Transient Temperature Evolution Research Articles

3D infrared temperature maps measurements of ablative materials during plasma wind tunnel experiments

Accurate surface temperature and recession measurements are crucial experimental data for plasma wind tunnel testing of ablative thermal protection materials. In this work we propose a novel methodology to reconstruct infrared temperature maps on 3D geometries undergoing surface recession. An optical calibration technique is used to extract 3D metric information from the 2D thermal images, thanks to a specific calibration target with control points. The evolution of the sample shape during the experiment is tracked from a side view, using a visual-range camera with dedicated image processing, and reconstructed in 3D under the assumption of axisymmetry. The surface temperature is projected on the time-varying 3D geometry from the calibrated thermograms. The technique is demonstrated on a graphite ablation experiment in air plasma. The reconstructed maps provide detailed multidimensional information about the transient temperature evolution, overcoming traditional approaches that are limited around the stagnation point. The technique allows to study ablation mechanisms with further detail, improving experimental data for material qualification and validation of simulation codes.

Prediction and validation of melt pool dimensions and geometric distortions of additively manufactured AlSi10Mg

A finite element–based thermomechanical modeling approach is developed in this study to provide a prediction of the mesoscale melt pool behavior and part-scale properties for AlSi10Mg alloy. On the mesoscale, the widely adopted Goldak heat source model is used to predict melt pool formed by laser during powder bed fusion process. This requires the determination of certain parameters as they control temperature distribution and, hence, melt pool boundaries. A systematic parametric approach is proposed to determine parameters, i.e., absorption coefficient and transient temperature evolution. The simulation results are compared in terms of morphology of melt pool with the literature results. Considering the part-scale domain, there is increasing demand for predicting geometric distortions and analyzing underlying residual stresses, which are highly influenced by the mesh size and initial temperature setup. This study aims to propose a strategy for evaluating the correlation between the mesh size and the initial temperature to provide correct residual stresses when increasing the scale of the model for efficiency. The outcomes revealed that the predicted melt pool error produced by optimal Goldak function parameters is between 5 and 12%. On the part-scale, the finite element model is less sensitive to mesh size for distortion prediction, and layer-lumping can be used to increase the speed of simulation. The effect of large time increments and layer lumping can be compensated by appropriate initial temperature value for AlSi10Mg. The study aids practitioners and researchers to establish and validate design for additive manufacturing within the scope of desired part quality metrics.

Influence of Spacers and Skid Sizes on Heat Treatment of Large Forgings within an Industrial Electric Furnace

The influence of stacking patterns, through the different spacer and skid sizes, on the transient temperature distribution uniformity of large-size forgings in a 112-m3 electrical heat treatment furnace was investigated by conducting CFD simulations and real-scale experimental validation. A 3D CFD model of the electrical furnace was generated, including a heat-treating chamber, axial flow fans, large size blocks, skids, and spacers. Real-scale temperature measurements on instrumented test blocks during the heat treatment process were carried out to validate the CFD simulations. Results indicated that the CFD model was capable enough to determine the transient temperature evolution of the blocks with a maximum average deviation of about 6.62% compared to the experimental measurements. It was found that significant temperature non-uniformities of up to 379 K on the surfaces of the blocks due to the non-optimum stacking pattern were experienced by the blocks. Such non-uniformities could be reduced between 24% to 32% if well-adapted spacer and skid sizes were used in the stacking configurations. Based on simulation results and experimental validation work, optimum spacer and skid sizes for uniform temperature distribution were proposed for different stacking patterns.

Numerical Study of Temperature Evolution During Friction Element Welding

Abstract Welding of dissimilar materials is critical in industries where mixed materials with high strength-to-weight ratios are urgently needed. Friction element welding (FEW) is a promising solution, with the ability to join high strength materials for a wide range of thicknesses with low input energy and a short processing time. However, the temperature evolution and the influence of different processing parameters remain unclear. To bridge this knowledge gap, this work develops a coupled thermal–mechanical finite element model to study the FEW process. The simulation results agree well with the experimental measurements of material deformation and transient temperature evolution. It is found that the friction element’s rotational speed has the greatest impact on friction heat generation, followed by the processing times for different steps. The aluminum layer is heated during the penetration and cleaning steps, thus a lower rotational speed during the penetration step can help prevent the aluminum layer from undesired overheating. The steel layer and the friction element are mainly heated during the cleaning and welding steps. The strong heating, potentially melting, will be beneficial to the friction element’s plastic deformation and bond formation. To enhance the heating of the steel layer and the friction element, faster rotational speeds or longer processing periods could be employed during the cleaning and welding steps. The results by this study establish the relationship between processing conditions and the temperature evolution of different parts, which will guide the design and optimization of the FEW technique for various applications.

