Thermal Conductivity Properties Research Articles

Heat generation effects on the MHD Nimonic 80A-Fe3O4 water hybrid nanofluid flow over a wedge with influence of shape factor of nanoparticles

This study reports both MagnetoHydroDynamics (MHD) and heat generation aspects of a water-based hybrid nanofluid flow with various shapes of the nanoparticles involving Nimonic 80A and [Formula: see text], over a moving wedge. Similarity transformations were adapted to obtain non-dimensional equations and solved using MATLAB bvp4c code. All the results and graphs were formulated after a positive outcome of our results with that available in existing literature. Nusselt number, which signifies the heat transfer rate in a flow, increased with an increase in empirical shape factors of the nanoparticle with a contrasting decrease in the drag experienced during the flow, represented by the skin friction coefficient. The velocity profile decreased at a rate of 0.75% for [Formula: see text] to [Formula: see text] due to the augmenting Lorentz forces while it augmented by 18.9% for an augmenting velocity ratio parameter from [Formula: see text] to [Formula: see text] due to the no-slip boundary conditions. Both the Nusselt number and skin friction coefficients decreased with an increase in magnetic parameter. An increase in the nanoparticle concentration resulted in an incrementing streamline value along with increasing temperature profile due to increasing thermal conductivity of the fluid flow system. The physical significance of the study involves in its applications in nuclear, steel industries, MRI scanning for its anti-corrosive and high thermal conductivity properties.

Thermal-mechanical enhancement investigation of shape memory polymer nanocomposite for anti-/deicing

The oriented arrangement of graphene oxide (GO) and magnetic graphene oxide (MGO) in shape memory epoxy resin (EP) by employing the coupling effect of electric and magnetic fields were investigated. The heat transfer experiments showed that the thermal conductivity of the aligned shape memory MGO/GO/EP composites was 90.29% higher than that of the random doped composites. Through the two-dimensional aligned of MGO, the tensile strength of the shape memory MGO/GO/EP composite was significantly improved. The tensile strength reaches 24.52 and 22.67 MPa along the X and Y direction respectively, which increased of 53.92% and 42.31%. The shape recovery experiments showed that the shape recovery and shape fixity of the two-dimensional aligned composites were 95.55% and 91.49%, which increased by 4.44% and 7.82%. The results demonstrated that the two-dimensional directional arrangements of MGO layers significantly enhance the heat transfer and mechanical properties of shape memory polymer. The improvement of thermal conductivity and mechanical properties directly affected the anti-deicing performance of the composites. Hence, the deicing time of the shape memory MGO/GO/EP composite was 324 s, which represented an 18.2% improvement of the deicing efficiency.

Enhanced thermal conductivity and mechanical properties of extruded Mg-4La-2Al-0.3Mn alloy via hot forging

The Mg-4La-2Al-0.3Mn (LA42) alloy, known for its remarkable thermal conductivity of 110 W/(m⋅K), faces limitations owing to its inherently low strength. In this study, a composite deformation process, involving hot forging and extrusion, was investigated to enhance both the thermal conductivity and mechanical properties of the LA42 alloy. The findings revealed that the composite deformation process effectively precipitated an increased number of solute atoms from the matrix, thereby mitigating the lattice distortion effect and resulting in a superior thermal conductivity of 148.2 W/(m⋅K). Additionally, the combination of hot forging and extrusion proved to be efficient in achieving more pronounced grain refinement with increased dislocation density. Consequently, the yield strength of LA42 alloy was substantially enhanced while maintaining a high elongation, reaching values of 211.1 MPa and 12.5 %, respectively. These exceptional overall properties establish a competitive edge when compared to other state-of-the-art magnesium alloys reported previously.

