Temperature-dependent Thermal Properties Research Articles

Research on the Thermal Behaviour of a Selectively Laser Melted Aluminium Alloy: Simulation and Experiment.

A 3D Finite Element (FE) model was developed to investigate the thermal behaviour within the melt pool during point exposure to Selective Laser Melting (SLM) processed AlSi10Mg powder. The powder–solid transition, temperature-dependent thermal properties, melt pool convection, and recoating phase were taken into account. The effects of Exposure Time (ET) and Point Distance (PD) on SLM thermal behaviour were also investigated and showed that the short liquid phase time and high cooling rate of the melt pool reduced the viscosity of the melt pool at a lower ET or a higher PD. This resulted in poor wettability and the occurrence of balling and micropores. At a higher ET or lower PD the melt pool became unstable and allowed for easy formation of the self-balling phenomenon, as well as further partial remelting in the depth direction resulting in the creation of larger pores. The proper melt pool width (119.8 μm) and depth (48.65 μm) were obtained for a successful SLM process using an ET of 140 μs and a PD of 80 μm. The surface morphologies and microstructures were experimentally obtained using the corresponding processing conditions, and the results aligned with those predicted in the simulation.

Deep drawing of press hardening steels

Press hardening of low alloy steel sheets is an efficient way of manufacturing high strength automotive components relevant for passenger safety in case of a crash. The press hardening process combines the advantages of good formability at elevated temperatures as well as high strength and good form accuracy after quenching in the closed die. Since cooling during forming and subsequent quenching has a significant influence on the mechanical behaviour of a steel sheet, a strongly coupled thermo-mechanical model has been developed for the simulation software ABAQUS. Accurate simulation results require the knowledge of temperature dependent thermal and mechanical material properties as well as occurring interactions between the sheet and the die. They were determined in a series of experiments and provide the input for the numerical model. During the quenching step in the closed die, the high strength of the component is achieved by a martensite phase transformation. This transformation is strongly influenced by the deformation in the heavily bent areas as well as the temperature evolution of the sheet. Accurate results for the shape of the final components and for the properties within the operating service time can only be obtained if the numerical model accounts for the microstructure formation including the TRIP (Transformation Induced Plasticity) effect. This is accomplished by means of a user subroutine. Consequently, the model allows to analyse the forming and cooling process in the closed die in detail throughout the entire process cycle. Concluding, the final geometry, the wall thickness distribution of the component and the press forces during forming are used as parameters to compare the simulation results with forming experiments and to validate the chosen material model.

Evaluation of residual stresses in multipass dissimilar butt-welded of SS316L to Inconel625 using FEA

In the present analysis, thermo-mechanical process was employed to study the thermal and structural behaviour of three pass dissimilar butt-joints of SS316L to Inconel625 alloys. The temperatures evolution and residual stresses developed in the weldments were reported for each pass in the transverse direction to fusion zone. The Ansys Parametric Design Language (APDL) used for modelling and analysis of welding process with the double ellipsoidal heat source. The temperature dependent thermal and mechanical properties used in the simulation process. The residual stress is compressive in SS316L side compared to Inconel 625. The residual stress is within the yield limits of both base materials. The results obtained from the simulation process will be helpful for maintaining the structural integrity.

A modified fractional order generalized bio-thermoelastic theory with temperature-dependent thermal material properties

In present work, the theory of a modified fractional order generalized bio-thermoelasticity with variable thermal material properties is developed. To keep the dimensions of fractional order thermoelastic theory consistent, a new parameter is first introduced into the generalized fractional order heat conduction equation. One-layered skin tissue with variable thermal properties is used for the numerical evaluation after the accuracy of the modified fractional order bio-thermoelastic model is verified. The effects of fractional order parameter, the added parameter and temperature-dependent thermal properties on the responses of skin tissue are discussed and illustrated graphically.

Performance, Thermal Stability and Optimum Design Analyses of Rectangular Fin with Temperature-Dependent Thermal Properties and Internal Heat Generation

In this study, we analysed the thermal performance, thermal stability and optimum design analyses of a longitudinal, rectangular fin with temperature-dependent, thermal properties and internal heat generation under multi-boiling heat transfer using Haar wavelet collocation method. The effects of the key and controlling parameters on the thermal performance of the fin are investigated. The thermal stability criteria and optimum design parameter were established. From the investigation, the study reveals that the performance of the fin is enhanced as the boiling condition parameter or the exponent decreases. It is also established that the optimum fin length (at which Q/ζ reaches a maximum value) increases as the non-linear thermal conductivity term β, increases. Furthermore, the study shows that the optimum value of M can be obtained based on the value of the non-linear term. The computational results obtained in this study were compared with established numerical solutions and is found to be in good agreement with the standard numerical solutions.

