In the present work, Janus monolayers WSSe and WSTe are investigated by combining first-principles calculations and semiclassical Boltzmann transport theory. Janus WSSe and WSTe monolayers show a ...direct band gap of 1.72 and 1.84 eV at K-points, respectively. These layered materials have an extraordinary Seebeck coefficient and electrical conductivity. This combination of high Seebeck coefficient and high electrical conductivity leads to a significantly large power factor. In addition, the lattice thermal conductivity in the Janus monolayer is found to be relatively very low as compared to the WS2 monolayer. This leads to a high figure of merit (ZT) value of 2.56 at higher temperatures for the Janus WSTe monolayer. We propose that the Janus WSTe monolayer could be used as a potential thermoelectric material due to its high thermoelectric performance. The result suggests that the Janus monolayer is a better candidate for excellent thermoelectric conversion.
Phase change materials (PCMs) possess very high heat storage capacity and are capable of maintaining a constant temperature during phase change, which makes them most prominent candidates for solar ...energy storage systems, heating, and cooling systems. The low thermal conductivity of PCM results in slow heat transfer and low heat storage and release rate, which is a major drawback for their practical applications. This review focuses on the enhancement of thermal conductivity by the introduction of highly thermally conductive metallic and carbon-based nanoparticles, metallic foams, expanded graphite and encapsulation of PCM. Carbon-based nanoparticles including carbon fiber, carbon nanotubes, and graphene show better performance than metal-based nanoparticles due to lower density and better dispersion. The thermal conductivity of the composite phase change material (CPCM) depends on the shape, size, aspect ratio and concentration of nanoparticles. The thermal conductivity of CPCM increases by increasing concentration and aspect ratio of the additive. Metallic foam and expanded graphite possess high thermal conductivity and good thermo-physical properties and also prevent leakage of PCM during phase change. The porosity of foam has a huge impact on thermal conductivity than pore size. Encapsulated PCM has well-enhanced thermal conductivity and long-lifetime due to the high thermal conductive shell which also protects the PCM from direct contact with the environment.
•The models for thermal conductivity tensor of two types honeycombs are proposed.•Impact of the wall uniformity within honeycomb on the thermal property is quantified.•Honeycomb ETC's max anisotropic ...porosity reduces as thermal conductivity ratio rises.
The effective thermal conductivity (ETC) is a critical parameter for simulating macroscopic heat transfer processes in composite materials, which estimation is particularly critical where the thermal conductivity of the composite phases is completely different. The huge difference in thermal conductivity of the composite phases makes their volume fraction modulation a classical way to reach the desired thermal conductivity. Nevertheless, the typical manufacturing process of honeycomb cellular structures allows various degrees of stretching of the structure, leading to various honeycomb geometries. In these ‘real’ structures some of the honeycomb wall sides are twice as thick as other parts, modifying the symmetry of the system with respect to honeycomb with uniform wall side thickness. A noticeable example of these composites is that of a hexagonal metallic honeycomb structure filled with phase change material (PCM) which is a widely utilized material in the field of thermal storage and thermal management by exploiting the heat absorbed/released by the PCM phase during its melting/solidification. While the thermal response of a PCM composite during a thermal cycle is not only defined by thermal conductivity (but also by cell size), this represents the basis for the with the optimization of a system based on a composite PCM.
For this reason, in this study, steady-state simulations of heat transfer in unit honeycomb cells in different directions perpendicular to the cell axis are conducted to quantify the impact of morphology on the thermal property of the different wall types within honeycomb structures. The results demonstrate that in both SHS and DHS, the porosity exhibiting maximum anisotropy of ETC decreases as the thermal conductivity ratio increases. Moreover, simple predictive models for calculating the ETC in all directions are proposed for each type of honeycomb, considering a wide range of porosity and thermal conductivity ratio, with a relative error limited to 2 %.
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Achieving glass‐like ultra‐low thermal conductivity in crystalline solids with high electrical conductivity, a crucial requirement for high‐performance thermoelectrics , continues to be a formidable ...challenge. A careful balance between electrical and thermal transport is essential for optimizing the thermoelectric performance. Despite this inherent trade‐off, the experimental realization of an ideal thermoelectric material with a phonon‐glass electron‐crystal (PGEC) nature has rarely been achieved. Here, PGEC‐like AgSbTe2 is demonstrated by tuning the atomic disorder upon Yb doping, which results in an outstanding thermoelectric performance with figure of merit, zT ≈ 2.4 at 573 K. Yb‐doping‐induced enhanced atomic ordering decreases the overlap between the hole and phonon mean free paths and consequently leads to a PGEC‐like transport behavior in AgSbTe2. A twofold increase in electrical mobility is observed while keeping the position of the Fermi level (EF) nearly unchanged and corroborates the enhanced crystalline nature of the AgSbTe2 lattice upon Yb doping for electrical transport. The cation‐ordered domains, lead to the formation of nanoscale superstructures (≈2 to 4 nm) that strongly scatter heat‐carrying phonons, resulting in a temperature‐independent glass‐like thermal conductivity. The strategy paves the way for realizing high thermoelectric performance in various disordered crystals by making them amorphous to phonons while favoring crystal‐like electrical transport.
Different length scales of the mean free path of charge carriers and phonons direct twofold enhancement in hole mobility with simultaneous realization of glass‐like thermal conductivity, leading to an ultra‐high thermoelectric performance in Yb‐doped AgSbTe2.
Thermal energy storage systems have been recognized as one of the most efficient ways to enhance the energy efficiency and sustainability, and have received a growing attention in recent years. The ...use of phase change materials (PCMs) in building applications can not only improve the indoor thermal comfort but also enhance the energy efficiency. The necessity to enhance thermal conductivity of the PCMs is evident due to its low energy charging/discharging rates. Therefore, the high thermal conductivity additives or inserts to enhance thermal conductivity or to form the composite PCM are sought to achieve high energy charging/discharging rates. In this paper, the experimental and theoretical methods to enhance the thermal conductivity of the PCMs are summarized, and the thermal conductivity inserts/additives in recent investigations are listed and summarized. The evaluation of each thermal conductivity enhancement method is discussed.
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.
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.
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.
The demand for flexible conductive materials has motivated many recent studies on conductive polymer–based materials. However, the thermal conductivity of conductive polymers is relatively low, which ...may lead to serious heat dissipation problems for device applications. This review provides a summary of the fundamental principles for thermal transport in conductive polymers and their composites, and recent advancements in regulating their thermal conductivity. The thermal transport mechanisms in conductive polymer–based materials and up‐to‐date experimental approaches for measuring thermal conductivity are first summarized. Effective approaches for the regulation of thermal conductivity are then discussed. Finally, thermal‐related applications and future perspectives are given for conductive polymers and their composites.
Conductive polymer–based materials can offer novel applications such as flexible electronics and wearable biosensors. However, their intrinsically low thermal conductivity limits their applications. This review provides a summary of the fundamental principles for thermal transport in conductive polymers and their composites, recent advancements in regulating their thermal conductivity, and their thermal‐related applications.
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