Temperature-dependent Thermal Properties Research Articles

A phase density based enthalpy model for laser assisted phase change process

Diffusion dominated laser assisted phase change process in a pure metal is numerically investigated using the enthalpy based fixed-grid approach. The single equation based on the total enthalpy (sensible and latent heat) is used in the whole domain (solid, liquid and vapor) to describe the transport processes in individual phases. To simulate in line with the experiment for laser drilled cavity in a cylinder, density variation due to change of phase has been taken into account in the proposed axisymmetric model. The proposed model also includes temperature dependent thermal properties. An iterative enthalpy update equation is developed to capture the evolution of the complicated melt as well as vapor front. To resemble a true laser beam, a Gaussian laser pulse is irradiated on the substrate surface. The drilled cavity depth predicted using the proposed model is compared with the available experimental results and a good agreement is found.

A novel carbon nanofibre/phenolic nanocomposite coated polymer system for tailoring thermal behaviour

Carbon nanofibre (CNF)/phenolic nanocomposite coatings were applied to the phenolic substrate for tailoring thermal behaviour under rapid temperature changes. A finite element (FE) model was developed in this work for transient thermal analysis of coated samples. The effects of thickness and CNF content of the CNF/phenolic nanocomposite coating on reducing temperature gradient field within the samples as well as transient time to steady state were investigated. Temperature-dependent thermal properties including thermal conductivity and heat capacity of phenolic and its nanocomposites containing 2, 4 and 16wt% CNF were experimentally determined and employed in the FE analysis. The results showed that the temperature gradient field and transient time within the polymers can significantly be decreased by using a CNF/phenolic nanocomposite coating.

Modeling the response of composite beam–slab assemblies exposed to fire

This paper presents the development of a three-dimensional nonlinear finite element model for evaluating the response of composite beam–slab assemblies subjected to a combination of gravity and fire loading. The behavior of typical beam–slab assemblies with different shear connection types (welded–bolted shear tab and all-bolted double-angle connection), exposed to different fire scenarios, was modeled using ANSYS. The finite element model accounts for temperature dependent thermal and mechanical properties of constituent materials, connections, and composite action. Transient time domain coupled thermal-stress analysis is performed to obtain the temperature distribution and deformation response of the composite beam–slab assembly. The finite element model is validated by comparing the predicted and measured thermal and structural response parameters of three composite beam–slab assemblies tested under fire conditions. The comparisons show that the proposed model is capable of predicting the fire response of beam–slab assemblies with good accuracy. Research from the analysis clearly shows that the composite action between the beam and slab significantly enhances the fire performance of composite beam–slab assemblies. It is concluded that the proposed finite element model could be used as a feasible tool to evaluate the fire response of composite floor systems.

Development of Residual Stress during Manufacturing of Spiral Welded Pipes

Spiral welded pipes (SWPs) are produced from forming and welding of plate or strip material with seam running its entire length in a spiral form. The relative structural weakness of these pipes is due to high residual stress developed during welding, which depends on various parameters and their interaction. Finite element method (FEM) was used to predict the temperature and stress fields in a 56-inch spirally welded steel pipe. Temperature-dependent thermal and mechanical properties of steel were incorporated in the model. Arc welding was modelled as a three-dimensional (3D) volumetric moving heat source. The residual stresses produced after the completion of the welding process were investigated. For validation, the numerically predicted residual stress was compared with measured values using split-ring and hole-drilling methods. It was found that von Mises stress attained high values in the cooling cycle after the solidification of the molten zones. Moreover, the effect of welding speed on the level of residual stress was studied. Increasing the welding speed with constant power resulted in reduction of the width of the high stress zone.

The temperature dependent thermal properties of ex vivo porcine liver tissue heated from 20°C to 90°C

Thermotherapy uses a heat source which raises temperatures in a target tissue, and the temperature rise depends on the thermal properties of a tissue. Little is known about the temperature dependent thermal properties of a tissue, which prevents an accurate prediction of the temperature distribution of a target tissue that is undergoing thermotherapy. The present study reports the key thermal parameters (specific heat capacity, thermal conductivity and heat diffusivity) that was measured on ex-vivo porcine liver while being heated from 20° C to 90° C. The results show that all the thermal parameters resulted in the plots with asymmetrical quasi-parabolic curves with temperature, being convex downward with their minima at the turning temperature of 35-40° C. The largest change was observed for a thermal conductivity, which decreased by 9.6% from its initial value (at 20° C) at the turning temperature (35° C) and rose by 45% at 90° C from its minimum (at 35° C). The minima were 3.567 mJ/(m3.K) regarding the specific heat capacity, 0.520 W/(m.K) regarding the thermal conductivity, and 0.141 mm2/s regarding the thermal diffusivity. The minimum at the turning temperature was unique and is suggested to be taken as a characteristic value of the thermal parameter of the tissue. The study indicates that the key thermal parameters varied largely with temperature, which resulted in having a substantial influence on the temperature distribution of the tissue undergoing thermotherapy. Keywords: thermal properties, ex-vivo porcine liver, temperature, specific heat capacity, thermal conductivity, thermal diffusivity, thermotherapy

