Laser Flash Method Research Articles

Thermal parameters of cylindrical power batteries: Quasi-steady state heat guarding measurement and thermal management strategies

In this work, a new quasi-steady state heat guarding measurement method for the thermophysical parameters of cylindrical batteries is proposed. The effectiveness of the heat guarding method is evaluated by the finite element analysis and the measurement of a standard ANSI 304 stainless steel sample. The heat loss is minimized to 2.4% maximum for cylindrical batteries under test based on numerical simulation. With the optimization of the test configuration, the experimental characterization of batteries was conducted to determine the thermal parameters accurately. The experimental results show that the axial thermal conductivity of 18650 and 21700 batteries are within 11.8–15.4 W·m−1 °C−1 and 12.6–16.7 W·m−1 °C−1, respectively, which are much lower than the material test values by the laser flash method. Axial thermal conductivity increases with temperature and SOC, and the specific heat increases linearly with temperature but varies little with SOC. This study demonstrates a fast, cost-effective and nondestructive way to obtain the axial thermal conductivity and specific heat of cylindrical batteries simultaneously and accurately. The subsequent thermal analysis on the thermal design of cylindrical batteries is also conducted based on the measured thermal parameters, which facilitate appropriate thermal management strategies for different types of cylindrical batteries.

Thermal properties of spark plasma sintered Inconel 625 modified by titanium zirconium mixed carbide

Nickel-based superalloys are an important group of advanced engineering materials used for high-temperature and/or corrosive environments. Lately, in order to improve their mechanical properties, carbide reinforcement is added to a metal matrix, creating composites of improved hardness, shear resistance, or tensile resistance. In order to preserve the wide applicability of those materials, thermal properties, and corrosion resistance must also be evaluated. Presented research evaluated the thermal properties of Inconel 625—(Ti,Zr)C0.85 composites obtained at 1000 °C by spark plasma sintering process. Sinters containing 5–20 mass% of carbide phases were initially characterized in terms of their density, phase composition, and microstructure. A thorough examination of their thermal properties included: dilatometry, laser flash analysis, and differential scanning calorimetry. Conducted experiments revealed that a growing amount of carbide reinforcement decreased the thermal diffusivity and conductivity of samples. Other materials had a nonlinear correlation with that parameter. Performed analysis allowed to make an initial evaluation of oxidation resistance at 800 °C. It was shown that above 5 mass% addition of (Ti,Zr)C0.85 there is a considerable mass gain change shown by samples during the first hour of oxidation before passive layers were created. Suitable chemical reactions were predicted in order to describe the oxidation process of obtained composites.

Numerical and analytical modelling of effective thermal conductivity of multi-walled carbon nanotubes polymer nanocomposites including the effect of nanotube orientation and interfacial thermal resistance

Multi-walled carbon Nanotube (MWCNT) fillers are extensively used to improve the thermomechanical properties of polymers. In this study, five different weight fractions (0%, 0.25%, 0.50%, 0.75%, and 1%) of MWCNT-polymer nanocomposites were prepared by the solution mixing technique. The thermal conductivity of MWCNT-polymer nanocomposites was investigated using the laser flash method. The closed-form solution of the modified Mori-Tanaka homogenization method was developed for the accurate estimation of the thermal conductivity of nanocomposite materials after considering the influence of interfacial thermal resistance (ITR). The finite element simulation of RVE modelling was utilized to predict the thermal conductivity of nanocomposites with and without consideration of the interfacial thermal resistance effect. A perfect bond was assumed between MWCNT and polymer for both numerical and analytical studies. The thermal conductivity results obtained from the closed-form solution of the modified Mori-Tanaka method were in good agreement with both the finite element simulation (FEM) and experimental results.

