Thermophysical Properties Of Materials Research Articles

Preparation and characterization of a heat storage material: Shape-stabilized KNO3 using a modified diatomite-based porous ceramic as the skeleton

The applications of salts-based phase change materials (PCMs) are greatly restricted by their corrosion to containers and low thermal conductivity. To address these issues, a modified diatomite-based porous ceramic (MDPC) was prepared to shape-stabilize KNO3 salt in this paper. Particularly, effects of graphite content on the pore structure of diatomite-based porous ceramic (DPC) and MDPC on the thermophysical properties of shape-stabilized KNO3 were investigated. The results showed that 30 wt% graphite increased apparent porosity of DPC up to 67.21% and enlarged average pore diameter from 0.71 to 3.58 μm, while weakened its compressive strength from 19.12 to 5.51 MPa. The MDPC effectively prevented leakage of molten KNO3 to avoid its corrosion problem, and possessed an excellent chemical compatibility with KNO3 salt. Additionally, the MDPC hardly changed phase transition temperature of shape-stabilized KNO3, while increased latent heat of composites from 51.70 to 60.21 J/g due to its higher apparent porosity. The MDPC was also shown to enhance thermal conductivity of shape-stabilized KNO3 from 1.16 to 1.52 W/(m·K) at 25 °C, which was attributed to that the MDPC with a larger pore size was more easily infiltrated by molten salt, contributing to a lower apparent porosity of composites. Compared with pure KNO3, thermal conductivity and thermal stability of shape-stabilized KNO3 were seen to be significantly improved by 238% and 60 °C, respectively. This work therefore solved two key challenges for the application of KNO3 salt, and proposed an effective way to improve thermophysical properties of such heat storage material.

Study on heat transfer characteristics of hollow composite thermal barrier structure at high temperature

Air interlayers are often used as a part of thermal insulation structure and form a system with solid materials to reduce heat transfer. However, the heat transfer process in the composite structure is affected by many factors at high temperatures. In this paper, a series of heat preservation systems with air gap and solid structure were proposed. Based on the research background of heat preservation in the riser of ingot casting, the heat transfer process in the composite structure was systematically studied by means of numerical simulation and experiment. The heat transfer laws under different geometric structures, thermophysical properties of materials, and surface emissivity were obtained, which could provide theoretical basis for the design of heat preservation structures at high temperatures.

The Moon at thermal infrared wavelengths: a benchmark for asteroid thermal models

Thermal-infrared measurements of asteroids, satellites, and distant minor bodies are crucial for deriving the objects’ sizes, albedos, and in some cases, also the thermophysical properties of the surface material. Depending on the available measurements and auxiliary data, such as visual light curves, spin and shape information, or direct size measurements from occultations or high-resolution imaging techniques, a range of simple to complex thermal models are applied to achieve specific science goals. However, testing these models is often a difficult process and the uncertainties of the derived parameters are not easy to estimate. Here, we make an attempt to verify a widely accepted thermophysical model (TPM) against unique thermal infrared (IR), full-disk, and well-calibrated measurements of the Moon. The data were obtained by the High-resolution InfraRed Sounder (HIRS) instruments on board a fleet of Earth weather satellites that serendipitously scan the surface of the Moon. We found 22 Moon intrusions, taken in 19 channels between 3.75 μm and 15.0 μm, and over a wide phase angle range from −73.1° (waxing Moon) to +73.8° (waning Moon). These measurements include the entire Moon in a single pixel, seen almost simultaneously in all bands. The HIRS filters are narrow and outside the wavelength regime of the Christiansen feature. The similarity between these Moon data and typical asteroid spectral-IR energy distributions allows us to benchmark the TPM concepts and to point out problematic aspects. The TPM predictions match the HIRS measurements within 5% (10% at the shortest wavelengths below 5 μm) when using the Moon’s known properties (size, shape, spin, albedo, thermal inertia, roughness) in combination with a newly established wavelength-dependent hemispherical emissivity. In the 5–7.5 μm and in the 9.5–11 μm ranges, the global emissivity model deviates considerably from the known lunar sample spectra. Our findings will influence radiometric studies of near-Earth and main-belt asteroids in cases where only short-wavelength data (from e.g., NEOWISE, the warm Spitzer mission, or ground-basedM-band measurements) are available. The new, full-disk IR Moon model will also be used for the calibration of IR instrumentation on interplanetary missions (e.g., for Hayabusa-2) and weather satellites.