A new approach for the estimation of temperature-dependent thermal properties by solving transient inverse heat conduction problems

A new method is proposed for estimating temperature-dependent thermal properties using solutions to transient inverse heat conduction problems. The prior information on the functional form of the thermal properties is not necessary for the proposed approach. The unknown thermal property is treated as the optimization variable, and the errors to be minimized are the differences between the calculated temperatures and the measured ones. The least-squares method is employed for the solution of the ill-posed inverse problem. The main contribution of this work is to introduce the complex-variable-differentiation method into transient inverse heat conduction problems, for the calculation of sensitivity coefficient. The inverse estimations of the heat capacity, the thermal conductivity and the thermal diffusivity are reported. Examples are given to demonstrate the effectiveness, efficiency and accuracy of the inverse approach as well as the potential to engineering applications. The effects of measurement errors on the inverse results are also investigated.

A review of the processing, composition, and temperature-dependent mechanical and thermal properties of dielectric technical ceramics

The current review uses the material requirements of a new space propulsion device, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) as a basis for presenting the temperature-dependent properties of a range of dielectric ceramics, but data presented could be used in the engineering design of any ceramic component with complementary material requirements. A material is required for the gas containment tube (GCT) of VASIMR® to allow it to operate at higher power levels. The GCT’s operating conditions place severe constraints on the choice of material. An electrically-insulating material is required with a high-thermal conductivity, low-dielectric loss factor, and high-thermal shock resistance. There is a lack of a representative set of temperature-dependent material property data for materials considered for this application and these are required for accurate thermo-structural modelling. This modelling would facilitate the selection of an optimum material for this component. The goal of this article is to determine the best material property data values for use in the materials selection and design of such components. A review of both experimentally and theoretically determined temperature-dependent and room temperature properties of several materials has been undertaken. Data extracted are presented by property. Properties reviewed are density, Young’s, bulk and shear moduli, Poisson’s ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, thermal expansion coefficient, and the factors affecting maximum service temperature. Materials reviewed are alumina, aluminium nitride, beryllia, fused quartz, sialon, and silicon nitride.

Anomalous transport and thermal properties of NiTi and with Cu and Fe-doped shape memory alloys near the martensitic transition

The temperature dependent electrical and thermal properties including electrical resistivity (ρ), specific heat (CP), Seebeck coefficient (S) and thermal conductivity (κ) have been studied for the polycrystalline NiTi, Ti50Ni40Cu10 and Ti50Ni48.5Fe1.5 shape memory alloys from 10–400 K. It was found that the electrical resistivity and Seebeck coefficient exhibit a typical metallic behavior throughout the temperature range investigated. A significant thermal hysteresis between warming and cooling was observed in all the three alloys which is a manifestation of the first-order nature of martensitic transitions. Our results indicate the presence of two stage martnesite transformations, i.e. B2 → B19 → B19′ for Ti50Ni40Cu10 while B2 → R → B19′ for NiTi and Ti50Ni48.5Fe1.5 alloys. An analysis on the measured thermal conductivity reveals that the anomalous feature in κ at the B19 ↔ B19′ transformation for Ti50Ni40Cu10 is essentially attributed to the electronic contribution, while an enormously large peak in warming run observed at the B19 → B2 transformation is due to the change in lattice thermal conductivity.

Investigations on welding residual stress and distortion in a cylinder assembly by means of a 3D finite element method and experiments

In the present work, both experimental and numerical simulation methods are used to investigate the characteristics of welding distortion and residual stress distribution. A 3D thermo-mechanical Finite Element Analysis (FEA) method is used to predict the welding distortion and residual stress of cylinder-shaped multi-pass layer weldments. Each weld pass is performed using a quarter-circle balanced welding procedure. To investigate the influence of deposition sequence and welding heat input on the welding distortion and residual stress, a continuous welding procedure is also calculated. The corresponding FEA models considered a moving heat source, the deposition sequence, and temperature-dependent thermal and mechanical properties. The results predicted by 3D FEA model are generally in good agreement with the measurements. Finally, the numerical and experimental results suggest that both deposition sequence and heat input affect welding distortion and residual stress distribution. Furthermore, the 3D thermal-mechanical FEA method can predict cylinder-type welding distortion.

