Highly anisotropic polyolefin elastomer (POE)/natural graphite (NG) composites with high through‐plane thermal conductivity and excellent mechanical properties, in which NG sheet perfectly aligns ...along one direction, are prepared by two‐roll milling, hot compression, and mechanical cutting. The through‐plane thermal conductivity coefficient of POE/NG composites is markedly improved to be 13.27 W m−1 K−1 at an NG loading of 49.30 vol%. When the composite is used as a thermal management material, it shows excellent heat dissipating capability in the through‐plane direction, which is very important for thermal management in electronic applications. This effective method is highly probable to be widely used for the facile fabrication of polymer‐based thermal management materials.
Highly through‐plane thermally conductive polyolefin elastomer based composites filled with commercial nature graphite (NG) without any treatments are fabricated by a conventional melt‐mixing method of a two‐roll milling method. The as‐fabricated composites with NG flakes perfectly vertically aligning in the matrix reveal high through‐plane thermal conductivity (13.27 W m−1 K−1).
Advanced thermoelectric technology offers a potential for converting waste industrial heat into useful electricity, and an emission-free method for solid state cooling. Worldwide efforts to find ...materials with thermoelectric figure of merit, zT values significantly above unity, are frequently focused on crystalline semiconductors with low thermal conductivity. Here we report on Cu(2-x)Se, which reaches a zT of 1.5 at 1,000 K, among the highest values for any bulk materials. Whereas the Se atoms in Cu(2-x)Se form a rigid face-centred cubic lattice, providing a crystalline pathway for semiconducting electrons (or more precisely holes), the copper ions are highly disordered around the Se sublattice and are superionic with liquid-like mobility. This extraordinary 'liquid-like' behaviour of copper ions around a crystalline sublattice of Se in Cu(2-x)Se results in an intrinsically very low lattice thermal conductivity which enables high zT in this otherwise simple semiconductor. This unusual combination of properties leads to an ideal thermoelectric material. The results indicate a new strategy and direction for high-efficiency thermoelectric materials by exploring systems where there exists a crystalline sublattice for electronic conduction surrounded by liquid-like ions.
•Preparation of hybrid nano-composites and nanofluids.•Stability measurement and enhancement methods of hybrid nanofluids.•Factors affecting thermal conductivity of hybrid nanofluids.•Mechanisms ...involving in thermal conductivity enhancement of hybrid nanofluids.•Correlations to predict thermal conductivity to hybrid nanofluids.
Innumerable studies are conducted on nanofluids containing single type nanoparticles and attributes of such colloidal mixture have been well elucidated and prospected. Furtherance in nano-composites has entitled production of hybrid nanomaterials (nanoparticles) and remarkable researchers are exploring hybrid nanofluid characteristics. The cardinal objective of this study is to provide a comprehensive review on thermal conductivity of hybrid nanofluids by overviewing experimental, numerical and ANN (artificial neural networking) studies. Assorted factors that affect thermal conductivity such as nanoparticle type, concentration of nanoparticles, types of base fluid, size of nanoparticle, temperature, addition of surfactant, pH variation and sonication time are analyzed in present paper. Additionally, synthesis of hybrid nano-composites, preparation of hybrid nanofluids, approaches for stability measurement and enhancement, methods of thermal conductivity measurement and reasons for thermal conductivity enhancement are discussed. Miscellaneous empirical correlations developed by researchers for thermal conductivity prediction of hybrid nanofluids are also compiled and presented. Results suggest that enhancing temperature and concentration increases thermal conductivity and proper selection of hybrid nanoparticles plays a prime role in attaining stability of hybrid nanofluids.
This paper presents an investigation on the thermal conductivity of nanofluids using experimental data, neural networks, and correlation for modeling thermal conductivity. The thermal conductivity of ...Mg(OH)2 nanoparticles with mean diameter of 10nm dispersed in ethylene glycol was determined by using a KD2-pro thermal analyzer. Based on the experimental data at different solid volume fractions and temperatures, an experimental correlation is proposed in terms of volume fraction and temperature. Then, the model of relative thermal conductivity as a function of volume fraction and temperature was developed via neural network based on the measured data. A network with two hidden layers and 5 neurons in each layer has the lowest error and highest fitting coefficient. By comparing the performance of the neural network model and the correlation derived from empirical data, it was revealed that the neural network can more accurately predict the Mg(OH)2–EG nanofluids' thermal conductivity.
Cover Image Sajid Ur Rehman; Butt, Faheem K; Zeeshan Tariq ...
International journal of energy research,
03/2021, Letnik:
45, Številka:
4
Journal Article
Recenzirano
The cover image is based on the Short Communication Elucidating the role of lattice thermal conductivity in Π‐phases of IV‐VI monochalcogenides for highly efficient thermoelectric performance by ...Sajid Ur Rehman et al., https://doi.org/10.1002/er.6174.