A framework for modelling the manufacturing process of friction welded lightweight structures

The rotary friction welding (RFW) is nowadays an industrial well-established and common welding technique since it allows the combination of a wide range of ferrous and non-ferrous materials, for instance, aluminium alloy and steel in order to create a lightweight structure. Therein, the major challenge is, due to the diverging physical properties, to determine suitable and stable parameters for the welding process. In this context, there is a great industrial demand for appropriate simulation tools to capture the relevant physical phenomena within the welding process and thereby to identity the optimal welding parameters. Various holistic models have been constituted to simulate the RFW process. Whereby, the major differences concern the methods of modelling the material and frictional behaviour. In a recent work, a straightforward material model based on a Carreau fluid formulation together with a shear strength confined Coulomb friction model has been adopted. The main motivation of this paper is to validate the capability and the precision of this proposed modelling approach as well as to represent some modelling aspects in a more tangible way. For that purpose the RFW process of a couple of aluminium to steel welded joints with different process parameters were simulated. Subsequently, a validation of the simulated and measured process variables was done concerning the comparison of the flash formation, the final shortening, the transient shortening rate and temperature evolution. • Representation of an approach for modelling the rotary friction welding process. • Detailed derivation of the used finite element model. • Explanation concerning to the friction and contact modelling. • Description of the applied meshing and remeshing procedure. • Comparison of experimental and simulation results.

Printability of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 metallic glass on steel by laser additive manufacturing: A single-track study

The amorphous structure of metallic glasses (MGs) endows them with extraordinary properties. Formation of MGs requires sufficiently high cooling rates to bypass crystallization, which results in their limited sizes by conventional processing routes such as casting. Laser additive manufacturing (LAM) technique is featured by high solidification rate that provides the potential for scalable fabrication of MGs. In this work, through high throughput laser single-track melting experiments, we studied the LAM processing window of a Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (at.%) MG to achieve materials with near-full density and minimal crystallization. We observed different types of single-track features including cracking, lack-of-fusion, and partial crystallization under different combinations of laser processing parameters. To rationalize the processing-structure relationships during LAM of MGs, finite-element thermal modeling was performed to monitor the transient temperature evolution and site-specific cooling rate in the melt pool. Our work provides significant insight into the LAM protocol optimization towards fully amorphous, well-bonded, and dense MG coatings on dissimilar crystalline materials.

Influence of Joule effect on thermal response of nano FinFET transistors

Integrated circuits based on FinFET nanodevices suffer from thermal processes related to heat dissipation caused by phonon transport bottlenecks. In this work, we report a numerical study of quasi-ballistic transport behavior in 20 nm FinFET transistors. Using a mathematical formulation, numerically implemented by the finite element method , we successfully validate the transfer characteristics and temporal temperature evolution compared with experimental and numerical works. We found that the proposed model, given by a calibrated charge drift-diffusion model coupled with the enhanced ballistic diffusive heat transport equation, predicts the experimental I–V characteristics and the transient temperature evolution well. The error given by this comparison is less than 10% in the I DS -V GS and T-t characteristics, respectively. We show that the proposed equations provide an improved approximation compared to the dual-phase lag and the Cattaneo-Vernotte models. From an engineering viewpoint, we found that the self-heating is concentrated at the end of the channel region at the drain side; this phenomenon was confirmed from literature by experimental results. • We report a numerical study of the quasi-ballistic transport behavior in 20 nm FinFET devices. • The model is able to predict the I(V) characteristics and heating phenomenon compared to experimental and numerical data. • The self-heating is concentrated at the end of the channel region at the drain side of the devices.

