Thermal Diffusion Characteristics Research Articles

Some problems related to thermophysical properties of selected barrel steels

The paper discusses selected issues related to the thermophysical properties of selected barrel steels, which the authors have been dealing with over the last few years, i.e. 38HMJ (1.8509), 30HN2MFA, X37CrMoV5-l hot-work tool steel (1.2343), DUPLEX (1.4462) and MARAGING 350 (1.6355). In some of them, i.e. in the X37CrMoV5-1 hot work tool steel, 38HMJ, 30HN2MFA, a ferrite-austenite phase transition occurs, which causes shrinkage of the material. During a series of shots, multiple shrinkage of material degrades the barrel channel and deteriorates the ballistic parameters of the cannon barrel. Another problem concerns the apparent specific heat that we get from the DSC measurement and the dependence of the specific heat on temperature in the form that we use for the numerical simulations. The point is that the phase transition effect should not be taken into account twice, i.e. in the thermal diffusivity characteristics and in the specific heat characteristics. For all selected steels the thermophysical properties, i.e. thermal diffusivity, thermal conductivity, specific heat and thermal expansion, were obtained in a wide range of temperature, so they can be used as input data for numerical simulations.

Effect of Pore Evolution on Thermal Diffusivity and Radiation Characteristics of Thermal Barrier Coatings after High-Temperature Exposures

Studying the impact of pores is crucial to enhancing the service performance of coatings, since they are a typical microstructure feature of thermal barrier coatings. In this paper, a coating prepared by the APS method was employed as the study object, and a scanning electron microscope and optical microscope were used to calculate the porosity after spraying or high-temperature exposures. Based on this, numerical calculations and simulations were used to evaluate the impacts of the pore structure and porosity on the heat conductivity and radiation characteristics of the coating. The results showed that, at high-temperature exposures, the horizontal pores inhibited thermal conductivity and radiation, but the column pores increased heat conductivity and radiation. The heat conductivity of the coating linearly decreased as the porosity increased, whereas the extinction coefficient increased, although at a slower and slower pace. When the porosity reached 15%, if the porosity was further increased, the thermal radiation energy did not change much, indicating that increasing the porosity would only block the heat radiation to a certain amount. This new and time-saving technique for materials research utilizing simulation and numerical computing may be utilized to optimize the microstructure of coatings to increase their service performance.

Thermal Diffusivity Characteristics of the IN718 Alloy Tested with the Modified Pulse Method.

The article presents the use of the modified pulse method (MPM) to determine the temperature characteristics of the thermal diffusivity of alloy 718. The experiment was carried out in the temperature range of 20-900 °C during the double heating of the sample with an interval of two weeks. The results of our own research showed a good correlation in the temperature range of 300-500 °C, during the first heating of the sample, with the recommended changes in thermal diffusivity by NPL & ASM and data from the MPDB database. On the other hand, clear deviations in the results occurred in the range of temperature changes up to about 300 °C, most likely responsible for the electron component of the conductivity of this alloy, and in the range above 700 °C, where there is a clear minimum that may be caused by the δ phase precipitation phenomenon.

Relationship between Thermal Diffusivity and Mechanical Properties of Wood

This paper describes an experimental study of the relationships between thermal diffusivity and mechanical characteristics including Brinell hardness, microhardness, and Young’s modulus of common pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and small-leaf lime (Tilia cordata Mill.) wood. A dependence of Brinell hardness and thermal diffusivity tensor components upon humidity for common pine wood is found. The results of the measurement of Brinell hardness, microhardness, Young’s modulus, and main components of thermal diffusivity tensor for three perpendicular cuts are found to be correlated. It is shown that the mechanical properties correlate better with the ratio of longitude to transversal thermal diffusivity coefficients than with the respective individual absolute values. The mechanical characteristics with the highest correlation with the abovementioned ratio are found to be the ratio of Young’s moduli in longitude and transversal directions. Our technique allows a comparative express assessment of wood mechanical properties by means of a contactless non-destructive measurement of its thermal properties using dynamic thermal imaging instead of laborious and material-consuming destructive mechanical tests.