Some studies on weld bead geometries for laser spot welding process using finite element analysis

Nd:YAG laser beam welding is a high power density welding process which has the capability to focus the beam to a very small spot diameter of about 0.4 mm. It has favorable characteristics namely, low heat input, narrow heat affected zone and lower distortions, as compared to conventional welding processes. In this study, finite element method (FEM) is applied for predicting the weld bead geometry i.e. bead length (BL), bead width (BW) and depth of penetration (DP) in laser spot welding of AISI 304 stainless steel sheet of thickness 2.5 mm. The input parameters of laser spot welding such as beam power, incident angle of the beam and beam exposure time are varied for conducting experimental trials and numerical simulations. Temperature-dependent thermal properties of AISI 304 stainless steel, the effect of latent heat of fusion, and the convective and radiative aspects of boundary conditions are considered while developing the finite element model. The heat input to the developed model is assumed to be a three-dimensional conical Gaussian heat source. Finite-element simulations of laser spot welding were carried out by using Ansys Parametric Design Language (APDL) available in finite-element code, ANSYS. The results of the numerical analysis provide the shape of the weld beads for different ranges of laser input parameters that are subsequently compared with the results obtained through experimentation and it is found that they are in good agreement.

Analysis of heat transfer in deformed liver cancer modeling treated using a microwave coaxial antenna

In interstitial microwave ablation (MWA), cancer is treated by applying localized heating to the tumor tissue. Some of the challenges associated with the selective heating of cancer cells, without damaging the surrounding tissue, entail a control of heating power for appropriate temperature distribution. This paper is carried out on the computer simulation of liver cancer treated using a microwave coaxial antenna (MCA). The mathematical models consist of a coupled electromagnetic wave equation, bioheat equation and mechanical deformation equation. In numerical simulation, these coupled mathematical models are solved by using an axisymmetric finite element method (FEM) with temperature dependent thermal and dielectric properties to describe the microwave power absorbed, specific absorption rate (SAR) distribution, temperature distribution and strain distribution in liver tissue. The comparison of the simulated results in model with and without deformation is also considered in order to approach realistic tissue modeling. The results show that the model with deformation, which is the more accurate way to simulate the physical characteristics of therapeutic liver cancer compared to the literature results and hence leads to more useful in the medical approach.

Enhancing the ABAQUS thermomechanics code to simulate multipellet steady and transient LWR fuel rod behavior

A powerful multidimensional fuels performance analysis capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO 2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth, gap heat transfer, and gap/plenum gas behavior during irradiation. This new capability is demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multipellet fuel rod, during both steady and transient operation. Comparisons are made between discrete and smeared-pellet simulations. Computational results demonstrate the importance of a multidimensional, multipellet, fully-coupled thermomechanical approach. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermomechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

Numerical investigation of the effect of volatilization and the supercritical state of pore water on maturation of organic matter in the vicinity of igneous intrusions