Numerical analysis on the behaviour of reinforced concrete frame structures in fire

Numerical approach using finite element method has been used to evaluate the behaviour of reinforced concrete frame structure subjected to fire. The structure is previously designed in accordance with Eurocode standards for the design of structures for earthquake resistance, for the ductility class M. Thermal and structural response are obtained using a commercially available software ANSYS. Temperature-dependent nonlinear thermal and mechanical properties are adopted according to Eurocode standards, with the application of constitutive model for the triaxial behaviour of concrete with a smeared crack approach. Discrete modelling of concrete and reinforcement has enabled monitoring of the behaviour at a global, as well as at a local level, providing information on the level of damage occurring during fire. Critical regions in frame structures are identified and assessed, based on temperatures, displacements, variations of internal forces magnitudes and achieved plastic deformations of main reinforcement bars. Parametric analyses are conducted for different fire scenarios and different types of concrete aggregate to determine their effect on global deformations of frame structures. According to analyses results, the threedimensional finite element model can be used to evaluate the insulation and mechanical resistance criteria of reinforced concrete frame structures subjected to nominal fire curves.

Study on the plane induction heating process strengthened by magnetic flux concentrator based on response surface methodology

In the surface heat treatment process of metals, the induction heating strengthened by ferromagnetic metal powder bonded magnetic flux concentrator (MPB-MFC) possesses more advantages due to its high efficiency. However, the further research of strengthen mechanism of MPB-MFC is still needed. It is necessary to establish the analytical model for accurately control and optimization of the plane induction heating process with MPB-MFC. In this paper, the coupled electro-magnetic-thermal multi-physics FEM model of the MPBMFC assisted induction heating is established, which involves the consideration of the temperature dependent thermal and magnetic material properties. The comparison between the results of several middle-frequency experiments and the simulation proves that the precision of simulation model is reliable. In addition, the influence of combined input variables on the final temperature is studied based on the response surface methodology (RSM), which could provide a comprehensive understanding for the process control and optimization in industrial production.

Performance of reinforced concrete slabs under hydrocarbon fire exposure

This paper presents numerical results on the fire resistance of reinforced concrete (RC) slabs subjected to the severe hydrocarbon fire exposure. The hydrocarbon fire curve represents a possible fire scenario in parking structures, tunnels, and in petro-chemical facilities. A three-dimensional (3D) nonlinear finite element (FE) model is developed to simulate the thermo-mechanical response of a RC slab that incorporates temperature dependent thermal and mechanical properties of concrete and steel reinforcement, respectively. Transient thermal-stress analysis is performed to study the cross-sectional temperature distribution and resulting deflections in the slab during simultaneous application of heat exposure and sustained loading. The predicted temperature distribution within the slab and mid-span deflection are compared with published experimental data. The predicted FE results are in good agreement with the experimental data throughout entire fire exposure duration. The validated FE model is applied in a parametric study to study the fire resistance of RC slabs under different slab configurations and hydrocarbon fire exposure. The varied parameters included fire exposure scenario, service load level, aggregate type, and concrete cover thickness. Results from the numerical analysis showed that hydrocarbon fire exposure has a significant influence on the fire resistance of RC slabs. In particular, the fire resistance of a slab under hydrocarbon fire exposure is 22.4% lower than that of a slab under the standard ISO834 fire exposure. Further, load level has a major effect on the fire resistance of RC slabs under hydrocarbon fire.

Characterisation of temperature-dependent heat conduction in heterogeneous concrete

Considering the heterogeneity, a mesoscopic simulation method was developed to analyse the heat conduction behaviour of heterogeneous concretes. In the numerical homogenisation technique, the concrete was regarded as a heterogeneous material consisting of three components (aggregate, mortar matrix and interfacial transition zones (ITZs)). Both two- and three-dimensional random aggregate structures of concrete were established. The temperature-dependent thermal properties of the mortar and aggregate were obtained based on experimental data from the literature, and those of the ITZ were determined by comparing the simulation results with measured values. The heat conduction equations were solved using the finite-element method: the three components were meshed separately and continuity of the heat fluxes at interfaces was applied. Good agreement was found between the simulation results and available test observations. The simulation results indicate that both the effective thermal conductivity (ETC) and a more accurate temperature field of concrete can be obtained using this mesoscale simulation method considering the temperature dependency of the materials' thermal properties. Aggregate shape was found to have a negligible influence on the ETC of concrete, but the type of aggregate cannot be ignored due to their different thermal conductivities. The ETC of concrete increased with increasing aggregate content and decreased with increasing temperature.

