Significant Improvement In Thermal Conductivity Research Articles

Techniques for Enhancing Thermal Conductivity and Heat Transfer in Phase Change Materials in Hybrid Phase Change Material–Water Storage Tanks

In recent years, extensive research has been dedicated to enhancing energy efficiency and promoting environmental sustainability in heating and cooling systems. Among the promising solutions, phase change materials (PCM) technology stands out as a key area of exploration. This study focuses on improving the thermal performance of PCM–water hybrid tanks by investigating methods to enhance thermal conductivity and heat transfer. Through experimental testing using techniques such as copper matrices, steel twisted matrices, and copper spirals, this study demonstrates significant improvements in thermal conductivity, particularly with the use of copper matrices. The integration of a copper matrix placed in the PCM reservoir increased the heat transfer coefficient and thermal conductivity of the PCM, and thus, the total phase transformation time for solidification was reduced by 79.19% and for melting by 54.7%. Our experimental results demonstrate that the integration of a copper matrix can increase latent heat transfer from 55,677.6 J up to 125,274.6 J, marking a 125% enhancement over the experiment with pure PCM. Additionally, comparisons of the energy storage potentials for different PCMs underscore the benefits of integrating PCMs into hybrid storage tanks. These findings highlight the immense potential of PCM technology to increase energy storage efficiency in heating and cooling applications.

Comparative study of Hiemenz flow in hybrid Carreau nanofluid (Fe3O4-Cu/kerosene-engine oil): nonlinear effects, Newtonian heating and viscous dissipation

ABSTRACT This study is important because it helps us understand how different factors affect the flow of a special liquid with nanoparticles, giving us useful insights for real-world applications in engineering and technology. This research endeavours to explore and contrast the distinctive characteristics of steady, 2-D magnetohydrodynamic (MHD) and stagnation point (Hiemenz) flow in Carreau hybrid nanofluid {Fe3O4-Cu/kerosene-engine Oil} over a nonlinear stretching-shrinking surface with its counterpart, Carreau nanofluid. Employing the laws of conservation encompassing mass, momentum, energy, and concentration, our methodology probes into the multifaceted effects induced by factors like the suction-injection, viscous dissipation, Newtonian heating, Hiemenz flow, thermophoresis, and Brownian motion. This exploration involves the transformation of governing partial differential equations (PDEs) into a system of ordinary differential equations (ODEs) through similarity transformations. Subsequently, the intricate non-linear ODEs are meticulously solved using the bvp4c technique, an adept MATLAB built-in function, facilitating a comprehensive understanding of the intricate dynamics within the system. In addition, the study considers the Newtonian heating effect and a numerical comparison is performed to verify the results. Using two different types of nanoparticles dispersed in kerosene-engine oil, it was demonstrated that increasing Weissenberg parameter values resulted in significant improvements in thermal conductivity and thermal velocity. A comparison of Carreau nanofluid thermal and concentration velocities with Carreau hybrid nanofluid showed that Carreau nanofluid values are lower (Weissenberg parameter). Higher Biot numbers are associated with reduced temperature velocity and elevated concentration velocity.

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In high-energy-demand regions, such as the Arctic, the building sector is focused on reducing the carbon footprint and mitigating environmental impact. To achieve this, phase change materials (PCMs) are being investigated for thermal energy storage due to their high latent heat of fusion. However, their limited applications arise from poor thermal conductivity. In addressing this issue, the research delves into the preparation and characterization of nano-PCMs. These materials, synthesized in a laboratory setting, exhibit enhanced thermal performance compared to pure PCMs, attributed to the incorporation of nanoparticles in the material composition. Therefore, in the study, three paraffins with different melting temperatures (10, 15 and 18 °C) are modified by incorporating titanium oxide at various concentrations (0.05, 0.1, 0.2 and 0.5 mass%). Thermal conductivity and latent heat capacity measurements were undertaken using a thermal conductivity measuring apparatus and differential scanning calorimetry, respectively. The aim was to evaluate the enhanced performance of the modified PCMs in comparison with pure PCMs and to assess their suitability for cold climate regions. Results showed that nanoparticle incorporation increased thermal conductivity by up to 37%, albeit with a slight reduction in latent heat capacity of up to 12%. Among the samples, RT18 exhibited the most significant improvement in thermal conductivity, while RT10 experienced a minor decrease in enthalpy values. Ultimately, RT10 was identified as the optimal PCM option for cold climates, as its phase change temperature range aligns with the outdoor temperatures in the Arctic.