This study presents a numerical investigation of the effect of volatilization and the supercritical state of pore water on maturation of organic matter in host rocks based on the heat flow models assuming the instantaneous and finite-time intrusion mechanisms of magma. A 15 m thick, well-dated basic sill in the DSDP 41-368 hole near Cape Verde Rise, eastern Atlantic is selected as an example due to the sufficient thermophysical parameters of rocks and the definite burial and thermal history of the shale host rocks. Results indicate: (1) The effect of the temperature-dependent thermal properties of pore water at a hydrostatic pressure of 414 bar on the predicted vitrinite reflectance ( R r) is less than 0.1% no matter which intrusion mechanism of magma is assumed and can hence be ignored reasonably; (2) The consideration of volatilization of pore water can reduce the predicted R r of host rocks significantly. In case of the instantaneous intrusion mechanism, the maximum deviation of the predicted R r caused by pore-water volatilization reaches 1.3% at the location of half the sill thickness away from the contact (i.e. X / D = 0.5), and the deviation above 0.5% can occur in the region from 0.3 to 1.0 in the form of X / D . In case of the finite-time intrusion mechanism, the maximum deviation of the predicted R r due to pore-water volatilization attains 1.15% at X / D = 0.25, and the region where the deviation is larger than 0.5% lies between 0.15 and 0.6 in the form of X / D ; (3) If hydrothermal convection in the host rocks is allowed for, the predicted R r of the overlying host rocks is less than that of the underlying host rocks at the same X / D in the inner region of the contact aureole of igneous intrusions, whereas the phenomenon is converse in the outer region. In contrast, the measured R r profile shows that at the same X / D , R r of the overlying host rocks is totally higher than that of the underlying host rocks. Thus, it is not the hydrothermal convection in the overlying host rocks that resulted in the asymmetry of the current R r profiles below and above the sill; (4) The predicted R r based on the heat conduction model assuming the finite-time intrusion mechanism and pore-water volatilization matches well with the measured one out of the region where the R r geothermometer is unreliable due to the effect of volatilization of pore water. This demonstrates that the finite-time intrusion mechanism of magma, together with pore-water volatilization, possibly represents natural conditions. ► The temperature dependence of thermal properties of pore water can be ignored. ► Volatilization of pore water can reduce the predicted R r significantly. ► Hydrothermal convection in host rocks can not result in the present R r profile. ► Finite-time intrusion and pore-water volatilization represent natural conditions.

TiO2films annealing temperature-dependent properties in terms of the Amlouk-Boubaker opto-thermal expansivityψAB

In this study, TiO2 films were grown at room temperature by sol-gel process using titanium (IV)-isopropylat as precursor. XRD, EDS and MEB analyses proved that an eventual annealing treatment caused the TiO2 amorphous phase to shift to a crystalline anatase phase. Optical measurements were carried out via absorbance spectra in 500–2500 nm wavelength domain. From these optical measurements, the temperature-dependent conjoint optical and thermal properties were deduced using the Amlouk-Boubaker opto-thermal expansivity ψAB.

Coupled hydro-thermal modeling of ice ring formation around a pilot LNG cavern in rock

A new method of storing LNG (Liquefied Natural Gas) in a lined, hard rock cavern has been developed and verified by the construction and operation of a pilot plant in Korea. Creation of an ice ring is one of the core techniques in LNG storage in a lined rock cavern. The ice ring serves not only as a primary barrier against the intrusion of groundwater into an LNG cavern, but also as a secondary protection in case of leakage of LNG. Dry conditions within an ice ring protect a containment system against cracking due to the freezing of groundwater. Therefore, it is crucial to estimate and control the thickness and location of the ice ring when designing and operating an underground LNG storage cavern. In order to find suitable numerical scheme that simulates field results, the behavior of the ice ring around the pilot LNG cavern is investigated by hydro-thermal-coupled analyses. Through coupled analyses composed of three cases (CASE_1: constant thermal properties, CASE_2: temperature-dependent thermal properties, and CASE_3: phase change consideration in addition to CASE_2), the position and thickness of the ice ring, the temperature distributions and the groundwater level around the cavern are estimated and compared with measured data obtained from the pilot LNG cavern. The results show that the temperature distribution and groundwater level around the LNG cavern can be estimated reliably within an error of less than 4 °C and 1.0 m, respectively. The accuracy of numerical modeling is increased when the temperature-dependent properties are taken into account. The effect of phase change during freezing and thawing of groundwater is relatively small due to the dryness inside the ice ring and low porosity of the rock mass. These results imply that the adopted numerical method can be applied to full-scale underground LNG caverns for the control of the ice ring.

Investigation into temperature field of nano-zirconia ceramics precision grinding

A heat transfer model for the precision grinding process on nano-zirconia ceramics has been investigated. Based on the analysis of the processing properties of nano-zirconia ceramic materials, a theoretical model for the temperature field in the grinding of nano-zirconia ceramics was established. The model was then simulated and analysed under different grinding conditions. The effect of temperature dependent thermal properties and heat flux profile on temperature distribution in the workpiece has also been investigated. Parametric studies were carried out to study the effect of different input parameters such as the depth of cut, work feed rate and grinding speed on temperature distribution in the contact zone and in the workpiece across the grinding width and along the direction of movement. The results showed that, as the grinding wheel cut into the workpiece, the workpiece temperature rose sharply, and then levelled-off, with a high temperature gradient on the surface of workpiece. As the grinding depth of cut increased, a local high temperature took place in the grinding contact zone.