Interface Tracking Investigation of the Sliding Bubbles Effects on Heat Transfer in the Laminar Regime

Helium gases are utilized to remove fission products from the molten salt fast reactor (MSFR) core during operation. Helium gases and other volatile fission products may be introduced into the intermediate heat exchanger channels. The effect of these gases on heat transfer is essential for the MSFR to operate properly, especially in laminar flow regimes. The computational fluid dynamics code PSI-BOIL was selected to examine this problem because of its interface tracking capability. A periodic square duct simulation created the flow regime, resulting in a sliding bubble regime. Following that, we examined the impact of heat transfer using an extended nonperiodic channel simulation with a succession of corner bubble arrays. Due to the combined effects of low thermal diffusivity and laminar flow characteristics, it is shown that the length of heat transfer augmentation may extend to at least five bubble diameters downstream of the bubble placement. Finally, we examined the impact of interphasic heat transfer between an inert gas and a liquid. The bulk of the heat transfer amplification effect was due to the motion of the bubbles rather than interphasic heat transfer.

Study on highly thermostable low‐k polymer films based on fluorene‐containing polyetherimides

AbstractHighly thermostable low‐k polymer films with potential applications as dielectric materials in microelectronic industry were synthesized starting from 9,9‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]fluorene dianhydride and various diamines. A polyetherimide/silica nanocomposite film was obtained using methyltriethoxysilane as precursor of inorganic phase. The chemical structure was confirmed by FTIR and 1H NMR spectroscopy. Water vapor's sorption capacity, thermal stability, glass transition temperature, thermal diffusivity, specific heat, thermal conductivity, and dielectric characteristics of the films were determined. All the films exhibited excellent thermal stability, with an initial decomposition temperature in the range of 500–530°C. They showed low dielectric constant of 1.98–2.86 and low dielectric loss of 0.0037–0.011, at a frequency of 1 Hz and room temperature. The subglass γ‐ and β‐relaxations, primary α‐relaxation, and conductivity relaxation processes were discussed according to the chemical structure of the samples. Quantitative structure–property relationship (QSPR) study was conducted, and linear regression models were formulated to describe the causal relationships between different parameters and polyetherimide properties.

Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

Thermal Diffusion Characteristics in Permafrost during the Exploitation of Gas Hydrate

Methane hydrate is the vast potential resources of natural gas in the permafrost and marine areas. Due to the occurrence of phase transition, the gas hydrate is dissociated into gas and water and absorbs lots of heat. The incomprehensive knowledge of endothermic reaction in permafrost sediments still restricted the production efficiency of hydrate commercial development. This endothermic reaction leads to a complex thermal diffusion in permafrost, which directly influences the phase transition in turn. In this research, the heat during the exploitation is transferred in two forms (specific heat and latent heat). Besides, the melting point is not constant but depends on the pore size of the reservoir rock. According to these features, a thermal diffusion model with phase transition is established. To calculate the governing equation, the pore size distribution is obtained by using the nuclear magnetic resonance (NMR) method. The heating tests are conducted and simulated to calibrate the coefficient (i.e., transverse surface relaxivity) of NMR. Then, the temperature field evolution of the hydrate reservoir during the exploitation is simulated by using the calibrated values. The results show that the temperature curves have a typical plateau related to the pore size distribution, which is effective to obtain the surface relaxivity. The heat transfer is remarkably limited by the endothermic effect of the phase transition. The hydrate recovery efficiency may depend largely on the heating capacity of the engineering operation and the rate of gas production. Compared to the conventional petroleum industry, it is significant to control the maximum temperature and temperature distribution in engineering operations during hydrate development. This research on the temperature behavior during onshore permafrost hydrate production could provide the theoretical support to control heat behavior of offshore hydrate production.