Polyphenylene oxide/boron nitride–alumina hybrid composites with high thermal conductivity, low thermal expansion and ultralow dielectric loss

AbstractTraditional integrated circuit (IC) packaging materials and printed circuit board substrate materials suffer from several limitations including low thermal conductivity, high coefficient of thermal expansion (CTE), and poor dielectric properties. Although significant efforts have been made to enhance these properties, achieving a single composite system with simultaneous high thermal conductivity, extremely low CTE, and dielectric loss remains a formidable task. In this study, we propose a hybrid polymer composite system that addresses these challenges. Our approach involves utilizing a thermosetting polyphenylene oxide (PPO) as the resin matrix, while incorporating boron nitride (BN) sheets with high thermal conductivity and alumina (Al2O3) spheres with favorable fluidity as fillers. To optimize the composite properties, the filler surfaces are modified using dopamine and silane coupling agents, ensuring proper interface control. The composites exhibit significant improvements in thermal conductivity, reduced dielectric loss and CTE, while maintaining excellent processibility. Specifically, with a composition of 25 vol% BN and 25 vol% Al2O3, the thermal conductivity of the composite reaches 2.18 W·m−1 K−1, surpassing neat PPO resin by a factor of 10.9. Simultaneously, the CTE decreases from 2.27% to 1.18% between 50 and 260°C, and the dielectric loss reduces from 0.0024 to 0.0011 at 10 GHz, as compared to neat PPO resin.Highlights The reported novel hybrid composite offers a promising solution to the limitations of traditional IC packaging materials. The reported hybrid composite exhibits significantly improved thermal conductivity, ultralow dielectric loss, and reduced coefficient of thermal expansion, while maintaining excellent processibility. The thermal conductivity of the composites reaches 2.18 W·m−1 K−1, surpassing that of the neat resin by a factor of 10.9, meanwhile the dielectric loss is as low as 0.0011 at 10 GHz, which is extremely difficult to achieve simultaneously for thermosetting polymer composites. Synergetic effects were realized with the hybridization of fillers with different dimensionality, and proper filler surface modification.

Research of the thermal storage properties of thermally conductive carbon fiber-reinforced paraffin/olefin block copolymer composite phase change materials with thermotropic flexibility

This study focuses on the fabrication and evaluation of paraffin (PA)/olefin block copolymer (OBC)/carbon fiber (CF) composite phase change materials (CPCMs) prepared using the melt impregnation process. The resultant PA/OBC/CF CPCMs exhibit superior thermal stability below 200 °C and maintain excellent shape stability at 60 °C. These characteristics are attributed to the alternating soft and hard segments of OBC, wherein the hard segments prevent liquid leakage from PA. The distinct structure of OBC further lends flexibility and recyclability to the PA/OBC/CF CPCMs. The latent heat of these CPCMs ranges from 169.1 to 197.6 J/g. Notably, the CPCMs variant (PA/OBC/CF-1) with 2 wt% CF addition retains 95 % of its initial latent heat even after 100 thermal cycles, thereby demonstrating superior cycling stability. The thermal conductivity of CPCMs with 10 wt% CF is 1.3 times that of pure PA. This significant improvement in thermal conductivity is attributed to the heat conduction pathways provided by the fibrous CF. These results indicate that the fabricated CPCMs offer substantial promise for utilization in low-temperature waste heat recovery applications.

