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High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe2O3 and TiO2 were prepared via a pressureless sintering. A Fe2O3–TiO2 system with different Fe2O3/TiO2 ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe2O3 and TiO2 rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe2O3/TiO2 ratio led to a new phase of FeAlTiO5, which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO5 and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe2O3/TiO2 ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material.

Large-caliber gun barrels are coated, on their internal surface, by hard and refractory metallic layers. The thermophysical properties of such coatings are generally very different of bulk materials ones, and liable to evolve following the thermal cyclings. Nevertheless, the knowledge of these properties is necessary for modeling the gun barrels behavior. In the present work, a photothermal microanalysis method has been used to measure the local thermal diffusivity within such a coating. The periodic excitation is localized on a micrometer-scale spot and the temperature evolution in the thermally excited zone is monitored by photoreflection on a spot with similar size. Local thermal properties are identified from thermal transfer function analysis, i.e., phase-lag evolution versus frequency. Results obtained on an aged chromium coating, on which several local diffusivity measurements have been undertaken along the depth, are presented. The diffusivity is higher near the surface than toward the interior of...

Considering the risk of leakage and the complexity of processing technology, a passive cooling first wall has been developed in the low magnetic side. The anticipated heat flux limit of the first wall is about 0.3 MW/m2. In order to enhance thermal transfer, the main materials of the first wall is made of copper alloy (CuCrZr) and graphite tile. A layer of flexible graphite is placed in the interface of CuCrZr and graphite tile to increase thermal contact resistance. Transient thermal analysis has been used to predict the whole heat transfer process for normal operating discharge in a day. Through the simulation, we can get the temperature change history of each component in 24 hours. The temperature and stresses of the passive cooling first wall are found to be within the acceptable limits. The maximum temperature of this first wall is about 307 °C which appears on the graphite tile. The results of the maximum temperature distribution are imported into the structure for calculation. Finally, the elasto-plastic fatigue analysis method is used to check the structural analysis results, and the results show that the structure meets the high parameter discharge mode of more than 480,000 times.

International audience; This paper presents a thorough analysis of direct microwave heating as a sintering process of ceramic materials. It questions why susceptor-assisted microwave heating is used in most experimental works, although direct microwave coupling is preferable for taking advantage of the possible beneficial effects of the microwave field on the sintering phenomena. This issue was investigated by conducting both experiments and numerical simulations. The experiments consisted of sintering alumina and yttria doped zirconia powder samples in a 2.45 GHz resonant cavity with automatic thermal monitoring, whereas the numerical simulations coupled electromagnetics, thermal transfer and sample deformation. Alumina and yttria doped zirconia are widely used materials and they exhibit different microwave field behaviours (transparent and absorbent, respectively), which are representative of most ceramic materials. The influence of the insulating material was discussed by considering different sintering cell designs. The very low coupling capacity of alumina made its direct heating very difficult. It was therefore necessary to apply a strong electric field to heat it. This situation promoted the absorption of microwave energy by other elements such as the insulating material, leading to heating instabilities and degradation of the insulation cell. In the case of zirconia, its coupling properties change abruptly with increasing temperature. It is poorly absorbent at low temperature, highly absorbent at intermediate temperature and it finally becomes reflective at the end of the sintering process. The consequences of this behaviour are (i) a very difficult control of direct heating (ii) a propensity to form damaging hot spots and (iii) the impossibility to reach high temperatures without forming plasma. Therefore, this experimental and numerical study showed that direct microwave heating is not suitable for conducting reliable and homogeneous sintering of classical ceramics. This explains why susceptor-assisted heating is most of time preferred.

Polymeric composites with good thermal conductive and improved mechanical properties are in high demand in the thermal management materials. Construction of a three-dimensional (3D) structure has been proved to be an effective method to obtain polymeric composites with improved through-plane thermal conductivity (TC) for efficient thermal management of electronics. However, the TC enhancement of the obtained polymeric composites is limited, mainly due to poor control of the 3D thermal conductive network. Additionally, achieving high thermal conductive properties and enhanced mechanical properties simultaneously is of great challenge for polymeric composites. In this work, a 3D boron nitride framework (BNF) with a well-defined vertically aligned open structure and designed wall density fabricated by a unidirectional freezing technique was applied. The as-prepared BNF/polyethylene glycol (PBNF) composites exhibit enhanced through-plane TC, excellent thermal transfer capability (ΔTmax = 34 °C), and improved mechanical properties (Young's modulus enhancement up to 356%) simultaneously, making it attractive to thermal management applications. Strong correlation between the TC and mechanical properties of the PBNF composites and the wall density of the BNF scaffolds was found, providing opportunities to tune the TC and mechanical properties through the controlling of wall density. Furthermore, the models between TC and Young's modulus of PBNF composites were established by using the data-driven method "sure independence screening and sparsifying operator", which enables us to predict TC and Young's modulus of the polymeric composites for designing promising composite materials. The design principles and fabrication strategies proposed in this work could be important for developing advanced composite materials.

The high gas-sensing performance of semiconductors is mainly due to the high surface-to-volume ratio because it permits a large exposed surface area for gas detection. This paper presents an evaluation study for the effects of nano-CuO coating parameters on the CO gas-sensing performance. The effects on gas-sensing performance and heat transfer efficiency of CuO coating were evaluated by investigating the effects of coating parameters (concentration, temperature, and solution speed) on thickness, grain size, and porosity. The CuO nanoparticle coatings were synthesized using the oxidation method at various operating conditions. Coating characteristics were investigated using X-ray diffraction, energy dispersive X-ray Spectroscopy, field emission scanning electron microscopy, and electrical resistivity meter. The average coating thickness, grain size, and porosity were around 13 μm, 48 nm, and 30%, respectively. The thermal transfer and gas-sensing properties of CuO coating were evaluated according to the total surface area of the coating formed at various operating conditions. The gas-sensing and thermal transfer performance were obtained from the optimization of coating parameters based on the coating morphology to achieve the highest contact surface area. The coating’s surface area was increased by 350 times, which improved the heat transfer efficiency of 96.5%. The result shows that the coating thickness increased with the increase in solution concentration and decrease the temperature. The results also show that the sensitivity of the coating for CO gas was increased by 50% due to the reduction of coatings grain size.

