Large Thermal Conductivity Research Articles

Enhanced thermoelectric performance of TiS2 via large thermal conductivity reduction by solid solution alloying with TiSe2

Enhanced thermoelectric performance of TiS2 via large thermal conductivity reduction by solid solution alloying with TiSe2

Theoretical substantiation of the device parameters for drying the green mass of essential oil crops in a vacuum drum dryer

Purpose. To substantiate theoretically the main structural parameters of the device for drying the green mass of essential oil crops in a vacuum. Methods. In the process of theoretical substantiation of the device for drying the green mass of essential oil crops in a vacuum drum dryer, the methods of technical analysis of the movement of the green mass along the blades and the inner surface of the drying drum, planimetry, and trigonometry were used. The dependencies for calculating the design parameters of the device were derived on the basis on algebraic methods. The analysis of the formulas was based on graphical dependencies constructed on their basis. Results. A preliminary experiment using straw mass on the SVB-10 vacuum drum dryer found that a grass bundle is formed in one complete rotation, the central part of which is difficult to dry. To prevent the formation of the grass tourniquet, it was proposed to use L-shaped blades attached to the inner surface of the drum. It was found that to ensure the turning of the green mass and the rational use of the drying drum space, the height of the blade should be equal the length of the L-shaped blade visor. Dependencies have been developed to calculate the angle between the canopy and the blade, the condition for the blade height, their rational number, and the maximum portion mass of green mass that can be loaded into the developed device. A general view of the device for drying green mass of essential oil crops in a vacuum drum dryer was also proposed. Conclusions. Due to the large internal friction angle and low thermal conductivity, it is advisable to use a drying drum with L-shaped blades attached to the inner surface of the drum, with the height of the blade equal to the length of the canopy. The use of L-shaped blades ensures uniform mixing of the green mass of essential oil crops during the rotation of the drying drum and prevents the formation of a harness. The number of blades, their geometric dimensions depend on the radius of the drying drum, the friction angle of the green mass of essential oil crops on the metal surface, the permissible technological gap, and the specified weight of the portion loaded into the vacuum drum dryer. Keywords: green mass of essential oil crops, vacuum, L-shaped paddle, vacuum drum dryer, drying drum, canopy, herbal bundle, drying, friction angle.

Nanoscale Energy Transport Dynamics across Nonbonded Solid-Molecule Interfaces and in Molecular Thin Films.

Thermal conductance across a solid-solid interface requires an atomic- or molecular-level understanding, especially when a system is in a non-equilibrium state and/or consists of nanosized materials with prominent differences in structures, properties, and vibrational behaviors. Here, we report the lattice dynamics of graphite-supported molecular thin films of ethanol, whose layers exhibit in-plane hydrogen-bonded chains and out-of-plane van der Waals stacking with clear structural anisotropy. The direct structure-probing method of ultrafast electron diffraction reveals a surprising temperature difference of more than 400 K at pico- to sub-nanosecond times across the graphite-ethanol interface, yet the temporal behavior signifies a reasonably large thermal boundary conductance. This apparent conflict in a non-equilibrium condition can be resolved by considering the coupling of out-of-plane motions, instead of the commonly used temperature-based model, at transient times for energy transport across the interface separated by van der Waals interactions with mismatched unit sizes and no strong bonds. The importance of spatiotemporally resolved structural dynamics at the atomic or molecular level is emphasized.

Cross-plane thermal transport in layered materials

The cross-plane (across-layers) phonon thermal transport of five diverse, layered semiconductors is investigated by accounting for higher-order four-phonon scattering, phonon renormalization, and multi-channel thermal transport. For materials having relatively large cross-plane thermal conductivity (AlB6, MoS2, and MoSi2N4), phonons contributing to cross-plane conductivity have an order of magnitude larger mean free path than that for the basal-plane thermal transport, whereas the opposite effect is observed for materials with low thermal conductivity (MoO3 and KCuSe). The contribution from the wave-like coherent transport channel is less than 5% in all considered materials. Our work unravels the contrasting role of nanostructuring on the basal- vs cross-plane thermal conductivity of low and high thermal conductivity layered materials.

Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

Zinc oxide (ZnO) shows great potential in electronics, but its large intrinsic thermal conductivity limits its thermoelectric applications. In this work, we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO 〈0001〉 nanowires based on first-principles and molecular dynamics simulations. Under the synergistic effect of band degeneracy and weak phonon–electron scattering, P-type (ZnO)73 nanowires achieve an ultra-high power factor above 1500 μW⋅cm−1⋅K−2 over a wide temperature range. The lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size dependence. When the ZnO nanowire diameter exceeds 12.72 Å, the carrier transport properties increase significantly, while the thermal conductivity shows a slight increase with the diameter size, resulting in a ZT value of up to 6.4 at 700 K for P-type (ZnO)73. For the first time, the size effect is also illustrated by introducing two geometrical configurations of the ZnO nanowires. This work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.