Thermal stress analysis of spiral laser-welded tube

Laser welding of mild steel tube was carried out under the nitrogen assisting gas ambient. Finite element method (FEM) was used to predict the temperature and stress fields in a laser spirally welded tube with 1.6 mm wall thickness and 75 mm diameter. Temperature-dependent thermal and mechanical properties of steel were incorporated in the model. Laser was modeled as a 3D volumetric moving heat source. The residual stresses produced after the completion of the laser welding process were investigated. Moreover, the effect of welding speed on the level of residual stress was studied. It was found that von Mises stress attained high values in the cooling cycle after the solidification of the molten zones. The residual stress developed in the welding region was measured using the XRD technique and results were compared with the predictions. Optical microscopy and SEM were used for metallurgical examination of the welding sites. The numerically predicted residual stress was in good agreement with the XRD results. Increasing the welding speed with constant power resulted in reduction of the width of the high stress zone.

Simulação numérica do crescimento da lentilha de solda obtida pelo processo de soldagem a ponto por resistência elétrica no aço inox AISI 304

O crescimento das lentilhas de solda obtidas pelo processo de soldagem a ponto por resistência elétrica em chapas de aço inoxidável AISI 304 foi analisado através de simulação numérica com o método de elementos finitos, sendo utilizado para essa finalidade o programa comercial ANSYS. O modelo matemático utilizado considerou: acoplamento entre os campos elétricos e térmicos em regime transiente; a variação das propriedades elétricas e térmicas do aço AISI 304 com a temperatura e condições de contorno térmicas de convecção. A geometria tridimensional analisada, axissimétrica, permitiu a simplificação para uma geometria bidimensional. Os resultados obtidos com o modelo foram comparados com resultados experimentais apresentados na literatura. Foram consideradas espessuras de chapas de 1, 2 e 3 mm, e diferentes diâmetros de face para os eletrodos. As simulações determinaram os tempos necessários de aplicação de diferentes valores de corrente para obtenção dos diâmetros e penetração das lentilhas de solda recomendados em cada situação. Os resultados mostraram também que com o uso de maiores correntes menos energia é consumida na formação da lentilha de solda.

Heat flow and deep temperatures in the Southeast Basin of France: Implications for local rheological contrasts

Abstract Triassic salt at 5–10 km depth may drive some of the recent tectonic features in southeastern France. We estimate the likely temperature range of the salt using two different approaches. The first of these, based on the extrapolation of deep temperatures obtained in oil exploration wells, predicts temperatures at a depth of 8 km to be in the range of 230–300°C. However, this prediction could be biased by a lack of deep measurements and problems related to lateral heat transfer caused by thermal conductivity contrasts. The second approach can overcome these problems by modelling the actual heat transfer for appropriate basin geometry, including temperature-dependent thermal properties, and a mantle heat flow of 35 mW.m−2. This latter value enables us to reproduce available temperature measurements and surface heat flow data. Here we evaluate the stationary temperature field along two sections constrained by seismic profiles, one at a local scale across the Vistrenque graben and the other at a more regional scale across the Southeast Basin. Our findings suggest that the temperatures in the deepest parts of the evaporitic layer (11 km depth) can reach up to 398°C, but can be as low as 150°C on the edge of the basin at the top of the salty layer. This temperature difference leads to important changes in salt viscosity. Results indicate that at a depth of 8 km, lateral viscosity contrasts within the evaporitic layer may reach 40. Such rheological contrasts might favour and amplify local subsidence, as seems to have been the case near the two Palaeogene half-grabens of Vistrenque and Valence, where deep hot zones are identified.

Numerical and Experimental Investigation of Pulsed Laser Welding of Hastelloy C-276 Alloy Sheets

In this paper, a three-dimensional finite element model is developed to compute thermal phenomena of 0.5 mm thick Hastelloy C-276 alloy sheets during pulsed laser beam welding (PLBW). Temperature-dependent thermal properties of Hastelloy C-276 alloy, effect of latent heat of fusion, and the convective and radiative boundary conditions are taken into account in the model. The space-time temperature distributions in a butt-joint weld produced by the PLBW process are predicted from the beginning of welding to the final cooling. The heat input to the model is assumed to be a double ellipsoid heat source. The finite element calculations are performed by using ANSYS code with the parametric design capabilities. Experiments were carried out to determine the temperature evolution during welding and to measure the cross section profile of the weld bead. By comparing the simulation results with the corresponding experimental findings, it is found that they are in a good agreement. The validity and applicability of the numerical simulation model are confirmed.