Revealing the anisotropy in thermoelectric transport performances in CNT/PANI composites

Although the carbon nanotube (CNT) based organic composites thermoelectric materials arouses considerable attentions, up to now the anisotropy in their thermoelectric performances has been overlooked. Herein, strong anisotropy in the temperature-dependent thermal and electrical transport properties have been demonstrated for organic composites thermoelectric materials, made by cold pressing the CNT powders coated by in situ polymerized polyaniline (PANI). The Seebeck coefficient, electrical and thermal conductivity are larger along the direction perpendicular to the cold pressing axis compared to the direction parallel to pressing axis. The anisotropy observed in the thermal conductivity and electrical conductivity maximizes at a CNT content of 30–40% (expressed in mass%), while the one observed for the Seebeck coefficient is small. The highest thermoelectric performances of the thermoelectric composites are achieved at a CNT mass ratio of ∼40% for both multi-walled CNT (MCNT)/PANI and single-walled CNT (SCNT)/PANI at a direction perpendicular to the cold pressing axis. These results highlight the importance of optimizing the CNT contents during the in situ polymerization with PANI to achieve a homogeneous nanostructure and reducing the agglomerate of the uncoated CNTs, in order to obtain high thermoelectric properties.

Temperature-dependent thermal and thermoelectric properties of n -type and p -type Sc1−xMgxN

Scandium Nitride (ScN) is an emerging rocksalt semiconductor with octahedral coordination and an indirect bandgap. ScN has attracted significant attention in recent years for its potential thermoelectric applications, as a component material in epitaxial metal/semiconductor superlattices, and as a substrate for defect-free GaN growth. Sputter-deposited ScN thin films are highly degenerate $n$-type semiconductors and exhibit a large thermoelectric power factor of $\ensuremath{\sim}3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/\mathrm{m}\text{\ensuremath{-}}{\mathrm{K}}^{2}$ at 600--800 K. Since practical thermoelectric devices require both n- and p-type materials with high thermoelectric figures-of-merit, development and demonstration of highly efficient p-type ScN is extremely important. Recently, the authors have demonstrated p-type $\mathrm{S}{\mathrm{c}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{g}}_{x}\mathrm{N}$ thin film alloys with low $\mathrm{M}{\mathrm{g}}_{\mathrm{x}}{\mathrm{N}}_{\mathrm{y}}$ mole-fractions within the ScN matrix. In this article, we demonstrate temperature dependent thermal and thermoelectric transport properties, including large thermoelectric power factors in both n- and p-type $\mathrm{S}{\mathrm{c}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{g}}_{x}\mathrm{N}$ thin film alloys at high temperatures (up to 850 K). Employing a combination of temperature-dependent Seebeck coefficient, electrical conductivity, and thermal conductivity measurements, as well as detailed Boltzmann transport-based modeling analyses of the transport properties, we demonstrate that p-type $\mathrm{S}{\mathrm{c}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{g}}_{x}\mathrm{N}$ thin film alloys exhibit a maximum thermoelectric power factor of $\ensuremath{\sim}0.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/\mathrm{m}\text{\ensuremath{-}}{\mathrm{K}}^{2}$ at 850 K. The thermoelectric properties are tunable by adjusting the $\mathrm{M}{\mathrm{g}}_{\mathrm{x}}{\mathrm{N}}_{\mathrm{y}}$ mole-fraction inside the ScN matrix, thereby shifting the Fermi energy in the alloy films from inside the conduction band in case of undoped $n$-type ScN to inside the valence band in highly hole-doped $p$-type $\mathrm{S}{\mathrm{c}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{g}}_{x}\mathrm{N}$ thin film alloys. The thermal conductivities of both the n- and p-type films were found to be undesirably large for thermoelectric applications. Thus, future work should address strategies to reduce the thermal conductivity of $\mathrm{S}{\mathrm{c}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{g}}_{x}\mathrm{N}$ thin-film alloys, without affecting the power factor for improved thermoelectric performance.

