Thermal Conductivity Enhancement Research Articles

Bidirectional anisotropic bacterial cellulose/polyvinyl alcohol/MXene aerogel phase change composites for photothermal conversion enhancement

The issues of inherent low thermal conductivity, slow heat transport rate and easy leakage are critical challenges for accelerating solar-thermal energy harvesting and storage for organic solid-liquid phase change materials (PCMs). Aerogel carriers with thermal conductivity enhancement based on ice temple methods show favorable potential for PCMs solar thermal applications. Comparing with disordered and unidirectional freezing, bidirectional freezing can assemble efficiently in multiple dimensions and result in long-range ordered structures. In this paper, bacterial cellulose/polyvinyl alcohol/MXene aerogels were constructed by bidirectional freezing. The anisotropic PCMs composites were from vacuum impregnation PEG into aerogel networks. By controlling crystallization and growth of ice crystals through the dual temperature gradients, the PCMs composites obtained enhanced heat transfer efficiency in horizontal and vertical directions. Bidirectional aligned PCMs with PDMS wedge angle of 0° and 20° exhibit high thermal conductivity of 0.716 W m−1 K−1 and 0.768 W m−1 K−1, which were 184% higher than that of PEG, and photothermal conversion efficiency of 55.17% and 76.91%. Remarkably, the PCMs composites with a 20° PDMS wedge angle also exhibited a high PCM loading capacity (96.3%) and a high enthalpy (157.7 J/g). The results show that bidirectional anisotropic PCMs composites have excellent overall performance and are expected to improve solar thermal application.

Preparation of Highly Thermally Conductive Hexagonal Boron Nitride‐Polyvinyl Alcohol/Polydimethylsiloxane Composite Using Combined Freeze‐Drying and Spatial Confining Forced Network Assembly Method

With the rapid advancement of electronic products, an increasing number of electronic components are being integrated onto chips, leading to a higher power consumption per unit area. Consequently, effective heat dissipation has become increasingly important. To address this heat dissipation challenge, this article introduces and prepares a highly thermally conductive polymer composite based on freeze‐drying, coupled with the spatial confining forced network assembly (SCFNA) method. The freeze‐drying process is used to create a three‐dimensional thermal conductive network. This network provides a well‐defined heat path. The SCFNA method enhances the regularity of the thermal conductive network within the matrix. Ultimately, this results in the significant thermal conductivity enhancement of the polymer composite. After freeze‐drying, when the mass ratio of hexagonal boron nitride to polyvinyl alcohol is 4:1, the sample prepared by SCFNA presents 72.6% higher thermal conductivity than the one obtained through direct infiltration. This achievement holds significant value for the advancement of polymer composites with high‐thermal conductivity and excellent mechanical properties. It can improve the low‐dissipation performance of polymer thermal conductive composite systems, meet the needs of high‐performance and low‐dissipation use of thermal management materials, and reduce the working temperature of electronic chips.

Preparation of an Aluminum Powder Composite with Double-Shell Nanostructure: Enhanced Thermal Conductivity Utilizing a Magnetic Orientation Effect

Preparation of an Aluminum Powder Composite with Double-Shell Nanostructure: Enhanced Thermal Conductivity Utilizing a Magnetic Orientation Effect

In51Bi32.5Sn16.5@SiO2 microcapsules-based composite phase change materials with high thermal conductivity and heat storage density for electronics thermal management