Layered ceramics based on InGaO3(ZnO)2: Preparation and experimental investigation of high-temperature heat capacity and thermal conductivity

This paper reports on a method for producing ceramics from a high-purity, submicron InGaO3(ZnO)2 powder synthesised using a PVA-assisted gel combustion method, as well as an experimental study of the thermophysical properties of the ceramic materials obtained. The platelet-like crystallites of the InGaO3(ZnO)2 obtained were several microns long and up to several hundred nanometres thick. Layered ceramics obtained by sintering compacted InGaO3(ZnO)2 powders at temperatures of 1373–1773 K had a bulk density that was 68–96 % of the theoretical density. The temperature dependence of heat capacity in the range 306–1346 K was studied experimentally for InGaO3(ZnO)2 using the DSC method. It was found that, in the range 323–1173 K, layered InGaO3(ZnO)2 ceramics had a low thermal conductivity, which decreased from 2.0–1.3 W/(m K. The results obtained make it possible to consider this material as a promising thermal barrier coating.

Origami-based metamaterial with switchable abnormal expansion function

The coefficient of thermal expansion (CTE) is an important parameter for the thermophysical properties of materials. Mostly, in aerospace engineering, satellites, hypersonic vehicles, precision instruments and microelectronic packages, numerous thermal deformation structures in severe environment full of drastic temperature changes are required to be controlled precisely. Therefore, the development of adjustable thermal expansion materials is of significance in engineering applications. Based on the Miura-ori structure, this paper adopts materials with respectively diverse CTEs as components to generate thermal stresses mismatch principle and proposes a design method for origami metamaterials with adjustable in situ positive/negative/zero expansion functions. Employing the methods of finite element calculation and deformation analysis, the deformation results of this metamaterial are displayed and discussed. Also, an origami metamaterial with adjustable positive/negative/zero expansion function can be obtained by adjusting the material distribution of the structure. Moreover, the mapping relationship between the folding angle and the geometric parameter of the structure is established. In the light of this design method of tunable CTE metamaterials, additionally, the metamaterial can achieve precise control of thermal deformation and optimize service reliability in extreme environments.

Effect of interstitial compounds in controlling thermal contact conductance across pressed joints at cryogenic temperature and low contact pressure

• Study of thermal contact conductance across joints at low temperature and contact pressure. • Effect of interstitials across joints formed with combinations of AA2219, Ti6Al4V and AISI 321. • Silicon compound enhances thermal contact conductance up to 25 times while acrylate sealant enhances by 8 times. • Epoxy adhesive coating reduces thermal contact conductance by about 50%. • Design monograms are generated to aid selection of joints and interstitials. Heat transfer across pressed joint is significantly governed by thermal contact conductance which in turn depends on thermophysical properties of materials in contact, surface properties, contact pressure, working temperature and interstitials present at the interface. Application of interstitials is an effective technique to control thermal contact conductance at ambient temperature. In the present study, thermal contact conductance across joints at cryogenic temperature in presence of interstitials like silicon based conductive compound, epoxy based adhesive layer and acrylate based anaerobic sealant are explored. These interstitials have different thermophysical characteristics and retain their properties at cryogenic temperature. The joints are investigated for low contact pressure applications, for which thermal contact conductance control is difficult. Specimens are made from cryogenic compatible alloys namely Aluminium alloy AA2219, Stainless steel AISI 321 and Titanium alloy Ti6Al4V with a surface roughness of 0.9 µm. Each interstitial is applied across all six similar and dissimilar pressed joints formed between the materials and thermal characteristics are evaluated experimentally. Investigation is carried out over a temperature range of 150 K to 300 K, with a contact pressure of 140 kPa. The silicon compound enhances thermal contact conductance up to 25 times that of a bare joint while acrylate sealant enhances up to 8 times. The epoxy adhesive coating reduces thermal contact conductance by about 50%. Based on results, monograms are generated for joints based on thermal contact conductance and enhancement factor observed .

