Heat Conduction In Materials Research Articles

Study of the thermal measurement depth of a skin calorimeter using simple RC and TF models

An experimental and theoretical study of the heat capacity thermal measurement depth of a skin calorimeter has been carried out. This calorimeter consists of a thermopile placed between a thermostat and an aluminum measuring plate, which is placed on the sample to be measured. We performed simulations using the finite element method (FEM) with inert samples of different sizes. From these simulations, Transfer Functions (TFs) between the calorimeter's thermostat temperature and the temperature of the measuring plate were determined. Compact thermal models (RC models) able to determine the heat capacity of the sample were also determined. We conclude that, in the case of heat-conducting materials, a single time constant is enough to represent the TF. However, at least two time constants are required for heat-insulating materials. In this work we also studied the time dependence of the thermal measurement depth, concluding that this dependence is exponential. Finally, we present some experimental measurements performed on inert samples and on human skin, which are coherent with the results of the simulation.

Flexible heat-conductive polyimide composite materials

Flexible heat-conductive polyimide composite materials

Study on Extraordinarily High-Speed Cutting Mechanics and Its Application to Dry Cutting of Aluminum Alloys with Non-Coated Carbide Tools

The friction/adhesion between the tool and chip is generally large in metal cutting, and it causes many problems such as high cutting energy/rough surface finish. To suppress this, cutting fluid and tool coating are used in practice, but they are high in energy/cost and environmentally unfriendly. Therefore, this paper investigates the extraordinarily high-speed cutting (EHS cutting) mechanics of mainly soft and highly heat-conductive materials and proposes their application to solve the friction/adhesion problem in an environmentally friendly manner. In order to clarify the EHS cutting mechanics, a simple analytical model is constructed and experiments are conducted with measurement of the cutting temperature and forces. As a result, the following points are clarified/found: (1) heat softening at the secondary plastic deformation zone rather than the primary plastic deformation zone, (2) friction coefficient drop to 0.170 in EHS cutting, and (3) gradually increasing trend of cutting temperature in EHS cutting. Finally, EHS cutting is applied to dry cutting of aluminum alloys with a non-coated carbide tool and compared to conventional wet cutting with a DLC-coated carbide tool, and it is shown that a coating/coolant can be omitted in this region to achieve environmentally friendly cutting.

Influence of an inclined thick partition on free convection heat transfer performance under surface radiation in a hollow block

In the present work, a computational analysis of the combined energy transfer by free convection, radiation, and heat conduction in 2D hollow block with an inclined partition was carried out. The inclined partition was made of a heat-conducting material and had a finite thickness. The closed space inside the brick was filled with air (Pr = 0.71) and the airflow is laminar. The external surfaces of the vertical borders are considered to be isothermal, and the remaining horizontal surfaces are supposed to be adiabatic. The finite difference technique is employed to work out numerically the differential equations. The in-house computational code was verified in detail using various problems. The major characteristics that determine the considered phenomena are surface emissivity of internal walls, Ra number, and material of solid walls and partition. As a result of the research, the distributions of streamlines and isotherms combined with the average Nusselt numbers were obtained. Depending on the material of the partition, the flow structure in the cavity changes significantly, which reflects the distribution of streamlines, namely, for the materials with low thermal conductivity the convective cell in the upper part of the cavity is elongated, while in the lower part it is shifted to the lower and left borders. The isotherms reflect the more intensive heating in the left part of the area. With an increase in the thermal conductivity coefficient, the streamlines reflecting the nature of the flow are restructured. It was shown that the presence of an inclined partition significantly reduces the intensity of convective heat transfer.

Programmable and Surface-Conformable Origami Design for Thermoelectric Devices.