Hydration behavior and microstructure of cement-based materials modified by Field’s metal particles

The hydration of cement-based materials, especially at early ages, directly affects the development of matrix strength and the later durability. In this paper, in order to explore the hydration behavior and microstructure of cement-based composites modified by low melting point Field's Metal Particles (FMP), inverted cone method, standard Vicatometer method, isothermal calorimetry, and compressive strength test, TGA, SEM, and XRD are used to investigate the fresh properties, heat of hydration, matrix strength, hydration products and transition zone between FMP and cement matrix. The results show that the incorporation of FMP can improve the fluidity of cementitious composites by 31.6%, due to the hydrophilicity of FMP. Meanwhile, due to the small heat capacity and large thermal conductivity of low-melting FMP, the heat stored in FMP is naturally released and used to promote hydration reaction when the hydration rate slows down. Additionally, FMP does not affect the types of hydration products in cement-based composites, but the total amount of hydration products increased at 7 d, especially calcium hydroxide (CH). Unexpectedly, FMP can reduce the compressive strength of the hardened paste, due to the large particle size of FMP than cement particles and the presence of directionally growing CH crystals in the interface transition zone between FMP and cement matrix.

Adsorption Affinities of Small Volatile Organic Molecules on Graphene Surfaces for Novel Nanofiller Design: A DFT Study.

The adsorption of organic molecules on graphene surfaces is a crucial process in many different research areas. Nano-sized carbon allotropes, such as graphene and carbon nanotubes, have shown promise as fillers due to their exceptional properties, including their large surface area, thermal and electrical conductivity, and potential for weight reduction. Surface modification methods, such as the "pyrrole methodology", have been explored to tailor the properties of carbon allotropes. In this theoretical work, an ab initio study based on Density Functional Theory is performed to investigate the adsorption process of small volatile organic molecules (such as pyrrole derivatives) on graphene surface. The effects of substituents, and different molecular species are examined to determine the influence of the aromatic ring or the substituent of pyrrole's aromatic ring on the adsorption energy. The number of atoms and presence of π electrons significantly influence the corresponding adsorption energy. Interestingly, pyrroles and cyclopentadienes are 10 kJ mol-1 more stable than the corresponding unsaturated ones. Pyrrole oxidized derivatives display more favorable supramolecular interactions with graphene surface. Intermolecular interactions affect the first step of the adsorption process and are important to better understand possible surface modifications for carbon allotropes and to design novel nanofillers in polymer composites.

Development of a novel cement-based grout with enhanced thermal and sealing performance for borehole heat exchangers

Filling a borehole with proper grout is important for maintaining the safety and performance of borehole heat exchangers (BHEs). The current grouts have problems of large shrinkage and low thermal conductivity, which may restrain BHE efficiency and pose safety risks. To address this, this study explores solutions to enhance the thermal and sealing performance of cement-based grout, specifically for BHE applications. A novel grout, composed of ordinary Portland cement (OPC)-calcium sulfoaluminate (CSA) cement-gypsum ternary system and graphite, was developed and thoroughly examined. The developed grout exhibited good flowability and volumetric stability, meeting the required compressive strength in one day. It displayed high thermal conductivity, ranging from 1.606 to 2.504 W/mK at oven-dry conditions and 2.173 to 3.532 W/mK at saturated conditions. At last, numerical modeling was conducted to compare the thermal performance of boreholes using the novel grout developed in this study and a conventional grout. Numerical models prove that using developed grout can improve the thermal performance of boreholes and decrease the borehole resistance, thus lessening the required borehole length, further reducing the costs and carbon emissions of borehole construction. Overall, the developed grouts showcased enhanced thermal and sealing performance. They can be applied in BHE systems not only to enhance operational efficiency and safety, but also to reduce costs and carbon footprints.

Effect of the heat flow distribution and thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble

A novel non-intrusive thermal diffusion measurement (TDM) method has been proposed for measuring the phase flowrates of gas–liquid slug flows in our previous research. Since the structure of TDM was arbitrarily designed and needed to be optimized for accurate measurement, the effect of the heat flow distribution and the thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble (TB) is further investigated by using the CFD tool in this paper. The wall temperature and temperature rise are used to describe the wall temperature response, and their variation rules with heat flow distribution and the thermophysical properties of the pipe wall and fluid are presented and analyzed based on heat transfer. The simulation results indicate that the optimal heating length for a large wall temperature rise and small power consumption is 0.6D, and the optimal pipe material should be with small density and specific heat and a suitable thermal conductivity of about 15 W/(m·K). Moreover, the wall temperature response is obvious, especially for TBs moving in the liquid with large fluid thermal conductivity, density, and specific heat, and small viscosity. The paper can clarify the wall temperature response mechanism of the heated pipe wall and provide a theoretical basis for the development of the TDM method.

