Thermal Conductivity Enhancement Research Articles

Influence of reinforcement with multimodal distribution on thermophysical properties and fracture behavior in Al-Si/SiC composites infiltrated under super-gravity field

Super-gravity field assisted infiltration is reported as an effective method to obtain the nearly fully-dense Al-Si/SiC composites at relatively lower temperature, which inhibit the interfacial reaction and result in the enhancement of thermal conductivity (TC) and bending strength (BS). Currently, SiC reinforcement with multimodal distribution was designed to further enhance the TC and BS with lower coefficient of thermal expansion (CTE) of Al-Si/SiC composites. For the composites with monomodal SiC distribution, enlarging the size of SiC results in an enhancement of TC with the sacrifice of BS. Interestingly, for the composites with multimodal SiC distribution, the TC can be stabilized within an extended range (175-187W/m·K at 373K) with reduced CTE and higher BS. When the large to small size ratio was 1:2, the optimal comprehensive properties (CTE: 8.66×10-6K-1 ranged from 323 to 373K, TC: 179.2W/m·K at 373K, BS: 309 ± 9MPa) can be obtained. Hasselman-Johnson, Turner, and Kerner models are established to better understand the thermophysical properties, while the fracture behavior is discussed based on the track of crack propagation.

Highly thermally conductive BNNS/PANF dielectric composite boards prepared by a facile compression moulding process

The structural design of an efficient heat conduction channel is critical for heat dissipation in electronic packaging material. The build of oriented boron nitride nanosheet (BNNS) network inside polymers has attracted much attention due to its excellent thermal conductivity and dielectric properties. However, to fabricate a BNNS/polymer composite, complex method and low thermal conductive resin for binding BNNS network are commonly involved, which severely restrict its facile production and enhancement in thermal conductivity. Herein, by utilizing para-aramid nanofibers (PANF) as assistance to BNNS to form thermal conduction network, we obtained high performance composite boards with good formability and adjustable sizes via a simple compression moulding of the BNNS/PANF aerogels. The composite boards exhibit a remarkable in-plane thermal conductivity of 10.62 W/m K−1 at 50 wt% BNNS loading, outstanding practical thermal management capability, excellent thermal stability, low dielectric constant and loss, showing great potential for electronic packaging applications. This facile construction strategy provides a feasible way for the large-scale production and application of high-performance thermal management materials in the future.

Analysis of variable fluidic properties with varying magnetic influence on an unsteady radiated nanofluid flow on the stagnant point region of a spinning sphere: a numerical exploration

Abstract The purpose of this article is to invent the impact of inconstant properties of fluids on the nanofluidic stream towards the stagnation area of a revolving sphere. The motion is treated as an unsteady radiated flow with a nonlinear sort of heat radiation. It is presumed to have Brownian motion & thermophoretic impact in our flow model. Additionally, a variable magnetic influence is addressed perpendicularly on the spherical surface. A suitable alteration has been applied to make dimensionless of our prime flow profiles. The translated equations and the limiting restrictions are solved through a numerical approach. The well established method RK4 Shooting technique is utilized here with Maple 2017 software. In the exploration of the consequences of requisite parameters on thermal, concentration, and flow features, numerous schematics are involved. The nature of physical quantities like Nusselt numbers, friction coefficients, and Sherwood numbers is stated in a tabular manner. It is perceived from the outcomes that the fluid velocity towards the x-direction is reduced for the variable viscosity parameter, whereas the unsteadiness parameter promotes it. The enhancement of inconstant thermal conductivity brings a positive influence on the thermal profile of fluid. Nusselt number drops against the thermal radiation & variable viscosity with a rates 4.50% and 25.88% correspondingly.