Notes on using temperature-dependent thermal diffusivity—forgotten rules

New materials and structures are applied in order to maintain the engineering products more and more efficient. Different types of thermal analysis/modelling of such materials and structures are also needed for the proper planning or design. The thermal analysis/modelling processes are supported by many commercial codes but in some cases, the experts might have applied a self-developed method also. The success of the analysis/modelling depends on many factors, but the basis is the correct application of the heat conduction theory which is more important in case of transient thermal processes. As the used tools are more and more powerful, the users pay less attention to the theory background, according to the author experience. It seems that the long tradition of the inconsistent application of the temperature-dependent thermal diffusivity is continuing, even strengthened by the increased availability of data of the temperature-dependent thermal properties. Regarding the origination of the thermal diffusivity, this might lead to the misinterpretation or misunderstanding of the nonlinear heat conduction problem solution procedures. This paper calls attention to avoid this, shows what kind of mistakes might occur related to this widely observable practice, summarizes the proper application and interprets where and how one could find room for the temperature-dependent thermal diffusivity.

Thermal and molten pool model in selective laser melting process of Inconel 625

Nowadays, additive manufacturing via topology optimization creates new opportunities for weight reductions in aerospace industry where high fly-to-buy ratio is desired. Selective laser sintering of advanced engineering materials like nickel super alloys are also expanding to reduce the cost and time of the manufacturing in aerospace industry. Elevated temperature and temperature gradients are critical factors in selective laser sintering of metals and they significantly affect the quality and integrity factors of produced parts such as microstructures, porosity, residual stresses, and distortions. Therefore, the aerospace industry needs advanced simulation tools to predict the temperatures, temperature gradients, and molten pool geometries to better understand the physics of the selective laser melting process as well as for the process optimizations. This article introduces an adjustable finite element-based multi-physics and multi-software platform thermal model, for laser additive manufacturing in powder bed systems to predict the transient temperature and the molten pool geometry. The developed model is able to simulate 3D transient temperature and molten pool shape in the laser additive manufacturing process by including the features of melting and solidification, porous media, and temperature-dependent thermal material properties for different materials. A set of experiments of Inconel 625 is carried out in order to measure the size of the molten pool and to validate the developed thermal model. An experimental study on temperature distribution carried out with titanium and an experimental study on molten pool sizes carried out with Inconel 625 in the literature are also compared with the developed thermal model. The estimation errors of the developed model are in the range of 11–18%.

Polymer Analyses for an Adapted Process Design of the Pipe-Extrusion of Polyetherimide

Over the last years, the use of high performance thermoplastic materials increased significantly especially in aviation applications. Thus, the processing of these high temperature polymers became more and more interesting. Especially, the groups of polymers like polyphenylene sulfide (PPS), polyether ether ketone (PEEK) or polyetherimide (PEI) are in the focus of recent developments and investigations. These materials show excellent thermal, mechanical and chemical properties while processing remains still challenging. Especially the influence of processing temperatures, temperature depending viscosities, the specific heat capacities and the thermal expansion show a high impact to the quality of the produced parts, e.g. degradation and dimensionally stability. Thus, this paper shows experimental characterizations in regard to the processing of PEI by pipe extrusion processes. In this context, a suitable methodology for the determination of appropriate process parameters is shown, which includes the comprehensive determination of temperature dependent thermal, thermomechanical and degradation properties of specific PEI extrusion materials.

A mesh-free Monte-Carlo method for simulation of three-dimensional transient heat conduction in a composite layered material with temperature dependent thermal properties

A new solution for the three-dimensional transient heat conduction from a homogeneous medium to a non-homogeneous multi-layered composite material with temperature dependent thermal properties using a mesh-free Monte-Carlo method is proposed. The novel contributions include a new algorithm to account for the impact of thermal diffusivities from source to sink in the calculation of the particles’ step length (particles are represented as bundles of energy emitted from each source), and a derivation of the three-dimensional peripheral integration to account for the influence of material properties around the sink on its temperature. Simulations developed using the proposed method are compared against both experimental measurements and results from a finite element simulation.

Tailor-made temperature-dependent thermal conductivity via interparticle constriction.

Managing heat is a major challenge to meet future demands for a sustainable use of our energy resources. This requires materials, which can be custom-designed to exhibit specific temperature-dependent thermal transport properties to become integrated into thermal switches, transistors, or diodes. Common crystalline and amorphous materials are not suitable, owing to their gradual changes of the temperature-dependent thermal conductivity. We show how a second-order phase transition fully controls the temperature-dependent thermal transport properties of polymer materials. We demonstrate four major concepts based on a colloidal superstructure: (i) control of transition temperature, (ii) width of phase transition regime, (iii) multistep transitions, and (iv) step height of the transition. Most importantly, this unique control over thermal conductivity is only governed by the interparticle constriction, the particle composition, and its mesostructure. Our concept is therefore also applicable to a wide variety of other particulate materials.

