Thermal Conductivity Enhancement Research Articles

Enhanced Thermal Conductivity of High-Density Polyethylene Composites with Hybrid Fillers of Flaky and Spherical Boron Nitride Particles.

The synergistic effect between different fillers plays a crucial role in determining the performance of composites. In this work, spherical boron nitride (BN) and flaky BN are used as hybrid fillers to improve the thermal conductivity (TC) of high-density polyethylene (HDPE) composites. A series of HDPE composites were prepared by adjusting the mass ratio (1:0, 4:1, 2:1, 1:1, 1:2, 1:4, and 0:1) of spherical BN and flaky BN. The SEM results indicate that the spherical BN (with a particle size of 3 μm) effectively filled the gaps between the flaky BN (with a particle size of 30 μm), leading to the formation of more continuous heat conduction paths with the composite. Remarkably, when the mass ratio of spherical BN to flaky BN was set to 1:4 (with a total BN filling amount of 30 wt%), the TC of the composite could reach up to 1.648 Wm-1K-1, which is obviously higher than that of the composite containing a single filler, realizing the synergistic effect of the hybrid fillers. In addition, the synergistic effect of fillers also affects the thermal stability and crystallization behavior of composites. This work is of great significance for optimizing the application of hybrid BN fillers in the field of thermal management.

Enhancing thermal conductivity and dielectric properties of Al2O3@Si/polyphenylene oxide composites by surface functionalization

Recently, soaring developments in 5 G technology have raised an intensive challenge in developing polymer composites with excellent thermal conductivity and dielectric properties. Herein, Al2O3 @Si/MPPO composites were developed through synergistic modification and solution mixing methods. The double bond reaction between Al2O3 @Si and MPPO enhanced the interfacial force and greatly reduced the interfacial thermal resistance and interfacial polarization, leading to highly thermally conductive composites with excellent dielectric properties. The resultant polymer composites exhibited high thermal stability, excellent dynamic mechanical properties, a low dielectric loss of 0.00292, and a high thermal conductivity (TC) of 1.49 W/(m·K), which was 5.21 times higher than that of the pure MPPO resin, making it an ideal thermal management material for electronic devices.

Molecular dynamics study of thermal transport across diamond/cubic boron nitride interfaces

The thermal transport properties at the interface of diamond and cubic boron nitride (c-BN) heterostructures significantly influence heat dissipation in high-power electronic and optoelectronic devices. However, a fundamental understanding of the various parameters modulating the interfacial thermal conductance is still lacking. In this work, we employ non-equilibrium molecular dynamics (NEMD) simulations to systematically investigate the effects of system size, temperature, and defect density on the interfacial thermal conductance across diamond/c-BN interfaces. The results indicate a positive correlation between system length and interface thermal conductance when below the phonon mean free path threshold, attributable to ballistic phonon transport regimes in smaller domains. Additionally, we observe an incremental enhancement in interface thermal conductance with increasing temperature, stemmed from intensified phonon-phonon interactions and reduced boundary scattering of thermal energy carriers. The introduction of vacancy and twinning defects is found to hinder interfacial thermal transport due to heightened phonon scattering processes that impede phononic transmission. The interatomic interactions and lattice dynamics are analyzed to provide insights into the underlying thermal transport physics at the atomistic scale. By tuning the system length from 4 to 16 nm, temperature from 300 to 500 K, and defect density from 0 to 0.4%, we achieve tunable control of the interfacial thermal conductance. Our study elucidates the multiscale mechanisms governing thermal transport across diamond/c-BN and provides potential pathways to actively tailor interfacial thermal properties through structural and temperature engineering. The fundamental understandings are valuable for optimizing heat dissipation and enabling thermal management solutions in next-generation power electronics leveraging these materials.