The size effect on the thermal expansion of ZrO2/ZrW2O8 fabricated by the conventional thermal sintering process is investigated systematically. The small-sized sample with dense microstructure and few ZrW2O8 decomposition exhibits near-zero thermal expansion. While the microstructure and thermal expansion property of the large-sized sample deteriorates due to the serious decomposition of ZrW2O8. The finite element analysis is used to investigate the thermal transfer during the quenching, demonstrating that the smaller specific surface area (SSA) of the large-sized sample is the direct reason of the size effect, and the core causes are the instability of ZrW2O8 and the low thermal conductivity of the ZrO2/ZrW2O8. A thermal conductive pathway is further designed for the large-sized sample to verify and attenuate the size effect by increasing the SSA. The technique of ultra-low sintering temperature is urgently recommended to effectively solve the obstruction caused by the size effect.

Controlling thermal anisotropy structure is important for emerging heat management applications such as thermal shield, thermal camouflage, and heat concentration. In this work, alternating stack epoxy composites (AECs) are prepared, inspired by the multilayer structure of an onion. Hexagonal boron nitride (h-BN) and expanded vermiculite (E-ver) are used as fillers in epoxy resin (Epon), taking as heat-dissipation layers and heat-insulation layers, respectively. Vertical heat isolation and local hotspot protection are endowed by the effective structural design. The temperature rise time of top surface is delayed by 404.2%, and the stabilized temperature is reduced by 10–15 °C (the bottom is heated to 120 °C); meanwhile, the whole composites are heated to 80 °C with good heat-dissipation performance, compared with those of homogeneous materials. There are two thermal phenomena synergistically in the anisotropy structure: excellent thermal protection when heating and good heat dissipation when cooling. Further, a thermal transfer mechanism of heat insulation and heat dissipation is analyzed based on numerical simulation and experiment. The multilayer epoxy composites are promising for the development of high-performance thermal products such as heat spreader, equipment cooling, and thermal hose.

This paper describes a new type of sensor that can monitor electrical signals for external stress or damage and heat transfer. It is composed of conductive pencil lead graphite, which is sensitive, affordable and easy-to-handle. This work was to detect mechanical damages in composites using Pencil Lead Drawn Paper Sensor (PLDPS). To measure electrical resistance (ER) via bending, by narrowing the distance between glass plates attached with PLDPD, ER increased stepwise while ER decreased with widening the distance reversely. The PLDPS can easily change the shape in a rectangular vortex. ER change responded well in tensile and flexural tests, while it showed leveling off under cyclic compression. Two-dimensional ER mapping was used during impact, drilling and heat transfer tests for detecting damage and thermal transfer. Compared to strain gauges, PLDPS can be applied inexpensively to detect damages successfully under various mechanical tests.

We report microstructure, magnetocaloric effect and thermal transfer properties of highly orientated Nd0.8Pr0.2Co5 alloy prepared by powder metallurgical processing. Two spin-reorientation transitions of easy magnetization direction, easy plane to easy cone at TSR1 = 206 K, easy cone to easy axis at TSR2 = 242 K, are observed. The present textured alloy exhibits a rotating entropy change of 2.6 J/(kg·K) and refrigerant capacity of 155 J/kg under a magnetic field of 2 T, and high thermal conductivity of 11 W/(m·K). The sintered Nd0.8Pr0.2Co5 alloy with good combination of excellent magnetocaloric and thermal transfer properties are promising for scientific research and practical applications as room-temperature rotating magnetic refrigeration materials.

The continuous increase in the level of greenhouse gas (GHG) emissions and the increase in fuel prices are the main driving force to utilize various source of renewable energy. Among the clean energy technologies, solar energy is recognized as one of the most promising choice since it is free and provides clean and environmentally friendly energy. The objective of this paper is to improve the heating capabilities of evacuated tubes solar cookers that operates based on a closed loop thermosyphon action, and utilize thermal oil as the heating medium. Two identical evacuated tube solar cookers have been designed and built to study the influence of inserting metallic wires or nanographene particles on the thermal performance of the cooker. Also, the study was based on the thermal transfer of natural convection of the thermal oil movement within the evacuated tubes. The metallic wires and the nanographene particles are inserted inside the evacuated tube, which is filled with the heat exchange oil. One cooker is always tested without any modifications, i.e. taken as a reference point. The other cooker is the developed cooker, i.e. with wires or particles. Steel, aluminum and copper wires have been examined, and the number of wires has been varied between 5, 10 and 15. It has been found that the copper wires improve the rate of heat transfer compared with steel wires, aluminum wires and the nanographene particles. It has been also obtained that there is a critical number of wires, i.e. 10 wires, above that the rate of heat transfer by natural convection decreases and this is due to the increased friction which resists the natural convection currents. Finally, adding nanographene particles increases the viscosity of the oil, which increases the resistance to natural convection currents and consequently decreases the rate of heat transfer by natural convection.

From resolution of two-dimensional equation of heat in dynamic frequency regime, we have plotted evolution curves of temperature according to depth of material or in lateral direction. They will allow us to evaluate thermal behavior of towed material. Aim of study is to use fibers as a thermal insulating material by proposing a method for determining effective thermal insulation layer in dynamic frequency regime.

The thermal efficiency limitation of the Flat-plate Micro Heat Pipe (FMHP) is a major challenge in the development of the FMHP, where the effect of wick structure and wettability on its thermal performance is studied to improve the thermal efficiency of the FMHP. In this work, a copper spiral woven mesh and copper foam Composite Wick FMHP (CW-FMHP) is designed based on the conventional Copper Foam Wick FMHP (CFW-FMHP), and its thermal performance is analyzed regarding the wick structure and internal gas–liquid two-phase flow characteristics. An oxidized copper spiral woven mesh and copper foam Composite Wick FMHP (OCW-FMHP) has been further developed through the modification of composite wick wettability. The performance tests are carried out with the thermal transfer characteristics of CW-FMHP, OCW-FMHP, and CFW-FMHP under different filling rates and different thermal powers. The experimental results show that the thermal transfer performance of CW-FMHP reaches the optimal under a liquid filling rate of 150%, where the maximum thermal power is 15.7 W, 35.3% higher than that of the CFW-FMHP under the same filling rate. Moreover, the dynamic response characteristics of the CW-FMHP are significantly improved. The thermal resistance of the CW-FMHP is 0.48 °C/W under the filling rate of 150% at the thermal power of 10 W with a reduction of 9.4% compared to the CFW-FMHP under the same condition. Furthermore, the optimal filling rate for OCW-FMHP is lower compared with the CW-FMHP. The maximum thermal power of OCW-FMHP increases to 17.8 W while the thermal resistance reduces to 0.34 °C/W under the liquid filling rate of 140%. This implies that the composite wick structure designed in this work can improve the thermal transfer performance of the FMHP, and the composite wick with wettability modification is more effective regarding both thermal resistance and maximum thermal power.