Combining phase change microcapsules and various matrix materials can construct novel composite phase change materials (CPCMs). These composite materials hold immense potential for electronics thermal management, owing to their adjustable heat storage capacity and stable shape. Most previous studies focus on enhancing the thermal conductivity of CPCMs by adding thermally conductive fillers or modifying the microcapsule shells. Nevertheless, achieving both high thermal conductivity and heat storage density simultaneously remains a challenge. In this paper, low melting point alloy (In51Bi32.5Sn16.5) was introduced as core material of the microcapsule to enhance the thermal conductivity, due to its significantly higher thermal conductivity compared to commonly used organic or inorganic phase change materials (PCMs). In51Bi32.5Sn16.5@SiO2 microcapsule was synthesized through the sol-gel polymerization method. Furtherly, a form-stable CPCMs consisting of the microcapsules and silicone rubber (SR) matrix were prepared for electronics thermal management. The In51Bi32.5Sn16.5@SiO2 microcapsules exhibit an impressive thermal conductivity of 13.49 Wm−1 K−1, acting as a dual-functional filler for thermal storage and thermal conduction enhancement. Hence, the CPCMs possess a significantly enhanced thermal conductivity of 0.45 Wm−1 K−1, representing a remarkable improvement of 350 % compared to that of pure SR. In addition, the phase change heat storage density of the CPCMs was as high as 71.73 J/cm3. Notable, the prepared CPCMs demonstrate exceptional heat dissipation performance, resulting in a remarkable 23 °C reduction in chip temperature when applied for thermal management. This study offers a novel perspective on the preparation of microcapsule-based CPCMs for electronics thermal management.

Construction of AlN oriented skeletons using in-situ reaction strategy and their enhancement effect on the thermal conductivity of epoxy composites

The development of electronic devices towards miniaturization and integration has put forward higher requirements for polymer-based composites with high thermal conductivity (TC). Aluminum nitride (AlN) is one of the most promising fillers thanks to its high TC (∼320 W m−1 K−1) and outstanding physicochemical properties. However, the traditional composites filled with randomly dispersed AlN particles generally require extremely high filling fraction to enhance the TC, leading to increased production cost and degraded mechanical performance. To address this issue, an innovative strategy combining freezing casting and in-situ reaction process was proposed to directly construct vertically aligned AlN skeletons, which was further used as reinforcements to enhance the TC of epoxy (EP) composites. The close arrangement of AlN particles along the vertical direction was not only beneficial for enhancing the TC, but also improving the mechanical strength. The AlN/EP composites achieved an extremely high TC of ∼8.25 W m−1 K−1 at the AlN filling fraction of 56.2 vol%, which was 45.83 times higher than that of pure EP. The actual thermal management applications and finite element simulations also demonstrated the oriented AlN skeletons exhibited a more significant TC enhancement than that of randomly arranged AlN. Furthermore, the as-prepared AlN/EP composites also exhibited superior thermal stability and dielectric properties, presenting a broad application prospect as thermal management materials for the next-generation electronic devices.

Experimental investigation on the performance of binary carbon-based nano-enhanced inorganic phase change materials for thermal energy storage applications

Phase change materials (PCMs) are considered potential resources for Thermal energy storage (TES) applications. However, the PCMs are limited because of their lower thermal conductivity, resulting in a significant decrease in heat transport and energy storage capability. The foremost objective of the present research is to formulate a novel salt hydrate PCM filled with binary carbon-based nanoparticles (graphene and multi-walled carbon nanotubes) at various weight concentrations and examine the thermophysical properties. A two-step approach is used to formulate binary nanomaterials dispersed salt hydrate PCM. The formulated binary nanocomposite's thermo-physical properties like morphological behaviour, thermal stability, chemical stability, melting enthalpy, optical performance, rate of heat transfer and thermal reliability were characterized. The binary nanoparticle-enhanced nanocomposites can form a decent thermal network, resulting in a remarkable enhancement in thermal conductivity by 160 % (1.2 W/mK) compared to pure salt hydrate. Moreover, a remarkable improvement in optical absorptance and a reduction in optical transmittance by 82.55 % for 0.7 wt% graphene and 0.07 wt% MWCNT enhanced salt hydrate PCM (SAHGrM-0.07) than pure salt hydrate PCM. In addition, the formulated nanocomposites possess excellent heat storage capability, chemical and thermal stability after 300-thermal cycling. The binary carbon-based nanoparticle-enhanced salt hydrate nanocomposites offered acceptable thermal and chemical stability, thermal reliability, and heat transmission characteristics, by this means reflecting its appropriateness for medium-temperature solar TES applications.