Thermal characterization of acrylonitrile butadiene styrene-ABS obtained with different manufacturing processes

Polymers are widely employed in many areas, e.g. transport, packaging, electronic devices, etcetera. Among them, acrylonitrile–butadiene–styrene (ABS) is one of the most employed polymers due to its mechanical properties, its ease to mechanize and recyclability. Nevertheless, according to the fire properties, ABS behaviour is usually worse than other polymers, therefore, they have to be upgraded with flame retardant additives. To characterize the fire behaviour of a certain material is necessary to address several typology of tests, providing relevant properties such as thermal conductivity, flammability and heat released. However, researchers may not always be able to run all tests due to the lack of apparatus or samples. Therefore, it is necessary to seek bibliographic sources. As one might expect, for a given material, the property values should be similar, regardless of who performs the test. However, sometimes slightly different results are obtained, which may be due to different causes, such as differences in test set-up and in material composition/manufacture. These differences in properties may lead researcher to doubt which data to use. This paper presents the results of different types of tests using neat ABS polymer. Additionally, these results are compared with the data from literature, discussing the similarities/differences and offering a more comprehensive characterization of ABS. The laboratory techniques included in this work are: thermogravimetric analysis, differential scanning calorimetry, laser flash analysis, smoke density, cone calorimeter, fire propagation and flammability.

Study on the micro conjugate heat transfer characteristics of coal reconstructed from CT images under the influence of temperature

Heat injection in coal seams, a new method to enhance gas drainage, is faced with problems such as low heat conduction efficiency and considerable heat dissipation. Based on experiments, this study reconstructed a micro heat transfer model through CT images to discuss the interaction between coal temperature rise-induced fracturing and the heat transfer performance of coal, which can provide a new insight into efficient heat injection and mining in coal seams. First, coal samples were modified by being heated at four temperatures and then scanned in situ by an industrial micro CT. Then, fractures were reconstructed by the interactive threshold segmentation and interactive top hat method to generate a 3D mesh model. Meanwhile, a conjugate heat transfer model including fracture fluid and coal matrix was established. Finally, the simulation result of thermal conductivity was compared with the results of the hot wire method and the laser flash method, and the influence of thermal fracturing structure evolution on coal heat transfer was analyzed. The following findings were obtained: The conjugate heat transfer model is applicable to fractured coal. The average relative error of its thermal conductivity is 5.85%, and it boasts high accuracy in characterizing heterogeneity and anisotropy. The fracture propagation and water evaporation of coal block heat transfer, while the adhesion and crystal contact surface expansion of heated coal are conducive to heat transfer. These two mechanisms compete, ultimately affecting the thermal conductivity. After the coal sample is heated within the temperature range of 40–100 °C, the fracture damage coalescence enhances the anisotropy of heat transfer in coal. The maximum difference in thermal conductivity between the bedding direction and the direction perpendicular to bedding is 0.181 W/(m·K), about 4.6 times larger than the initial difference. The research results lay a theoretical foundation for improving the heat transfer efficiency of heat injection in coal seams.

Thermal conductivity of the Cs-Pb system liquid alloys

ABSTRACT Thermal conductivity of liquid alloys of the caesium-lead system with a Pb content of 40, 50, 60, and 66.7 at. % is measured by the laser flash method in the temperature range from the liquidus line to 1173 K with an error of 4–6%. It is found that the thermal conductivity of the investigated alloys, obtained by mixing liquid metals Cs and Pb, drops by an order of magnitude to values: 0.5–4.0 W/(m K), characteristic of molten salts. It is shown that the thermal conductivity concentration dependence of the Cs-Pb system liquid alloys has a broad minimum near the equiatomic composition. An analysis of the obtained experimental data indicates the formation of a chemical short-range order in the liquid Cs-Pb system in the vicinity of the equiatomic composition, which indirectly confirms the existing ideas about the presence of Zintl complexes Cs4Pb4 in these melts.