Design and assessment on a bottom-cut shape for latent heat storage tank filled with metal foam

The utilization of phase change materials (PCMs) holds tremendous potential of heat storage domain. The PCM's refractory at the latent heat thermal energy storage (LHTES) unit bottom hinders the heat storage efficiency, despite the significant improvement in thermal conductivity achieved through the addition of metal foam. This study employs numerical simulation to examine the impact of applying bottom cross-cut on PCM's spatial distribution in a horizontal LHTES unit. The manuscript analyzes parameters including melting fraction, complete melting time, Rayleigh number, natural convection heat transfer gain, melting phase interface, velocity and temperature distributions, and heat storage. The findings indicate that the proximity to the heating tube results in a reduction of solid volume at the LHTES unit bottom. A 0.6 bottom cross-cut ratio leads to an 18.84 % faster heat storage rate compared to a concentric-circle unit. Furthermore, a bottom cross-cut ratio of 0.5 enhances natural convection heat transfer gain by 3.28 times.

Recyclable, Self-Healing, and Highly Thermal Conductive Natural Rubber Nanocomposites Enabled by a Dynamic Covalent Network with Carboxylated Boron Nitride Nanosheets

It is of great significance for saving resources and protecting the environment to endow rubber with excellent recycling ability. Recyclable and self-healing ENR/BN-COOH/GO nanocomposites were prepared through dynamic covalent crosslinking between epoxidized natural rubber (ENR) and carboxylated boron nitride (BN-COOH), and graphene oxide (GO) was used as a reinforcing filler. The constructed dynamic β-hydroxyl ester bond between ENR and BN-COOH resulted in the remarkable enhancement of interfacial interaction and effective energy dissipation, which contributed to good mechanical properties of the nanocomposites, increasing by 116 and 79% in comparison with ENR and ENR/GO, respectively. An exchangeable β-hydroxyl ester bond could regulate a network topology structure via a transesterification reaction at the interface, endowing ENR with desirable recycling and self-healing ability. Moreover, the significant improvement of thermal conductivity for ENR/BN-COOH/GO nanocomposites was achieved, reaching 2.853 W/(m·K) at only 6 wt % BN-COOH content, indicating the formation of effective thermal conductive paths via the β-hydroxyl ester bond and hybrid thermal conductive network of BN-COOH/GO. Meanwhile, the thermal conductivity of recycled samples still maintained a high level due to the construction of the stable thermal conductive network. Such a facile strategy exhibits a promising perspective in preparing recyclable and highly thermal conductive rubber nanocomposites for applications in efficient thermal management fields.

Significant Improvement of Thermal Conductivity of Polyamide 6/Boron Nitride Composites by Adding a Small Amount of Stearic Acid.

This study investigates the effect of adding stearic acid (SA) on the thermal conductivity of polyamide 6 (PA6)/boron nitride (BN) composites. The composites were prepared by melt blending, and the mass ratio of PA6 to BN was fixed at 50:50. The results show that when the SA content is less than 5 phr, some SA is distributed at the interface between BN sheets and PA6, which improves the interface adhesion of the two phases. This improves the force transfer from the matrix to BN sheets, promoting the exfoliation and dispersion of BN sheets. However, when the SA content was greater than 5 phr, SA tends to aggregate and form separate domains rather than being dispersed at the interface between PA6 and BN. Additionally, the well-dispersed BN sheets act as a heterogeneous nucleation agent, significantly improving the crystallinity of the PA6 matrix. The combination of good interface adhesion, excellent orientation, and high crystallinity of the matrix leads to efficient phonon propagation, resulting in a significant improvement in the thermal conductivity of the composite. The highest thermal conductivity of the composite is achieved when the SA content is 5 phr, which is 3.59 W m-1 K-1. The utilization of a composite material consisting of 5phr SA as the thermal interface material displays the highest thermal conductivity, and the composite also demonstrates satisfactory mechanical properties. This study proposes a promising strategy for the preparation of composites with high thermal conductivity.