Mechanism of enhanced thermal conductivity of hybrid nanofluids by adjusting mixing ratio of nanoparticles

At certain mixing ratios, hybrid nanofluids exhibit superior thermal conductivity performance compared with mono nanofluids, without significant enhancements in viscosity. Studying the microstructures formed by nanoparticles in the base fluid is key to revealing the mechanism of enhanced heat transfer in nanofluidic systems. Here, effects of varying the nanoparticle volume fraction (0.5–2.0 vol%) and Cu:Al volume mixing ratio (20:80, 40:60, 50:50, 60:40, and 80:20) of Cu-Al/Ar hybrid nanofluids were investigated using non-equilibrium molecular dynamics (NEMD) simulations at a temperature of 85 K. The mechanism of thermal conductivity enhancement was elucidated through quantitative analysis of the nanolayer structure and atom trajectory. The results showed that the thermal conductivities of Cu-Al/Ar hybrid nanofluids with a mixing ratio of 20:80 were lower than those of the corresponding Cu/Ar mono nanofluids with volume fraction below 1.3 vol% due to the low quantity of Cu nanoparticles. However, when the quantity of Cu nanoparticles was increased by using mixing ratios from 40:60 to 80:20, the thermal conductivities were higher at all volume fractions. Compared to Cu/Ar nanofluids, the thermal conductivity of Cu-Al/Ar hybrid nanofluids improved from 0.149 to 0.166 W/(m·K) which was higher 2.76 % to 14.48 % as the mixing ratio increased from 20:80 to 80:20 at 2.0 vol%. Radial distribution function (g(r)), the number density and diffusion rate calculations indicated that the density and velocity of Ar atoms around Cu atoms were higher than those of Al atoms due to stronger interactions between Cu-Ar atoms. The main reason for the enhanced thermal conductivity of hybrid nanofluids with increasing mixing ratio was the higher unit nanolayer density and Brownian motion velocity.

Acceleration of heat discharge of composite lauric acid using magnetic dopant

Composite phase-change materials (PCMs), consisting of nanoparticle metal or metal oxide suspended in an organic PCM, are considered promising for overcoming the significant drawbacks of organic PCM, particularly their relatively low thermal conductivity. This paper presents an experimental study of the performance of composite PCMs in terms of chemical stability, thermal stability, phase transition temperature, latent heat, thermal conductivity, and viscosity related to freezing characteristics. The composite PCM consists of an organic PCM of lauric acid (LA) and magnetic dopants of Fe3O4 and CoFe2O4 at concentrations of 2, 5, and 10 wt%. The freezing data revealed the time and temperature characteristics related to the beginning of freezing, the end of the solidification process, and the total crystallisation period. For dopant concentrations below 5 wt%, the dopant increased the heat transfer rate and accelerated the solidification process. However, its effectiveness at the highest dopant concentration of 10 wt% was highly dependent on the microstructure of the dopant particles and its effect on viscosity and thermal conductivity. Based on the data analysis, we proposed a maximum dopant concentration of 5 wt% for the optimum performance of the composite LA using a magnetic dopant—dependent on the particle size that determined the interparticle magnetic dipolar interaction. However, compared with previous experimental findings for non-magnetic dopant particles, the composite FA using a magnetic dopant showed a lower thermal conductivity enhancement and lower time savings for solidification.

Thermal conductivity enhancement and shape stability of composite phase change materials using MIL-101(Cr)-NH2/expanded graphite/multi-walled carbon nanotubes

Low heat conductivity and leakage much restrict the effective use of phase changing materials (PCMs) in heat energy management. Here, an expanded graphite (EG)/ multi-walled carbon nanotube (MWCNT) / metal organic framework (MOF: MIL-101(Cr)-NH2) composite was developed to solve these issues. The porous MOF can avoid the loss of liquid paraffin wax (PW). The heat conductivity of composite PCMs (CPCMs) was improved using EG/MWCNT with a mass ratio of 4:1. The thermophysical properties, heat stability and chemical compatibility of CPCMs were comprehensively investigated. Results demonstrate the successful preparation of CPCMs without any chemical reaction. The MOF (35 %)/EG(4 %)/MWCNT(1 %)/PW(60 %) CPCM exhibits superior thermophysical properties and its melting enthalpy (74.59 J/g) is near the theoretical level after 500 heating/cooling cycles. It exhibits a 792 % increment in heat conductivity from pure PW.