The effects of interfacial thermal contact resistance between yarns and matrixes on the thermophysical property of the plain woven C/SiC composite

The plain woven C/SiC composites with high thermal shock resistance are widely used in aerospace applications. For this composite, thermal contact resistance (TCR) has an unneglectable contribution to the thermophysical property. In this work, the influence of the TCR on the thermophysical property of a real 2D plain woven C/SiC composite is studied. X-ray CT scanning is used to obtain the microstructures of the C/SiC composite, and the complex structures are restructured and transformed into standard cube grids based on the theory of the intersection of rays and triangles. Combining with finite difference method (FDM) and multiple GPUs acceleration, an efficient approach for numerically predicting the thermophysical property of the real C/SiC composite is established. Based on the Laser Flash Method (LFM) and Differential Scanning Calorimeter (DSC) method, the effective thermal conductivities (ETCs) of the C/SiC composite at different temperatures are obtained experimentally. The results show that ETCs predicted by our numerical method are closer to the measured ones when TCR is considered. Through the numerical simulation and theoretical analysis, the correlation between the ETC and TCR is obtained, which is proved to be a typical Logistic function, and the physical meanings of various constants in the correlation are determined and discussed. Besides, the thermal response time increases with the TCR increasing, simultaneously, the distributions of isotherms and heat-flux trajectories more approach the distributions of fiber yarns in the material.

Investigations on Thermal Conductivity of Two-Phase WC-Co-Ni Cemented Carbides through a Novel Model and Key Experiments

Excellent thermal conductivity is beneficial for the fast heat release during service of cemented carbides. Thus, thermal conductivity is a significant property of cemented carbides, considerably affecting their service life. Still, there is a lack of systematic investigation into the thermal conductivity of two-phase WC-Co-Ni cemented carbides. To remedy this situation, we integrated experiments and models to study its thermal conductivity varying the phase composition, temperature and WC grain size. To conduct the experiments, WC-Co-Ni samples with two-phase structure were designed via the CALPHAD (Calculation of Phase Diagrams) approach and then prepared via the liquid-phase sintering process. Key thermal conductivity measurements of these prepared samples were then taken via LFA (Laser Flash Analysis). As for modeling, the thermal conductivities of (Co, Ni) binder phase and WC hard phase were firstly evaluated through our previously developed models for single-phase solid solutions. Integrating the present key measurements and models, the values of ITR (Interface Thermal Resistance) between WC hard phase and (Co, Ni) binder phase were evaluated and thus the model to calculate thermal conductivity of two-phase WC-Co-Ni was established. Meanwhile, this model was verified to be reliable through comparing the model-evaluated thermal conductivities with the experimental data. Furthermore, using this developed model, the thermal conductivity of two-phase WC-Co-Ni varying with phase-fraction, temperature and grain size of WC was predicted, which can contribute to its design for obtaining desired thermal conductivities.

Influence of the matrix material on the thermal properties of the short carbon fiber reinforced polymer composites manufactured by material extrusion

In the past decades, additive manufacturing field has moved from prototyping to industrial applications. In this regard, the development of the new materials and their characterization is gaining importance. Most of the previous studies focused on the effect of fiber concentration and orientation on the material properties. However, the influence of the matrix material on composite thermal properties is not considered extensively. Therefore, the aim of this study is to investigate the thermal properties of the short carbon fiber reinforced polymer composites by varying the matrix material. The techniques included the Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry Analysis (DSC), Thermo-mechanical Analysis (TMA) and Laser Flash Analysis (LFA). According to the results, matrix material has high impact on the thermal conductivity and coefficient of thermal expansion, whereas the variation of the glass transition temperature and specific heat capacity is not changing significantly compared to the neat polymer. The study can be used as a design guideline to increase the quality of the printed parts.

A Mineralogical Model for Thermal Transport Properties of Rocks: Verification for Low-Porosity, Crystalline Rocks at Ambient Conditions