Analysis of thermal storage behavior of composite phase change materials embedded with gradient-designed TPMS thermal conductivity enhancers: A numerical and experimental study

Phase change materials (PCMs) exhibit considerable potential for utilization in energy storage and temperature regulation applications, primarily attributed to their notable latent heat capacity. Nevertheless, the intrinsically limited thermal conductivity of PCMs necessitates the use of thermal conductivity enhancers (TCEs) that possess adjustable features to compensate for greater heat storage efficiency. Porous structures with flexible design freedom have garnered growing interest in contrast to traditional random foams, owing to their significantly larger surface areas and fully interconnected pore networks. This study fabricated three polar form-designed triply periodic minimal surfaces (TPMS) porous structures using selective laser melting (SLM) based on various radial density gradients, namely the uniform density, the linear gradient, and the Boltzmann gradient. The TPMS porous structures were incorporated as TCEs within a paraffin matrix to form composite TPMS-PCMs. The melting behavior of composite TPMS-PCMs during the charging process was investigated by employing both visual experiments and numerical methods. A thorough analysis was undertaken regarding the progression of solid-liquid phase interfaces, temperature distribution, convection distribution, and heat storage rate to elucidate the mechanisms that contribute to enhanced heat transfer. The findings indicate that the configuration of the density gradient has a notable impact on the melting behavior of composite TPMS-PCMs by tuning heat transfer paths. The heat storage rate of the linear gradient case is the highest among the three, reaching 12.1 W, 1.6 times that of the uniform density case, and twice that of the Boltzmann gradient case. Although the Boltzmann gradient case has the lowest heat storage rate, it demonstrates exceptional performance in terms of temperature uniformity. The average temperature gradient along the radius during melting is 348.6 °C/m, which is only 59% observed in the linear gradient case and 56% in the uniform density case. These findings substantiate the effectiveness of the radial gradient density design in the control of the thermal storage process of composite TPMS-PCMs. They serve as a reference for optimizing thermal storage and temperature control systems that rely on latent heat storage in the future.

Thermal characteristics enhancement of Paraffin Wax Phase Change Material (PCM) for thermal storage applications

This study investigates the integration of graphene nanoplatelets and nano SiO2 into paraffin wax to enhance its thermal energy storage capabilities. Dispersing graphene nanoplatelets and nano SiO2 nanoparticles at weight percentages of 0.5 and 1.0 respectively, in paraffin wax yielded mono and hybrid phase change materials (HYB). Transmission electron microscopy, Field Emission Scanning Electron Microscopy and X-ray diffraction were used to determine the size and phases of secondary particles of graphene nanoplatelets and nano SiO2. Differential Scanning Calorimetry, Thermogravimetric Analysis and Thermal Conductivity Measurement were employed to investigate the impact of hybrid nanoparticles on thermo physical characteristics of paraffin wax. The weight fraction of nano particles distributed in the PCMs is directly related to the enhancement of thermal conductivity of hybrid PCM. The highest enhancement in thermal conductivity was observed when hybrid nanoparticles were present at a weight fraction of 1 %. The analysis shows that mixing graphene nanoplatelets and nano SiO2 with paraffin wax was uniform and the hybrid nanoparticles boosted its thermal conductivity by 38 %, 42 %, and 50 %, respectively. Experimental evidence indicate that the addition of nanoparticles can decrease the melting temperature and increase the solidification temperature of hybrid phase change materials (PCMs). When dispersed in large quantities, nanoparticles can alter properties like latent heat, specific heat, and viscosity. These promising findings suggest that graphene nanoplatelets and nano SiO2 can enhance paraffin wax's thermal properties for thermal storage application.

Oriented BN/BNNT heterostructure constructed by interface engineering strategy for polyamide-imide composite film with advanced flexibility and thermally conductive properties

Thermal conductive polymeric materials have aroused increasing attention as thermal management materials in the field of intelligent electronic devices due to their intriguing advantages. However, the discontinuity of phonon transmission path construction represents the bottleneck for thermal conductivity enhancement of composite materials, which limits the practical application of composite materials. Herein, flexible polyamide-imide (PAI) thermally conductive composite films with hierarchical structure composed of synergistically assembled functionalized boron nitride nanosheets (FBN) and polydopamine (PDA)-modified boron nitride nanotubes (FBT) by layer-by-layer assembly strategy are constructed. Benefitting from the optimized interface engineering with the ordered oriented arrangement FBN/FBT filler structure, the obtained composite film with optimized hybrid filler contents exhibits the super high thermal conductivity of 71.1 W·m−1·K−1, prominent thermal conductivity enhancement as high as 3663 % and excellent mechanical flexibility. The introduction of FBT can further expand the thermal contact area attributed to its inherent high thermal conductivity and aspect ratio. Additionally, the consecutive dual-channel phono transmission paths can be constructed in PAI composites under the synergistic action of FBN and FBT, further improving the phonon transmission density and suppressing phonon scattering, which endows PAI composite films with excellent thermal conductivity under low load of filler. The resulting multifunctionalities make the PAI composite films promising for flexible intelligent wearable electronic devices as thermal management materials.