Effect of carbon capture on desulfurization gypsum/carbide slag phase-change composites for waste removal and renewable energy storage

To promote the recycling of industrial waste and produce ultra-low carbon energy storage materials with low-energy consumption this work innovatively proposes to capture carbon dioxide using the mixture made of 70 wt% desulphurization gypsum and 30 wt% carbide slag via a aqueous solution method, and the carbonized mixture used as skeleton material to prepare phase-change composites via cold pression & hot sintering method, and then thermal property, mechanical property and chemical compatibility are investigated. Results show that the carbon capture rate of the skeleton material can reach up to 10.6% at room temperature and can encapsulate the PCM (NaNO3) intact. C-PCC3 has good thermal stability and can undergo 2058 heating/cooling cycles. Compared with the PCC3 (absent carbon capture), the C-PCC3 exhibited a notable enhancement in thermal conductivity by 2.7%. Nevertheless, there was a decrease in mechanical strength from 134.1 MPa to 44.9 MPa, and a reduction in thermal energy storage density from 483.2 J/g to 459.3 J/g. Based on both macroscopic properties and microscopic morphology, the phase change composite materials fabricated in this work exhibit excellent comprehensive property.

Enhancing thermal conductivity of water/CeO2-MWCNTs hybrid nanofluid: experimental insights and artificial neural network modeling

Enhancing thermal conductivity of water/CeO2-MWCNTs hybrid nanofluid: experimental insights and artificial neural network modeling

Fused Deposition Modeling of Isotactic Polypropylene/Graphene Nanoplatelets Composites: Achieving Enhanced Thermal Conductivity through Filler Orientation.

High-performance thermally conductive composites are increasingly vital due to the accelerated advancements in communication and electronics, driving the demand for efficient thermal management in electronic packaging, light-emitting diodes (LEDs), and energy storage applications. Controlling the orderly arrangement of fillers within a polymer matrix is acknowledged as an essential strategy for developing thermal conductive composites. In this study, isotactic polypropylene/GNP (iPP/GNP) composite filament tailored for fused deposition modeling (FDM) was achieved by combining ball milling with melt extrusion processing. The rheological properties of the composites were thoroughly studied. The shear field and pressure field distributions during the FDM extrusion process were simulated and examined using Polyflow, focusing on the influence of the 3D printing processing flow field on the orientation of GNP within the iPP matrix. Exploiting the unique capabilities of FDM and through strategic printing path design, thermally conductive composites with GNPs oriented in the through-plane direction were 3D printed. At a GNP content of 5 wt%, the as-printed sample demonstrated a thermal conductivity of 0.64 W/m · K, which was 1.5 times the in-plane thermal conductivity for 0.42 W/m · K and triple pure iPP for 0.22 W/m · K. Effective medium theory (EMT) model fitting results indicated a significantly reduced interface thermal resistance in the through-plane direction compared to the in-plane direction. This work shed brilliant light on developing PP-based thermal conductive composites with arbitrarily-customized structures.

Preparation of KH550-grafted-nanosilica microspheres to improve the mechanical, thermal and wear resistance properties of fluoroelastomer

We presents an innovative approach to addressing the mechanical properties limitations of fluororubber (FKM) in the industrial field. A novel functionalized nano-silica spheres (SiO2), grafted with amino groups, were constructed by utilizing chemical grafting. The surface modification of the nanosilica microspheres enables the formation of C=N bonds between the amino-functionalized nanosilica microspheres and FKM promoting high dispersion and strong interfacial bonding of SiO2, resulting in an exceptional mechanical enhancement function for FKM composite. Compared to original FKM, the FKM/SM-A-10 composite demonstrates remarkable improvements in both tensile strength and hardness by 242% and 49%, respectively. Additionally, there is a notable 40% enhancement in thermal conductivity of the FKM/SM-A-10 composite. This straightforward and efficient manufacturing approach for achieving high-performance FKM proves to be a valuable and practical foundation for industrial design.