Transient temperature evolution of pulverized coal cloud deflagration in a methane–oxygen atmosphere

Pulverized coal cloud deflagration in a methane–oxygen atmosphere is a fairly intricate process owing to transient turbulent combustion accompanied by gas–particle premix flow. We developed a comprehensive computational fluid dynamics model that considers gas–solid two-phase flow, interaction between gaseous and discrete coal particles, and homogeneous–heterogeneous reactions. Numerical results revealed nonconforming and random particle temperature at different instants. The temperature threshold and distribution of high-temperature particles were quantitatively and qualitatively analyzed using the simulation results. Particle accumulation and agglomeration reported for previous experiments was verified and interpreted using turbulence theory. In addition, we analyzed the coupling and heat-mass transfer between coal particles and gas. This investigation has yielded the detailed mechanism of heat transfer for a dust explosion and provided valuable information for prediction, precaution, and control of an explosion involving discrete particles.

On the experimental and theoretical model for ice crystal characteristics near a substrate

For better understanding the mechanism of ice cohesion on a solid substrate, an experimental study on ice crystal structure growing from a substrate is conducted. The characteristics of crystal structure as well as their growing patterns in different supercooling degrees are observed and recorded. Besides, theoretical analysis has been carried out to identify the heat diffusion effect on crystal growing.Different from the uniform morphology and constant growing velocity observed in previous researches, it is found that the side branches upon bottom part of the crystal are usually wider and more disorderly configured while those upon upper part are always more slender and more regularly distributed. In addition, crystal growing velocity changes continuously in vertical direction with a trend of convergence. Higher supercooling degree enhances such structure evolution and advances convergence of the growing velocity. Crystal structure diversity is determined by the principle of local transient temperature evolution due to the thermal diffusion from substrate. A model is presented to estimate local supercooling degree at different height from substrate and its regularity of evolution. Comparisons are made between our results and relevant literatures for correlation.

Modification of residual stress distribution in welded joint of titanium alloy with multi electron beam heating

Abstract Welding residual stresses usually have some negative effects on mechanical properties of the welded structure. A multi electron beam heating method was proposed to modify the residual stress of the weld. A finite element model was established to analyze the welding transient temperature and residual stress evolution in the multi electron beam joint of titanium alloy. The computed results were validated by the measurement using blind hole drilling method. The residual stress evolutions during the multi electron beam welding and heating were analyzed to explain the residual stress modification. The effects of multi beam shape and heating group offset on residual stress distribution were discussed based on the established numerical model.

Numerical study on vapor–liquid phase change in an enclosed narrow space

Based on the multiphase lattice Boltzmann method, a transient model of vapor–liquid phase change in an enclosed narrow space during startup operation is developed and numerically analyzed to investigate the two-phase dynamics and heat transfer behaviors in the confined flat two-phase thermosiphon. The transient temperature distribution, vapor–liquid interface evolution and thermal performance are investigated over a wide range of heat load and liquid filling ratio. The results indicate that, as heat load increases, the intermittent nucleation boiling, fully developed nucleation boiling and film boiling sequentially takes place at the evaporator section of the confined flat two-phase thermosiphon. Correspondingly, the transient temperature evolution shows the periodic large-amplitude fluctuation, the random medium-amplitude fluctuation, and gentle small-amplitude fluctuation. The fully developed boiling is desirable for the heat transfer enhancement on the evaporator surface due to smaller temperature fluctuation and lower thermal resistance. The moderate liquid filling ratio ensures the desired interaction between the evaporator and condenser, resulting in superior thermal performance. To optimize the thermal performance, the optimal liquid filling ratio is about 40%.

Thermocouple temperature measurement during high speed electron beam welding of SS 304

Measurement of temperature during high-speed electron beam welding (EBW) is a difficult task as the local temperature changes much faster compared to the response of the thermocouple. Estimation of response lag of thermocouple and subsequent correction of the measured temperature is presented here for the first time for high energy, high speed electron beam welding. Temporal evolution of temperature at some selected locations of stainless steel samples were recorded using thermocouple during electron beam welding and subsequently the measured temperature were corrected to nullify the effect of response lag of the thermocouples. Two numerical predictions, one based on commercial finite element model, and the other based on an existing, indigenous, and well tested CFD (Computational Fluid Dynamics) model are used for validation of the measured temperature duly corrected against response lag of the thermocouple. A reasonable match was observed between corrected temperature and the calculated temperature data. Effect of energy input and welding speed on transient temperature evolution are also validated and reported.