Systematic exploration of the L-PBF processing behavior and resulting properties of β-stabilized Ti-alloys prepared by in-situ alloy formation

Aim of this work is to gain a comprehensive understanding of the effects of an increasing β-phase stability of Ti-alloys on the L-PBF processing behavior. For this purpose, seven different Ti-alloys with an increasing concentration of the β-phase stabilizing elements Fe and V were prepared by L-PBF and in-situ alloy formation. The Molybdenum equivalent (Moeq) of the examined alloys, as a measure of β-phase stability, was varied systematically between −3.3 and 25. It is shown that a homogeneous distribution of elements is achievable by in-situ alloying. The experiments prove that the investigated alloys can be processed by a single L-PBF parameter set with high relative density above 99.8%. This finding is substantiated by calculated thermo-physical material properties and an analytical model. To understand the underlying metallurgical effects governing the L-PBF results, the samples were investigated extensively by EDS, EBSD, XRD, light microscopy and compression tests. The β-phase fraction varies in dependence of the Moeq between 0% and 99%. Because of rapid solidification inherent in L-PBF a Moeq of 10 is sufficient to receive more than 90% β-phase. The same amount of β-phase after furnace cooling was only observed in alloys with Moeq of 20 or more. While all alloy compositions can be processed with high relative density of over 99.8%, alloys with a Moeq between 15 and 20 show a brittle material behavior in as-built state, resulting in cracking during L-PBF. This behavior is attributed to the formation of ω-phase during L-PBF. In contrast, the highest β-stabilized alloy with a nominal Moeq of 25 exhibits a very high ductility with a fracture strain exceeding 50%.

Nanofluids Characterization for Spray Cooling Applications

In this paper the mathematical and physical correlation between fundamental thermophysical properties of materials, with their structure, for nanofluid thermal performance in spray cooling applications is presented. The present work aims at clarifying the nanofluid characteristics, especially the geometry of their nanoparticles, leading to heat transfer enhancement at low particle concentration. The base fluid considered is distilled water with the surfactant cetyltrimethylammonium bromide (CTAB). Alumina and silver are used as nanoparticles. A systematic analysis addresses the effect of nanoparticles concentration and shape in spray hydrodynamics and heat transfer. Spray dynamics is mainly characterized using phase Doppler interferometry. Then, an extensive processing procedure is performed to thermal and spacetime symmetry images obtained with a high-speed thermographic camera to analyze the spray impact on a heated, smooth stainless-steel foil. There is some effect on the nanoparticles’ shape, which is nevertheless minor when compared to the effect of the nanoparticles concentration and to the change in the fluid properties caused by the addition of the surfactant. Hence, increasing the nanoparticles concentration results in lower surface temperatures and high removed heat fluxes. In terms of the effect of the resulting thermophysical properties, increasing the nanofluids concentration resulted in the increase in the thermal conductivity and dynamic viscosity of the nanofluids, which in turn led to a decrease in the heat transfer coefficients. On the other hand, nanofluids specific heat capacity is increased which correlates positively with the spray cooling capacity. The analysis of the parameters that determine the structure, evolution, physics and both spatial and temporal symmetry of the spray is interesting and fundamental to shed light to the fact that only knowledge based in experimental data can guarantee a correct setting of the model numbers.

Development of thermoplastic composite materials based on modified polypropylene

To improve the physical-mechanical and thermophysical properties of polypropylene-based thermoplastic composite materials, we performed modification of a polymer matrix by reactive extrusion of polypropylene in the presence of benzoyl peroxide and polysiloxane polyols. Modified polypropylene was compounded with basalt, carbon, and para-aramide reinforcing fillers in a screw-disc extruder. It was established that the reinforcement of modified polypropylene by basalt fibers ensured a 110% increase in tensile strength. The reinforcement of modified polypropylene by carbon fibers allowed fabricating thermoplastic composite materials with tensile strength increased by 14%. The maximum reinforcing effect was observed by using para-aramide fibers as reinforcing fibers for modified polypropylene with tensile strength increased by 30% as compared with initial polypropylene. It was determined that the obtained thermoplastic composite materials based on modified polypropylene can be processed into products by the most productive methods (extrusion and injection molding). The developed materials exhibited improved thermal stability. The proposed ways of modification methods provide substantial improvement in physical-mechanical and thermophysical properties of modified polypropylene-based thermoplastic composite materials as compared with initial polypropylene. In addition, they ensure a significant increase in service properties of the products prepared from thermoplastic composite materials based on modified polypropylene.