Thermal and fluid analysis of dry cask storage containers over multiple years of service

A detailed three-dimensional thermal and fluid analysis of a vertical dry storage cask with a canister containing 32 high-burnup pressurized water reactor (PWR) spent fuel assemblies for a storage of 50 years was carried out using a CFD simulation. The input decay heat value was calculated based on a Westinghouse 17 × 17 PWR fuel assembly using the well validated package ORIGAMI imbedded in SCALE, with a total heat load of 38.44 kW for year 5 and 10.67 kW for year 55. The temperature-dependent and anisotropic thermal properties of the fuel assemblies, filling gas within the canister, and air covering the canister were considered in order to preserve accuracy. A peak temperature of 621.4 K occurred in the upper part of the fuel assemblies for at year 5, deceasing to 423.0 K after 50-year service. The simulation results shed light on the temperature and flow environment within the canister for an operational time of 50 years.

Multi-boiling Heat Transfer Analysis of a Convective Straight Fin with Temperature-Dependent Thermal Properties and Internal Heat Generation

In this study, by using the finite volume method, the heat transfer in a convective straight fin with temperature-dependent thermal properties and an internal heat generation under multi-boiling heat transfer modes are analyzed. In this regard, the local heat transfer coefficient is considered to vary within a power-law function of temperature. In the present study, the coexistence of all the boiling modes is taken into consideration. The developed heat transfer models and the corresponding numerical solutions are used to investigate the effects of various thermo-geometric parameters on the thermal performance of the longitudinal rectangular fin. The results shows that the fin temperature distribution, the total heat transfer, and the fin efficiency are significantly affected by the thermo-geometric parameters of the fin and the internal heat generation within the fin. The obtained results can provide a platform for improvements in the design of the fin in the heat transfer equipment.

Modeling of thermal response and ablation in laminated glass fiber reinforced polymer matrix composites due to lightning strike

Abstract Thermal response and ablation of laminated glass fiber reinforced polymer matrix composites subjected to lightning strike are studied. The associated nonlinear time-dependent heat transfer model includes specific features of lightning arcs observed in physical measurements such as lightning channel radius expansion, non-uniform lightning current density, and associated heat flux. Moving spatially and temporally non-uniform lightning-current-induced heat flux boundary and moving boundary due to material phase transition caused by rapid surface ablation are also included. To predict moving phase boundary in the laminated anisotropic composites, an element deletion method is developed and embedded into finite element analysis (FEA), which is performed using ABAQUS. The Umeshmotion + ALE method based on the user subroutine Umeshmotion and arbitrary Lagrangian–Eulerian (ALE) adaptive mesh technique is also used, when applicable (i.e., moving phase boundary is confined within a top layer of the composite laminate). Heat transfer analysis is performed for a non-conductive laminated glass fiber reinforced polymer matrix composite panel representing the SNL 100-00 wind turbine tip. Thermal response of the panel subjected to pulsed and continuing lightning currents at three different lightning protection levels, LPL I, LPL II, and LPL III, is studied. Temperature-dependent anisotropic thermal properties of the composite panel are included in the analysis. The FEA results include temperature distributions and ablation zone profiles. The results show the Umeshmotion + ALE method is sufficient for the pulsed lightning current at all three LPL levels since the moving phase boundary, i.e. the ablation front, is found to be confined within the top layer of the laminate. For the continuing lightning currents at all three LPL levels, the Umeshmotion + ALE method is not applicable since the moving phase boundary comes to rest at depths exceeding the thickness of the top layer of the composite laminate.

Temperature and pressure dependent electronic, mechanical and thermal properties of f-electron based ferromagnetic barium neptunate

Overall thermal dependence of electronic, thermodynamic and mechanical properties of BaNpO3 oxide have been investigated via full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). Different approximations such as local density approximation (LDA), generalized gradient approximation (GGA), Hubbard approximation potential (GGA+U) have been employed to achieve the optimized calculation results. The calculated structural, electronic and mechanical parameters are consistent with the available experimental and theoretical data. The elastic parameters at different pressures have also been calculated. Half-metallic nature is reflected from the spin polarized band profile of the present material. Moreover, the temperature and pressure dependent thermodynamic properties including Debye Temperature, specific heat capacity, grueinessien parameter, Entropy, thermal expansion, etc have been calculated via quasiharmonic Debye model.