Thermal grease has been widely used in the thermal management of electronic packaging due to its excellent filling ability between heat resource and heat sink, yet those grease tend to have low thermal conductivity. Increasing the filler content in thermal grease will enhance the thermal transfer capacity but impair its filling performance. Here, we report a thermal grease with optimal thermal conductivity and filling capacity prepared from alkyl silicone oil, hydrogen silicone oil, alumina ${(\mathrm{A}1_{2}\mathrm{O}_{3})}$ , zinc oxide (ZnO) and silver (Ag). The silver particles effectively connect the fillers in the grease, improving the overall thermal conductivity while ensure proper viscosity. This adjustable interaction between thermal conductivity and viscosity makes it possible to adjust the thermal transfer capacity of the grease without causing a decrease in the filling performance. The prepared thermal grease exhibits a combination of satisfactory thermal conductivity ${(3.0\ \text{Wm}^{-1}\mathrm{K}^{-1})}$ and lower viscosity (~322.7 Pa.s), those excellent properties indicate their great potential in the application of electronic packaging.

Artificial intelligent, human augmentation and interactive robotic engineering are shaping the world rapidly. This trend demands big data transmission rate, but the memory bandwidth was limited. High-bandwidth memory (HBM) was developed to solve this limitation. However, the HBM packages require 2/2 µm Cu line space to have optimum data efficiency. Thus, they are either packed together with GPU or ASIC dies to form a High Performing Computing (HPC) package. The packaging can be either packaged by 2, 4, 6 or 8 HBMs. This causes a package to become very large and generate severe package warpage. HPC package requires extremely high thermal dissipation, but the package warpage induces higher bond line thickness (BLT), causes lower thermal transfer efficiency. Thus, it is crucial to develop a higher and flexible to large-area thermal dissipation package. In this paper, liquid thermal dissipation (LTD) package is developed to enable large package thermal dissipation requirements. In this study, test vehicle A with the size of 50 * 50 mm2 FCBGA (flip chip ball grid array) was built with LTD interface. The LTD material was filled between the chip surface and heat spreader (HS), it was a liquid form metal with melting point > 10 °C. To compare with solid TIM (thermal interface material) (like Silicon base), LM (liquid metal) TIM does not cause any defect issues such as delamination, coverage decrease, crack and interface layer in the thermal cycle process. In addition, the function of HS-EL (with enhanced layer) can increase the efficiency of heat transfer because of the area ratio of heat transfer (surface area of HS-EL/surface area of chip) > 1 and the effect of high heat flux. Moreover, the HS-EL can be easily designed according to the heat source of chip. The studies were divided into three parts. For the first part, two steps of thermal simulations were conducted. The thermal simulation applied two types of TIM materials; one was using LM and the other was Silicon base as a baseline. Both were built with 80 µm BLT. Results showed that the chip temperature using LM TIM was 16.21 °C lower than that of Silicon base TIM. And the delta temperature between chip surface and HS-EL was 3.45 °C as compared to HS normal with 10.78 °C for using the LM TIM. Lastly, for index theta Junction-to-Case (JC), HS-EL of 0.23 °C /W i s better than HS normal of 0.72 °C /W. Next, the LTD package was built using flip chip assembly line. Two types of HSs (HS normal, HS-EL) were designed using different surfaces to enhance the thermal dissipation areas. The samples of LTD packages were tested for 12 thermal reflow cycles with peak temperature of 245 °C. No LM TIM was leaked for both HSs types. 3D X-ray then was conducted and found that the interfacial area of LM TIM coverage was over 95% between chip-to-LM TIM and LM TIM-to-HS. Mechanical tests were then performed. The average data of pull force was 242.99 kg and shear force was 415.48 kg respectively. The delta temperature between glass substrate and HS was measured. HS and HS-EL had 39.6% and 51.2% respectively lower than Silicon based TIM. Finally, the assembled FCBGA packages with LM TIM were stressed for reliability tests. It passed MSL4 preconditioning with 700 thermal cycles under −55 ∼125°C. At the intermittent readouts of 200 and 700 thermal cycles, the coverage of LM TIM was well intact and exceeded 96.8% between the two interfaces. Again, 3D X-Ray was conducted and confirmed no leakage LM TIM was found. In summary, we have developed a highly thermal dissipated package for large HPC package. It solves the package warpage induces thermal transfer issues. LM TIM package does not have any delamination and well contact to chip surface and HS. Neither crack nor voids were found at the interface before and after reliability tests. The package was validated by thermal simulation and real sample built. It passed multiple reflow cycles and reliability tests. The full descriptions of the development results will be discussed in this paper.

Purpose The purpose of this paper is to investigate the thermal transfer properties of electric heating fabric system which contains heating units or conductive yarns by numerical simulation, in order to optimize and evaluate the thermal performance of heating clothing. Design/methodology/approach Two kinds of FEM models are created by ANSYS system: macro-scale models of the fabrics system with heating units and air layer; and meso-scale models of the plain-woven fabrics were established embedded with the stainless yarns. In the macro-scale model, the interior and surface temperature field distribution were simulated and analyzed based on different heating unit size, heating power, heating region, air layer thickness and ambient temperature. For meso-scale models, the effects of the conductive yarns temperature, covering fabrics and pore-filling material on the temperature field distribution were simulated and analyzed. Findings With the increasing of the air layer thickness or the effective conductivity, the heat transfer along the direction of fabric thickness decreases gradually. The heat transfer along the fabric plane can be increased by dispersing the heating region. With the increasing of the conductive yarns’ temperature or the covering fabrics’ conductivity, the heat transfer distance along the fabric warp direction can be increased. Filling the internal pores of the fabric with 10 wt% SiC/TPU hybrid materials can effectively increase the in-plane heat transfer and improve the temperature uniformity on the surface of heated fabrics. Originality/value The finite element method was used to establish the simulation models of the heating fabric systems. The influence of several parameters on the thermal performance was analyzed and discussed, as well as the internal and external temperature distribution in the macro and micro scales models.