Compressible thermal interface materials with high through-plane thermal conductivity from vertically oriented carbon fibers

The mechanical properties especially the compression performance are very important for thermal interface materials (TIMs) to mitigate warpage failure caused by stress concentration and reduce contact resistance in practical applications. However, high thermal conductivity and excellent mechanical properties are generally incompatible in traditional TIMs. Herein, we fabricate a high-performance carbon fiber-based TIM by using an extrusion method based on the flow shearing effect. The vertically oriented composite shows a through-plane thermal conductivity up to 18.5 W·m−1·K−1 at 20 wt% carbon fiber content, which is 92.7 times that of pure matrix and 6.3 times that of the random structure. Moreover, the as-prepared material exhibits low hardness of 56 (Shore 00) and outstanding elastic compression performance of 51.4% compression under a pressure of 45 psi. These excellent properties are primarily attributed to the high orientation of the carbon fibers (CFs), thereby establishing a direct and effective thermal conductivity path in the vertical direction. In addition, the synergistic effect of carbon fibers and alumina particles is also beneficial for building thermal conduction pathways. Our work provides an insight to further research in fabricating high-performance flexible TIMs as a promising candidate for applying in advanced thermal management fields.

Interface stress analysis and bonding strengthening exploration of metal layer on the laser-activated copper-clad AlN

Aluminum nitride ceramics has excellent thermal conductivity and insulation property, making it a kind of excellent electronic packaging material. But enhancing the bonding strength between the metal layer and aluminum nitride (AlN) ceramic is a challenging problem. Especially regarding the lack of accurate data analysis on the stress between interfaces, enhancing adhesive strength still relies on blind attempts. By using the finite element method, this study reveals that the shear stress generated between the metal/ceramic interface is concentrated at the interface edge. Based on this finding, a method of inserting micro-pore arrays at the edge is proposed to enhance the interfacial bonding strength. The simulation results show that by inserting micro-pores with an appropriate density, the interface shear stress between metal and ceramic can be reduced obviously by 36 %. Finally, vertical peel-off verification experiments were designed. After inserting micro-pores to the interface, the bonding strength of the interface increased from 8.75 MPa to 11.69 MPa, and the performance was improved by 33.6 %. The experimental results were consist with the simulation results and indicated that the micro-pores had a significant effect on improving the bonding strength.

Boron nitride nanosheets from high shear exfoliation for high-performance thermal conductivity films

Boron nitride nanosheets (BNNSs) with intrinsically ultra-high thermal conductivity have attracted more and more attention and various methods have been proposed to prepare BNNSs-based thermally conductive adhesives. In this work, a liquid phase shear exfoliation process was proposed to prepare BNNSs. BNNSs can be directly prepared by exfoliating h-BN particles dispersed in isopropanol at a controlled rotational speed range of 16,000–22,000 rpm and the maximum yield of BNNSs is up to 32.1%. After the BNNSs were modified with polydopamine (M-BNNSs), the dispersion performance of BNNSs in water was significantly improved. BNNSs were incorporated into a cellulose nanofiber-based adhesive, and the highly thermally conductive films were prepared by a flow-delay process. A tested in-plane thermal conductivity of up to 23.23 W·m−1·K−1 and excellent mechanical properties are demonstrated and thermal infrared images provide a more visual representation of the high thermal conductivity and heat dissipation properties of the film, indicating the promising application of the film in the field of thermal conductivity.

Bidirectionally High‐Thermally Conductive and Environmentally Adaptive Graphene Thick Films Enabled by Seamless Bonding Assembly for Extreme Thermal Management

AbstractWith the rapid development of high‐power electronics in aerospace, communication, and energy storage systems, the huge heat flux poses an increasing threat to the safety of electronic devices. Compared with thin films of a few micro thicknesses, high‐quality graphene thick film (GTF) exceeding hundreds of microns thickness is a promising candidate to solve thermal management challenges owing to higher heat‐flux. However, traditional GTF usually has lower thermal conductivity and weak mechanical properties attributed to disordered sheet alignment and frail interfacial adhesion. Here, a seamless bonding assembly (SBA) strategy is proposed to attain GTF over record hundreds of microns with robust coalescence interfaces. For the GTF‐SBA with ≈250 µm thickness, the in‐plane and through‐plane thermal conductivities are 925.75 and 7.03 W m−1 K−1, approximately two times and 12 times those of the GTF prepared by traditional adhesive assembly method, respectively. Furthermore, the GTF‐SBA demonstrates remarkable stability even after cycled harsh temperature shocks from 77 to 573 K, ensuring its environmental adaptability for long‐term service in extreme conditions. These findings provide valuable insights into the interfacial design of graphene bulk materials and highlight the potential applications of high‐performance graphene‐based materials for extreme thermal management demands.

