Display omitted
•Various experimental data for thermal conductivity of Al2O3/Water nanofluid are extracted.•Two (ANN) algorithms are used to predict relative thermal conductivity of Al2O3/Water ...nanofluid.•Effect of the temperature, particle size, and concentration are compared.•Results from applied algorithms are compared in order to find the best method for prediction of relative thermal conductivity.
Various parameters affect thermal conductivity of nanofluid; however, some of them are more influential such as temperature, size and type of nano particles and volumetric concentration. In this study, artificial neural network as well as least square support vector machine (LSSVM) are applied in order to predict thermal conductivity ratio of alumina/water nanofluid as a function of particle size, temperature and volumetric concentration. LSSVM, Self-Organizing Map and Levenberg-Marquardt Back Propagation algorithms are applied to predict thermal conductivity ratio. Obtained results indicated that these algorithms are appropriate tool for thermal conductivity ratio prediction. The correlation coefficient values are very favorable and equal to 0.88125 and 0.87575 and 0.89999 by applying SOM, LM-BP algorithms and LSSVM, respectively.
•Thermal conductivity of 1D heterostructure CNT@BNNT is systematically investigated.•Temperature, size and chirality dependence of thermal conductivity is studied.•Feasible strategies to modulate ...thermal conductivity is proposed and demonstrated.•Understanding of the fundamental physics of phonon transport is enhanced.
Investigating thermal transport in van der Waals heterostructures is of scientific interest and practical importance for their applications in a broad range. In this work, thermal conductivity of one-dimensional heterostructure consisting of carbon and boron nitride nanotubes is systematically investigated via molecular dynamics simulations. Thermal conductivity is found to have strong dependences on temperature, length and diameter. In addition, the axial strain and intensity of van der Waals interaction are demonstrated to be able to modulate thermal conductivity up to about 43% and 37%, respectively. Moreover, the dependence of thermal conductivity on the chirality of constituent nanotubes is studied. These results are explained based on lattice dynamics insights. This work not only provides feasible strategies to modulate thermal conductivity, but also enhances the understanding of the fundamental physics of phonon transport in one-dimensional heterostructures.
Recently, using a first principles approach, we predicted that zinc blende boron arsenide (BAs) will have an ultrahigh lattice thermal conductivity, Kappa , of over 2000 Wm super(-1) K super(-1) at ...room temperature (RT), comparable to that of diamond. Here, we provide a detailed ab initio examination of phonon thermal transport in boron arsenide, contrasting its unconventional behavior with that of other related materials, including the zinc blende crystals boron nitride (BN), boron phosphide, boron antimonide, and gallium nitride (GaN). The unusual vibrational properties of BAs contribute to its weak phonon-phonon scattering and phonon-isotope scattering, which are responsible for its exceptionally high Kappa . The thermal conductivity of BAs has contributions from phonons with anomalously large mean free paths (~2 mu m), two to three times those of diamond and BN. This makes Kappa in BAs sensitive to phonon scattering from crystal boundaries. An order of magnitude smaller RT thermal conductivity in a similar material, zinc blende GaN, is connected to more separated acoustic phonon branches, larger anharmonic force constants, and a large isotope mixture on the heavy rather than the light constituent atom. The striking difference in Kappa for BAs and GaN demonstrates the importance of using a microscopic first principles thermal transport approach for calculating Kappa . BAs also has an advantageous RT coefficient of thermal expansion, which, combined with the high Kappa value, suggests that it is a promising material for use in thermal management applications.
Monolayer excitonic laser Ye, Yu; Wong, Zi Jing; Lu, Xiufang ...
Nature photonics,
11/2015, Letnik:
9, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Two-dimensional van der Waals materials have opened a new paradigm for fundamental physics exploration and device applications because of their emerging physical properties. Unlike gapless graphene, ...monolayer transition-metal dichalcogenides (TMDCs) are two-dimensional semiconductors that undergo an indirect-to-direct bandgap transition, creating new optical functionalities for next-generation ultra-compact photonics and optoelectronics. Although the enhancement of spontaneous emission has been reported on TMDC monolayers integrated with photonic crystals and distributed Bragg reflector microcavities, coherent light emission from a TMDC monolayer has not been demonstrated. Here, we report the realization of a two-dimensional excitonic laser by embedding monolayer WS2 in a microdisk resonator. Using a whispering gallery mode with a high quality factor and optical confinement, we observe bright excitonic lasing at visible wavelengths. This demonstration of a two-dimensional excitonic laser marks a major step towards two-dimensional on-chip optoelectronics for high-performance optical communication and computing applications.
The electron-phonon interaction is well known to create major resistance to electron transport in metals and semiconductors, whereas fewer studies are directed to its effect on phonon transport, ...especially in semiconductors. We calculate the phonon lifetimes due to scattering with electrons (or holes), combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon interaction, all from first principles, and evaluate the effect of the electron-phonon interaction on the lattice thermal conductivity of silicon. Unexpectedly, we find a significant reduction of the lattice thermal conductivity at room temperature as the carrier concentration goes above 10(19) cm(-3) (the reduction reaches up to 45% in p-type silicon at around 10(21) cm(-3)), a range of great technological relevance to thermoelectric materials.
