral deformation curves, and fire resistance were reported in detail. The results demonstrated that fire protection delayed the degradation of bending stiffness and significantly increased the fire resistance. Further comparisons of fire resistance between SRCFST columns with and without fire protection indicated that the fire resistance of SRCFST column with protection thickness of 12 mm is 3.32 times higher than that of that without fire protection under an equal load level. A sequentially coupled thermal-stress finite element (FE) analysis model was develped and validated against the tested results. The measured thicknesses of fire resistive coating were compared with the predicted results to evaluate the applicatibility of the existing design method of concrete-filled steel tubular (CFST) columns to SRCFST columns with thick fire-resistive coating. The results indicated that the current design method should be adjusted or modified further to provide safe and accurate predictions of the thickness of fire protection for SRCFST columns.

Development of full electromagnetic plasma burn-through model and validation in MAST

This paper describes the improvement of the electromagnetic plasma burn-through model. Full circuit equations describing the currents in solenoid, poloidal field coils, and toroidally conducting passive structures have been integrated into the differential equation system of the plasma energy and particle balances in DYON. This enables consistent calculation of the time-evolving loop voltage at a plasma position only using operation signals in a control room, which are current (or voltage) waveforms in solenoid and poloidal field coils and prefill gas pressure. The synthetic flux loop data calculated in the modelling agrees well with the measurement in MAST, confirming the validity of the loop voltage calculation. The electromagnetic modelling also enables calculation of 2D time-evolving poloidal magnetic flux map, thereby modelling the plasma volume evolution during the plasma break-down and burn-through phase. Only using the control room operation signals used in 34 ohmic start-up discharges with the direct induction start-up scenario in MAST, the electromagnetic plasma burn-through modelling has reproduced the time-evolution of plasma current, electron density and temperature, and plasma volume, showing a reasonable level of agreement with experimental measurement.

Transient electron energy-loss spectroscopy of optically stimulated gold nanoparticles using picosecond pulsed electron beam

Ultrafast phenomena in gold nanotriangles (AuNTs) were investigated using a transient electron energy-loss spectroscopy (TEELS) technique under irradiation from a 150-fs pulse laser with a wavelength of 780 nm. This investigation was conducted using a time-resolved transmission electron microscopy method that was developed to measure the dynamics of nanomaterials. Enhancement of the intensity and energy-width broadening of the energy loss were observed at the EEL peaks associated with surface and bulk plasmons on the AuNTs. The TEELS measurement revealed two decay processes of 7.8 ps and longer than 100 ps that compensate for relaxation times of excited surface plasmons using transient absorption spectroscopy. The results show that the bulk and surface plasmons have the same time evolution, i.e., that the excited electrons on the surface and in the bulk have the same relaxation processes in both electron–phonon and phonon–phonon interactions. The time evolution of electronic and lattice temperatures was also estimated based on the measured relaxation time using a two-temperature model, which revealed the volume expansion of the AuNTs and clarified the energy shifts of plasmons. Details of excited electrons in nanoparticles investigated via plasmon energy loss are expected to facilitate improvement in the performance for energy harvesting of photons in nanostructure-controlled materials.

Flame structure analysis and flamelet modeling of turbulent pulverized solid fuel combustion with flue gas recirculation

In this work, carrier-phase direct numerical simulation (CP-DNS) is conducted for a pulverized coal flame in a temporally evolving turbulent jet with flue gas recirculation (FGR). Detailed gas phase kinetics are considered and heavy hydrocarbon molecules up to C20 are included to accurately represent tars in the volatile matter. The structure of the pulverized coal flame is analyzed with different flamelet models considering two mixing scenarios, namely the mixing of recirculated flue gases with the other fuel or oxidizer streams. In the first model approach, the mixing of recirculated flue gases with the gaseous fuels released from the coal particle is characterized with a fuel-split-based flamelet (FLT-FS) model. In the second approach, the mixing of flue gases with the transport air is described with an oxidizer-split-based flamelet (FLT-OS) model. In total, five trajectory variables are introduced in the flamelet table to represent the pulverized coal combustion states with FGR. The suitability of the flamelet models is evaluated through an a priori analysis for both the fully ignited state, as well as (more challenging) the igniting states. Comparisons show that both the FLT-FS model and the FLT-OS model perform well in predicting the thermo-chemical quantities for the fully ignited state. The FLT-OS model performs slightly better than the FLT-FS model in predicting the gas temperature and specific species mass fractions. This is due to the fact that the partial oxidization of the gaseous fuels by the hot flue gases outside the mixing layers cannot be reproduced by the FLT-FS model. While the state at the beginning of ignition can still be accurately predicted by the FLT-OS model, discrepancies can be observed for the tar species C20H10 and the intermediate species CO at a later stage when many particles ignite and the reason for this is explained. Further analysis in the flamelet solution spaces shows that the gaseous fuels are ignited on the fuel-lean side. The time evolution of the gas temperature from the beginning of ignition to the fully ignited state can be overall characterized by both flamelet models.