AbstractThermal conductivity (K) describes the response of matter to temporal or spatial variations in temperature (T). To quantify the effect of varying mineralogy on heat transport of rocks, an accurate (±2%) contact-free heat transfer method was applied at ambient T to multiple sections from 33 different low porosity, continental, igneous and metamorphic rocks. Thermal diffusivity (Dheat) was measured using laser-flash analysis, which was previously used to construct our large mineralogical database and which mitigates spurious radiative transfer found in other techniques. These measurements constrain K, because K is the product of Dheat with the known (or calculable) properties of density and specific heat measured at constant pressure (P). Compositions, proportions, and orientations of minerals, plus rock density, average grain-size (L), and porosity were characterized for 61 sections from 29 silicate rocks plus 5 sections from 3 marbles. Our database was used to evaluate component summation (averaging) formulae that were recently developed by considering Fourier’s laws, and to quantify the dependence of K and/or Dheat on key rock descriptors. We found that: (1) phase proportions and compositions are the main cause of variations; (2) minor porosity and foliation have minor effects; and (3) within ~5%, isotropic rocks follow Dheat = ½{[Σ(fi/Di)]−1 + Σ(fiDi)} where fi is volumetric mineral fraction, analogous to the Voigt-Reuss-Hill average for elastic moduli. Using this formula predictively depends on the accuracy of fi and Di. Quartzo-feldspathic rocks can be described by a new formula that uses only quartz fraction and plagioclase composition. Combining our mineralogical model with a universal formula for Dheat(T) and a thermodynamic identity for K(P) accurately constrains conductive thermal transport for Earth’s low porosity, crystalline rock layers.

Thermal and Mechanical Properties of Cu-Graphite Composites with Spatial Anisotropy

In the present study, we analyzed the thermal and mechanical properties of Cu-graphite composites (CGCs) with spatially anisotropic graphite layers. These composites were fabricated using a combination of electroless plating and spark plasma sintering (SPS) processes. Thermal conductivities and thermal expansion coefficients of the composites were measured using differential thermal analysis (DTA) and a laser flash method. In particular, the thermal expansion coefficients of the composites were investigated by comparative analysis, which was conducted by processing prototypes in a vertical direction with a parallel sector in the direction of the upper and lower axial pressure. The Cu reinforced with the graphite flake showed better thermal properties compared to the graphite fiber, while the graphite fiber led to better mechanical properties. This investigation was conducted to better understand the dependence of thermal properties on the morphologies of the graphite layers (i.e., flake and fiber types) in the Cu matrix. The bending strength and friction coefficient of the composites were also investigated. Taken together, the results from this work offer fruitful, yet practical information to utilize the CGCs as a thermal management material, essential for electric and electronic devices.

Inter-laboratory Comparison on Thermal Diffusivity Measurements by the Laser Flash Method at Ultra-high Temperature

Inter-laboratory Comparison on Thermal Diffusivity Measurements by the Laser Flash Method at Ultra-high Temperature

Density, Thermal Expansion, Enthalpy, Heat Capacity, and Thermal Conductivity of Calcium in the Temperature Range 720–1290 K

Thermophysical properties of solid and liquid calcium (99.75 wt % pure) were experimentally studied with high accuracy in the temperature range 720–1290 K using dilatometer measurements, gamma-ray attenuation measurements (the gamma-ray method), high-temperature drop calorimetry, and the laser flash method. The behaviors of the density, enthalpy, and thermal conductivity of calcium in the fusion–crystallization region were studied. The enthalpy of fusion was measured as 8075 J/mol, the relative density change upon fusion as 3.3%, and the relative change in thermal conductivity upon fusion as 26%. The results were compared to the respective values in the related literature. The measurements at temperatures above 720 K either significantly amend the available literature data, or are currently unique. The constancy of the heat capacity of liquid calcium in the temperature range 1115–1290 K was verified. Fitting equations were derived, and recommended values of the investigated properties of calcium were tabulated for 720–1290 K, the temperature range where calcium is in the condensed state.

Manufacturing of stereolithographic 3D printed boron nitride nanotube-reinforced ceramic composites with improved thermal and mechanical performance

Boron nitride nanotubes (BNNTs) are the perfect candidate for nanofillers in high-temperature multifunctional ceramics due to their high thermal stability, oxidation resistance, good mechanical properties, high thermal conductivity, and radiation shielding. In this paper, 3D printed ceramic nanocomposite with 0.1 wt% of BNNT was prepared by fusing it at high temperatures. Samples were built with three different print directions to study the effect of print layers on mechanical performance along with BNNT addition. Dynamic mechanical analysis is performed to study the length effect of nanoscale reinforcements on the mechanical properties of the printed ceramic composites reporting significant improvements up to 55% in bending strength and 72% in bending modulus with just 0.1 wt% BNNT addition. A 63% thermal diffusivity improvement of ceramic by adding BNNTs is observed using laser flash analysis. The bridging and pull-out effect of nanotubes with a longer aspect ratio was observed with high-resolution microscopy. Such composites’ modeling and simulation approaches are crucial for virtual testing and industrial applications. Understanding the effect of nanoscale synthetic fillers for 3D printed high-temperature ceramics can revolutionize future extreme environment structures.