Enhanced thermal conductivity and mechanical properties of boron nitride@polymethylacrylimide/epoxy composites with self-assembled stable three-dimensional network

Constructing a three-dimensional (3D) network of fillers with high thermal conductivity is considered to be an effective strategy to obtain ideal thermal management materials (TMM). However, 3D filler network is often disrupted by the subsequent processing and forming processes , and it is difficult to incorporate high levels of fillers into lyophilized aerogels, which is a key factor limiting their widespread use. In this work, boron nitride@polymethylacrylimide/epoxy (BN@PMI/EP) composites with a stable 3D BN network were prepared by freeze-drying and hot-pressing. A water-soluble copolymer quaternary ammonium salt has been synthesized by the solution polymerization. BN@PMI aerogel was obtained by the freeze-drying of ammonium salt and BN solution, and thermal imidization. BN@PMI aerogel has a six-membered imine ring structure that can be loaded with a high content of BN, which ensures the stability of the 3D BN network structure and facilitates the subsequent impregnation of EP in vacuum, which is one of the innovations of this work.The stable and complete 3D BN network leads to the enhancement of thermal conductivity, and the out-of-plane and in-plane thermal conductivities of BN@PMI/EP reach 1.21 W·m–1·K–1 and 2.76 W·m–1·K–1 at BN loading of 40% (mass), respectively. Meanwhile, the excellent mechanical properties and results of finite element simulation and actual experiments confirm that BN@PMI/EP is a potential TMM.

Progress and perspective on thermal conductivity enhancement of phase change materials

Progress and perspective on thermal conductivity enhancement of phase change materials

A Comprehensive Evaluation of Recent Studies Investigating Nanofluids Utilization in Heat Exchangers

This comprehensive review critically examines recent research concerning the application of nanofluids in heat exchangers. The utilization of nanofluids, which are colloidal suspensions of nanoparticles in a base fluid, has garnered significant attention in enhancing heat transfer performance. Various studies have explored the potential benefits and challenges associated with incorporating nanofluids into heat exchanger systems. Through a systematic analysis of recent literature, this review assesses the effectiveness of nanofluids in improving heat transfer efficiency and overall performance of heat exchangers. Key parameters such as nanoparticle concentration, size, and type are thoroughly evaluated to understand their influence on heat transfer characteristics. Additionally, factors such as stability, flow behavior, and thermal conductivity enhancement are scrutinized to provide a comprehensive understanding of nanofluid behavior in heat exchangers. The review also addresses potential limitations and areas requiring further investigation to optimize the utilization of nanofluids in heat exchanger applications. By synthesizing recent findings, this review aims to contribute to the advancement of knowledge in the field of heat exchanger technology and nanofluid applications. Ultimately, the insights provided in this review offer valuable guidance for researchers and engineers seeking to enhance heat transfer processes through the implementation of nanofluid-based heat exchangers. Nanofluids offer advantages like enhanced thermal conductivity and tailored properties, promising optimized heat exchanger designs, leading to energy efficiency and reduced costs. However, challenges remain, such as nanoparticle dispersion and cost-effectiveness, necessitating further research for refinement. Interdisciplinary collaboration is crucial for advancing nanofluid applications, fostering innovation to meet demands for sustainable heat transfer solutions.

Enhancing Thermal Conductivity of Phase Change Materials Using Nanomaterials and its Effectiveness in Cooling Solar Cells

The latent heat storage system is considered the most promising technology in thermal energy storage (TES) because of its many advantages. This technique uses phase change material (PCM) as a TES medium. However, the low thermal conductivity (TC) of PCM is the major drawback of the system. Previous studies have shown that the addition of nanomaterials to PCM generally increases its TC. On the other hand, researchers tend to study the possibility of using enhanced PCM to cool solar cells. In fact, raising the solar cell’s operating temperature negatively impacts its efficiency. This problem is considered one of the biggest problems in solar energy systems, and researchers are still working to solve it. This paper focused on the possibility of enhancing the TC of paraffin by adding different shapes of silver nanomaterials to it (silver nanoparticles, silver nanowires and nanohybrid with silver nanoparticles and silver nanowires). Nanomaterials were added at volume fractions of 0.5% and 1%. Then, the study examined the ability to use this improved material to reduce the temperature of solar cells. We used the “Solidworks” program to create a 3D system, and then we used the “Ansys Fluent” software to simulate five cases; PV without PCM, PV with PCM, PV with PCM enhanced by nanoparticles, PV with PCM enhanced by nanowires, PV with PCM enhanced by nanohybrid (a mixture of nanoparticles and nanowires). The results show that using PCM enhanced by nanowire at a volume fraction of 0.5% gave the best results in decreasing the temperature of PV. The average temperature of PV declined by 14.9[Formula: see text]. In addition, the efficiency of PV rose by about 7.6%. Followed by using PCM enhanced by nanoparticles at a volume fraction of 1%. The average temperature of PV declined by 12.9[Formula: see text]. Moreover, the efficiency of PV rose by about 6.6%.