Thermoelectric devices (TEDs) show great potential for waste heat energy recycling and sensing. However, existing TEDs cannot be self-adapted to the complex quadratic surface, leading to significant heat loss and restricting their working scenario. Here, surface-conformable origami-TEDs (o-TEGs) are developed through programmable crease-designed origami substrates and the screen-printing TE legs. Compared with "π" structured TEDs, the origami design (with heat conductive materials) changed the heat-transferring direction of the laminated TE legs, resulting in an enhancement in enlarging ΔT/THot and Vout by 5.02 and 3.51 times. Four o-TEDs with different creases designs are fabricated to verify the heat recycling ability on plane and central quadratic surfaces. Demonstrating a high Vout density (up to 0.98-2 at ΔT of 50K) and good surface conformability, o-TEDs are further used in thermal touch panels attached to multiple surfaces, allowing information to be wirelessly transferred on a remote display via finger-writing.

Investigation of the combination of microwave heating and calcium alginate capsule rejuvenation healing methods for cold mix asphalt considering the type of compaction effort

Healing behavior of asphalt mixes can affect the pavement life and life cycle cost. Effects of encapsulated rejuvenators and microwave heating methods (as two approaches to improve self-healing behavior) on the cold mix asphalt (CMA) were studied separately and simultaneously at different compaction conditions (i.e., different types and levels of compaction). For this aim, capsules of calcium alginate (CAG) loaded with waste sunflower oil (WSO) and waste engine oil (WEO) were used as encapsulated rejuvenators and iron (Fe) powder was used as a heat conductive material to spread microwave heating into the samples. Moreover, the synergetic effect of powder-based heat-absorbing additives and encapsulated rejuvenators on the healing performance (HP) was also investigated. The chemical test results showed that the Fe powder is compatible with the bitumen emulsion. Pre- and post-healing semi-circular bending (SCB) fracture experiments were conducted before and after healing to check for the effect of the healing method and compaction effort on the HP of CMA. The results indicated higher effectiveness of the microwave heating rather than the encapsulated rejuvenators for facilitating the healing of cracked areas in asphalt mixes. Combining microwave heating and encapsulated rejuvenation methods was not successful in improving the HP, and the healing index was reduced 10 to 15% when both methods were combined. Compaction condition was more influential than the healing method, and the adverse impact of inadequate compaction could not be compensated with any healing methods. It was shown that the healing index can be improved by more than 10% when a proper compaction was applied to the specimens.

Development and Characterization of Hybrid, Temperature Sensing and Heating Yarns with Color Change.

A person's body temperature is an important indicator of their health status. A deviation of that temperature by just 2 °C already has or can lead to serious consequences, such as fever or hypothermia. Hence, the development of a temperature-sensing and heatable yarn is an important step toward enabling and improving the monitoring and regulation of a person's body temperature. This technology offers benefits to several industries, such as health care and sports. This paper focuses on the characterization and development of a hybrid yarn, which can measure and visualize temperature changes through a thermoresistive and thermochromic effect. Moreover, the yarn is able to serve as a flexible heating element by connecting to a power source. The structure of the yarn is designed in three layers. Each layer and component ensures the functionality and flexibility of the yarn and additional compatibility with further processing steps. A flexible stainless steel core was used as the heat-sensitive and heat-conducting material. The layer of polyester wrapped around the stainless steel yarn improves the wearing comfort and serves as substrate material for the thermochromic coating. The resulting hybrid yarn has a reproducible sensory function and changes its resistance by 0.15 Ω between 20 and 60 °C for a length of 30 cm. In addition, the yarn has a uniform and reproducible heating power, so that temperature steps can be achieved at a defined length by selecting certain voltages. The thermochromic color change is clearly visible between 28 and 29 °C. Due to its textile structure, the hybrid sensory and actuating yarn can easily be incorporated into a woven fabric or into a textile by means of joining technology sewing.

On a three-phase-lag heat conduction model for rigid conductor

We study a thermal model associated with a heat-conducting material based on a three-phase-lag constitutive equation for the heat flux, a model that leads to a Moore–Gibson–Thompson type equation for the thermal displacement. We are researching the compatibility of the three-phase-lag constitutive equation in concern with the second law of thermodynamics, thus discovering restrictions to be imposed on the involved thermal coefficients. On this basis, we manage to obtain the well-posedness problem of the model as the uniqueness of the solutions and their continuous dependence on the given data. Finally, we show that such a model not only allows the propagation of damped in time waves but also exponentially decaying in time thermal standing mode waves. We also show that if the thermodynamic restrictions are not fulfilled, then we can be led to instability. Through the present treatment of the thermal model in question, we obtain important information on the associated Moore–Gibson–Thompson type equation for the thermal displacement.