Nonlinear photoacoustic imaging dedicated to thermal-nonlinearity characterization

We proposed a nonlinear photoacoustic (PA) technique as a new imaging contrast mechanism for tissue thermal-nonlinearity characterization. When a sine-modulated Gaussian temperature field is introduced by a laser beam, in view of the temperature dependence of the thermal diffusivity, the nonlinear PA effect occurs, which leads to the production of second-harmonic PA (SHPA) signals. By extracting the fundamental frequency PA and SHPA signal amplitudes of samples through the lock-in technique, a parameter that only reflects nonlinear thermal-diffusivity characteristics of the sample then can be obtained. The feasibility of the technique for thermal-nonlinearity characterization has been studied on phantom samples. In vitro biological tissues have been studied by this method to demonstrate its medical imaging capability, prefiguring great potential of this new method in medical imaging applications.

Low-Energy Ablation and Low Thermal Diffusivity of a CFRC Composite Modified by SiC

The use of materials for aerospace devices, such as rocket nozzles and thermal shields, depends primarily on their thermal and structural characteristics. Ceramic materials and carbon composites have been studied for this purpose. This work measures and investigates the ablation and thermal diffusivity of hybrid matrix composites of carbon–silicon carbide matrix reinforced by carbon fiber (C/C-SiC). Silicon powder was added to a phenolic thermoset matrix with proportions of 5, 10, and 20 %. In addition, the liquid polymer infiltration (LPI) process using a silicone polymer was used to produce the same composites. A thermal plasma torch was used to obtain the ablation and effective thermal diffusivity characteristics of the materials. The morphologies, microstructures, and chemical compositions of the samples were investigated by scanning electron microscopy and energy-dispersive spectrometry (SEM/EDS) and X-ray diffraction (XRD). The thermal diffusivities of the composites were found to be in the range of 0.2–1.5 × 10−6 m2·s−1 from 700 °C to 1000 °C, respectively. The void volume fraction of the composites was approximately 20 % and decreased the thermal diffusivity.

Interface intermixing and interdiffusion characteristics in MOVPE grown spontaneous AlxGa1-xAs/GaAs (100) superlattice structures using high resolution X-ray diffraction

Thermal diffusion characteristics in naturally grown ultra-nanoscale superlattice structures have been studied. In absence of any suitable direct experimental tool due to the physical resolution limit, here we rely on the theoretical analysis of x-ray rocking curve simulations coupled with the diffusion equation to arrive at the diffusion characteristics across the interfaces of spontaneously grown AlxGa1-xAs/AlyGa1-yAs superlattice structures. The simulation approach presented here is a combination of a virtual interdiffusion code and a code on x-ray diffraction. We have obtained the variation in the actual diffusion coefficient as a function of time at different temperatures from the decay rates of the integrated satellite peak intensities. We have also found the diffusion coefficient to be highly nonlinear across the interface with time. The satellite decay equation could fit the experimental data taking the maximum Al composition alone at each time step. The pre exponential factor and the activation enthalpy values for interdiffusion are found out to be 0.17–0.25 cm2/s and 0.5–0.6 eV for Al diffusion whereas 0.01–0.11 cm2/s and 3.45–3.5 eV for Ga diffusion, respectively in the studied temperature range of 500 °C–700 °C. The interdiffusivity increases with temperature from 500 °C to 625 °C and decreases for further rise in temperature as the compositional contrast between the two layers decreases significantly at higher temperatures.

Implication of Electrode Material Choice on Failure Characteristics of Lithium-Ion Batteries

Thermo-mechanical failure of electrode material in lithium battery system is a cause of concern for battery health and safety. With the advent of high energy storage materials and faster charging mechanisms, consideration towards the risk of failure is a substantial component in the selection of battery materials. In this work, we present a novel approach towards characterization and selection of thermally stable and mechanically favorable electrode materials using material indices. The selection process is based on a coupled thermo-mechanical multiphysics model, which solves for the deformation in the electrode during lithiation/delithiation considering the possibility of plastic deformation under high rates of charging. The thermal generation in electrode material is considered from four different mechanisms including, polarization heating due to surface charge accumulation and over potential, entropic heating due to free energy variation during lithiation/delithiation process, joule heating due to internal resistance offered by the electrode material and heat generation due to dislocation movement and phase transformation in the case of plastic deformation. Several material indices are developed for comparison of electrode materials based on their mechanical strength, fracture resistance, thermal generation and thermal diffusion characteristics. The mechanical based indices compare the electrode materials based on their capacity to generate stress during operation, resistance towards crack propagation under fatigue loading, ability to handle plastic deformation and stability under the conditions of fast charging. The thermal indices equate the thermal performance of the electrode materials based on the ability to generate less and diffuse more heat during operation. Three commonly used cathode and anode materials are compared using the above-mentioned indices and the results are verified against prior experimental data. In conclusion, these material indices provide a basis for comparison of newer high energy electrode materials against the industrially used materials, and provide crucial information regarding key material properties which affect the thermal and mechanical stability and performance of these novel materials.