Designing High-Porosity Porous Structures with Complex Geometries for Enhanced Thermal Conductivity Using Selective Laser Melting and Heat Treatment

Designing High-Porosity Porous Structures with Complex Geometries for Enhanced Thermal Conductivity Using Selective Laser Melting and Heat Treatment

Enhanced tough recyclable hemiaminal dynamic covalent network with boron nitride composites material with high thermal conductivity at low filler content

The demand for thermal interface materials (TIMs) with outstanding heat dissipation capability is increasing due to the advancements of multifunctional, miniaturized and well-integrated electronic devices. Simultaneously, as the accumulation of e-waste continues to grow, the recyclability of TIMs has emerged as a pressing concern. Herein, we introduce a novel approach that combines flow casting and hot pressing to create a tough recyclable hemiaminal dynamic covalent network with boron nitride composites film, which shows exceptional recyclability and high thermal conductivity. This approach was accomplished by combining hemiaminal dynamic covalent networks (HDCNs) with ionic liquid crystal exfoliated boron nitride nanosheets (ILC(Cl)-BNNS) via in situ polymerization. The obtained HDCN/BNNS composites film can enjoy a remarkable in-plane thermal conductivity of 2.72 Wm−1K−1 under a BNNS loading of 9.00 wt%, thus achieving an impressive ≈1195% in thermal conductivity enhancement. Furthermore, the HDCN/BNNS composite film enables the recycling of the composites under mild conditions, resulting in the facile recovery of BNNS with nearly pristine morphology and an impressive yield of 72.50%. This work presents a novel approach for the design of recyclable and high-performance TIMs, offering promising prospects for future applications.

Enhancement of interfacial thermal conductance by introducing carbon vacancy at the Cu/diamond interface

Effective heat dissipation of semiconductor devices is crucial for their extended lifespan and operational stability, and the interface of semiconductors provides an effective window for thermal design and management. In this work, we have systematically investigated the effect of the carbon vacancy on the thermal conductivity of diamond and the interface thermal conductance (ITC) of Cu/diamond by using both first-principles calculation and molecular dynamics methods. Although the carbon vacancy leads to a decrease in the thermal conductivity of diamond, a marked increase in ITC from 37.98 MWm−2K−1 to about 177 MWm−2K−1 for diamond (1 1 1) plane and from 78.8 MWm−2K−1 to about 241 MWm−2K−1 for diamond (0 0 1) plane is observed between Cu and diamond with carbon vacancy. The increase of the ITC is mainly due to the anharmonic phonon scattering, revealed by the phonon density of states and phonon participation ratio.

A honeycomb-inspired carboxymethyl chitosan-covalently link NH2-black phosphorene biobased cellulose green nanocomposites with tremendously enhancement fire safety and thermal conductivity

Biobased carboxymethyl chitosan-modified black phosphorene (BP-CMC) was prepared through an amidation reaction between amino group functionalized black phosphorene (NH2-BP) and CMC. Density functional theory (DTF) express that the adsorption energy between urea and phosphene is −6.28 eV, indicating a strong interaction. The resulting BP-CMC was further applied to reinforce the mechanical, flame-retardant and thermal conductivity performance of honeycomb cellulose nanofiber (CNF) film via vacuum filtration. Cone calorimetry test (CCT) result exhibits that the introduction of 30 wt% BP-CMC significantly promoted the fire safety of CNF. For instance, a 98.41% reduction in smoke production rate (SPR), 92.00 % decline in CO release and a 61.31% decrease in heat release rate (HRR) were observed compared to neat CNF. Furthermore, Thermogravimetric infrared (TG-IR) indicates a significant decrease in the release of flammable gases. Raman spectra verify that the incorporation of 30 wt% BP-CMC improves the graphitization degree of residual chars, thus limiting the transfer of heat and oxygen. The improvement in fire safety is attributed to the formation of an intumescent flame-retardant system, which is rich in carbon source (CMC), acid source (BP) and gas source (amino). Simultaneously, the introduction of 30 wt% BP-CMC into CNF leads to considerable enhancement in thermal conductivity (up to 17.49 %), thermal diffusion (utmost to 43.45 %) and heat capacity (increased by 19.23 %). Moreover, the 30 wt % addition of BP-CMC into CNF possesses excellent mechanical properties with the improvement of toughness (increased by 143.50 %) and tensile strength (increased by 140.90 %). This strategy not only provides a new strategy for functionalizing BP but also upgrades the application potential of BP nanosheets in the fire safety of polymer composite films.