Probing the thermal resistance of solid-liquid interfaces in nanofluids with molecular dynamics.

The significance of interfacial thermal resistance in the thermal conductivity of nanofluids is not well understood, in part because of the absence of measurements of this quantity. Here, we study the interfacial thermal resistance for metal-oil nanofluids of interest as heat transfer fluids for concentrating solar power, using density functional theory and molecular dynamics simulations. Insights on the role of chemical interactions in determining the interfacial thermal resistance are revealed. The results presented here showcase a general picture in which the stronger the chemical interactions between species at the interface, the lower the associated interfacial thermal resistance. The implications toward nanofluid design are discussed. We show that, for this important family of metal-oil nanofluids, the interfacial thermal resistance values are low enough so that it is possible to afford a reduction in particle size, minimizing stability and rheological issues while still offering enhancement in the effective thermal conductivity with respect to the base fluid.

Enhancing interfacial thermal transport efficiently in diamond/graphene heterostructure by involving vacancy defects

The enhancement of interfacial thermal conductance is critical to the efficient heat dissipation in micro- and nano- devices. The introduction of defects is a special method to improve the interfacial thermal conductance. For diamond/graphene heterostructure, the effects of defects in graphene and diamond on interfacial thermal conductance are investigated by molecular dynamics simulation. The increasing of defects in graphene causes the interfacial thermal conductance decreasing first and then increasing. The interfacial thermal conductance will remarkably rise with the increasing of the radius and number of vacancy defects in diamond. The thermal transport process at the interface experiences three stages according to the overlap energy of diamond and graphene. The mechanism of vacancy defect effectively enhancing interfacial thermal conductance is explained by interfacial modes of phonon density of states. The progress made so far could provide a special idea and guidance for improving heat dissipation for micro- and nano-devices.

High-Flexible Phase Change Composites with Enhanced Thermal Conductivity for Electronic Thermal Management

High-Flexible Phase Change Composites with Enhanced Thermal Conductivity for Electronic Thermal Management

Heat transfer and flow characteristics of cuo-al2o3 hybrid nanofluids in slotted finned channels

This study aimed to investigate the heat transfer coefficient of CuO-Al2O3 hybrid nanofluids within a microchannel heatsink, focusing on the impact of flow rate and volume fraction. The thermal conductivity and viscosity of hybrid nanofluids with different particle ratios were investigated. The results showed that the nanofluids have a more remarkable enhancement in thermal conductivity than water. Employing the hybrid nanofluids enhanced the heat transfer coefficient significantly. Furthermore, a slight growth in the friction factor was observed.

Simulation of effect of Nanoparticle dispersed PCM for Cooling of Photovoltaic Panels

Solar photovoltaic (PV) panels are commonly and widely employed source of renewable power generation. Nonetheless, they suffer from very inferior poor light to energy conversion efficiency. This drawback is aggravated further by 0.02% for every Kelvin rise in solar cell temperature. This paper presents a modelling work on PV cooling techniques through phase change material layer integration on rear PV surface. The PCM layer can absorb the excess heat generated in the panel. Making a composite of highly conductive nanomaterial and this PCM as a layer will boost the heat transfer and maintain PV temperatures close to optimum. Vaseline (Petrolatum or soft paraffin) was selected as the PCM due to easy availability. Graphene nanomaterial was the thermal conductivity enhancer. The cooling effect of the PCM nanocomposite was tested at three different front surface temperature. It was found that addition of PCM layer brings the cooling effect at PV front. This effect further enhances on the addition of PCM nanocomposite layer.

Role of four-phonon processes in thermal conductivity of two-dimensional materials and thermal-transport enhancement arising from interconnected nanofiller networks in polymer/nanofiller composites.