The Thermophysical and Physicochemical Properties of the Aqueous Dispersion of Graphene Oxide Dual-Beam Thermal Lens Spectrometry.

Modern heat-conducting materials require special attention to analyze their thermophysical properties. Compared to classical methods, thermal lens spectrometry (TLS) has advantages due to its high sensitivity to physical and chemical composition. To avoid a systematic error in the analysis of complex systems, it is necessary to realize the limits of the applicability of the method. This study considers the features of thermal-diffusivity measurements by TLS in the stationary state for dispersed systems with absorbances up to 0.05. The limits of applicability of the method in analyzing heterogeneous systems are shown, and a mathematical apparatus is proposed for indicating a systematic error in finding thermal diffusivity that does not exceed 1%. Graphene oxide (GO), which has attractive physicochemical properties, was used as the object of analysis. GO belongs to 2D objects, the study of which requires highly sensitive methods and special attention when discussing the results. The thermophysical properties of aqueous dispersions of graphene oxide in a wide range of concentrations (up to 2 g/L) and lateral sizes (up to 4 µm) were studied by TLS. It has been found that with increasing nanophase concentration, the thermal diffusivity of graphene oxide dispersions passes through a minimum, which can be used in solving thermal insulation problems. It has been established that prolonged laser irradiation of the dispersion leads to a change in thermal diffusivity, which indicates the photochemical reduction of graphene oxide.

Surface Acoustic Waves Equip Materials with Active De‐Icing Functionality: Unraveled Glaze Ice De‐Icing Mechanisms and Application to Centimeter‐Scale Transparent Surfaces

Enabling active de‐icing functionality on low heat conductive and transparent materials is a requirement for several seminal industries in critical economic sectors. However, developing efficient and environmentally friendly de‐icing methods still fails because of compatibility problems with large‐scale devices and real‐world conditions. In this paper, de‐icing several square centimeters covered with thick layers of glaze ice is approached through nanoscale activation by surface acoustic waves (SAWs). De‐icing functionality is demonstrated with a self‐supported piezoelectric material (LiNbO3) and a piezoelectric film (ZnO) deposited on fused silica, the latter system proving the compatibility of the method with materials of practical relevance. Its applicability to large and transparent substrates is demonstrated by placing the interdigitated electrodes (IDTs) required for activation close to the substrate's edges, leaving most of the surface unaltered. The de‐icing mechanism of glaze ice by SAW activation is revealed by simulating the SAW propagation on ice‐covered surfaces and by experimental analysis of the ice melting process. This involves a combination of ice mechanical stress activation and heating through the initially formed water/ice front. Possible Joule effects due to ohmic losses in the IDTs have been discarded, monitoring local temperature variations during SAW activation at and out of resonance conditions.

Research on PVT Module Operating at High Temperature

At present, the research and development of PVT modules by researchers and engineers worldwide is still in the stage of small-scale production and research and development. Most PVT modules use ordinary photovoltaic cells. In order to ensure their best operating efficiency, the output hot water temperature is generally not more than 30°C. To obtain high temperature hot water, secondary heating is required, such as using heat pump, so the overall system cost is high. Based on the above problems, this paper studies and develops a new PV-thermal integrated module, re-optimizes the overall structure, selects the characteristic high-temperature resistant crystalline silicon photovoltaic cell (black silicon) and solar special heat-absorbing coating to improve the operating temperature of the PVT module, and uses graphene heat conductive material to increase the contact area of heat conduction and heat transfer, which is packaged and processed. After a series of experimental tests, the operating temperature of the PVT module reaches 60°C, and it can stably obtain high-quality hot water above 50°C. The PVT module can work under high temperature conditions for a long time, effectively improving the overall energy conversion efficiency of the system, and the generated hot water can directly meet the needs of daily life and space heating without secondary heating, has a good market development prospect.