Experimental Studies and Analytical Analysis of Thermophysical Properties of Ethylene Glycol–Water-Based Nanofluids Dispersed with Multi-walled Carbon Nanotubes

The present study investigates the thermal conductivity and dynamic viscosity of ethylene glycol–water solutions dispersed with oxidized multi-walled carbon nanotubes. The physico-thermal properties and Mouromtseff number (Mo) were used to evaluate the heat transfer properties of the nanofluids. Ethylene glycol–water mixtures were chosen as base fluids, and the volume fraction of ethylene glycol varied from 100 % to 0 % (pure water). Oxidized multi-walled carbon nanotubes in weight percentages of 0.0625, 0.125, 0.25, and 0.5 were dispersed in ethylene glycol–water mixtures to achieve the best stability. The stability of the nanofluids was monitored by UV–Vis spectroscopy for 2 months. The dispersion of multi-walled carbon nanotubes in the base fluids resulted in a significant improvement in thermal conductivity. To derive correlations for thermal conductivity and dynamic viscosity, 1 500 data points were collected for all possible combinations of temperature, weight percent of multi-walled carbon nanotubes, and ethylene glycol content. The Mouromtseff number (Mo) showed that dilute nanofluids at low concentrations are the most effective heat transfer medium in turbulent flow.

Assessment of the engineering properties of biomass recycled aggregate concrete developed from coconut shells

This study examines the potential of using biomass recycled aggregates developed from coconut shells to replace aggregates in structural concrete. Compared with natural aggregate (NA), coconut shell has many disadvantages as coarse aggregate in concrete due to the differences in structure, particle shape, and density from NA. Therefore, the contribution of this study is to improve the possibility of using agricultural byproducts in structural concrete. The main experimental work is to clarify the effect of using crushed coconut shell aggregate (CCSA) and synthetic biomass recycled aggregate (SBRA), which are developed based on coconut shell, to replace NA with comparable mechanical properties, shrinkage properties, thermal conductivity, microstructure of concrete. The results indicated that the mechanical strength of concrete with SBRA in 3d and 28d achieved at least 90 % and 80 % strength of that of natural aggregate concrete (NAC), respectively. In addition, compared with NAC, crushed coconut shell aggregate concrete (CCSAC) and synthetic biomass recycled aggregate concrete (SBRAC) show significant improvements in thermal conductivity, showing excellent building energy saving potential. Compared with CCSA, the cement paste matrix surrounding the SBRA can effectively prevent water loss and reduce the thickness of interfacial transition zone (ITZ) to less than 10 mm, thus ensuring the volume stability of concrete; The lower water-cement ratio and carbonized SBRA (C-SBRA) had positive effects on improving the properties of CCSAC and SBRAC, respectively.

Development of high thermally conductive and electrically insulated epoxy nanocomposites with high mechanical performance

AbstractDeveloping polymer‐based nanocomposites with high thermal conductivity, mechanical performance, and electrical insulation becomes a huge challenge in both academia and industry. In this article, the synergistic effects of boron nitride (BN) nanosheets and carbon nanotubes (CNTs) on mechanical properties and thermal conductivity of epoxy nanocomposite adhesives were investigated. The results showed that the addition of one‐dimensional CNTs and two‐dimensional BN nanosheets into the epoxy matrix contributes to the formation of a three‐dimensional network and a larger contact surface between the nanofillers and the epoxy matrix. The hybrid filler of BN and CNTs provided significant improvements in thermal conductivity and mechanical properties of epoxy nanocomposite adhesives. At 1.06 vol% of BN‐CNTs, epoxy nanocomposite adhesives provide higher Young's modulus, fracture toughness (K1C), energy release rate (G1C), lap shear strength, and thermal stability compared with epoxy/BN nanocomposite adhesives. The thermal conductivity of epoxy/BN‐CNT nanocomposites recorded its maximum values of 0.49 K m−1 k−1 at 3.79 vol% and increased by 335% compared with 133% in case of epoxy/BN at the same fraction of 3.79 vol%.