Heat treatments were applied to alloy steels (X210Cr12 and HS6-5-2-5) using concentrated solar energy as the thermal energy source. The characteristic of this treatment is that the thermal energy is transferred unidirectionally from the surface of the piece to the other layers. The studied steels were chosen due to the high temperatures recommended for the proposed heat treatments. The results of temperature measurements during heating of the samples with concentrated solar energy matched well with corresponding simulations in terms of the temperature evolution. Because the heating is unidirectional, the temperature is not constant through the height of the sample, resulting in a variation of the hardness with the height. The results of this study show that the hardness of the samples treated by concentrated solar energy was greater than that achieved using conventional thermal treatment. Investigation of the modulus of elasticity and wear showed that application of the two types of heat treatment (conventional or with concentrated solar energy) produced comparable results. Heat treatment with solar energy can achieve positive results when the sample volume is large. It can be concluded that heat treatment with solar energy is fast and ecological, and yields results comparable to those achieved by conventional heat treatment.

Owing to distinguished thermal transfer property, graphene has attracted much attention as filler to enhance the heat transfer effect of polymers. However, the actual enhancement efficiency of thermal conductivity for graphene filled polymers is lower than that predicted value. One available solution would be to integrate two-dimensional graphene into three-dimensional interconnected graphene that can fully utilize graphene’s performance. Herein, we report a three-dimensional interconnected graphene microsphere by liquid nitrogen driven assembly approach. When used as thermally conductive fillers for epoxy resin, the graphene microspheres exhibit high enhancement efficiency (437%) of thermal conductivity per 1 wt% loading, leading to the maximum out of-plane thermal conductivity of 0.96 Wm−1 K−1. This increase is attributed to the well-organized three-dimensional network in graphene microspheres, which establish an effective heat conduction path inside the epoxy resin. These methods and results have laid a new foundation for the continued development of highly thermally conductive polymer materials.

The macroscopic mechanical properties of metallic lattice structures produced by additive manufacturing are key considerations in the design and application of multiscale structures. Indeed, these properties are relevant to the microstructure heterogeneities and geometric discrepancies that are severely influenced by the build orientation of struts in lattice structures. This report focuses on the effect of build orientation on microstructure, geometric accuracy and mechanical properties in AlSi10Mg samples produced by selective laser melting (SLM) and explores the microscopic mechanism of thermal transfer during melting via both experimental and simulation methods. The simulation results show that the cooling rate of the upper zone is two times larger than that of the lower zone with a wider thermal accumulation area. The experimental results indicate that the grain size and porosity of the lower zone of inclined struts with orientation angles are greater than those of the upper zone. It was determined that the deviation between the as-designed size and the as-built value for the inclined struts is minor, compared to that of vertical struts. In addition, the surface roughness of the inclined struts increases. Furthermore, the mechanical properties of the samples can be strengthened when the build orientation of the struts varies from 35.5° to 90°. The results of this study will facilitate the enhancement of the stability of the SLM manufacturing technique for metallic lattice structures in a robust and practical manner.

To minimize the heat loss through single-pane windows, we investigate the effects of elevating low-emissivity (low-e) film from glass pane. With an insulating air gap, not only heat conduction but also radiative thermal transfer can be suppressed. The thermal transmittance is reduced from 5~7 W/(m2K) to less than 2.8 W/(m2K). The water condensation resistance is enhanced. The visual transmittance and haze are satisfactory. The structural resilience of the hollow structure is excellent.

Computer Integrated Circuit (IC) microprocessors are becoming more powerful and densely packed while cooling mechanisms are seeing an equivalent improvement to compensate. A significant limit to cooling performance is thermal transfer between die and heatsink. In this meta study we evaluate carbon nanotube (CNT) thermal interface materials (TIMs) in order to determine how to maximise thermal transfer efficiency. We gathered information from over 15 articles focused on the thermodynamic parameters of CNT TIMs from databases such as Scopus, IEEE Xplore and ScienceDirect. Articles were filtered by key words including ‘carbon nanotubes’ and ‘thermal interface materials’ to identify scientific articles relevant to our research on TIMs. From our meta study we have found that enhancing CNTs will provide the best improvement in TIMs. The parameters analysed to determine TIM performance included thermal resistance, thermal conductivity and the effect of CNT concentration on computer operation time. Through our investigation we understood that increasing the concentration of CNT from 0 to 2 wt % increases the operation time from 75 seconds at 66°C to 200s at 63°C as well as increasing the thermal conductivity by 1.82 times for the AS5 thermal paste with 2 wt % CNT. Furthermore, CNT TIM pastes with less thickness have a lower thermal resistance of 0.4 K/W. However not all these parameters have been tested with computer chips. This means that in order to increase current heat transfer efficiency limit, we must integrate these parameters into experimental models. Keywords: Thermal Interface Material; Thermal Paste; Carbon Nanotubes; Thermal Transfer Efficiency; Integrated Circuit; Heat Sink; Heat Dissipation.

The aim of the present study is to model the steady heat transfer of the engine polyamide intake manifold. Under the condition of a steady flow, the intake manifold wall temperature and the intake air temperature were measured to examine the effect of the thermal boundary layer on the heat transfer. Experimental data is used to generate the numerical model of airflow simulation through the intake manifold.

Graphene films have attracted much attention as a heat dissipation material due to their unique thermal transfer behavior that exceeds that the performance of graphite. However, the very high thermal annealing temperature (~ 3000 °C) required to reduce the graphene oxide (GO) films leads to high manufacturing costs and restricts its broader application in thermal management applications. In this study, a modified-graphene (m-Gr) film was fabricated by vacuum-filtering GO suspensions with added glucose, followed by thermal annealing at 1000 °C. Oxygen-containing functional groups were effectively eliminated during annealing and activated carbon atoms from the decomposition of glucose molecules repaired defects in the graphene sheets to restore large areas of the π-conjugated structure. The as-obtained m-Gr films showed excellent in-plane thermal conductivity ~ 1300 Wm−1 K−1 and much more efficient heat removal than pristine-reduced graphene oxide films. This high thermal conductivity of m-Gr films provides opportunities for their use in next-generation commercial electronics.