The physical properties and especially viscosity and thermal conductivity are essential parameters for evaluating the heat transfer and flowing drag coefficients when designing a nanofluid system. ...This review presents a state of the art research progress of both the experimental and theoretical researches on viscosity and thermal conductivity of nanofluids. The results indicate that the viscosity and thermal conductivity of nanofluids are generally functions of particle loading, size, temperature and sometimes particle shape in their experimental range. Effect of material types is regularity on thermal conductivity but irregular on viscosity since the thermal conductivity of Graphene, CNTs, Au nanofluids is greatly higher than ordinary nanofluids but no orderliness could be found in viscosity for different particle types. Particle loading has a positive correlation with the relative viscosity and thermal conductivity but effects of particle size, shape, base fluid property and temperature are not unified. Although many influence factors have been considered, the main defect of the current modeling research is the failure of predicting the results in separate works due to the wide differences. Finally, the challenges and opportunities for the future studies are identified.
In this study, tetraethylorthosilicate and dimethyldiethoxysilane were employed to modify high-entropy (La0.2Y0.2Sm0.2Eu0.2Nd0.2)2Zr2O7 (5RE2Zr2O7) ceramic aerogels to address the challenges of ...particle agglomeration and pore structure collapse that occur during the calcination step in the preparation of high-entropy ceramic aerogels. Following the modification, the specific surface area of the ceramic aerogel increased significantly from 32.22 m2/g to 148.65 m2/g to 201.61 m2/g. Simultaneously, the formation of defective fluorite or pyrochlore crystal structures led to reduced thermal conductivity in the three types of high-entropy ceramic aerogels, namely 5RE2Zr2O7 (from 0.212 W m−1•K−1 to 0.139 W m−1•K−1), 5RE2ZSA (from 0.065 W m−1•K−1 to 0.049 W m−1•K−1), and DDS/5RE2ZSA (from 0.046 W m−1•K−1 to 0.039 W m−1•K−1), compared to their respective non-high-entropy counterparts. Balancing the porous structure of high-entropy ceramic aerogels with an adequate number of defective fluorite or pyrochlore crystals is challenging. Addressing this challenge is a key direction for advancing high-entropy aerogels in the future.
Display omitted
Aiming at developing high thermal conductivity copper/diamond composite, an unconventional approach applying self-assembled monolayer (SAM) prior to the high-temperature sintering of copper/diamond ...composite was utilized to enhance the thermal boundary conductance (TBC) between copper and diamond. The enhancement was first systematically confirmed on a model interface system by detailed SAM morphology characterization and TBC measurements. TBC significantly depends on the SAM coverage and ordering, and the formation of high-quality SAM promoted the TBC to 73 MW/m2-K from 27 MW/m2-K, the value without SAM. With the help of molecular dynamics simulations, the TBC enhancement was identified to be determined by the number of SAM bridges and the overlap of vibrational density of states. The diamond particles of 210 μm in size were simultaneously functionalized by SAM with the condition giving the highest TBC in the model system and sintered together with the copper to fabricate isotropic copper/diamond composite of 50% volume fraction. The measured thermal conductivity marked 711 W/m-K at room temperature, the highest value among the ones with similar diamond-particles volume fraction and size. This work demonstrates a novel strategy to enhance the thermal conductivity of composite materials by SAM functionalization.
The precisely-controlled scalable nanointerface by the organic monolayer was firstly implemented in the fabrication of pronounced high thermal conductive composite through the high-temperature plasma sintering process. Display omitted
•Self-assembled monolayer is firstly applied in the fabrication of high thermal conductive composite material by sintering.•The number of chains and the phonon transmission via each chain molecule determines the interfacial thermal conductance.•The nanointerface with extensive area in the composite can be precisely controlled by the scalable experimental process.•A marked thermal conductivity is realized for the copper/diamond composite.
The construction of heat conduction paths in the polymer matrix is essential to improve the thermal management performance of polymer composites. A three-dimensional (3D) thermally conductive network ...with regular filler structures is very attractive for building fast conductive paths in polymer composites. Herein, a unique 3D interconnected tannic acid modified boron nitride (BN) and C network (M-BN/C) was successfully fabricated by the carbonization of M-BN/thermoplastic polyurethane (TPU) skeletons, which were obtained via simple salt template assisted strategy to enhance the thermal transfer properties of composites. The highly thermally conductive epoxy composites (M-BN/C/EP) were then prepared by impregnating epoxy resin (EP) into the 3D M-BN/C network. The thermal conductivity of the composites with a M − BN loading of 23 wt% is as high as 1.524 W/(m·K), which exhibits a significant enhancement of 702% compared with pure EP. In addition, our composite exhibited outstanding thermal behaviors during heating and cooling processes. Furthermore, the finite element heat conduction simulation further analyzes the heat conduction mechanism of epoxy composites from the theoretical level. This work provides a new idea to significantly enhance the thermal conductivity of thermal management materials.
Thermoelectric technology enables the harvest of waste heat and its direct conversion into electricity. The conversion efficiency is determined by the materials figure of merit
Here we show a maximum
...of ~2.8 ± 0.5 at 773 kelvin in n-type tin selenide (SnSe) crystals out of plane. The thermal conductivity in layered SnSe crystals is the lowest in the out-of-plane direction two-dimensional (2D) phonon transport. We doped SnSe with bromine to make n-type SnSe crystals with the overlapping interlayer charge density (3D charge transport). A continuous phase transition increases the symmetry and diverges two converged conduction bands. These two factors improve carrier mobility, while preserving a large Seebeck coefficient. Our findings can be applied in 2D layered materials and provide a new strategy to enhance out-of-plane electrical transport properties without degrading thermal properties.
PDF