Experimental and numerical assessments of thermal transport in phase change material embedding additively manufactured triply periodic minimal surfaces: A comparative evaluation

Phase change materials (PCMs), due to their inherent low conductivity, are presently restricted in their potential applications for thermal energy storage (TES) systems. Extensive effort has been made over the past few years to investigate the potential of porous materials, such as metal foams, as effective thermal conductivity enhancers (TCEs) for PCMs. Porous materials have superior specific surface area over conventional honeycomb structures and fins, providing great potential in thermal storage systems. In this study, taking advantage of the implicit function of triply periodic minimal surface (TPMS), new varieties of lattices with continuous surface structures were developed and then manufactured by using AlSi10Mg powder via selective laser melting (SLM). A three-dimensional transient phase-change heat storage model of TPMS (Primitive and I-WP) structure-paraffin composite PCMs was adopted to study both the phase-change heat transfer performance and heat storage capability of TPMS-PCMs during the phase transition. Meanwhile, the evolution of the solid–liquid interface and temperature–time history were investigated by utilizing the visualized thermal storage experiments. The findings revealed that embedding TPMS lattice decreased the natural convection effect, resulting in a maximum flow velocity of liquid paraffin wax (PX) within TPMS-PCMs that was only 0.1 times that of pure PX. The melting onset time of TPMS-PCMs was advanced by 82.2 %-91.1 %, and the duration of phase change was shortened by 68.3 %-75.9 %, respectively. In addition, the total heat storage of TPMS-PCMs fell from 4464.0 J to 4217.2 J compared to pure PX, but their average heat storage rate rose from 1.04 to 4.58 J/s. Primitive rod (PS)-type TPMS-PCM was the most potential among the three types of TPMS lattices as the TCE for PCM because it achieved the highest heat storage rate with the most negligible overall heat storage loss.

Study on thermal conductivity of micron BN-nano SiO2 combined modified epoxy resin composites

Epoxy resin has attracted widespread attention in the field of power electronic packaging due to its favorable processing technology, high adhesion, and excellent dielectric properties. The enhancement of thermal conductivity in epoxy resin through the incorporation of diverse particles is a prominent area of interest in the realm of modified insulation materials. In this study, hexagonal boron nitride (h-BN) and silicon dioxide (SiO2) with good thermal conductivity were used as doped fillers to modify epoxy resin (EP). The analysis of experimental results indicated that the thermal conductivity of materials with a total doping amount of 20 wt% and a mass ratio of BN to SiO2 of 70:30 to 60:40 could increase the thermal conductivity by 118.1~126.0%. In contrast to pure EP, the thermal conductivity of composite epoxy resin materials has been significantly enhanced.

Thermal conductivity improvement of adipic acid by the addition of AlO(OH) and AlO(OH)@SiO2 core-shell nanoparticles

Phase change materials (PCMs) can store and release a high amount of thermal energy at various operating temperatures. They can be integrated in both thermal management and thermal storage systems. However, the low thermal conductivity of PCMs is a challenge to tackle since it adversely affects the charge and discharge times in (the aforementioned applications). The aim of this study is to improve the thermal conductivity of adipic acid, which is a non-hazardous widely-available organic PCM capable of storing ∼250 J/g of thermal energy at 150 °C. To achieve this goal, boehmite nanoparticles (AlO(OH)) and core@shell nanoparticles boehmite@silica (AlO(OH)@SiO2) are dispersed in molten adipic acid at low concentration (i.e., 0.05. 0.1, and 0.2 wt%). The thermal conductivity measured using modified transient plane source technique (MTPS) shows that the presence of AlO(OH) and AlO(OH)@SiO2 core-shell nanoparticles leads to an increase of the thermal conductivity of adipic acid by 20 % and 14 %, respectively. This enhancement of thermal conductivity is achieved without reducing the enthalpy of the phase transition based on calorimetric measurements. As shown by thermogravimetric analysis, the mass loss of adipic acid is shifted toward higher temperature upon the addition of nanoparticles. Furthermore, the subcooling in nano-PCMs is decreased by 1.3 K compared to the one in pure adipic acid. These promising results bode well for the utilization of enhanced adipic acid as a PCM in thermal energy storage application.