Phase change material (PCM) has been widely used in thermal management for its high latent heat and low price. However, further development of its application is limited by the low thermal conductivity. Oscillating heat pipe (OHP), an effective thermal transfer device, can be used to enhance the heat transfer of PCM and then improve the thermal performance. In this paper, both novel 3D-OHPs and regular OHPs were hired for PCM thermal performance enhancement. PCM coupled with two kinds of novel 3D-OHPs (4 layers 3D-OHP and 3 layers 3D-OHP) system and PCM coupled with multiple 2D-OHPs system were experimentally investigated. Results showed that the paraffin wax/3D-OHP system needed more time for completely melting of paraffin wax than paraffin wax/OHPs system. The temperature of wall and paraffin wax in the former system was lower during melting process. In the solidification process, both two systems performed better than paraffin wax only. The solidification time of the paraffin wax/4 OHPs system was about 0.48 times than that of pure paraffin wax and the paraffin wax/4-layers 3D-OHP only 0.29 times, which meant that paraffin wax/3D-OHP system had better performance.

The demands for achieving microencapsulated phase-change materials (MEPCMs) with high thermal-energy storage ability have motivated increasing research interest in inorganic filler-modified MEPCMs. However, challenges for such MEPCMs still exist in the pursuit of good compatibility of inorganic particles with the core or shell material. Here, a novel type of octadecylamine-grafted graphene oxide (GO-ODA) -modified MEPCMs using melamine-formaldehyde (MF) resin as the shell material and the mixture of GO-ODA and n-octadecane as the core material was fabricated via in-situ polymerization. The alkylated GO with a thickness of ∼1 nm was confirmed to be highly compatible with the core material. The as-prepared MEPCMs with a regular spherical shape were dispersed without any agglomeration, and the size decreased with increasing the filling amounts of GO-ODA. The incorporation of GO-ODA promoted the crystallization of n-octadecane, resulting in an observable reduction in supercooling degree. The encapsulation efficiency of MEPCMs was calculated to be over 88.0%, and the melting/freezing latent heats reached to a level as high as 207.2 J g−1 and 202.5 J g−1, respectively, even at a tiny loading level of 0.5%. Besides, the GO-ODA incorporated MEPCMs showed a good thermal cycling stability during a phase change. Moreover, a substantial enhancement in thermal transfer rate and a less marked heating effect for the MEPCMs containing GO-ODA were observed from the thermal conductivity tests and infrared thermography analysis. The findings suggested that the prepared MEPCMs are promising for applications in the fields of thermal energy storage and temperature regulation due to their enhanced thermal transfer performance and prominent phase-change enthalpy.

Interlaminar debonding (delamination) is a major problem for carbon fiber-reinforced plastic (CFRP) when it is used in thermal protection systems subjected to rapid heating, such as in a re-entry situation. In this study, the possibility of avoiding delamination by controlling material porosity was investigated experimentally and numerically. CFRP specimens having various initial porosities (mid-density CFRP) were prepared and rapid heating tests (∼6 MW/m2) were performed, and the specimens were examined to determine whether delamination had occurred. To predict the delamination, heat transfer and pyrolysis gas-induced internal gas pressure growth were simulated numerically as a function of heating time. The parameters regarding temperature-dependent chemical reaction rate, orthotropic coefficients for gas permeability, and flatwise tensile strength were determined by individual experiments using the CFRP specimens. The coupled analysis of thermal transfer and pyrolysis gas flow following Darcy’s law was conducted by finite-difference form, employing the experimentally obtained parameters. When the gas pressure exceeds the flatwise tensile strength of CFRP, delamination is assumed to occur. The numerical results show good agreement with the experimental results, and it is concluded that delamination can be eliminated by using mid-density CFRP.

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.

There are remarkable theoretical efforts geared towards understanding the impact of fabrication-induced defects on the operational behaviour of a single layer graphene. These studies have been focused mainly on atomic defects, while nanoscale pinholes and patches of two layers thick (bilayer) attached on a monolayer graphene are inevitable during the synthesis process. In this work the influence of these nanoscale defects on the graphene thermal conductivity is studied via non-equilibrium molecular dynamics simulations. The thermal conductivity of a single layer zigzag and armchair oriented graphene is modelled capturing the effect of voids and bilayer imperfections. A single layer graphene sheet with a size of 50 nm × 10 nm is analysed having an elliptical defect of up to 6 nm (major axis). Our results exhibit a reduction of over 20% in thermal conductivity with increasing temperature and about 75% drop with increasing void size. The decrease in the thermal conductivity is 15% for the single layer graphene with a bilayer defect of 6 nm in diameter. This study demonstrates a dramatic influence of defect shape on the thermal conductivity of graphene, where defects with elliptical shapes demonstrate a higher thermal transfer in graphene compared to circular ones. This work provides a guideline of how to quantify the effect of fabrication induced defects on thermal conductivity of graphene.

In the development of hexagonal boron nitride (h-BN)-based polymeric composites with high thermal conductivity, it is always challenging to achieve a dense filling of h-BN fillers to form a desired high-density thermal transfer network. Here, a series of boron nitride nanosheets (BNNSs)/epoxy resin (EP) bulk composites filled with ultrahigh BNNSs content (65-95 wt %) is successfully constructed through a well-designed mechanical-balling prereaction combined with a general pressure molding method. By means of this method, the highly filled BNNSs fillers are uniformly dispersed and strongly bonded with EP within the composites. As a result, the densely BNNSs-filled composites can exhibit multiple performances. They have excellent mechanical properties, and their maximum compression strength is 30-97 MPa. For a BNNSs/EP composite with filling ultrahigh BNNSs fraction up to 90 wt %, its highly in-plane thermal conductivities (TC) are 6.7 ± 0.1 W m-1 K-1 (at 25 °C) to 8.7 ± 0.2 W m-1 K-1 (200 °C), respectively. In addition, the minimum coefficient of thermal expansion of BNNSs/EP composites is 4.5 ± 1.3 ppm/°C (only ∼4% of that of the neat EP), while their dielectric constants are basically located between 3-4 along with their dielectric loss tangent values exceptionally

Multifunctional sandwich panel presents a unique Integrated Thermal Protection System (ITPS) for hypersonic vehicles. In this paper, a novel method to evaluate the effective thermal properties of metal alloy lattice core sandwich panels is presented. The thermal transfer process between lattice core and face sheet was analyzed, and the behavior schemes were detached in three categories according to the existence of insulation material filling and active convection. For each category, equations were presented to calculate the effective density, specific heat and thermal conductivity for pyramid lattice core and tetrahedral lattice core using Representative Volume Element (RVE). Two sandwich panels were constructed separately with the two lattice cores made by the material of titanium alloy. Numerical Simulation based on Finite Element Method (FEM) was employed to verify the effective techniques. Two kinds of FEM models were built with detailed solid element level and simplified effective solid element level. The heat transfer process from top sheet to bottom sheet across lattice core were simulated, consistency of temperature responses could be observed obviously between the different level FEM simulations. It could be concluded that the effective properties deduced with the method in this paper are accurate to predict the thermal performance of titanium alloy lattice core sandwich panels, and are very promising for potential application in the analysis and design of TPS for hypersonic vehicles.