Electrically regulated thermal conductivity of aramid polymer systems

Aramid polymers, renowned for their electronic insulation and thermal conductive properties, are widely adopted as thermal management materials in power electronics. However, the thermal conductivity of aramid polymers under electric field has not been thoroughly understood. In this study, we investigated the thermal conductivity of amorphous and aligned aramid polymer systems under electrical field utilizing equilibrium molecular dynamics simulations. Simulation results showed that the alignment of polymer chain can significantly enhance the thermal conductivity of aramid polymer systems, achieving up to 10.13 W/m-K. Moreover, polarization of aligned aramid polymer was observed when the applied electric field exceeded 14 V/nm. Interestingly, the thermal conductivity of aligned aramid polymer was selectively modulated by the applied electric field. To unravel the underlying phonon mechanism, the molecular orientation of polymer chains and phonon spectral information were analyzed. Our study provides guidance into understanding thermal transport mechanism and thermal conductivity modulation in polymers.

Multistage Porous Carbon Derived from Enzyme-Treated Waste Walnut Green Husk and Polyethylene Glycol for Phase Change Energy Storage.

The thermal storage performance, cost, and stability of phase-change materials (PCMs) are critical factors influencing their application in the field of thermal energy storage. Porous carbon, with its excellent support, thermal conductivity, and energy storage properties, is considered one of the most promising support matrix materials. However, the simple and efficient synthesis of high-performance and highly active bio-based materials under mild conditions still faces challenges. In our work, a novel method for preparing new functional composite phase-change materials based on enzyme treatment technology and using waste walnut green husk biomass and polyethylene glycol as raw materials was developed. The enzymatic treatment method exposes the internal structure of the walnut green husk, followed by the adjustment of the calcination temperature to increase the adsorption sites of the biochar, thereby stabilizing polyethylene glycol (PEG). The porous properties of walnut green husk biochar effectively regulate the phase-change behavior of polyethylene glycol. In the biochar carbonized at 600 °C, the PEG loading reached 72.09%, and the absorption heat of the solid-solid phase-change material (SSPCM) reached 194.76 J g-1. This work not only enriches the application of biomass in heat storage but also demonstrates the broad prospects of SSPCMs in solar thermal utilization.

Design and performance study of ultra-high temperature CaMnO3/polysilylaryl-enyne absorbing material

This work describes the preparation and properties of a novel category of thermosetting microwave absorbing composite materials. The composites were prepared by a simple solution casting process, employing high temperature resistant polysilylaryl-enyne (abbreviated as PSAE) resin as matrix and perovskite CaMnO3 (abbreviated as CMO) ceramic filler as absorbent filler. The microstructure, electromagnetic, wave absorbing and thermal properties of the CMO-PSAE composites were all examined. The results showed that the increasing fraction of CaMnO3 filler not only densified the microstructure of the composites, but also greatly improved their temperature resistance, thermal conductivity and wave absorption properties. The CMO-PSAE composite doped with 50 vol% CaMnO3 ceramic filler showed the strongest ability to absorb electromagnetic waves, with an effective absorption bandwidth (EAB) of 4.16 GHz and a minimum reflection loss is −53.01 dB. Besides, the thermal conductivity of the composite reached 1.106 W/(m·K). Furthermore, this composite material has exceptional thermal resistance, with the highest Td5 reaching 650 °C. Composites with varying doping levels can be used for specific performance needs in practical scenarios. Thus, such novel CMO-PSAE composites exhibit potential applications in the electromagnetic countermeasure field under high-temperature environments.

Quasi-Hyperbolic Framework Graphite Foam-Based Composites with High Thermal Conductivity and Electromagnetic Shielding Properties Fabricated by an Electrochemical Expansion Method.

Nowadays, the rapid development of electronic devices requires composites with high thermal conductivity and good electromagnetic shielding properties. The key challenge lies in the construction of high-performance conductive networks. Herein, an electrochemical expansion graphite foam (EEG) with a quasi-hyperbolic framework was prepared by an electrochemical expansion method, and then the epoxy resin (EP) was filled to fabricate the composites. The graphite plate was first electrochemically intercalated and then foamed, in which plasticization was caused by weak oxidation in intercalation and the quasi-hyperbolic framework was induced by foaming during expansion. These processes were characterized by Fourier transform infrared (FTIR), micro-Raman, X-ray photoelectron spectroscopy (XPS), and so on. Based on the highly efficient quasi-hyperbolic framework and high-quality graphite structure, the thermal conductivity of the composite reached 43.523 W/(m·K), and total electromagnetic interference (EMI) shielding (SET) reached 105 dB. The heat transfer behavior was simulated by finite element analysis (FEA) in detail. This method of preparing high thermal conductivity and electromagnetic shielding materials has a good application prospect.