Experimental and numerical study on thermal management performance of PCM-based heat sinks with various configurations fabricated by additive manufacturing

Due to the low thermal conductivity of PCM, the enhancement of thermal performance becomes a crucial issue for the application of PCM-based heat sinks in electronic device cooling. To address this, efficient and integrative PCM-based heat sinks using fin and structured porous material (SPM) are designed and fabricated by additive manufacturing (AM). This work aims to investigate thermal performance of PCM-based heat sinks and the role of fin and SPM used as thermal conductivity enhancers (TCEs). The enhanced heat transfer mechanisms in PCM-based heat sinks using different types of TCEs are determined, and parametric analysis is conducted considering various volume fractions of TCEs (10 %, 15 %, and 20 %). Moreover, the effects of heating power levels and convective heat transfer coefficients on thermal behavior of PCM-based heat sink are analyzed. The results indicate that incorporating SPM in heat sink enhances thermal performance more effectively than using fins for an equivalent TCE fraction. Both heating power and convective heat transfer coefficient have a significant on thermal performance. This research demonstrates the potential of the novel heat sink with SPM in cooling electronic devices and provides the experimental and numerical database for the optimal design and future application of PCM-based heat sink.

Linear stability analysis of micropolar nanofluid flow across the accelerated surface with inclined magnetic field

PurposeThe purpose of this paper is to study the two-dimensional micropolar fluid flow with conjugate heat transfer and mass transpiration. The considered nanofluid has graphene nanoparticles.Design/methodology/approachGoverning nonlinear partial differential equations are converted to nonlinear ordinary differential equations by similarity transformation. Then, to analyze the flow, the authors derive the dual solutions to the flow problem. Biot number and radiation effect are included in the energy equation. The momentum equation was solved by using boundary conditions, and the temperature equation solved by using hypergeometric series solutions. Nusselt numbers and skin friction coefficients are calculated as functions of the Reynolds number. Further, the problem is governed by other parameters, namely, the magnetic parameter, radiation parameter, Prandtl number and mass transpiration. Graphene nanofluids have shown promising thermal conductivity enhancements due to the high thermal conductivity of graphene and have a wide range of applications affecting the thermal boundary layer and serve as coolants and thermal management systems in electronics or as heat transfer fluids in various industrial processes.FindingsResults show that increasing the magnetic field decreases the momentum and increases thermal radiation. The heat source/sink parameter increases the thermal boundary layer. Increasing the volume fraction decreases the velocity profile and increases the temperature. Increasing the Eringen parameter increases the momentum of the fluid flow. Applications are found in the extrusion of polymer sheets, films and sheets, the manufacturing of plastic wires, the fabrication of fibers and the growth of crystals, among others. Heat sources/sinks are commonly used in electronic devices to transfer the heat generated by high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes to a fluid medium, thermal radiation on the fluid flow used in spectroscopy to study the properties of materials and also used in thermal imaging to capture and display the infrared radiation emitted by objects.Originality/valueMicropolar fluid flow across stretching/shrinking surfaces is examined. Biot number and radiation effects are included in the energy equation. An increase in the volume fraction decreases the momentum boundary layer thickness. Nusselt numbers and skin friction coefficients are presented versus Reynolds numbers. A dual solution is obtained for a shrinking surface.

Bio-Inspired Double-Layered Hydrogel Robot with Fast Response via Thermo-Responsive Effect.