Defects can significantly degrade the thermal conductivity of ThO2, an advanced nuclear fuel material as well as a surrogate for other fluorite-structured materials. We investigate how point defects ...in ThO2 impact phonon mode-resolved thermal transport. By incorporating phonon modes from lattice dynamics, we decompose the trajectory and heat flux to phonon normal mode space and extract key phonon properties, including phonon relaxation times and their contributions to thermal conductivity. We implement two methods. The first method is based on the Green Kubo formalism to resolve the contribution of each phonon mode to thermal conductivity. The second resolves the lifetime of individual phonon modes and the thermal conductivity is calculated using the Boltzmann transport equation within relaxation time approximation. Notably, a lower contribution of acoustic modes is revealed compared to perturbative approaches considering only three-phonon scattering processes. The effects of four types of point defects are evaluated. The strongest impact on a reduction in thermal conductivity is from Th interstitials, followed by Th vacancies. O interstitials/vacancies have a similar impact, albeit smaller than defects on the thorium sublattice. These observations are consistent with previous studies.
High hardness is desirable for thermal insulation materials in various applications to improve wear resistance. However, hard materials like diamond, Si3N4, and SiC are often accompanied by high ...thermal conductivity, due to their strong covalent bonds and high Young’s modulus, which increase sound velocity and benefit heat transportation. How to achieve concurrent high hardness and low thermal conductivity remains a challenge in thermal insulation materials. In this work, we report (Yb+Ca) co-doped α-SiAlON (Yb0.5Ca0.75Si7.5Al4.5O1.5N14.5, a solid solution of α-Si3N4) with a low thermal conductivity of 3.4 W/(m·K) and a hardness of 18.1 GPa at 25℃. The thermal conductivity of α-SiAlONs co-doped by (Yb+Nd/Lu) were also studied, and we found that phonon scattering could be significantly increased only when there was a remarkable difference in cation mass and radius between the co-doping cations, like that between Yb3+ and Ca2+. Additionally, high-entropy α-SiAlONs co-doped by five kinds of cations were studied (e.g., Nd0.1Gd0.1Dy0.1Er0.1Yb0.1Si9.5Al2.5ON15), and we found that the high-entropy strategy is not so effective in pursuing low thermal conductivity in α-SiAlONs. The contribution of different phonon scattering mechanisms in the α-SiAlONs was discussed based on inverse thermal diffusivity. Compared with most other ceramics (e.g., 8YSZ and rare-metal zirconates) with low thermal conductivity, (Yb+Ca) co-doped α-SiAlON has a lower bulk density, higher hardness, and higher toughness, which makes it a potential candidate material for applications requiring both thermal insulation and good mechanical properties.
•Concurrent high hardness (18.1 GPa) and low thermal conductivity (3.4 W/(m·K)) are realized in (Yb+Ca) co-doped α-SiAlON.•(Yb+Ca) co-doped α-SiAlON shows advantages in higher hardness, lower bulk density and higher toughness.•The high-entropy strategy seems not so effective in pursuing low thermal conductivity in α-SiAlONs.•The key to achieve low thermal conductivity in α-SiAlONs is to increase extrinsic phonon scattering.
·Random distribution of the inclusions in a composite material is simulated by a finite element model.·Effective thermal conductivity is calculated through finite element method.·Proposed numerical ...procedure is validated by experimental results and compared to empirical model results.
Many materials (e.g. soil) are multi-phase composites in engineering, and the thermal conductivity of mixtures is a critical parameter for analyzing the temperature field. Owing to its heterogeneity, the effective thermal conductivity of multi-phase materials is also not deterministic. The prediction of the thermal properties of a multi-phase material remains a challenging task. In this study, soil is considered to be a typical multi-phase material. A numerical simulation model is established by the finite element method to predict the meso-scale effective thermal conductivity of soil. Monte Carlo simulation is employed to account for the random distribution of voids. Comparisons among numerical, experimental and empirical results suggest that the proposed model can predict reasonably accurate results. In addition, the effective thermal conductivity of unfrozen soil, partially frozen soil and fully frozen soil is calculated. The effects of soil type, porosity and saturation degree on effective thermal conductivity are considered via parametric studies. The proposed numerical method can be used as an effective supplement to empirical model and experimental tests for evaluating the thermal conductivity of multi-phase materials.
•Inclusion of n-eicosane reduces temperature more significantly than paraffin wax.•A higher latent phase completion time was found in case of 3mm diameter pin-fin.•A higher enhancement in operation ...time is obtained in case of 3 mm diameter pin-fin.•The maximum thermal capacities of 2.24kJ/K and 2.90kJ/K are obtained for 3mm tpin-fin.•Thermal conductance of 6.95×10-1W/K and 5.69×10-1 are obtained for paraffin wax and n-eicosane.
The present paper covers the comparison of two different configurations (square and circular) pin-fin heat sinks embedded with two different phase change materials (PCMs) namely paraffin wax and n-eicosane having different thermo-physical properties were carried out for passive cooling of electronic devices. The pin-fins, acting as thermal conductivity enhancers (TCEs), of 2mm square and 3mm circular fin thickness of constant volume fraction of 9% are chosen and input heat fluxes from 1.2kW/m2 to 3.2kW/m2 with an increment of 0.4kW/m2 are provided. Two different critical set point temperatures (SPTs) 45°C and 65°C are chosen to explore the thermal performance in terms of enhancement ratios, enhancement in operation time, latent heating phase duration, thermal capacity and conductance. The results show that 3mm diameter of circular pin-fins has the best thermal performance in passive thermal management of electronic devices.
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