ANFIS modelling of effective thermal conductivity of ethylene glycol and water nanofluids for low temperature heat transfer application

Nanofluids have been proven to be promising coolants for heat transfer application due to their superior thermal properties. In the present work, experimental studies were carried out to investigate the thermal conductivity of ethylene glycol (EG) and water mixture (35:65 v/v in ratio) based CuO, Al2O3 and TiO2 nanofluids. The study has considered nanofluid containing nanoparticles in the concentration range of 0.2 to 2 wt%. The effect of nanoparticle concentration on thermal conductivity was investigated in terms of effective thermal conductivity (ratio of thermal conductivity of nanofluid to that of base fluid) at low temperatures (5 to 25 °C). Results indicated significant improvement in thermal conductivity at lower temperature of nanofluids. Enhancement of 6.34%, 4.87% and 3.59% in thermal conductivity was obtained for 2 wt% of concentration at 5 °C for CuO, Al2O3 and TiO2 nanoparticles respectively compared to EG:Water. Correlations for effective thermal conductivity were developed by regression considering two input (temperature, concentration) and three input (temperature, concentration and nanoparticles thermal conductivity) parameters using experimental results. An intelligent model, adaptive neuro-fuzzy inference system (ANFIS) approach was used to model the effective thermal conductivity of nanofluids. ANFIS model performed better than the correlations developed.

Principal component analysis approach to dispersed graphene oxide decorated with sodium dodecyl sulfate cement pastes

Although researchers have investigated the properties of nanomaterials in cement paste, the relationship between cement paste properties and dispersion properties is not yet understood. Understanding dispersion properties may reveal how nanomaterials changes cement paste properties. In this study, Taguchi-based principal component analysis (PCA) was used to uncover the mechanism of interaction between dispersion and cement paste properties. Using graphene oxide (GO) with smaller particles, higher zeta potential of dispersion, and higher sodium dodecyl sulfate levels led to greater splitting tensile strength, ultrasonic pulse velocity, and hydration rate and lower thermal conductivity, electrical resistance, porosity, and percentage of water absorption. Optimum sodium dodecyl sulfate usage significantly improves the mechanical properties and degree of hydration due to hydrophobic association. A significant improvement in thermal conductivity, calcium hydroxide content, and porosities of 21.33%, 13.88%, and 10.21% was achieved in the cement pastes using a 0.1% GO and a 0.1% sodium dodecyl sulfate by weight instead of cement. The dispersion properties significantly affect the properties of cement pastes, which accounts for 97% of product variability.

Effect of Al2O3 with Different Nanostructures on the Insulating Properties of Epoxy-Based Composites.

High thermal conductivity insulating dielectrics with good electrical properties have received widespread attention due to the continuous development of power systems and power electronic technologies. In this paper, the effects of differently structured nano alumina fillers on the thermal conductivity and insulating properties of polymer-based composites were studied. It was found that all three types of Al2O3 nano-fillers enhanced the thermal conductivity of the composites, and the thermal conductivity increased more dramatically with increasing filler particle size. It is worth noting that Al2O3 nanowires (NWs) exhibited the most significant improvement in thermal conductivity. The volume resistivity of the composites first increased and then decreased with increasing mass fraction of fillers, and Al2O3 nanoplates (NPLs) showed the most significant improvement in the insulation performance of the composites. The dielectric constants of the composites increased with increasing mass fraction of fillers, while the dielectric losses first decreased and then increased with the same trend, yet the mass fractions of fillers for the three materials were different when the dielectric loss reached a minimum. In addition, all three types of filler increased the AC breakdown strength of the composites, but Al2O3-NPLs showed the most significant improvement on the breakdown performance of the composites.