SiO2@Al2O3 binary filler: A chance for enhancing the heat transport in rubber composites for tire applications

AbstractThe present study reports on the development of a new binary filler system for rubber composites, SiO2@Al2O3, where Al2O3 sheets are grown onto SiO2 nanoparticles aggregates by a sustainable water‐based soft‐chemistry approach. The aim is to synergistically integrate the intrinsic thermal conductivity properties of Al2O3 with the peculiar reinforcement ability of SiO2 in an easy one‐pot solution, which has been exploited to prepare polybutadiene (PB) model composites by a simple solvent casting technique. More in detail, the binary filler was used as‐prepared or suitably surface functionalized with 3‐(Trimethoxysilyl)propylmethacrylate (TMSPM). The filler compatibilization and interplay with the polymeric matrix have been inspected by solid state NMR in conjunction with scanning electron microscopy. These investigations highlighted that the presence of alumina in the binary filler does not undermine the capability of silica in generating polymer chains stiffening and indicated a significant effect of the silanization in providing better filler networking and interaction with the PB host ensuring, in principle, an enhanced thermal transport. Accordingly, thermal conductivity measurements revealed that SiO2@Al2O3 introduction in PB induces a remarkable upgrade of the heat transfer, which becomes much more relevant upon surface modification with TMSPM. These results appear encouraging, paving the possibility of applying SiO2@Al2O3 model system to more complex case studies, where both improved thermal conductivity and enhanced reinforcement are required, such as tires tread formulations.Highlights A new SiO2@Al2O3 binary filler system was proposed following a soft‐chemistry approach. The binary filler was functionalized to enhance its compatibilization. Fillers were dispersed in polybutadiene by a simple solvent casting technique. Thermal conductivity measurements revealed a remarkable upgrade of the heat transfer ability.

Study on the potential of multi-performance enhanced phase change materials in battery thermal management

Lots of research has proved the effectiveness of flexible composite phase change material (CPCM) in thermal management of electronic products. However, the key properties of materials, e.g., flexibility, thermal conductivity and resistance are mutually restricted, further limiting its application in practical thermal management engineering. Unfortunately, the above performance has not been comprehensively considered in the existing research. In this work, a novel shape-stabilized flexible CPCM with considerable comprehensive performance was proposed. Styrene-b-ethylene-co-butylene-b-styrene (SEBS) was used as a flexible matrix to expand the flexible temperature range, and ALN was used to improving the thermal conductivity (0.786 W·m−1·K−1), strengthening the three-dimensional thermal conductivity skeleton of expanded graphite and improving the resistivity to 5.16 × 1010 Ω·m. Meanwhile, the CPCMs showed excellent performance in cycle stability, the melting enthalpy only decreased by 1.29 % after 500 cycles. The result of thermal management exhibited that the maximum temperature (Tmax) and maximum temperature difference (ΔTmax) of the battery at 6C discharge rate were 43.64 °C and 2.39 °C respectively with the help of CPCMs. More importantly, it was also obtained that the thermal conductivity played a major role in the battery temperature control in the long-term operation, the increase of the thermal conductivity reduced ΔTmax by 68.05 %. This work will further provide technical support for the practical engineering application of flexible CPCMs for electronic thermal management.