Moisture and thermal diffusivity of lentil seed under convective infrared-microwave: Modelling with and without shrinkage

The effect of infrared radiation and microwave radiation on the moisture and thermal diffusivity characteristics of lentil seeds during infrared and microwave drying was investigated. Using mathematical equations, values and curves, moisture and thermal diffusivity were obtained. This study was to determine the moisture and thermal diffusivity of seed lentil with and without shrinkage at input temperatures 40°C and 60°C, infrared powers 1,000 W and 2,000 W and microwave power 270 W and 450 W, when the moisture content was reduced from 60 to 9% (d.b.). Drying rate was increased with increased air temperature, infrared radiation and microwave powers. Also drying rate decreased continuously with decreasing moisture content. The calculated values of moisture diffusivity by considering shrinkage were smaller than the values of moisture diffusivity without considering shrinkage. Moisture diffusivity with and without shrinkage decreased with decrease in moisture content of lentil seeds and thermal diffusivity with and without shrinkage decreased with increased moisture content. Both moisture and thermal diffusivity values decreased with increase in temperature.

Absorbance and thermal diffusion characteristics of charged ion in organic photovoltaic solar cell

An M.pudica-based organic solar cell model is developed for experimental investigation of UV light absorptivity within ethyl acetate and ethanol mixtures in order to predict charged ion mobility within a network of microchannels. A two-dimensional simulation of energy transport with a finite volume formulation is adopted, where the back field effect on the wafering technology and the optimisation of the energy conversion within the M.pudica-based organic solar cell can be investigated. A significant contribution of this study is the inclusion of the material characterisation of M.pudica as a potential source of energy supply. The developed model is proposed for performance improvement in the design of the organic solar cell. With a variety of imposed boundary conditions, the scalar transport variables and their responses to the environment are studied. The temperature specified on the faces with Dirichlet boundary condition is 100°C. The result of the surface temperature diffusion is presented. The temperature that diffuses into the cell layer ranges from 30°C to 77°C, suggesting a temperature range for manufacturing of the organic solar cell.

A study of thermal diffusivity of carbon-epoxy and glass-epoxy composites using the modified pulse method

Abstract Transient heat transfer is studied and compared in two planeparallel composite walls and one EPIDIAN 53 epoxy resin wall acting as a matrix for both composites. The first of the two walls is made of carbonepoxy composite; the other wall is made of glass-epoxy composite, both with comparable thickness of about 1 mm and the same number of carbon and glass fabric layers (four layers). The study was conducted for temperatures in the range of 20-120 °C. The results of the study of thermal diffusivity which characterizes the material as a heat conductor under transient conditions have a preliminary character. Three series of tests were conducted for each wall. Each series took about 24 h. The results from the three series were approximated using linear functions and were found between (0.7-1.35)×10−7m2/s. In the whole range of temperature variation, the thermal diffusivity values for carbon-epoxy composite are from 1.2 to 1.5 times higher than those for the other two materials with nearly the same thermal diffusivity characteristics.