A high-power long lifetime beam dump for the Thomson scattering diagnostic system in the XuanLong-50 experiment.

The Energy iNNovation's XuanLong-50 is a spherical torus experiment with up to 10s plasma operation duration. A 3 J/50Hz pulsed laser is used in the Thomson scattering diagnostic system that is developed to measure the time evolutions of plasma electron temperature and density profiles. The expected laser pulse number is about 7.5 × 106/year with a power load of 150W. To meet at least 1-year lifetime requirement, a Chevron type beam dump with polished molybdenum plates is designed and fabricated, which absorbs the laser beam energy in a 3D structure to reduce the laser fluence deposited on the material surface. To prevent the backscattered stray light from interfering with the Thomson scattering measurements, a 7.5m beam path with folding mirrors is set between the beam dump and the plasma scattering volumes. Details of the beam dump design procedure including the laser beam profile control, multi-pulse laser damage threshold, heat dissipation, Zemax modeling, folding mirror selection, and beam path enclosure are presented together with the testing results.

Linking Processing Parameters and Rheology to Optimize Additive Manufacturing of k-Carrageenan Gel Systems.

Additive manufacturing—in particular, three-dimensional (3D) printing—has been introduced since the late 1980s, offering a novel paradigm for engineering design and manufacturing, as it allows the fabrication of very complex structures. Additive manufacturing of hydrogels is a very popular method to produce scaffolds to be used in tissue engineering and other biomedical applications, as well as in other advanced technological areas. When printing a thermoreversible physical hydrogel, a subtle balance between thermal and rheological parameters exists. The characteristic times of the sol–gel transition, regulated by a well-defined thermal history, must be optimized with respect to the characteristic processing times. In this work, we use this thermo-rheological approach to the additive manufacturing of a physical hydrogel. A low-cost desktop 3D printer for thermoplastic polymers was suitably modified to print a 1.5 wt% solution of k-carrageenan. The thermal behavior of the printer was determined by performing experimental measurements of the temperature–time evolution during the different processing steps, from solution loading, to the extrusion of the incoming gel, to the final solidification stage. In parallel, linear viscoelastic oscillatory shear measurements were performed in a rotational rheometer under thermal histories as close as possible to those previously measured in the printing process. The comparison between the rheological results and the quality of printing under different thermal histories is presented and discussed, highlighting the main relations between rheological and processing behavior, which are helpful in the assessment and optimization of the printing conditions.

Modeling of the time evolution of the solidification front in ice cubes

The present work is aimed at putting forward a three-dimensional moving-boundary model to calculate the water solidification in ice trays subjected to operating conditions typically found in household appliances. To better understand the physical phenomena and validate the model, experiments were performed in a purpose-built closed-loop wind tunnel facility at -23 °C and air flow rate of 10 m³ h−1 using a single volume of 145 ml fed with distilled, mineral, and filtered tap water. The end of the solidification process was identified by monitoring the cooling curves with the aid of seven thermocouples placed within the ice cube. In the numerical front, the ice cube was modeled as a pyramid trunk and Stefan's formulation was applied to each of the domain boundaries so that the ice thickness could be calculated over time. Deviations within a ±10% error band were observed for all cases. A good agreement between the model predictions for the time evolution of the ice cube temperature and the experimental counterparts was also verified. In addition, literature data for the position of the solidification front and the remaining liquid fraction were fairly predicted by the model.

Thermal conduction effects on the accretion–ejection mechanism. Outflow process investigation

ABSTRACT Astrophysical jets emanating from different systems are one of the most spectacular and enigmatic phenomena pervading the Universe. These jets are typically bipolar and span hundreds of thousands of light years, some even longer than the diameter of our Milky Way. The study of the disc–jet systems is motivated by the observed correlation between ejection and accretion signatures and is still under debate. It was shown in our previous work the crucial role of thermal conduction in the dynamics of a thin viscous resistive accretion disc orbiting a central object and was provided an unprecedented wealth of discussion that has advanced our understanding of the inflow process. In this work, we expand our exploration by addressing the most outstanding basic questions concerning the launching, acceleration, and collimation processes of the jet in presence of thermal conduction. We also tackle in depth-analysis the effects of this physical ingredient on the time evolution of temperature and on mass fluxes such as inflow and outflow rates. We performed a series of 2.5-dimensional non-relativistic time-dependent numerical calculations of a disc–jet system using the PLUTO code. Our results revealed compelling evidence that thermal conduction contributes to launching a faster and more collimated jet. The mass extracted from the disc via the outflow channel is also affected by the presence of thermal conduction in the sense that the ejection efficiency is significantly improved.