Preparation and crystallization behavior of sensitive thermochromic microencapsulated phase change materials

A novel sensitive thermo-chromic microcapsules with inorganic/organic nanoparticles-embedded composite shell was designed and synthesized, and the thermal properties, thermo-chromic performance, crystallization behavior of ethyl myristate (EM) in confined spaces were studied in this paper. As the reaction proceeded, the aminated silica (NH2-SiO2) nanoparticles modified outer shell in the aqueous phase and isophorone diisocyanate (IPDI) in the oil phase gradually self-assembled at the inner interface, leading to the formation of an inorganic/organic polymers composite shell. The effect of NH2-SiO2 nanoparticles content on the crystallization behavior, microstructure, morphology, and phase-change properties as well as the thermal stability of MPCMs were investigated in detail. Interestingly, the covalent attachment of NH2-SiO2 nanoparticles on the capsules surface offered long-term chemical stability compared to that of conventional physical adsorption. The NH2-SiO2 nanoparticles were found distributed uniformly on the surface of MPCMs, and the onset crystallization temperature of MPCMs increased by 7.3 °C with NH2-SiO2 nanoparticles addition of 15% content, which counteracts the super-cooling phenomenon. Microcapsule temperature change optical microscopy and non-isothermal crystallization kinetics revealed that the crystallization of RS-MPCMs were homogeneous as well. RS-MPCMs have significant potential in green energy applications due to their latent heat storage, thermal stability, thermal conductivity, leakage prevention, and mechanical properties.

Low-Frequency Evolution Mechanism of Customized HEAs-Based Electromagnetic Response Modes Manipulated by Carbothermal Shock.

An emerging carbothermal shock method is an ultra-convenient strategy for synthesizing high-entropy alloys (HEAs), in which the intelligent combination of carbon support and HEAs can be serve as a decisive factor for interpreting the trade-off relationship between conductive gene and dielectric gene. However, the feedback mechanism of HEAs ordering degree on electromagnetic (EM) response in 2-18GHz has not been comprehensively demystified. Herein, while lignin-based carbon fiber paper (L-CFP) as carbon support, L-CFP/FeCoNiCuZn-X with is prepared by carbothermal shock method. The reflection loss of -82.6dB with thickness of 1.31mm is achieved by means of pointing electron enrichment within L-CFP/FeCoNiCuZn HEAs heterointerfaces verified by theoretical calculations. Simultaneously, low-frequency evolution with high-intensity and broadband EM response relies on a "sacrificing" strategy achieved by construction of polymorphic L-CFP/semi-disordered-HEAs heterointerfaces. The practicality of L-CFP/FeCoNiCuZn-X in complex environments is given prominence to thermal conductivity, hydrophobicity, and electrocatalytic property. This work is of great significance for insightful mechanism analysis of HEAs in the application of electromagnetic wave absorption.

Nanobiolubricant grinding: a comprehensive review

AbstractMinimum quantity lubrication (MQL), which considers the cost, sustainability, flexibility, and quality, has been actively explored by scholars. Nanoadditive phases have been widely investigated as atomizing media for MQL, aimed at enhancing the heat transfer and friction reduction performance of vegetable-oil-based biolubricants. However, the industrial application of nano-enhanced biolubricants (NEBL) in grinding wheels and workpiece interfaces as a cooling and lubricating medium still faces serious challenges, which are attributed to the knowledge gap in the current mapping between the properties and grindability of NEBL. This paper presents a comprehensive literature review of research developments in NEBL grinding, highlighting the key challenges, and clarifies the application of blind spots. Firstly, the physicochemical properties of the NEBL are elaborated from the perspective of the base fluid and nanoadditive phase. Secondly, the excellent grinding performance of the NEBL is clarified by its distinctive film formation, heat transfer, and multiple-field mobilization capacity. Nanoparticles with high thermal conductivity and excellent extreme-pressure film-forming properties significantly improved the high-temperature and extreme-friction conditions in the grinding zone. Furthermore, the sustainability of applying small amounts of NEBL to grinding is systematically evaluated, providing valuable insights for the industry. Finally, perspectives are proposed to address the engineering and scientific bottlenecks of NEBL. This review aims to contribute to the understanding of the effective mechanisms of NEBL and the development of green grinding technologies.

An Experimental Study on the Effect of Nanofluids on the Thermal Conductivity and Rheological Properties of a Coolant for Liquids

Thermal conductivity and viscosity are important properties for nanofluids as they significantly affect the flow and heat transfer process. To date, the rheological properties of water-based nanofluids have been well studied, while the results are scarce for non-aqueous nanofluids. In this study, the thermal conductivity and rheological properties of two different kinds of oxide nanofluids (CuO and Al2O3) in a typical commercial data center focusing on liquid coolants were systematically investigated at different mass fractions and temperatures. The results showed that the addition of nanoparticles can significantly improve the heat conduction capacity of mineral oil coolants. There is an average increase in thermal conductivity of up to 20–25%. The shear rate–shear stress and shear rate–viscosity curves all showed that mineral oil coolant-based oxide nanofluids behaved as Newtonian fluids and that nanoparticles did not cause the increment in viscosity. The effect of temperature on rheological properties was also studied, and the result showed that high temperatures resulted in low viscosity and shear stress. Finally, the effect of particle type was investigated, and it was found that no matter what kind of nanoparticles were added, their effects on the rheological behaviors were the same.