Устройство для создания защитного водоплёночного экрана от теплового излучения пожара

Introduction. A device for creating a water-film protective screen designed to protect the fireman in case of fire by significantly reducing the density of the radiant heat flux was studied by the author in this work. The proposed device, unlike analogues, does not have additional metal structures, for example, shields, while being able to create a stable liquid shield necessary to protect the fireman from the thermal radiation of a fire. By mathematical transformations, dependences are obtained for determining the thickness of the water film screen and the required value of the internal overpressure of the liquid in the device. In the course of mathematical transformations, an expression is obtained for determining the fluid pressure required for the expiration of a stable liquid film of a given thickness. Purposes and tasks. To learn how the device works. To create an experimental device to study the process of a water-film screen forming. To develop a methodology of experiments. To carry out an experiment to determine the device operating modes, depending on the fluid flow parameters. To determine experimentally the maximum value of the diameter of a continuous and stable water-film screen. To get a mathematical relationship to determine the thickness of the water-film protective screen and the value of the required overpressure of the liquid inside the device to obtain a continuous and stable screen. Methods. Natural experiment. Observation. Measurement. Description. Finding dependencies based on mathematical processing of experimental data. Results and discussion. A natural experiment was conducted. The results of research on the creation of a water-film protective screen have been obtained. The most optimal parameters of the device operation have been determined. It is established that the value of the diameter of the water film screen is 10 times greater than the value of the diameter of the channel of the device for the outflow of liquid. The use of known means of protection against the effects of radiant heat exposure contributes to a significant reduction in the distance from the point of use of fire extinguishing means to the point of fire occurrence. However, the devices used are made of heat-conducting materials, which makes it difficult to operate them as a means of protection against radiation from a thermal source of ignition at a small distance between them. In addition, the presence of metal structures reduces the possibility of using these devices when using additional fire extinguishing means. The basis for the regular operation of the proposed device for the formation and issuance of a protective liquid screen for fireman is to create a film curtain of liquid, the thickness and diameter of which is determined and regulated by the hydrodynamic operating mode and design characteristics. Conclusions. The proposed device works without additional metal structures (shields and nets), which makes it possible to use it at facilities with difficult access to an ignition source. Keywords: fire; thermal radiation; water curtain; water film; protective screen.

Topology optimization of thermal cloaks in euclidean spaces and manifolds using an extended level set method

Thermal cloaks are devices designed to shield an object against thermal detection, which have attracted growing interest in research. This paper proposes to design thermal cloaks using the level-set-based shape and topology optimization in the context of pure heat conduction. The cloaking effect is achieved by optimizing the distribution of two bulk heat conductive materials to eliminate the temperature disturbance induced by the introduction of the insulator (cloaking region) into a homogeneous thermal conduction medium. The optimized thermal cloaks are free of high anisotropy and nonhomogeneity commonly seen in the popular transformation thermotics or scattering cancellation methods. Due to the clear boundary characteristic of the level set representation, no sophisticated filtering techniques are required to suppress the appearance of ”gray regions” as opposed to the density-based topology optimization methods. Considering the fact that the device components that need to be thermally cloaked, e.g., sensors, can take an arbitrary free-form shape, a conformal thermal cloak on the manifold is also topologically optimized using the extended level set method (X-LSM), which has not been reported in the literature. The structural boundary is evolved by solving the (modified) Hamilton-Jacobi equation. The feasibility and robustness of the proposed method to design thermal meta-devices with cloaking functionality are demonstrated through a number of 2D and 3D (solid and shell) numerical examples with different cloaking regions (circular, human-shaped, spherical, and curved circular). This work may shed light on further exploration of the thermal meta-devices in the heat flux manipulation regime.