The main subject of the study is the physical parameters of thermal insulating materials based on flax fiber, including thermal transfer resistance and humidity, determined under operating conditions. In the experiments, slabs based on flax fibers and flax noils were used, as well as thermal insulation material from a mixture of flax and polyester fibers. Fibrous insulation slabs were laid in the attic floor of a one-story residential building located in the countryside in northern Belarus. Monitoring of the parameters studied was carried out in the autumn, winter, and spring. The thermal transfer resistance of the insulated attic floor was determined using heat flow sensors. According to the readings of thermocouples installed inside the structure, temperature distribution graphs were constructed to determine the effectiveness of thermal insulation on the attic floor. At a temperature of −17 °C, the thermal transfer resistance of insulation was 5.17–5.88 (m2°C)/W. The moisture content of thermal insulation materials after the winter period was in the range of 5.7–12.3%. The results obtained prove the effectiveness of thermal insulation slabs based on flax noils.

The weld geometry is an important factor which determines the quality of the weld. This work proposes a transitional and three-dimensional numerical model performed by the hydrodynamic software Ansys-Fluent. We are interested in the heterogeneous assembly of Al alloy and Mg alloy by laser beam welding. Aluminum and Magnesium plates are joined in butt configuration. The objective of this work is to simulate the temperature field, velocity field, fluid flow during the interaction between the laser beam and the material and to predict the dimensional characteristics of the laser welded joint. This makes it possible to better understand different physical phenomena (e.g. heat transfer, mass transport) generated in the molten pool. The results show that the simulated weld bead profile is in good agreement with those obtained by experiment.

Using the self-propagating exothermic reaction of nanoscale multilayer film can achieve effective bonding between solder and substrates at a much lower ambient temperature, but there are still many reliability issues which are yet to be understood. In this study, the Cu/Sn/Cu interconnect is prepared by using self-propagating exothermic reaction of Ni/Al nano-film, and the thermal transfer and mechanical response behavior of the Sn/Cu interconnect are investigated by numerical simulation. The work has taken into account the interaction between heat transfer and phase change, and coupling the influence of temperature on the thermal mismatch induced mechanical behavior. Furthermore, the results obtained from the macro-scale thermo-mechanical simulation are fed into a phase field model to predict the solidification microstructure of Sn during self-propagating exothermic reaction bonding.

Multilayer separate polymer injection in concentric dual-tubing is a special method for enhancing oil recovery in later development stage of the multilayer formation. During the injection process, heat exchange occurs among the inner tubing, tubing annulus and formation, making the thermal transfer process more complicated than traditional one. This work focuses on the polymer flowing characteristics during the multilayer separate polymer flooding injection process in the wellbore. A temperature&ndash, viscosity numerical model is derived to investigate the influencing factors on polymer dual-tubing injection process. Then, an estimate-correct method is introduced to derive the numerical solutions. Several influences have been discussed, including the axial temperature distribution, viscosity distribution, pressure drop, and flow pattern of polymer. Results show that under low injecting rates, below 5 m3/d, formation temperature will greatly decrease the polymer viscosity. When the injecting rates above 20 m3/d, the polymer just decreases 1&ndash, 3 mPa&middot, s at the bottom of well, which is really small. Additionally, the temperature distribution, the coefficient of friction under different injecting rates have been discussed. Generally, this method provides a new way to analyze thermal conductivity during the polymer injection process which is meaningful for polymer flooding in the oilfield application.

Metal matrix composite (MMC) materials have attracted tremendous interest since the early 2000s because of their superior physical, mechanical, thermal, and electrical properties compared to pure metals or alloys. The interest in developing MMCs can be explained by their unique features but especially by the fact that the properties can be tailored depending on the nature and concentration of the reinforcements. MMCs have found applications in a vast number of industries, such as aerospace, automotive, electronics which are the focus here. The constant increase of power and packing densities in power electronic devices has led to heat dissipation issues. Significant demand for developing an efficient heat-dissipating material with a high thermal conductivity (TC) and a low coefficient of thermal expansion (CTE) has appeared in the past decades. To meet this demand, it is necessary to fabricate a material compatible with the electronic chip while ensuring the reliability of the power modules. Among the large number of MMCs, copper (Cu) and aluminum (Al) are the most advanced composites for thermal management applications (i.e., base plate, heat sink, and exchanger). Often carbon materials (C) such as carbon fibers, diamond, graphene or carbon nanotubes are added to the metal matrix because of their high TC and low CTE values. Cu/C and Al/C composites materials have already demonstrated their superior properties compare to current electronic packaging. Lower and tailorable CTE were observed depending on the volume fraction of reinforcement (e.g., CTE decreases when C concentration increases). High heat dissipation capability was shown, which surpass commercial heat exchangers. The addition of a lightweight reinforcement lowered the density of the material, making them attractive for aeronautics applications. Finally, high stiffness at elevated temperatures was tested and resulted in dimensional stability for high-temperature applications. Also, it is worth to note that the final properties of MMCs depend not only on the primary constituent of the materials but also on the fabrication methods. In this paper, the Cu/C composites fabricated by powder metallurgy and hot uniaxial pressing are reviewed. Thermal analyses indicate that interfacial treatment is required to achieve high thermal and thermomechanical properties for all processing methods. An in-depth review of the interface control through novel surface treatments is presented such as interphase creation and unique processing methods. The review also focuses on the thermal transfer between the matrix and reinforcement. It is shown that proper control of the interfaces will form the right chemical/mechanical bonding, which enhances thermal and thermomechanical properties of the Cu/C composites.