Bio-inspired hydrogel robots have become promising due to their advantage of the interaction safety and comfort between robots and humans, while current hydrogel robots mainly focus on underwater movement due to the hydration-dehydration process of thermo-responsive hydrogels, which greatly limits their practical applications. To expand the motion of the thermo-responsive hydrogel robot to the ground, we constructed a hydrogel robot inspired by a caterpillar, which has an anisotropic double-layered structure by the interfacial diffusion polymerization method. Adding PVA and SA to PNIPAm will cause different conformation transitions. Therefore, sticking the two layers of hydrogel together will form a double-layer anisotropic structure. The ultra-high hydrophilicity of PVA and SA significantly reduces the contact angle of the hydrogel from 53.1° to about 10° and reduces its hydration time. The responsive time for bending 30° of the hydrogel robot has been greatly reduced from 1 h to half an hour through the enhancement of photo-thermal conversion and thermal conductivity via the addition of Fe3O4 nanoparticles. As a result, the fabricated hydrogel robot can achieve a high moving speed of 54.5 mm·h-1 on the ground. Additionally, the fabricated hydrogel has excellent mechanical strength and can endure significant flexibility tests. This work may pave the road for the development of soft robots and expand their applications in industry.

Effect of nanosized carbon nanotubes, Titanium Nitride and cubic Boron Nitride powders on mechanical and thermal properties of SLA 3D printed resin composites

AbstractThis study explores the development of nanocomposites by incorporating multi‐walled carbon nanotubes (MWCNT), titanium nitride (TiN), and cubic boron nitride (c‐BN) nano powders into photo‐polymer epoxy resins for use in Stereolithography (SLA) additive manufacturing. Mechanical and thermal properties were systematically investigated to assess their performance. Initially, MWCNT, TiN, and c‐BN nano powders were homogeneously mixed with the resin to ensure uniformity. The resulting mixtures were then processed using SLA technology to evaluate production quality and material performance. The study revealed significant improvements in mechanical and thermal properties compared to pure resin, aligning with previous research outcomes. Specifically, the incorporation of MWCNT led to a notable enhancement in thermal conductivity, showing an increase of 24.21% as the thermal conductivity coefficient increased from 0.19 to 2.36 W/m·k. On the other hand, c‐BN significantly boosted mechanical strength, resulting in a substantial 20.45% increase as the shore D hardness went from 88.53 to 106.64. These findings highlight the promising potential of nanocomposites across various industries including electronics, aerospace, automotive, construction, medical devices, and manufacturing.Highlights Developed nanocomposites with MWCNT, TiN, and c‐BN in SLA resin. c‐BN increased hardness by 20.45%, proving its effectiveness in composites. MWCNT enhanced thermal conductivity by 24.21%, boosting material performance. Pioneering use of TiN and c‐BN in SLA, addressing gaps in existing research. Applications span electronics, aerospace, automotive and medical devices.

Enhanced magnon thermal transport in yttrium-doped spin ladder compounds Sr14−xYxCu24O41

Magnons are quasiparticles of spin waves, carrying both thermal energy and spin information. Controlling magnon transport processes is critical for developing innovative magnonic devices used in data processing and thermal management applications in microelectronics. The spin ladder compound Sr14Cu24O41 with large magnon thermal conductivity offers a valuable platform for investigating magnon transport. However, there are limited studies on enhancing its magnon thermal conductivity. Herein, we report the modification of magnon thermal transport through partial substitution of strontium with yttrium (Y) in both polycrystalline and single crystalline Sr14−xYxCu24O41. At room temperature, the lightly Y-doped polycrystalline sample exhibits 430% enhancement in thermal conductivity compared to the undoped sample. This large enhancement can be attributed to reduced magnon-hole scattering, as confirmed by the Seebeck coefficient measurement. Further increasing the doping level results in negligible change and eventually suppression of magnon thermal transport due to increased magnon-defect and magnon-hole scattering. By minimizing defect and boundary scattering, the single crystal sample with x = 2 demonstrates a further enhanced room-temperature magnon thermal conductivity of 19Wm−1K−1, which is more than ten times larger than that of the undoped polycrystalline material. This study reveals the interplay between magnon-hole scattering and magnon-defect scattering in modifying magnon thermal transport, providing valuable insights into the control of magnon transport properties in magnetic materials.