Thermodensity coupling in phase-field-crystal-type models for the study of rapid crystallization

We self-consistently derive a formalism that couples a Phase Field Crystal (PFC) density field to thermal transport. It yields a theory for non-uniform transient temperature and density evolution, and includes local latent heat release during atomic rearrangements of the PFC density field. The basic formalism is applied to the basic PFC model, demonstrating the approach's capacity to capture solidification and recalescence. With an aim towards linking physical temperature to PFC temperature, a new classical density field theory for solid/liquid/vapor systems is then derived. It presents a different approach to those traditionally used in the PFC literature while still retaining the major advantages that have become the hallmark of PFC modelling. The new model is based entirely on physical density and temperature scales. We end the paper by applying the thermal-density coupling formalism to this new multi-phase density functional theory/PFC model.

Analytical formulation of effective heat transfer coefficient and extension of lumped capacitance method to simplify the analysis of packed bed storage systems

Analysis of the transient temperature evolution during charging or discharging of the packed bed thermal storage systems is immensely simplified with the formulation of an effective heat transfer coefficient between the solid storage materials and the heat transfer fluid. It can cut significant computational cost which is otherwise required for a complete numerical simulation. The lumped capacitance method, the simplest of the available options, is restricted only to the low Biot number scenarios and hence is seldom applicable to any real system. The formulation of the effective heat transfer coefficient allows the extension of the lumped capacitance method for moderate Biot numbers. The present work develops such a formulation to simplify the analysis of packed bed storage systems through analytical route. Earlier attempts in this direction were made through weighted average time method which is inherently restricted to the simple one-dimensional heat conduction problems. On the other hand, we find out the effective heat transfer coefficient starting from a general three dimensional analytical solution of the transient heat conduction and proceed with the well-known one term approximation which acts as the basis of the Heisler charts. The method is not dimensionally restricted and hence we can include realistic three dimensional shapes such as cuboid, short cylinder etc. in the formulation. We validate our method by comparing the resulting temperature profiles for the one-dimensional geometries which have been attempted earlier by the weighted average time method. We also provide the accuracy estimation (as a function of increasing Biot number) against the full numerical simulation for the geometries where the weighted average time is not applicable. Therefore, the current study provides the tool for an inexpensive theoretical estimation for the transient heat transfer behaviour in the thermal storage tanks which has long term design implications particularly for the large scale concentrated solar thermal power plants.

Theoretical study on thermal characteristic of MgO: PPLN crystal in high power optical parametric oscillator

This study focuses on the thermal characteristic of an end-pumped MgO: PPLN crystal by solving the transient temperature evolution model in a high power optical parametric oscillator. In this model, an approach based on contact mechanics theory is proposed to quantitatively calculate the heat transfer between rough contacting surfaces of crystal and heat sink. Based on the model, a parametric study has been performed to investigate the influence of the heat sink property, pump laserand crystal dimension on the thermal characteristic of the laser crystal. Obtained results reveal a closed correlation between the mentioned parameters and the thermal characteristic of the crystal indicating that a proper selection of the parameters is essential to control the crystal temperature and improve the performance of the laser.

Heat transfer behavior of elemental sulfur for low temperature thermal energy storage applications

Elemental sulfur provides a low-cost, high-performance thermal storage option for a wide range of applications and over an exceptionally wide range of temperatures (50 °C to over 600 °C). In previous efforts we have shown impressive performance for 200–600 °C, while in this study we examine the low-temperature (50–200 °C) thermal charge and discharge behavior of isochoric sulfur-based storage using a detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics. The model provides excellent agreement with experimental results. We show that sulfur exhibits lower viscosity because of reduction in the chain-length of polymeric sulfur caused by trace amounts of organic substances resulting in attractive charge and discharge performance. The results from the parametric analysis of pipe diameter on the charge and discharge heat transfer characteristics are used to develop a simple, generalized correlation that relates the transient sulfur temperature and liquid fraction evolution as a function of dynamically evolving buoyancy-Fourier number due to the solid-liquid phase change. This solid-liquid buoyancy-Fourier, BFs-l, correlation can be used for effectively designing sulfur-based thermal energy storage systems for transient operation in low temperature applications.