Fabrication of high thermal conductivity and wear resistance graphite/copper composites by microwave hot press sintering

Graphite/copper composites have great potential for tribological applications because of their high thermal and abrasion resistance. In this study, we successfully manufactured graphite/copper composites that demonstrated superior thermal conductivity and wear resistance by employing microwave hot press sintering (MHPS). The results demonstrated an enhancement in the density and hardness of the composites as the graphite particle size increased, owing to the influence of MHPS. Meanwhile, the graphite/copper composite with a graphite particle size of 300 µm has excellent thermal conductivity and friction properties, with a thermal conductivity of up to 679.5 W/mK and a wear rate of only 3.019 10−6 cm3/(N·m). The work is expected to provide a new route for the developing highly thermally conductive and abrasion-resistant materials.

Preparation of ZrP2O7-based fiber composites by in situ synthesis method

ZrP2O7-based fiber composites were prepared by in situ synthesis and their microstructure, thermal conductivity, mechanical and dielectric properties were determined. The chemical reaction with BPO4 as the phosphorus source and nano-ZrO2 as the zirconium source was initiated at 900°C, which promotes liquid-phase sintering and reduces the sintering densification temperature of the ZrP2O7-based fiber composites by generating small ZrP2O7 grains and low-melting B2O3. The lower sintering densification temperature and the appropriate amount of network formers effectively suppressed the high-temperature crystallization phenomenon of the high-silica-oxygen fibers, strengthened the interfacial bonding between the fibers and the matrix, and improved the interfacial debonding problem of the ZrP2O7-based fiber composites. It is found that the ZrP2O7-based fiber composites possess low dielectric constant, low dielectric loss, good thermal conductivity, and acceptable mechanical properties, which can meet the relevant application requirements of centimeter-wave technology.

A new ductile, tougher resin for impregnation of superconducting magnets

A major remaining challenge for Nb3Sn high field magnets is their training due to random temperature variations in the coils. The main objective of our research is to reduce or eliminate it by finding novel impregnation materials in replacement of the epoxies currently used. An organic olefin-based thermosetting dicyclopentadiene resin, C10H12, commercially available in Japan as TELENE® by RIMTEC, was used to impregnate a short Nb3Sn undulator coil developed by ANL and FNAL. This magnet reached short sample limit after only two quenches, compared with ∼100 when CTD-101K® was used. Ductility, i.e. the ability to accept large strains, and toughness were identified as key properties to achieve these results. In addition, we have been investigating whether mixing TELENE with high heat capacity ceramic powders such as Gd2O3, Gd2O2S, and HoCu2, increases the specific heat (Cp ) of impregnated Nb3Sn superconducting magnets. The viscosity, heat capacity, thermal conductivity, and other physical properties of TELENE with high-Cp powder fillers were measured in this study as a function of temperature and magnetic field. The TELENE-87 wt%Gd2O2S had a peak in Cp between 4.3 K and 5.3 K at fields between 0 and 8 T. We have also investigated the effect on the mechanical properties of pure and mixed TELENE under 10 MGy of gamma ray irradiation at the Takasaki Advanced Radiation Research Institute in Takasaki, Japan. TELENE-87 wt%Gd2O2S exhibited exceptional radiation resistance. Impregnating an undulator coil with TELENE mixed with Gd2O2S powder will verify whether the coils’ thermal stability further improves, or whether its low diffusivity will require engineering the material with high-thermal conductivity components. Short magnet training will lead to better magnet reliability, lower magnet margins, lower risk and substantial saving in accelerators’ commissioning costs. Part of this study is supported by the U.S.-Japan Science and Technology Cooperation Program in high energy physics operated by MEXT in Japan and DOE in the U.S.