Recent research has shed light on the importance of four-phonon scattering processes in the thermal conductivity (k) of 2D materials. The inclusion of 4 phonon scattering processes from first-principles has been shown to lead to a thermal conductivity of ∼1290 W m-1 K-1 in graphene at 300 K, significantly lower than the values predicted to be in excess of 4000 W m-1 K-1 based only on 3 phonon scattering processes. Four phonon processes are shown to be most significant for flexural ZA phonon modes, where the reflection symmetry selection rule (RSSR) is less restrictive for 4-phonon than 3-phonon scattering processes. This combined with the low frequencies of ZA phonon modes, leading to high populations, leads to higher 4-phonon than 3-phonon scattering of low frequency ZA phonon modes in graphene at 300 K. In this review, the role of parameters such as atomic structure, phonon dispersion and temperature on 4-phonon scattering processes in a wide range of 2D materials is reviewed. Materials such as graphene nanoplatelets (GnPs) have been extensively investigated for enhancement of the thermal conductivity of polymer composites. However, such enhancement is limited by the poor interfacial thermal conductance between the polymer and filler material. Interconnected filler networks overcome this issue through highly efficient continuous percolative heat transfer paths throughout the composite. Such 3D networks have been shown to enable ultra-high polymer thermal conductivities, approaching ∼100 W m-1 K-1, and even exceeding those of several metals. In this review, different techniques used to achieve such interconnected 3D filler networks, namely, aerogels, foams, ice-templating, expanded graphite, hot pressing of filler coated polymer particles, the synergistic effect between multiple fillers, and the stitching of filler sheets, are discussed and their impact on thermal conductivity enhancement are presented.

Study on preparation and heat transfer enhancement of expanded graphite/paraffin composites

Using paraffin as the phase change material, expanded graphite (EG) as the carrier, due to the good absorption and the high thermal conductivity of EG, the EG/paraffin composites were prepared. The EG/paraffin composites were characterized by scanning electron microscope (SEM), differential scanning calorimeter (DSC), thermal conductivity meter and temperature patrol instrument. The results show that with the decrease of paraffin content, the latent heat and temperature of phase change of EG/ paraffin composites decrease slightly, and the highest endothermic peak shifts to the left, however, in EG/ paraffin composites, with the increase of EG mass fraction, the thermal conductivity, thermal diffusivity and heat transfer enhancement ability are greatly improved.

Effect of graphene nanoplatelets relative size and polyethylene chain length on the enhancement of thermal conductivity of their composite

Effect of graphene nanoplatelets relative size and polyethylene chain length on the enhancement of thermal conductivity of their composite

Synergistic Enhancement of Thermal Conductivity Through Nano Diamond Coordinated Boron Nitride

Synergistic Enhancement of Thermal Conductivity Through Nano Diamond Coordinated Boron Nitride

Preparation and properties of phase-change materials with enhanced radial thermal conductivities based on anisotropic graphene aerogels.

In this study, anisotropic graphene aerogels are prepared using the heat-flow method. Then, graphene aerogels with nanosilver particles are prepared via a silver mirror reaction. The aerogels are soaked in paraffin wax and the effects on the properties of the wax are investigated. The thermal conductivity of pure paraffin wax is 0.2553 W m-1 K-1. For the prepared PCM, the aerogel content was 0.92 vol%; this increases to 1.2234 W m-1 K-1, which corresponds to a thermal conductivity enhancement efficiency of 582%. The axial thermal conductivity is 1.4953 W m-1 K-1, which corresponds to a thermal conductivity enhancement efficiency of 746%. The graphene aerogels with the nanosilver particles show high phase-change efficiency. Owing to the significant improvements in the axial and thermal conductivities, the radial and axial heat transfer properties show good consistency suitable for practical applications.