A systematic, carbon-based composite phase change materials with substantial increase of the thermal conductivity and energy storage density was assembled by encapsulating PEG into graphene foams (GF), CNTs and hierarchical porous materials derived from GF and CNT. The influence of preparation approaches on the microstructures, thermal conductivity and thermal energy densities of composites were assessed by various characterization tools. The results obtained indicated that graphene foam-CNT hybrid structures (GCNT) composites exhibit excellent thermal conductivity, 118% higher than pure PEG and 89.5% higher relative to that of GF/PEG@CNT (GPC) composites. The content and interconnected hierarchical porous carbons enhance thermal transfer in composites during the process of phase change. Notably, GCNT@PEG (GCP) had a maximum of up to 80 wt% PCM loading. This composite has a melting latent heat of 128.7 kJ/kg, up to 39.3% and 87.5% higher than those of other composites. CNTs have significantly enhanced the thermal transport of composite PCMs, but the interfacial thermal resistance of CNTs and graphene foam is the bottleneck of heat transfer of composite PCMs. The current results create the conditions for the application of novel hierarchical porous carbon composite PCMs for high-energy density, thermal energy conversion, and shape-stabilized PCMs (ssPCMs) with improved thermal conductivity.

The thermal properties (thermal transfer and thermal expansion coefficient) of the enhanced epoxy resin (MWCNT / x-TiO2) were studied by weight ratios with the values (0%, 3%, 5%, 7% and 10%) and a constant ratio of 3% of MWCNT. The ultrasonic technology was used to prepare the neat and composites which were then poured into Teflon molds according to standard conditions. Thermo-analyzer sensor technology was used to measure thermal transfer (thermal conductivity, thermal flow, thermal diffusion, thermal energy and heat resistance). The thermal conductivity, flow, and thermal conductivity values were increased sequentially by increasing the weight ratio of the filler while the results of stored energy values and thermal resistance decreased by increasing the percentage of salts. The thermal mechanical analysis was used to measure thermal expansion and elasticity coefficient. The scanning electron microscopy was used to interpret the results of thermal analysis and distribution of the nanoparticle within the polymer matrix.

A dew point (DP) sensor structure was proposed with active temperature control using the thermally conductive electrodes on the quartz crystal microbalance (QCM). Two copper wires were bonded on both sides of the QCM via the conductive adhesive as the main heat transfer components. The transmittal of the temperature and the fixation of sensitive cell were realized by the connection of electrode pins. Finite element analysis was carried out to theoretically validate the high-temperature transfer efficiency and good vibration characteristics of the structure with optimal dimensions. Gases with different DP were measured to evaluate the performance of the sensor. The accuracy of the DP sensor was found to be ±0.22 °C DP in the range of 5 °C DP ~16 °C DP by referencing to a commercial MICHELL S4000 DP meter.

Electronic and circuit components become smaller but easier to produce heat nowadays. Finding a kind of materials with high thermal conductivity to dissipate the heat is greatly needed. In this work, a fluorinated epoxy monomer, 3-trifluoromethyl phenylhydroquinone epoxy resin (3-TFMEP) with good mobility was synthesized. The fluorinated epoxy resins also show low dielectric constant and hydrophobic nature. Then a kind of inorganic filler, boron nitride (BN), with high thermal conductivity was chosen to make the hybrid resin mixture. The epoxy resins' mixture both showed the advantages of simple epoxy resins and considerable thermal conductivity. The good mobility of 3-TEMEP allows a larger addition of filler BN by the maximum mass fraction at 70 wt% in the epoxy resin, thus enhancing the thermal conductivity of 3-TEMEP up to 1.2 W/mK, which is about 10 time higher than the pristine 3-TFMEP epoxy resin. These properties ensure these fluorinated hybrid epoxy resins to have great potential in the application of thermal transfer in the area of electronic and circuit components.

A hybrid nanostructure consisting of montmorillonite−multi-walled carbon nanotube (Mt−MWCNT) was designed and assembled, and further used as reinforcing nanofillers for preparing epoxy-based composites. It was found that Mt could efficiently resist microcrack extension and hinder thermal transfer while MWCNTs anchored on the Mt nanosheets could facilitate the stress and heat transfers and provide mechanical interlocking with the epoxy matrix. Making use of the synergistic effect of Mt and MWCNT, considerable enhancement in thermal and mechanical properties was achieved in the composites. With addition of just 0.5 wt% Mt−MWCNT (Mt:MWCNTs = 10:1, w/w), the tensile strength and modulus of epoxy-based composites were improved by 42.0% and 20.3%, respectively, compared with pure epoxy. Furthermore, the storage modulus in the glassy region increased by 21.2%. Moreover, the glass-transition and onset decomposition temperatures were also significantly enhanced, implying the superior thermal stability of these composites.

Graphene conductive silk substrate is a preferred material because of its biocompatibility, flexibility and comfort. A flexible natural printed silk substrate circuit was fabricated by one step transfer of graphene oxide (GO) paste from transfer paper to the surface of silk fabric and reduction of the GO to reduced graphene oxide (RGO) using a simple hot press treatment. The GO paste was obtained through ultrasonic stirring exfoliation under low temperature, and presented excellent printing rheological properties at high concentration. The silk fabric was obtained a surface electric resistance as low as 12.15 KΩ cm−1, in the concentration of GO 50 g L−1 and hot press at 220 °C for 120 s. Though the whiteness and strength decreased with the increasing of hot press temperature and time slowly, the electric conductivity of RGO surface modification silk substrate improved obviously. The surface electric resistance of RGO/silk fabrics increased from 12.15 KΩ cm−1 to 18.05 KΩ cm−1, 28.54 KΩ cm−1 and 32.53 KΩ cm−1 after 10, 20 and 30 washing cycles, respectively. The results showed that the printed silk substrate circuit has excellent washability. This process requires no chemical reductant, and the reduction efficiency and reduction degree of GO is high. This time-effective and environmentally-friendly one step thermal transfer and reduction graphene oxide onto natural silk substrate method can be easily used to production of reduced graphene oxide (RGO) based flexible printed circuit.

A multi-field coupled numerical model was proposed to calculate the weld pool dynamics during the full-penetration laser beam welding of 12 mm thick aluminum alloy plates under the function of a longitudinal magnetic field. The model dealt with the melt flow, heat transfer, solid-liquid transition and magnetic diffusion phenomena in welding process. The Lorentz force directing from the keyhole to the liquid-solid interface was induced in magnetic field supported cases. The Marangoni convection near the weld pool surfaces was obviously weakened due to the electromagnetic braking effect, which was featured with decreased velocity and compressed vortex. The heat transfer condition was largely changed, resulting in declined weld pool dimensions. When the magnetic flux density applied was larger than 0.5 T, the convective heat exchange at the middle height of weld pool became notable again due to the reversed melt flow direction. The liquid-solid lines with lower curvature were achieved. The reinforcement of Hartmann effect became limited. The model and the simulated weld pool morphologies were verified in experiment.