Direct Characterization of Thermal Nonequilibrium between Optical and Acoustic Phonons in Graphene Paper under Photon Excitation.

Raman spectroscopy has been widely used to measure thermophysical properties of 2D materials. The local intense photon heating induces strong thermal nonequilibrium between optical and acoustic phonons. Both first principle calculations and recent indirect Raman measurements prove this phenomenon. To date, no direct measurement of the thermal nonequilibrium between optical and acoustic phonons has been reported. Here, this physical phenomenon is directly characterized for the first time through a novel approach combining both electrothermal and optothermal techniques. While the optical phonon temperature is determined from Raman wavenumber, the acoustic phonon temperature is precisely determined using high‐precision thermal conductivity and laser power absorption that are measured with negligible nonequilibrium among energy carriers. For graphene paper, the energy coupling factor between in‐plane optical and overall acoustic phonons is found at (1.59–3.10) × 1015 W m−3 K−1, agreeing well with the quantum mechanical modeling result of 4.1 × 1015 W m−3 K−1. Under ≈1 µm diameter laser heating, the optical phonon temperature rise is over 80% higher than that of the acoustic phonons. This observation points out the importance of subtracting optical–acoustic phonon thermal nonequilibrium in Raman‐based thermal characterization.

Modeling measurement situation in intelligent information and measurement system to determine thermo-physical properties of materials

Definition of thermo-physical properties in different thermal conductivity ranges of solid materials causes the need to consider numerous affecting factors, to create an information environment and model the measurement situation in the operation of intelligent information and measurement system. The purpose of the study is to reduce the measurement error of thermo-physical properties in materials. This problem is relevant and important in the process of controlling the reference parameters of products at the manufacturers. A theoretical framework for modeling the measurement situation is developed. This includes a conceptual model for the formation of the measurement situation, and a model of the research object domain. A mathematical model of the measurement situation and the methodology of its development is created. The problem of selecting the type of measurement situation in the range of investigated materials in terms of thermal conductivity is solved. The risk calculation algorithm of forming a measurement situation in an intelligent information and measurement system for determining the thermo-physical properties of materials is developed.

Modeling of thermal processes in construction of nonrigid pavements using bitumen concrete mixes

The remoteness of the construction site from the production base, large volumes of work, insufficient productivity of asphalt concrete plants for the preparation of hot asphalt concrete mixtures makes urgent the use of cold bitumen concrete mixes for the road construction. The preliminary mix preparation on the production sites with preservation of its properties for several months allows to increase the duration of the construction season. Purpose. Quality improvement of construction of non-rigid road surfaces using cold bitumen concrete mixes. Materials and methods. Models of road pavement structure based on cold bitumen concrete mixes are proposed to clarify the influence of the structural, climatic, technological and thermophysical properties of materials on the pavement quality. Research results. It is shown that the construction of road surfaces using cold bitumen concrete mixes even at positive ambient temperatures, does not provide the required surface quality. Conclusions. To improve the road paving quality using cold bitumen concrete mixes is necessary to heat the base before laying the cold mix. The heating temperature of the base depends on the layer thickness and ambient temperature.

Prediction of the Minimum Film Boiling Temperature of Quenching Vertical Rods in Water Using Random Forest Machine Learning Algorithm

A great amount of research is focused, nowadays, on experimental, theoretical, and numerical analysis of transient pool boiling. Knowing the minimum film boiling temperature (Tmin) for rods with different substrate materials that are quenched in distilled water pools at various system pressures is known to be a complex and highly non-linear process. This work aims to develop a new correlation to predict the Tmin in the above process: Random forest machine learning technique is applied to predict the Tmin. The approach trains a machine learning algorithm using a set of experimental data collected from the literature. Several parameters such as liquid subcooling temperature (Tsub), fluid to the substrate material thermophysical properties (βf/βw), and system saturated pressure (Psat) are collected and used as inputs, whereas Tmin is measured and used as the output. Computational results show that the algorithm achieves superior results compared to other correlations reported in the literature.