Enhanced Thermal Conductivity of Polymeric Composite with BN@C Hybrid Fillers

Enhanced Thermal Conductivity of Polymeric Composite with BN@C Hybrid Fillers

Flexible carbon‐based fluoropolymer composites for effective EMI shielding and heat dissipation

AbstractContemporary applications require protection against overheating and electromagnetic radiation interference, preferably with reduced mass and enhanced basic performance, such as flammability or chemical or UV resistance and often also low or non‐electrically conductive. Materials exhibiting all these functions can be designed, but there is usually not just one but several different materials with advanced processing requirements; therefore, a simple manufacturing method providing percolation path formation involving powder mixing and hot pressing of providing excellent flexibility terpolymer comprising tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride monomeric units (THV)‐based nanocomposites is presented here. The addition of the graphene nanoplatelets (GNPs) and multiwalled carbon nanotubes (MWCNTs) significantly improves the EMI shielding effectiveness, up to SETOT = 23 dB for the GNP filler, SETOT = 17 dB for the MWCNT/GNP filler per 1 mm samples thickness and enhances almost 900% the thermal conductivity to almost 2 W/mK per GNP filler. Besides this improvement, the electrical conductivity remains at a low level, not surpassing 1.5 S/cm, which is, as mentioned above, beneficial in many applications, especially thermal management. Moreover, the proposed material is an excellent alternative to flexible foam or sponges.Highlights Structural, electrical, EMI shielding, and thermal properties of flexible THV/GNP, THV/MWCNT, and THV/MWCNT/GNP nanocomposites are shown here. The oriented, long as over 1 mm filler paths are observed. The GNP filler provides the best thermal conductivity enhancement of over 800% compared to bare polymer. The EMI shielding effectiveness is dominated by absorption for all THV‐based nanocomposites. The electrical conductivity follows the power law, reaching σ = 1.49 S/cm for GNP‐filled nanocomposites.

Thermophysical properties of suspensions with [NI₃(μ₃-PPZA)₄CL₂] metal string complex microparticles

The study investigated the thermophysical properties of suspensions containing Ni₃(μ₃-ppza)4Cl₂ metal string complex (MSC) microparticles in aqueous glycerol solutions. The results showed that the use of microparticles of monocrystalline metal string complexes Ni₃(μ₃-ppza)4Cl₂ and Ni₅(μ₅-pppmda)4Cl₂ leds to the highest thermal conductivity enhancements and a decrease in freezing point. A comparative analysis of thermal conductivity enhancements of suspensions with micro- and nanoparticles was also conducted. Compared to the base fluid, at 5% volume fraction Ni₃-water-glycerol showed a 72% increase in thermal conductivity, while Cu-water-glycerol and Ni5-water-glycerol showed enhancements of 53% and 47%, respectively. The study suggests that the higher stability of suspensions with MSC microparticles, due to the formation of hydrogen bonds between the organic fragments of particles and water molecules, thier lower density and the formation of particle assemblies, is responsible for the significant thermal conductivity enhancement compared to nanofluids. The colloidal structure of suspensions with MSC microparticles greatly affects their thermophysical properties. Keywords: nanofluid, microfluid, metal string complex, thermal conductivity, suspension.

Development of hybrid MgO/GO modified microencapsulated phase change material for thermal energy management: An experimental approach

The microencapsulation technique addresses the concerns of phase change material (PCM) leakage, transportation challenges, and limited efficacy in thermal energy management applications. Nevertheless, the organic shell material has lower thermal conductivity, and significant leakage issues. To improve the ability of heat transfer as well as leakage prevention, a novel form of microencapsulated phase change material (MEPCM) with paraffin core, and melamine formaldehyde (MF) shell modified by hybrid magnesium oxide (MgO), and graphene oxide (GO) thermal conductivity enhancer (TCE) interface is fabricated through the process of in-situ polymerization. The results revealed a well-developed TCE interface layer in between the core, and the shell of the modified spherical microcapsules. The modified MEPCMs exhibited a maximum encapsulation rate of 88.0 %, and 177.84 J/g latent heat of melting. The thermal stability of the MEPCMs is increased by 50 °C to 70 °C, and the thermal conductivity is remarkably elevated to 0.44 W/mK. The leakage rate is significantly reduced by 98.58%. The excellent thermal energy storage/release performance of the modified MEPCMs is attributed to the TCE interface, which serves as an efficient medium for thermal conduction. The modified MEPCMs endure exceptional physical, and thermo-chemical properties, that are relevant for thermal energy management applications.