Influence of carbon nanotubes on thermal and electrical conductivity of zirconia-based composite

Carbon nanotubes (CNTs) are widely used in ceramic-matrix composites (CMC) as a filler. An individual carbon nanotube exhibits extremely high thermal conductivity, however, the influence of CNTs on the thermal conductivity of CMCs is moderate. In contrast, even a small quantity of CNTs significantly increases the electrical conductivity of CMCs. The present paper studies this contradictory influence for ZrO2-CNTs composites with 3, 5, 10 and 20 vol% multi-wall carbon nanotubes (MWCNTs). Their thermal and electrical conductivity was studied by the laser flash method and electrochemical impedance spectroscopy. The analysis reveals that the moderate influence of MWCNTs on the thermal conductivity of composites originates from the similar thermal conductivity of MWCNTs in a bundle and zirconia. On the other hand, the substantial difference in the electrical conductivity of MWCNTs and zirconia leads to an exponential increase in the electrical conductivity of the ZrO2-CNTs composite even with small additions of nanotubes.

Application of Ferromagnetic Microwires as Temperature Sensors in Measurements of Thermal Conductivity

A method for the determination of the thermal conductivity of polymer composite materials by using Co-based ferromagnetic microwires is proposed. Microwire segments were integrated into the samples of studied materials during their manufacture and used as current microheaters and resistance thermometers. As a representative material, we used a material based on nitrile butadiene rubber filled with hexagonal boron nitride after its low-temperature carbonization and a significant increase in thermal conductivity. The thermal conductivity values of composite samples determined during experiments varied from 1.0 W/(m·K) to 1.8 W/(m·K) depending on the percentage of boron nitride. The thermal conductivity values obtained are in good agreement with the estimates obtained by the standard laser flash method.

Investigation on thermal conduction of graphite film enhanced carbon fiber polymer composite by laser flash analysis

Laser flash analysis (LFA) is an advantageous transient method, widely used for measuring thermal diffusivity of solid materials nowadays. In this paper, the thermal conductivity of graphite film enhanced carbon fiber composite was measured by LFA and the results show an unusual size-dependent effect which was considered to be due to violation of homogeneous assumptions. To investigate the size effect, numerical analyses based on the representative volume element (RVE) models were implemented to evaluate the thermal conductivities of composites with periodic microstructures. Transient periodic boundary conditions (PBCs) were proposed and applied to the RVEs for simulating the LFA. Transient simulative results obtained by applying PBCs verify the size effect and are in better agreement with the experimental data than those obtained by applying conventional adiabatic conditions. Moreover, the classical steady-state analyses on RVEs were performed for comparison. The reason for size effect was discussed in details. The present work expands the application scope of LFA to measuring thermal conductivity of complex composite and provides a perception of discreetly selecting specimen size and modifying the general LFA technique.

Hydrothermal synthesis of a novel expanded vermiculite/xonotlite composite for thermal insulation

Natural disasters caused by global warming are threatening the survival of mankind. Reducing carbon emissions is an effective way to prevent global warming. In recent years, the construction industry is playing a dominant role in global energy consumption. Aimed to solve the problem of high energy consumption in the construction industry, a novel expanded vermiculite/xonotlite thermal insulation composite was successfully prepared via the hydrothermal method. The microstructure and thermal performance of the composite were systematically analyzed using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), laser flash analysis (LFA), and infrared thermal imaging. The test results indicated that xonotlite fibers could be inserted well into the interlayers of expanded vermiculite. And the intercalation of xonotlite greatly improved the thermal insulation performance of expanded vermiculite at high temperature. The thermal conductivity of this composite decreased with intercalation rate increasing. The composite with intercalation rate of 51.43 % had the lowest thermal conductivity of 0.2116 W/mK at 800 °C which was 55.36 % lower than the expanded vermiculite sample. Meanwhile, this composite had good thermal stability and high temperature resistance. In addition, the thermal expansion of vermiculite and the synthesis of nano-xonotlite fibers were comprehensively studied and discussed. This study will provide a new perspective and ideas for developing vermiculite-based thermal insulating materials.