An experimental and straightforward approach to simultaneously estimate temperature-dependent thermophysical properties of metallic materials

This article describes an experimental and straightforward technique towards the simultaneous estimation of temperature-dependent thermal conductivity and specific heat of metals. The thermal model is based on transient nonlinear one-dimensional heat conduction across a metallic sample, which is subject to a constant heat flux on the upper side, and insulated on the bottom side. The thermal analyses are performed in plates of 304 stainless steel and WC10Co cemented carbide. The Levenberg–Marquardt method is employed to provide the solution to an inverse heat conduction problem capable of simultaneously evaluating the temperature-dependent thermophysical properties using transient temperature measurements. Through sensitivity analysis, it is possible to obtain prior information about estimation feasibility and establish all experimental aspects. The imperfect contact at the heater-plate interface causes contact resistance effect, which is considered a reducing agent on heat flux. Beck's nonlinear function minimization technique is used to confirm the reliability of the inverse estimation technique by using the achieved outcomes to recover the heat flux imposed on the test plate. Furthermore, the statistical study into confidence bounds and comparison with literature reveal the robustness of the results. Finally, the accuracy of the developed approach is investigated through the analysis of the errors deriving from experimental and numerical procedures.

Modelling and Simulation of Thermo-Physical Property of Composite Material

Thermo-physical property measurement is a significant methodology as these properties are the input for designing thermal systems. Properties of materials like thermal conductivity, thermal diffusivity and specific heat capacity has to be estimated in prior to estimate the thermal performance of any material. In the present work, numerical simulations were performed to estimate the thermo-physical properties of a polymer based composite material using porous medium modelling. The weight fraction of the composites and fibres are incorporated into the simulations through porosity. The transient heat diffusion equation are solved using ANSYS Fluent for a polymer based composite material using semi-infinite transient conduction approach. The thermal conductivity and thermal diffusivity are estimated simultaneously for various volume fractions of polyester and banana fibre. The temporal temperature distribution data predicted from ANSYS Fluent is curve fitted using MATLAB and the obtained values of thermal conductivity and thermal diffusivity are compared with the previously reported experimental results and are found to be within a deviation of 7 % for all cases.

Simulation of laser cladding of a wear-resistant coating hardened with Al2O3 particles

The article is concerned with the matters of formation of heat fluxes during laser fusion of coating of the NiCrBSi system hardened with the addition of aluminum oxide fine powder. It is based on the simulation of the process of heating and melting of the CW coating with a laser and the specified thermophysical properties of the base material, coating and hardening additive of aluminum oxide powder. The numerical solution of the differential equations system is obtained and the temperature distribution in the coating over the thickness is determined depending on the power and time of action of the heat source. The obtained diagrams are analyzed, on the basis of which it is proposed to choose the parameters of laser processing. The prospects of applying a coating using the laser cladding technology to protect against wear of steel friction surfaces and restore hardened steel parts of friction assemblies are shown.

Structure Domain Size of Carbon Fibers

The internal micro-structure is an important factor affecting the thermal conductivity of materials. In this work, the relationship between micro-structure, thermal conductivity, and temperature variation for carbon fibers (CF) are systematically studied by using the transient electrothermal technique. When the temperature is below the critical temperature (about 110 K), the internal structure of carbon fiber deteriorates, resulting in a very different behavior of thermal conductivity variation with temperature. By introducing the thermal reffusivity theory, the structure domain size of CF can be represented by the phonon mean free path at 0 K. The thermal reffusivity change of two temperature ranges is studied, and the mean free path of phonons in CF before and after deterioration can be calculated as 317 nm and 234 nm, respectively. The results are in good agreement with the crystallite grain size of 288 nm determined by Raman study. The thermal reffusivity provides another feasible method to study the relationship between structure domain size and thermophysical properties of materials.