A reduced percolation threshold of hybrid fillers of ball-milled exfoliated graphite nanoplatelets and AgNWs for enhanced thermal interface materials in high power electronics

Thermal interface materials (TIMs) are essential components to deplete the accumulated heat with efficient thermal management in the majority of power electronic systems such that the interfacial thermal resistance (ITR) should be significantly reduced. A reduced percolation threshold of hybrid fillers of ball-milled exfoliated graphite nanoplatelets and AgNWs are used for enhanced thermal interface materials via the assembly of high-quality ball-milled exfoliated graphite nanoplatelets (BMEGN) and AgNWs on a flexible Polydimethylsiloxane (PDMS) substrate. BMEGN modified surface with increased specific area and reduced percolation interface, together with the generation of effective 3D thermal conductive pathways between the 2D graphite and 1D AgNWs, which was experimentally measured to possess the significant improvement in thermal conductivity. The proposed method of thermally conductive film of AgNWs at the loading of 2.0 mg/mL can dramatically increase the in-plane thermal conductivity (K//) to 29.2 W/mK, while the through-plane thermal conductivity (K┴) shows the value of 4.94 W/mK by using the reduced percolation threshold. Anisotropy reaches up to K///K┴ = 5.9 with the proposed percolation, which is much larger than filler only BMEGN, indicating that the effective thermal conductive path (TCP) can be networked on a PDMS polymeric to thermally dissipate high power electronics with enhanced heat management capability. Both CPU and IGBT tests of the proposed TIMs with fillers of AgNWs loading 2.0 mg/mL can effectively minimize temperature rise to ~16 °C and ~17 °C as favorably compared with thermal grease alone. Furthermore, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used for surface morphology, microstructure evolution, disorder evaluation, phase analysis and thermal stability of the composite material.

Fabrication of Poly(butylene succinate) phosphorus-containing ionomers microcellular foams with significantly improved thermal conductivity and compressive strength

Biodegradable microcellular foams with high comprehensive performances were highly desired for many applications. Differed from previous researches, poly(butylene succinate) ionomer (PBSI) foams fabricated by supercritical CO2 were promising for yielding high thermal conductivity and compressive feature. Novel PBSIs microcellular foams with different phosphorus-containing ionic group (PCIG) content (FPBSIs-K) were fabricated in the study. Then, the relationships between the structure and properties, including thermal conductivity, compressive strength and thermal safety of FPBSIs-K were investigated. Strikingly, owing to the physical cross linking by PCIG aggregation, the significant increases in the melt strength generated stronger surface tension and orientation force. Consequently, FPBSI7.5-K (7.5 wt% PCIG content) achieved about 100% closed cell structure, and high orientation for cells. Compared with those of PBS foams, FPBSI7.5-K achieved 10-folds, 9-folds and 5-folds increases in char yield, thermal conductivity and compressive strength, and their values were 15.4%, 315 mW/mk and 3.5 MPa, respectively. The mechanism for FPBSIs-K with significant improvements in thermal conductivity and compressive strength were proposed. Moreover, the incorporation of PCIG promoted FPBSIs-K to form a stable char layer and inhibit the release of combustible gaseous pyrolysis products. This work inspired to develop high-performances biodegradable microcellular foams for environment protection, lightweight structural materials and fire safety.

Thermal performance enhancement of a phase change material with expanded graphite via ultrasonication

It is desirable to improve the performance of phase change materials (PCM)-based thermal energy storage (TES) systems because it increases energy efficiency while decreasing primary energy consumption for low environmental loading. Given that PCM suffers from low thermal conductivity (e.g., due to high latent heat capacity and low phase separation), we investigated several efficient options to improve the thermal conductivity of organic PCM (n-octadecane) based on the addition of (0.1wt%) expanded graphite (EG). The suspension prepared via ultrasonication led to an improvement of 40% in thermal conductivity corresponding to 0.28W/m when compared to that of n-octadecane corresponding to 0.20W/mK. Additionally, the ultrasonication effectively dispersed EG in the PCM for an extended duration relative to the stirring method. A PCM-EG reaction was not evident under ultrasonication conditions. Thus, the thermal conductivity of the PCM exhibited maximum improvement when the two conditions involving extremely low amount of EG and its stable dispersion under sonication condition were maintained. The study demonstrated that a significant improvement in thermal conductivity is obtained with a very low amount of EG and that dispersion stability is obtained even with short ultrasonication times.