Enhanced Thermal Conductivity of EP Composites by Introducing BN-Al2O3 Hybrid

Enhanced Thermal Conductivity of EP Composites by Introducing BN-Al2O3 Hybrid

Metal ion-crosslinked thermoconductive sugar-functionalized graphene fluoride-based cellulose papers with enhanced mechanical properties and electrical insulation

Thermally conductive papers with electrical insulation and mechanical robustness are essential for efficient thermal management in modern electronics. In this study, we introduced a metal ion-assisted interfacial crosslinking strategy to strengthen sugar-functionalized graphene fluoride (SGF) and cellulose nanofibers (CNF) by hydrogen bonding and metal ion crosslinking that leads to simultaneous enhancements in thermal conductivity and mechanical properties. The facile sugar-assisted ball-milling exfoliation method was developed to achieve the exfoliation of graphite fluoride and hydroxyl group functionalization on the surface of graphene fluoride. Thanks to the good dispersibility of the SGF sheets in water, the flexible SGF/CNF composite papers with hydrogen bonding were prepared via vacuum-assisted filtration. We introduced hydrogen bonding and metal ion crosslinking into SGF/CNF papers to obtain densely packed composite papers. Ca2+ or Al3+ ion-crosslinked SGF/ CNF papers exhibited superior thermal and mechanical properties owing to hydrogen bonding and metal ion crosslinking. SGF/CNF-Ca2+ and SGF/CNF-Al3+ papers at 50 wt% of SGF yield in-plane thermal conductivities of 72.93 and 75.02 W m–1 K–1, and tensile strengths of 121.5 and 135.7 MPa, respectively. A thermal percolation value was observed at 12.6 vol% of SGF filler content. In addition, the SGF/CNF papers exhibited electrical insulation properties. These remarkable characteristics of the metal ion-crosslinked SGF/CNF papers are attributed to the densely packed structures caused by the strong interfacial interactions from hydrogen bonding as well as metal ion-crosslinking that could promote phonon transport. High-performance metal ion-crosslinked SGF/CNF papers with these fascinating advantages offer great potential for the thermal management of flexible electronics.

Thermal Energy Storage in Concrete by Encapsulation of a Nano-Additivated Phase Change Material in Lightweight Aggregates.

This work discusses the applicability of lightweight aggregate-encapsulated n-octadecane with 1.0 wt.% of Cu nanoparticles, for enhanced thermal comfort in buildings by providing thermal energy storage functionality to no-fines concrete. A straightforward two-step procedure (impregnation and occlusion) for the encapsulation of the nano-additivated phase change material in lightweight aggregates is presented. Encapsulation efficiencies of 30-40% are achieved. Phase change behavior is consistent across cycles. Cu nanoparticles provide nucleation points for phase change and increase the rate of progression of phase change fronts due to the enhancement in the effective thermal conductivity of n-octadecane. The effective thermal conductivity of the composites remains like that of regular lightweight aggregates and can still fulfil thermal insulation requirements. The thermal response of no-fines concrete blocks prepared with these new aggregates is also studied. Under artificial sunlight, with a standard 1000 W·m-2 irradiance and AM1.5G filter, concrete samples with the epoxy-coated aggregate-encapsulated n-octadecane-based dispersion of Cu nanoparticles (with a phase change material content below 8% of the total concrete mass) can effectively maintain a significant 5 °C difference between irradiated and non-irradiated sides of the block for ca. 30 min.

0D/2D Co-Doping Network Enhancing Thermal Conductivity of Radiative Cooling Film for Electronic Device Thermal Management.

The radiative cooling has great potential for electronic device cooling without requiring any energy consumption. However, a low thermal conductivity of most radiative cooling materials limits their application. Herein, a multishape codoping strategy was proposed to achieve collaborative enhancement of thermal conductivity and radiative properties. The hBN-coated hollow SiO2 particles were prepared based on electrostatic self-assembly technology, which were then mixed with hBN platelets and doped into a poly(vinylidene fluoride-co-hexafluoropropylene) substrate. Discrete dipole approximation theory was employed to reveal the mechanism and optimize the particle size. The results showed that the multishape codoping method can significantly improve the radiative performance, with 94.9% reflectivity and 91.2% emissivity. In addition, this zero-dimensional and two-dimensional composite doping structure facilitated the formation of a thermal conduction network, which enhanced the thermal conductivity of the film up to 1.32 W m-1 K-1. The high thermal conductivity radiative cooling film can decrease the heater temperature from 58.8 to 31.3 °C, with a further reduction of temperature by 7.2 °C compared to the radiative cooling substrates with low thermal conductivity. The net cooling power of the film can reach 102.5 W m-2 under direct sunlight. This work provides a novel strategy for high-efficiency electronic device cooling.