Size effect at discharging process of coconut oil as latent thermal energy storage

Coconut oil is one of the organic PCM materials with high thermal energy storage capability in the form of sensible and latent heat. Ideally, the latent heat storage occurs at a relatively constant temperature associated with phase change transition. Due to relatively low thermal conductivity, the size effect is important to optimize material performance, particularly at the discharging process related to latent heat release. This study will show the simulation results of the size effect in the solidification process of coconut oil by using ANSYS FLUENT. Three plastic balls with radii 2 cm, 3 cm, and 6 cm filled with coconut oil solidified from 308 K to 293 K, and several temperature detectors were placed in the ball to study the heat exchange process. The input parameters of density, heat capacity, thermal conductivity, and viscosity were taken from previous experimental studies. We reported the time evolution of temperature and liquid fraction until the molten coconut oil solidified from different detector positions in each ball.

Real-time prediction by data-driven models applied to induction heating process

Data-driven modeling approach constitutes an appealing alternative to the finite element method for optimizing complex multiphysics parametrized problems. In this context, this paper aims at proposing a parametric solution for the temperature-time evolution during the multiphysics induction heating process by using a data-driven non-intrusive modeling approach. To achieve this goal, firstly, a set of synthetic solutions was collected, at some sparse sensors in the space domain and for properly selected process parameters, by solving the full-order finite element models using FORGE® software. Then, the gappy proper orthogonal decomposition method was used to complete the missing data. Next, the proper orthogonal decomposition method coupled with the nonlinear sparse proper generalized decomposition regression method was applied to find a low-dimensional space onto which the original solutions were projected and a model for the low-dimensional representations was, therefore, created. Hence, a real-time prediction of the temperature-time evolution and for any new process parameters could be efficiently computed at the predefined positions (sensors) in the space domain. Finally, spatial interpolation was carried out to extend the solutions everywhere in the spatial domain by applying a strategy based on the nonlinear dimensionality reduction by locally linear embedding method and the proper orthogonal decomposition method with radial basis functions interpolation. It was shown that the results are promising and the applied approaches provide good approximations in the low-data limit case.

Enhancement of 3D Mass and Heat Transfer within a Porous Ceramic Exchanger by Flow-Induced Vibration.

This work investigates heat transfer enhancement for a porous ceramic heat exchanger. The effect of flow-induced vibration of exchanging air flow through porous tube banks has been tested. A numerical model able to assess the vibration effect on heat and mass transfer inside a porous ceramic exchanger has been carefully developed. A three-dimensional unstructured control volume finite element method (CVFEM) is developed to simulate the transport phenomena that arise during convective exchange. In this respect, several numerical tests have been conducted. The time evolution of temperature, liquid saturation, and pressure of the porous domain are analyzed and compared for two cases: with and without vibration. It is found that the vibration highly enhances the heat and mass transfer inside the ceramic exchanger. As a result, the gain of exchanging time to reach the thermal equilibrium between the hot air and the porous domain was 75% for the case of air vibration under sawtooth type at a frequency of fv = 5 Hz and Vmax = 10 m/s compared to nonvibrating exchange.

Modeling the pressure–temperature–time evolution of in situ shock veins: A terrestrial case study from Vredefort

AbstractNumerical computing software (via MathWorks MATLAB) has been developed to understand the relationship between shock wave passage in geological targets (i.e., heterogeneous media) and the formation of shock veins and associated high‐pressure/temperature polymorphs. This approach takes into consideration the pressure due to the passage of the shock front, subsequent rarefaction unloading pressures, and associated heating and cooling rates. The model is applied to calculate pressure–temperature–time conditions for coesite‐ and stishovite‐bearing shock veins within metaquartzites of the Vredefort impact structure of South Africa. To constrain the model, the position of the host metaquartzites at the time of impact is first reconstructed. The developed code then passes the appropriate shock conditions through the target to re‐create the shock wave, while simultaneously forming and cooling the shock veins via 2‐D steady‐state conduction. We have found that (1) at the time of shock vein formation (2.4 s following the initial contact of the projectile), the shock front pressure was 13.8 GPa and the width of the shock wave was of 27 km; (2) the melt within the shock veins initially reached ~3000 °C, which corresponds to the melting temperature of the target rock at 13.8 GPa. Simulation results indicate that conditions reach the stishovite stability field within 2 ms of vein formation (~10–14 GPa; 2000–3000 °C), followed by coesite within 1.29 s (~3–10 GPa; 600–2000 °C). The dwell time of the modeled shock vein system is 4.35 s. The shock vein system is completely solidified 33.4 s after the initial shock front passage. The calculated P–T–t path of the model indicates that the polymorphs within the shock veins of the metaquartzites at Vredefort formed under their normal stability field conditions following rarefaction wave decompression.