Enhancement of Thermal Conductivity of Poly(methylmethacrylate) Composites at Low Loading of Copper Nanowires

We report the synthesis of copper nanowires (CuNWs) and the enhanced thermal conductivity of poly(methylmethacrylate) (PMMA) composites at low-loading fractions of CuNW. The scanning electron microscope, X-ray diffractometer, thermal diffusivity meter, high-resistance meter, universal testing machine, and thermogravimetric analyzer were used to investigate the properties of CuNW/PMMA composites. The elongation strain to failure, toughness, and thermal stability of the PMMA composites significantly increased with increasing contents of CuNW. The CuNW/PMMA composites showed the thermal conductivity and volume resistivity of 0.85 W/mK and 7×1010Ω·m, respectively, at 2.0 wt% of CuNW. The significant improvement of thermal conductivity is attributed to the well-dispersed CuNWs in the PMMA matrix and the high aspect ratio of CuNWs. The experimental results of thermal conductivity fitted well with the Agari model.

Micromechanical estimation of effective thermal conductivities of metal matrix nanocomposites with local carbon nanotube agglomeration

This study aims to estimate effective thermal conductivities of metal matrix nanocomposites (MMNCs) containing carbon nanotubes (CNTs) using a new hierarchical micromechanical method. Nano-filler agglomeration made of CNTs into the MMNCs, frequently encountered in real engineering situations, is considered as the main novelty of this approach. Also, two important parameters, including CNT curvature and interfacial thermal resistance between the CNT and metal matrix are taken into account in the micromechanical modeling. The developed hierarchical approach is validated through the comparison with the experimental measurements available in the literature. When CNTs are not well dispersed into the metal matrix, by incorporating the interfacial thermal resistance, CNT curvature and agglomeration, the predictions are in good agreement with the experiment of MMNC thermal conductivities. The results reveal that the CNT agglomeration can dramatically decrease the MMNC thermal properties. It is confirmed that the key issues to enhance the thermal conductivity of CNT-reinforced MMNCs are homogeneous distribution of CNTs and decrease of CNT/metal interfacial thermal resistance. Also, it is observed that the MMNCs show a significant improvement of thermal conductivity by alignment of CNTs into the metal matrix. The effects of CNT volume fraction, diameter and length on the MMNC thermal conductivities are examined.

Study on epoxy resin-based thermal adhesive filled with hybrid expanded graphite and graphene nanoplatelet

Reinforced epoxy composite adhesives of expanded graphite (EG) and graphene nanoplatelet (GNPs) were prepared by hand layup and mechanical mixing method. Disk-shaped epoxy composite samples with EG and GNP mixtures in varying ratios were prepared to measure the thermal conductivity (TC) enhancement. Thermal characterization testing data showed high thermal conductivity enhancement with three different hybrid filler concentrations of 10, 25, and 35 wt%, respectively. The highest thermal conductivity of 3.6 W/m K was obtained for an epoxy adhesive composite having 30 wt.% EG and 5 wt.% GNP which was tested by guarded heat flow meter technique. This significant improvement in thermal conductivity can be attributed to the lowering of overall thermal interface resistance due to small amounts of nanofiller (GNP) improving the thermal contact between the primary microfillers (graphite). The synergistic effect of this hybrid filler system is lost at higher loadings of the GNP relative to expanded graphite. The structure of the graphite flake, GNP/epoxy, EG/epoxy and hybrid EG/GNP/epoxy composites was investigated by XRD. The EG prepared by acid intercalation and abrupt thermal expansion showed good compatibility with GNP and the epoxy resin. From scanning electron microscopy photographs, the formation of conducting network observed through the expanded graphite and GNPs in a low conducting epoxy matrix. The thermal decomposition temperature of the composite increased to 450 and 615 °C with the addition of 10 and 35 wt% of hybrid EG/GNP inside epoxy matrix, respectively. LAP shear strength of single and hybrid filled epoxy adhesive decreased at 35 wt.% loading than neat epoxy.