Segregation/cycling effects on thermophysical properties of salt hydrate phase change materials

AbstractEnergy storage systems designers normally use the thermophysical properties of phase change materials (PCMs) from the manufactures/suppliers data sheet. Unfortunately, sometimes PCMs systems do not behalf according to supplier data sheet, especially after cycling use. Designing systems based on these unrealistic data sheet make the system operates at off design conditions most of time. The problem is substantially appears in salt hydrates PCMs systems. In this short communication, a case study of such discrepancies in air free cooling is addressed. The system design was based on SP24E PCM data sheet, but results showed that liquids and solidus lines cannot shown on the temperature transient history during charging and discharging process, and complete solidification and melting could not be obtained. For further detailed investigations; differential scanning calorimeter (DSC) tests were conducted for SP24E PCM and completely different results than supplier data sheet were obtained DSC tests showed (a) a wide range of temperature variation during melting and solidifications, (b) phase change starts and ends at lower temperatures compared with supplier data sheet, and (c) phase change latent heat is lower than the one listed in supplier data sheet.

The generalized periodic boundary condition for microscopic simulations of heat transfer in heterogeneous materials

Porous and composite materials have been increasingly used in many heat transfer applications due to their enhanced thermal performance, and extensive studies have been conducted for a better scientific understanding of the heat transfer processes in such materials especially at the microscopic level. For heterogeneous materials with periodic microscopic structures, analysis can be performed over one such periodic unit if appropriate boundary conditions are applied. However, assumptions with no mathematical or physical justifications are often involved in previous studies, and this casts doubt on the accuracy and reliability of these results. In this study, a new set of boundary conditions are established based on rigorous mathematical derivations. The classical periodic boundary condition is generalized to incorporate the temperature differences between each pair of opposite boundaries of the periodic unit, and the global thermal gradient can be applied in arbitrary directions relative the structural periodicity. Also the interface between constituents in composite materials (or the fluid-solid interface in porous materials) is modeled according to the conjugate condition. This explicit approach incorporates the thermophysical properties of individual constituent materials and the possible thermal resistance at constituent interface, and thus provides a more complete and realistic representation of the heterogeneous system. This method with the generalized periodic boundary condition (GPBC) is carefully validated by comparing the temperature fields and effective conductivity for a two-dimensional (2D) heterogeneous model obtained from a direct simulation of a large domain size without using our boundary method and from one-unit simulations but with various periodic unit selections. The excellent agreement observed in these results indicates that our GPBC method correctly and accurately represents the underlying relationships in the thermal fields among periodic units. We also compare the simulation results for a 2D heterogeneous model with inclined poor conductivity rods in the middle, using our GPBC method and the insulated unit method (IUM) in previous publications; and remarkable differences in temperature fields and heat flux patterns are observed. Analysis and discussions are provided to show the unrealistic features in the IUM results due to the artificial assumptions on the boundary conditions. On the other hand, the temperature field from our GPBC method is consistent with intuitive physical considerations. The effects of constituent composition, conductivity and interface conductance on the effective thermal conductivity for a simple 2D heterogeneous material model, as well as the thermal flows with different Reynolds and Prandtl numbers through a staggered array of square blocks, are also examined. Despite the model simplicity, several interesting features are noticed, such as the heat flux response to changes in constituent conductivity and interface resistance and the saturation states of effective conductivity. Such information is valuable for a better understanding of the complex relationships between the microscopic structure and properties and the macroscopic thermal performances of composite and porous materials. The GPBC method developed in this work can also be readily implemented in typical numerical techniques in computational heat transfer such as the finite volume method, finite element method, and lattice Boltzmann method.

Measuring thermophysical properties of building insulation materials using transient plane heat source method

Thermophysical properties of building insulation materials vary with environmental and intrinsic factors, and accurate measurement of them is quite difficult and essential. This study aims to create a transient measuring method based on two transient plane heat source methods, including the constant heat rate source method and step-wise transient method through constructing a device. The present method is able to measure multiple thermophysical properties of various building insulation materials. The measurement errors of thermal conductivity are less than 3% for the EPS board and 5% for the XPS board. The measured thermal conductivities are much lower than those reported in the literatures for the foam glass board and cement foam board due to the difference in density of specimens. The measured thermal diffusivities and reference values have the same order of magnitude. A new data processing approach was investigated to obtain the thermal effusivities of the experimental materials; all measured values are close to those reported in previous studies. It is concluded that the created method is effective for the facile and accurate measurement of multiple thermophysical properties of the building insulation materials, and the findings can significantly improve the database of thermophysical properties for building insulation materials.