This paper proposes a numerical method to study the effect of pore shapes on the effective thermal conductivity (ETC) of cellular concrete by a two-dimensional model. Cellular concrete can be seen as a composite of two phases with pore and cement paste. The model is established by two steps. Firstly, a generation of two-dimensional representative volume element of cellular concrete microstructure is necessary. Secondly, a finite element method is adopted to simulate heat transfer through the pixelated microstructure. Simulations are validated against analytical approximations, as well as experimental data from the literature. The model can also be used to evaluate the pore size distribution and orientation effects that are hard to measure only in laboratory experiments. It is concluded that ETC decreases when triangle pores substitute for circular pores on account that the tortuosity increases continuously. The other shapes of non-circular pores (square, pentagon and hexagon) have negligible effects on ETC. For ellipse cases, ETC decreases with increase in aspect ratio and volume fraction of pore. In the case of aligned pores, the ETC is larger along the principal axis. However, the size distribution of pores seems to have an insignificant influence. The numerical results suggest that the finite element method (FEM) considering quantitative data of thermal transfer behavior of cellular concrete can be obtained by the pore shapes, and it may be of great help to the optimization of materials.

Hollow core units were developed in the 1950s when long-line prestressing techniques evolved. Ever since then extensive studies followed concerning this particular field for concrete structures. Design methods of hollow core slabs have no requirements for transverse reinforcements which make it more prone to shear failure especially at elevated temperatures. It is understandable that the behaviour of hollow core slabs under elevated temperatures is more complex than that of solid slabs. The longitudinal wholes cause discontinuity in thermal transfer even though webs are effective parts transferring thermal loads to the unexposed parts of the structural element. Even if several influencing parameters have been investigated in order to evaluate their influence on different failure mechanisms of the hollow core slabs at elevated temperatures, still further efforts are needed. This paper presents a review for influencing parameters, failure modes and code provisions for hollow core slabs at elevated temperatures.

It is difficult for traditional cooling liquids to meet equipment requirements due to the high power and high integration they demand. Nanofluids are nanoparticle dispersions with high thermal conductivities, thus they have been proposed for heat transfer applications. Boron nitride nanosheets (BNNSs) possess high thermal conductivities and excellent insulation properties. Here, we fabricated BNNS nanofluids and investigated their effects on thermal conductivity enhancements. We find that BNNSs can effectively enhance the thermal conductivity of water. The thermal conductivity of the BNNS nanofluids reached 2.39 W mK-1 at 24 vol% loading. The surface temperature changes of the nanofluids and water were observed during the heating process using an infrared camera. The results show that the nanofluids transfer heat much faster than water, indicating that the fabricated BNNS nanofluids have excellent thermal transfer properties.

Low energy Ar+ ion beam bombardment is adopted as a pretreatment process of diamond particles for fabricating diamond/aluminum composite. We demonstrate that the combined effects of higher defect density and concentration of oxygen functional groups on diamond {100} plane lead to a selective interfacial bonding in the raw diamond/aluminum composites. It limits the thermal transfer performance of the composite. With the help of ion implantation and cleaning effects, similar diamond surface states are obtained by a conversion of sp3 C to sp2 C which occurs on both the diamond {100} and {111} planes simultaneously. The similar surface states are beneficial for the aluminum matrix adhered to the bombarded diamond surface uniformly during the interfacial reaction. Furthermore, the mean interfacial thermal conductance between the bombarded diamond particles and the matrix reaches up to 9.3 × 107 W·m− 2·K− 1. The thermal conductivity of the diamond/aluminum composite is improved significantly to 713 W·m− 1·K− 1, indicating that low energy ion beam bombarded is a promising approach for further improving the interfacial bonding and the thermal conductivity of the diamond/aluminum composite.

Due to the increased power density of electronic devices, the heat originated from the core components increases the working temperature of the devices, enormously degrading their reliability and shortening their lifespan. So, effective heat dissipation from high-power electronic devices has become an urgent and complex problem. Herein, we report epoxy-based composites with an enhanced thermal conductivity by using reduced graphene oxide encapsulated copper sphere (Cu@rGO) hybrids as fillers. The Cu@rGO hybrid exhibits a 3D structure with high oxidation resistance. The obtained polymer composites exhibit a high thermal conductivity (7 W m−1 K−1), as the loading of the Cu@rGO hybrids is 80 wt%, which is 2.6 times higher than that of the polymer composites filled with only Cu spheres. The high thermal conductivity might be attributed to the synergistic effects between spherical Cu and rGO nano-sheets, which enhanced the oxidation resistance of copper and increased the thermal transfer path, along with the reduced interfacial thermal resistance between Cu and epoxy resins. In addition, the Cu@rGO/epoxy composites reveal a decreased thermal expansion coefficient (CTE), an increased glass transition temperature (Tg), and an enhanced shear strength. This unique 3D core–shell Cu@rGO structure and its epoxy composites with high thermal conductivity and dimensional stability could be suitable as excellent thermal interface materials in advanced electronic packaging techniques.

Insulating polymeric materials with excellent thermal and dielectric properties are highly promising for thermal management applications in future energy systems. However, a well-acknowledged problem is that traditional polymeric composites usually suffer from either low thermal transfer efficiency or high dielectric loss, failing to meet the requirements for simultaneous properties of high thermal conductivity and high electrical insulation. In this work, utilizing aminopropyltrimethoxysilane-functionalized boron nitride nanotubes (BNNT-APS) as fillers, an ideal dielectric epoxy nanocomposite is successfully fabricated. At a low BNNT loading of 10 wt%, the nanocomposites demonstrate a 650% thermal conductivity enhancement at both room temperature and cryogenic temperatures with the preservation of a low dielectric constant and dielectric loss. In addition, a 20% reduction of the coefficient of thermal expansion (CTE) at cryogenic temperatures is achieved at the same time. The superiority of the designed nanocomposites is suggested to stem from the outstanding intrinsic properties of BNNTs, effective surface modification by APS molecules, and low interfacial thermal resistance.