Calculational method in treating thermal diffusion characteristics in ternary gas mixtures

Calculational method in treating thermal diffusion characteristics in ternary gas mixtures

On the role of amorphous intergranular and interfacial layers in the thermal conductivity of a multi-walled carbon nanotube–copper matrix composite

The interface in multi-walled carbon nanotube (MWCNT)–metal matrix composites significantly effects the interfacial thermal diffusion characteristics vary due to the presence of an interphase. The thermal conductivities of MWCNT–copper (Cu) composites with and without amorphous impurity layers at the MWCNT–Cu interface as well as the Cu grain boundary have been studied. The measured thermal conductivities of composites containing chemically treated MWCNT with no amorphous impurity layers were much better than those containing pristine MWCNT. Interfacial and intergranular matrix amorphous layers, thought to originate from Cu oxide in Cu powders and amorphous carbon on the surface of the pristine MWCNT, were observed in the pristine MWCNT–Cu composite matrix. Interfacial amorphous layers a few nanometers thick generated at pristine MWCNT–Cu interfaces act as a thermal barrier and due to the relatively large thermal resistance of these layers the MWCNT are expected to act like elongated pores. Intergranular amorphous layers at the Cu grain boundaries also show thermal resistance, resulting in a decrease in the effective thermal conductivity of the Cu matrix. It is expected that amorphous carbon is partially removed by extended chemical treatment with sulfuric acid (H 2SO 4) and nitric acid (HNO 3), inhibiting amorphous layer formation and resulting in an increase in thermal conductivity of the composites. Our results suggest that extended chemical treatment with H 2SO 4 and HNO 3 is necessary not only for uniform dispersion of MWCNT in the ethanol solution, but also for preparation of clean surfaces free of amorphous carbon in the initial MWCNT for effective MWCNT–Cu composite fabrication.

Heat flow analysis of an FPSO topside model with wind effect taken into account: A wind-tunnel test and CFD simulation

The aim of this paper is to study the feasibility of a computational fluid dynamics (CFD) method to examine the effect of wind on the thermal-diffusion characteristics of floating production storage and offloading (FSPO) topside models subject to fire. It is motivated by the need to identify the fire loads on FPSO topsides, taking into account the effects of wind speed and direction as well as the effects of geometry of the FPSO topsides. The results of a wind-tunnel test and CFD simulation undertaken for these purposes on a 1/14-scale FPSO topside model of a VLCC class FPSO unit are reported here. In the wind-tunnel test, the locations of the heat source of the fire are varied, as are the speed and direction of the wind, and the temperature distribution is measured. CFD simulations, using the ANSYS CFX (2009) program, were performed on the test model, with the results compared with the experimental results. It is concluded that wind has a significant effect on the thermal-diffusion characteristics of the test model and that the CFD simulations are in good agreement with the experimental results. The insights developed in this study will be very useful for the fire engineering of FPSO topsides.

Thermal stability, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of PrNi 0.4Fe 0.6O 3− δ, a potential cathode material for IT-SOFCs

The potential use of a double B mixed-perovskite as a promising cathode material in intermediate temperature solid oxide fuel cells (IT-SOFCs) has been anticipated as a result of this work. A thorough investigation of some important parameters like thermal stability, thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of the PrNi 0.6Fe 0.4O 3− δ ceramic sample have been investigated as functions of temperature (20–1000 °C) and oxygen partial pressure (0.6–21,000 Pa). According to the measurements, the composition was phase stable at pO 2 > 1 Pa up to 1000 °C and shows p-type semiconductivity with a low conductivity versus pO 2 dependence. The perovskite has been found to have comparable thermal expansion coefficients with those of commonly used solid electrolytes like CeO 2 and ZrO 2 based oxides. In case of the chemical diffusion experiments higher oxygen diffusion mobility observed during reduction processes in comparison with those during oxidation have been explained by the already known formation of neutral defect clusters.

On hyperbolic heat conduction in solids: minimum mean free path of energy carriers and a method of estimating thermal diffusivity and heat propagation characteristics

The paper gives the analytical solution to the one dimensional hyperbolic heat conduction equation in an insulated slab-shaped sample that is heated uniformly on the front face with δ or laser impulse. The solution results in a formula that enables to estimate the minimum mean free path of energy carriers in the sample to detect the second sound (i.e. the thermal wave) at the sample rear face. A method of experimental data evaluation at the second sound effect is proposed, which gives the thermal diffusivity of the sample and the parameters of heat propagation.