Physical Adsorption of Polyacrylic Acid on Boron Nitride Nanotube Surface and Enhanced Thermal Conductivity of Poly(vinyl alcohol) Composites.

To fully tap into the potential of boron nitride nanotubes (BNNTs), addressing their inherent insolubility was imperative. In this study, a water-soluble polymer, poly(acrylic acid) (PAA), was employed as a surface-active reagent, using an accessible and scalable approach. The physical properties and structure of PAA-BNNT were meticulously confirmed through valuable characterization techniques, encompassing X-ray diffraction, scanning electron microscopy, Fourier-transform infrared, X-ray photoelectron spectroscopy, and thermogravimetric analysis. PAA-BNNT exhibited remarkable dispersion in water and demonstrated compatibility with the poly(vinyl alcohol) (PVA) matrix. When incorporating 30 wt % of PAA-BNNT (about 24.75 wt % net BNNT) into the PVA matrix, the thermal conductivity surged by over 21.7 times compared to pure PVA due to the uniform dispersion of high-concentration PAA-BNNT in the polymer matrix.

Molecular insights into thermal conductivity enhancement and interfacial heat transfer of molten salt/porous ceramic skeleton composite phase change materials

Molten salt has been considered as one of the most promising candidate materials for thermal energy storage (TES) systems owing to its remarkable energy density and consistent thermal performance. These properties render it particularly advantageous for the applications in concentrated solar power (CSP) and industrial process heat utilization. Nonetheless, their practical applications still face nonnegligible challenges such as the low thermal conductivity and risk of leakage. Packing molten salts into porous skeletons could be an effective way for addressing these issues. In the present work, the heat transfer characteristics of a composite phase change material (CPCM) consisting of binary chloride salt and a porous ceramic skeleton, are investigated at the microscale level using molecular dynamics (MD) simulations. Simulation results indicate that the integration of a porous SiC skeleton can substantially enhance the thermal conductivity of binary molten salt NaCl/KCl. At the temperature of 1000 K, a notable enhancement of 625.74 % in thermal conductivity has been observed. Moreover, the underlying mechanism of heat conduction enhancement has been revealed from the microscopic perspective. The results demonstrate that auxiliary thermal conductivity paths and interfacial heat transfer play primary roles in determining the thermal conductivity of CPCMs. The method of surface charge modification can effectively improve the interfacial heat transfer and the reason can be attributed to the additional thermal conductivity paths and the large number of particles involved in the interfacial heat transfer. The results gained in this work may provide insights into the heat transfer mechanism of composite molten salt/porous skeleton as well as practical guidance for designing CPCM for thermal storage applications.

Tensile strain induced enhancement of lattice thermal conductivity and its origin in two-dimensional SnC

Tensile strain induced enhancement of lattice thermal conductivity and its origin in two-dimensional SnC

Reversible two-way tuning of thermal conductivity in an end-linked star-shaped thermoset

Polymeric thermal switches that can reversibly tune and significantly enhance their thermal conductivities are desirable for diverse applications in electronics, aerospace, automotives, and medicine; however, they are rarely achieved. Here, we report a polymer-based thermal switch consisting of an end-linked star-shaped thermoset with two independent thermal conductivity tuning mechanisms—strain and temperature modulation—that rapidly, reversibly, and cyclically modulate thermal conductivity. The end-linked star-shaped thermoset exhibits a strain-modulated thermal conductivity enhancement up to 11.5 at a fixed temperature of 60 °C (increasing from 0.15 to 2.1 W m−1 K−1). Additionally, it demonstrates a temperature-modulated thermal conductivity tuning ratio up to 2.3 at a fixed stretch of 2.5 (increasing from 0.17 to 0.39 W m−1 K−1). When combined, these two effects collectively enable the end-linked star-shaped thermoset to achieve a thermal conductivity tuning ratio up to 14.2. Moreover, the end-linked star-shaped thermoset demonstrates reversible tuning for over 1000 cycles. The reversible two-way tuning of thermal conductivity is attributed to the synergy of aligned amorphous chains, oriented crystalline domains, and increased crystallinity by elastically deforming the end-linked star-shaped thermoset.