ASTI: Data assimilation system for particle and heat transport in toroidal plasmas

ASTI, a data assimilation system for integrated transport simulation of fusion plasma, has been developed to predict and control the fusion plasma behavior. ASTI employs the ensemble Kalman filter (EnKF) and smoother (EnKS) as data assimilation methods and the integrated transport simulation code for helical fusion plasma, TASK3D, as the system model. ASTI assimilates the time-series data of measured temperature and density radial profiles into the particle and heat transport simulation. In this study, we consider the uncertainties included in the density, temperature, transport model, neutral beam injection (NBI) heating model, and particle source model. We apply ASTI to 12 experimental data sets of the NBI-heated plasma in Large Helical Device (LHD) and investigate the validity of estimation and the prediction performance of ASTI. The obtained radial profile and time evolution of density, electron temperature, and ion temperature agree well with the experimental data sets. Faster and more accurate integrated transport simulation is realized byASTI than the previous integrated simulation of fusion plasmas.

Early-age heat flow and hydration in cementitious composites: numerical modelling based on temperature measurements

The heat generated during early age cement hydration causes a semi-adiabatic temperature rise of hardening concrete, while starting to develop its physical and mechanical properties. As a matter of principle, the heat generated by the hardening mixture depends on the cement properties and its hardening conditions like for instance the type of binders, quality of aggregates, water-to-cement ratio and type of formwork. A simple 1D numerical model can be formulated for simulating the evolution in time of this reaction, in order to identify the so called degree of hydration. The present paper proposes a detailed description of a theoretical approach which allow to assess the temperature development occurring in concrete elements at the early-age when the produced mixture is cured in semi-adiabatic boundary conditions. In this numerical procedure, the differential heat equation takes into account the heat that liberates to the environment through the formwork or concrete’s surface. This is done by considering the Arrhenius Principle and assuming a pre-defined shape of the adiabatic hydration curve of the concrete mixture. Hence, an indirect identification procedure of the aforementioned adiabatic curve is ideally carried out, as the simulated temperature evolution in semi-adiabatic conditions is brought to match the temperature measurements on a hardening concrete sample. This modelling procedure, enabling various boundary conditions, ranging from semi-adiabatic to isothermal, can be used to calculate the degree of hydration of a real in-situ cast concrete. Specifically, considering the variation of concrete strength class and element size some possible applications are proposed: this represents a simplified approach for the prediction of the temperature time-evolution in the concrete elements at early-age which may be also used as a practical tool for mitigating the risk of premature cracking.

Estimation of impurity release from planar liquid surface in plasma

A liquid metallic surface exposed to a plasma interacts with ions and electrons numerously. The surface becomes charged. Subsequently, the electric field is formed via the balance of incoming ion and electron currents. The kinetic energies and the momentum of the incoming ions and electrons are transferred to the surface. This is enhanced by the self-generated electric field and gives rise to notable pressures and energy fluxes on the surface. By adopting several plasma and liquid parameters to the physical models, the time evolution of the surface temperature can be characterized with the net energy flux, the net pressure, and the net impurity outgoing flux. The study suggests that electron temperature and ion mass significantly govern, but the ion to electron temperature ratio does not, the trend of the surface temperature. Besides, it is found that at long elapsed time at which evaporation becomes strong, the energy and impurity fluxes reduce in conjunction with the rate of change of the surface temperature lessens.

Time-resolved optical emission spectroscopy in CO2 nanosecond pulsed discharges

Nanosecond repetitively pulsed discharges at atmospheric pressure have shown comparatively high performances for CO2 reduction to CO and O2. However, mechanisms of CO2 dissociation in these transient discharges are still a matter of discussion. In the present work, we have used time-resolved optical emission spectroscopy to investigate the CO2 discharge progression from the initial breakdown event to the final post-discharge. We discover a complex temporal structure of the spectrally resolved light, which gives some insights into the underlying electron and chemical kinetics. We could estimate the electron density using the Stark broadening of O and C lines and the electron temperature with C+ and C++ lines. By adding a small amount of nitrogen, we could also monitor the time evolution of the gas temperature using the second positive system bands of N2. We conclude that the discharge evolves from a breakdown to a spark phase, the latter being characterised by a peak electron density around 1018 cm−3 and a mean electron temperature around 2 eV. The spark phase offers beneficial conditions for vibrationally enhanced dissociation, which might explain the high CO2 conversion observed in these plasma discharges.