Thermophysical properties of zinc gallate

Complex spinel oxides AB 2 O 4 are inorganic materials, which, due to their refractoriness and a whole range of functional properties, are widely in demand in various fields of the power industry and electronics. This paper reports on the results of an experimental study of the thermophysical properties of zinc gallate, which is a promising material for optoelectronics, solid-state lighting and catalytic and biomedical applications. Highly dispersed single-phase ZnGa 2 O 4 powder was synthesised by gel combustion. As a result of high-temperature sintering of pressed powder blanks, ZnGa 2 O 4 ceramics (≈95% of the theoretical) were produced. According to SEM, the material has a dense microstructure consisting of micron-sized spinel grains. The heat capacity of the material produced was investigated by relaxation, adiabatic and differential scanning calorimetry. By combining experimental data in the range of 8.7–1276 K, a single consistent temperature dependence of ZnGa 2 O 4 heat capacity was obtained for the first time. The analysis of the curve obtained showed no signs of phase transitions in the studied temperature range. Based on the results of calorimetric measurements within the range 0 K–1276 K, the temperature dependences of heat capacity, entropy, enthalpy change and Gibbs energy function were calculated. The absolute entropy of ZnGa 2 O 4 spinel at 298.15 K was 120.23 J/(K·mol). The thermal diffusivity of ZnGa 2 O 4 ceramics measured by laser flash method was 2.6 mm 2 /s at 300 K, decreasing to 0.46 mm 2 /s at 1174 K. Its thermal conductivity calculated using experimental data on heat capacity and thermal diffusivity at room temperature was 7.6 W/(m·K). The obtained data are of interest in terms of improving materials based on ZnGa 2 O 4 , which are promising for use in light-emitting diodes and new-generation power semiconductor devices. • Ultra-fine ZnGa 2 O 4 powder was synthesised by a PVA-assisted gel combustion method. • High-density ZnGa 2 O 4 ceramics with micrometre-sized grains (>1 μm) were produced. • The temperature dependence of heat capacity was measured from 8.7 K to 1276 K. • Thermal diffusivities and thermal conductivities of the ceramics prepared were studied.

Thermal conductivity of alumina-carbon composite brick and its related phase analysis in a dissected blast furnace

Excellent performance of refractories in blast furnace hearth is one of the important factors to ensure longevity of blast furnaces. As an emerging refractory for application in blast furnace, alumina-carbon composite brick combines the superior properties of carbon and alumina. Firstly, the thermal conductivity of alumina-carbon composite brick was measured by the laser flash method and the new device method to verify the feasibility of the new device method for thermal conductivity measurement. Secondly, the influence of heating temperature of the heating furnace and cooling water flow on the thermal conductivity of the alumina-carbon composite brick, and the comparison of the thermal conductivity of carbon brick, alumina-carbon composite brick and corundum brick were investigated to confirm the heat transfer mechanism of alumina-carbon composite brick. High thermal conductivity and erosion resistance to slag and hot metal of the alumina-carbon composite brick are consequent from: (a) reasonable composition combination of Al2O3, C, SiO2, SiC, etc., (b) dense structure, small pore diameter, and uniform distribution of the pores, (c) the generated SiC whiskers and Al6Si2O13, which can fill in the pores and reduce the porosity. Finally, the analysis on the phase distribution of the alumina-carbon composite brick in a dissected blast furnace was performed to illustrate the relationship between the erosion resistance and the thermal conductivity of alumina-carbon composite brick.