A study on thermal resistance evaluation of carbon nanotube buckypaper with cellulose material for thermal interface material

Multi-walled carbon nanotubes (MWCNTs), which has been studied as a heat conduction material, has excellent thermal properties, with thermal conductivity value of 3000 W/m·K. This study aims to reduce the thermal resistance of MWCNTs–buckypaper (BP) as a thermal interface material (TIM). Three methods are used in this experiment: ultrasonication, oxidation, and the addition of cellulose nanocrystal (CNC). The oxidation process is to remove impurities, which when prepared as a suspension, disturb the particle dispersion, and reveal a tendency to agglomerate. Therefore, a strong acid treatment removes impurities, and improves the dispersibility of nanofluids. The third method, the addition of CNC, which has been in the limelight recently, can affect structural stability, is eco-friendly, and is used for composite material synthesis with high tensile strength. These preeminent effects of CNC help improve the thermal resistance of CNC/treated CNT (C–tCNTs) mixed buckypaper. The thermal performances of TIMs used an ASTM D5470 standard tester, and various ratios of BP were tested using thermal resistance test. BP manufactured by adding MWCNTs and CNC had a resistance value of 0.776. This provided a 33.1 % decrease, compared to the oxidized MWCNTs BP. As a result, it was confirmed that CNC–CNTs BP has the possibility of being applied as TIM. • Cellulose nanocrystals, an eco-friendly material, are applied to carbon nanotubes. • It is made of paper-type buckypaper for use as a thermal interface material. • ASTM D5470 standard instrument is used for thermal resistance comparison. • It achieves maximum heat transfer performance at the optimum ratio.

High-thermally conductive composite polyimide materials

This review is devoted to analysis of works in the field of creating electrically insulating heat-conducting polyimide composite films based on powders of micro-, submicro- or nano-sized fillers with high dielectric and heat-conducting properties for use as effective thermal interface materials in various electronic devices in instrument making. Particular attention is paid to studies on the influence of the size of nano- and microparticles of inorganic fillers on the heat-nducting, dielectric, and physical-mechanical properties of nanocomposite polyimide materials. The analysis of the results of work on the study of the dependence of thermal conductivity on the ratios of micron and nanosized particles in mixtures and their number in polyimides and on the conditions of their polymerization was carried out to confirm the possibility of increasing the thermal conductivity values of promising polyimide materials from 0.12 W/(m•K) up to 5¸10 W/ (m•K). It is noted that the highest thermal conductivity of industrially produced modern polyimide films on market does not exceed 0.75¸0.8 W/(m•K). The task of creating inexpensive, but high-quality heat-conductive polyimide composite materials with sufficiently high thermal conductivity without deteriorating their strength and ductility characteristics is currently relevant and technically in demand.

Сравнительная оценка теплового состояния клина с термостойким покрытием в высокоскоростном воздушном потоке

The efficiency and maximum height, speed and duration characteristics of the flight path of high-speed atmospheric aircraft are largely determined by the temperature regime of the most heat-stressed structural elements, suchas the edges of airframe airfoils. Their active thermal protection systems contribute to solving a number of complex scientific and technical problems, the most promising and simple solution being heat-resistant inorganic materials of the oxide class. However, their use for the structural design of the edge as a monolithic structural element is difficult both in terms of technology and strength characteristics, especially in the heat shock mode. In this regard, a promising solution is an edge in the form of a core made of heat-resistant and heat-conducting materials with a high-temperature oxide ceramic lining, which protects from the environmental oxidative effects and provides the permissible temperature regime of the core due to thermal resistance determined by the thickness of the lining. The study examines the temperature conditions of the wedge-shaped edge with a heat-conducting core and a heat-resistant ceramic lining. When choosing materials for the core and lining, it is important to preliminary calculate and estimate the parameters of the edge performance, taking into account the data on the thermophysical and physicomechanical properties of the materials. The study comparatively analyzes the thermal state of a prefabricated wedge with a heat-conducting core made of hafnium boride, which is an advanced heat-resistant material, and molybdenum and nickel, which are more technological and cheap metal materials, with a lining of oxide heat-resistant ceramics

Experimental analysis on evaporative emission from ceramic coated fuel tank

Variations in the ambient temperature cause a type of emission called Diurnal emissions. When the fuel in a vehicle fuel tank vaporizes, they give rise to these emissions. To control the fuel evaporation at the most possible level, this research work deals with the coating of the fuel tank at its exterior with low heat-conducting ceramic materials which in turn lead to controlled evaporation due to external heat sources. Modeling of the coated fuel tank is done using modeling software, SOLIDWORKS, and the model is subjected to thermal analysis so as to choose a better material for the ceramic coating. Hence, the research work aims in determining the effects of ceramic coating over the fuel tank and compare the emission test results such as permeability test and break out fuel test with conventional fuel tank.