Efficient Simulation of Temperature Evolution of Overhead Transmission Lines Based on Analytical Solution and NWP

Transmission lines are vital components in power systems. Outages of transmission lines caused by overtemperature are a major threat to system reliability, so it is necessary to efficiently simulate line temperature under both normal operation conditions and foreseen fault conditions. Existing methods based on thermal-steady-state analyses cannot support the simulation of transient temperature evolution, and, thus, cannot provide timing information needed for taking remedial actions. Moreover, the conventional numerical method requires huge computational efforts and barricades system-wide analysis. In this regard, this paper derives an approximate analytical solution of transmission-line temperature evolution enabling efficient analysis on multiple operation states. Considering the uncertainties in environmental parameters, the region of overtemperature is constructed in the environmental parameter space to realize the overtemperature risk assessment in both the planning stage and real-time operations. A test on a typical conductor model verifies the accuracy of the approximate analytical solution. Based on the analytical solution and numerical weather prediction data, an efficient simulation method for temperature evolution of transmission systems under multiple operation states is proposed. As demonstrated on a Northeast Power Coordinating Council 140-bus system, it achieves over 1000 times of efficiency enhancement, verifying its potential in online risk assessment and decision support.

Proposed liquid-cooled nanowire lasers.

While the nanowire (NW) lasers have attracted much attentions as nanoscale coherent sources in recent years, the heat accumulation and temperature-rise-induced breakdown remain challenges to improving the lasers for practical applications. Here we propose a microscale liquid-cooled approach to address the issue. Calculated results show that, compared with conventional air-cooled lasing systems, liquid-cooled NW lasers can allow much higher thermal power. By keeping the NW temperature below 373 K, the allowed thermal power in water is about 21 times that in air (850 µW in water versus 40 µW in air). Transient temperature evolution reveals a much faster heat dissipation of the NW in water (30 ns) than in air (7 µs), indicating a much higher allowable repetition rate in water than in air (e.g., 10 MHz versus 100 kHz). Our results suggest a possible route to compact NW lasers with higher power, new materials and new operation modes.

Experimental and numerical investigation of temperature evolution during electromagnetic pulsed compaction of powders

The transient temperature evolution during electromagnetic pulsed compaction of powders is an important concern to densification mechanism, and a homogenous temperature field is beneficial for compaction densification. An experimental and numerical investigation of temperature evolution during electromagnetic pulsed compaction has been completed. Based on the thermodynamics of temperature evolution during electromagnetic pulsed compaction, a numerical model using multi-particle finite element method was developed to provide more detailed information of the temperature evolution. It has been found that the temperature rise during electromagnetic pulsed compaction is mainly induced by the plastic deformation work, while the temperature gradient within the powders is greatly caused by the frictional work. With the die wall/powder friction increasing, the radial temperature gradient becomes greater. With the inter-particle friction increasing, the axial temperature gradient becomes greater and it is strongly correlated to the non-uniform densification within the powders. More external work combined with greater compacting velocity leads to greater temperature rise in powders, and the axial temperature gradient is elevated because of the limited heat conduction in the shorter time.

Sensitivity analysis of the residual stress state in friction stir welding of high strength aluminum alloy

AbstractIn this paper, the friction stir welding process was numerically investigated for 6 mm thick aluminum alloy AA2024-T3. The finite element software COMSOL Multiphysics was used to calculate the transient thermal field during welding and the mechanical reaction depending on different mechanical clamping conditions and hardening models subsequently. A thermal pseudo-mechanical (TPM) heat source was implemented. Softening effects of the material due to precipitation hardening dissolution caused by the frictional heat were accounted for. The transient temperature evolution measured by thermocouple elements at various locations was compared to the numerical results. A good agreement was found for the thermal field. A sensitivity study of the mechanical models showed the strong influence of the clamping conditions and the softening model.