Применение наножидкостей в качестве теплоносителя в охладителях функциональных агрегатов автотракторной техники

One of the most important elements of the cooling system of any automotive internal combustion engine is a coolant. Most often, water and a mixture of water with antifreeze are used as a coolant. Its main function is to transfer heat or to cool the engine. Nanofluids are promising heat carriers, with the help of which it is possible to reduce the metal consumption of aggregates, increase safety in emergency transient modes accompanied by boiling. (Research purpose) The research purpose is studying the possibilities, features and prospects of using innovative heat carriers as coolants of automotive equipment, which will allow overcoming the inefficiency of water and ethylene glycol mixtures, which consists in low thermal conductivity. (Materials and methods) Nanofluids consisting of a base liquid and nanoparticles of a highly heat-conducting material were proposed as innovative heat carriers. Their use in transport power plant coolers will reduce their volume and weight. Mixing of ethylene glycol and copper nanoparticles is effective, in such cases it is important to investigate the effect of the volume fraction of copper nanoparticles and the base liquid on thermal characteristics or to reduce the size of the radiator. Copper nanoparticles have better thermal conductivity than other nanoparticles (for example, aluminum oxide). (Results and discussion) It has been proved that the use of nanofluids in heating and ventilation systems can give a significant increase in heat transfer. At present the science of nanofluids is in its initial stage, for the development of this direction it is necessary to conduct comprehensive experimental studies of their chemical and physical properties, theoretical analysis, and compilation of general calculated correlations. (Conclusions) It was revealed that nanofluids can be effectively used as heat carriers of transport engines, with their use the metal consumption of coolers is reduced, the safety of units in emergency modes, including those accompanied by boiling, is increased.

Improving the Intrinsic Thermal Conductivity of Epoxy Resin by Synergistic Effect between Rigid Groups and Hydrogen Bonds

AbstractAlthough introducing liquid crystal phase into epoxy resin for liquid crystal epoxy fabrication is one of the most conventional methods for improving the intrinsic thermal conductivity of epoxy resin, the complex molecular structure design and sophisticated synthesis process seriously limit its rapid expansion and further industrial application. Herein, the rigid groups of 4’4‐dihydroxybiphenyl were introduced into the main chain of epoxy resin by ring‐opening polymerization (ROP) to change the molecular structure of epoxy resin. The introduction of biphenyl groups enhances the “orderliness” of molecular structure and forms hydrogen bonds between molecules, which facilitates the transmission of phonons within the molecule. The intrinsic thermal conductivity of modified epoxy resin (MEP) reaches 0.29 W m−1 K−1. After adding the expanded graphite (EG) into the MEP matrix, the thermal conductivity of MEP/EG reaches 2.59 W m−1 K−1, which is 1133 % higher than that of EP. In addition, the MEP also has certain advantages in harsh environment, the |Z|0.01 Hz of MEP coating is higher than 1.4 times the value of EP coating after immersing in 3.5 wt% NaCl solution for ten days, which identified the excellent anticorrosion of MEP. The MEP prepared by this method can find great applications as heat conduction materials in harsh environment.

Development of Closed Type Linear Motor with Improved Cooling Performance

In this study, we examined a closed type linear motor with a continuous thrust of 10kN. First, the loss at the rated operation was calculated through a magnetic field analysis, and the dominant loss component was clarified. When the application was small with a low speed and large thrust, copper loss was dominant. Next, a heat transfer analysis was conducted by using a heat conductor that avoids the magnetic path, to confirm the structure that can reduce the winding temperature. The result shows that the winding temperature can be reduced under the target temperature (150°C) by placing the heat conductive material where the formation of an eddy current is difficult.