Heat extraction through conductive proppants

The absence of direct contact between the working fluid and the geothermal formation in closed-loop geothermal system (CLGS) limits its application to direct heating. Enhancing the CLGS heat extraction performance could lead to an effective utilization of CLGS for power generation purposes. Optimizing CLGS performance is still an active area of research. In this paper, we propose a fractured closed-loop geothermal system (FCLGS) with a conductive plug installed downhole and a fracture propped with conductive proppants to improve heat exchange performance of CLGS. Using an integrated numerical approach, we first explore the potential to improve the thermal conductivity of common types of proppants by applying metallic coatings. Applying a thick layer of copper coating to Aluminum Nitride proppants yields a thermal conductivity of 44.91 W/(mK), 24 times larger than that of uncoated sand. The proppant/coating with largest thermal conductivity is used for field-scale simulations. Heat extraction performance of FCLGS is evaluated at the field-scale under different parameter combinations. Numerical results show that incorporating a conductive plug into a fractured CLGS improves net power output by 30.60 %. Conductive plug shape and size play an important role in heat extraction in FCGLS. In addition, a circulation velocity of 2 m/s is observed to yield the highest increase in net power output.

Structural properties and epitaxial relation of cubic rock salt ScxAl1−xN/ScN/Si

ScN in the rock salt structure is a well-investigated material due to its desirable properties like the high hardness or large thermal conductivity. Recent computations by Adamski et al. [Appl. Phys. Lett. 115, 232103 (2019)] showed that ScN/GaN heterostructures exhibit an outstanding polarization gradient which would be beneficial for polarization induced electron gases. The pseudobinary semiconductor ScxAl1−xN, when maintaining the cubic rock salt structure, could be beneficial for tailoring the polarization gradient using the Sc dependency of material properties. The structural properties of rs-ScxAl1−xN are not fully discovered yet, thus in this work, DC-magnetron sputtered cubic rock salt ScxAl1−xN thin films with 0.55<x<1.00 were grown and analyzed on ScN(111)/Si(111). The epitaxial relation of ScN(111) thin films on the Si(111) substrate is determined to be ScN[110] ∥ Si[100]. Furthermore, concentration dependent properties like the lattice parameter of ScxAl1−xN were measured [a(ScN) = 4.50 Å, a(Sc0.55Al0.45N) = 4.30 Å] and the stress σ within the layers was determined. The crystal quality was evaluated using ω-scans, revealing FWHM=1.14° for Sc0.95Al0.05N. The diameters of the columns were determined by atomic force microscopy and scanning electron microscopy and they are range from 34 to 59 nm for 0.55<x<1.00. At x=0.55, ScxAl1−xN columns in the hexagonal wurtzite as well as cubic rock salt structure were detected. This information about the structural specifications of ScxAl1−xN in the rock salt structure forms the basis for further investigations and experimental confirmation of the electric properties of ScN/GaN heterostructures or even a ScxAl1−xN/GaN based approach for improved structures for high-electron-mobility transistors.

Preparation and thermal properties of a novel ternary molten salt/expanded graphite thermal storage material

In thermal energy storage, the use of phase change materials (PCM) is a very efficient energy storage method. In the field of medium temperature thermal storage, nitrate PCM have always been a research hotspot, but their relatively high melting point and relatively low latent heat of phase change severely limit their application in thermal energy storage. In this paper, LiNO3 and NaCl with higher latent heat value were selected to improve the thermal properties of nitrate. A novel ternary mixed molten salt of NaNO3-LiNO3-NaCl with high latent heat was prepared and studied. NaNO3-LiNO3-NaCl/EG composite phase change material (CPCM) was prepared by selecting expanded graphite (EG) with a large thermal conductivity as the carrier adsorption material for molten salt. The thermophysical properties, thermal stability, and heat transfer ability of PCM and CPCM were tested. The composition and microstructure of the materials were also characterized. The experimental results showed that compared with pure NaNO3, the phase change temperature of NaNO3-LiNO3-NaCl was reduced by 45.3 °C, and the latent heat of phase change was increased by 59.4 J/g. NaNO3, LiNO3, NaCl and EG had good compatibility, without chemical reaction between them. From the microscopic morphology of the composite material, it can be seen that the PCM was uniformly dispersed into the porous structure of EG without agglomeration. The ternary new molten salt had higher thermal decomposition temperature and better thermal stability. When the addition ratio of EG was 20 %, the thermal conductivity of the ternary molten salt increased from 1.350 to 5.017 W/m·K. EG greatly improved the heat transfer capacity of PCM. And the PCM added with EG still had a high latent heat of phase change. The results show that NaNO3-LiNO3-NaCl/EG has broad application prospects in the field of medium and high temperature heat storage.

Physical mechanism on ladderphane copolymers with electron localization and phonon delocalization for capacitive energy storage

In this article, the properties of trapezoidal polymer PSBNP-co-PTNI for capacitive energy storage are investigated theoretically, stimulated by the recent experimental reports [Chen et al., Nature 615, 62 (2023)]. The flatband structures of PSBNP-co-PTNI copolymer reveal that very large effective mass of electron results in Anderson electron localization and then small electric conductance. The TNI doping significantly decreases optical absorption in an ultraviolet region, which can significantly suppress photocurrent. Raman spectrum demonstrates that phonon Debye temperature can be significantly decreased, due to the U-process of phonon scattering by TNI doping, and then results in the phonon delocalization, and then the large thermal conductivity and thermal capacity. The simultaneous regulations on decreasing electric conductivity and on increasing thermal conductivity can significantly increase the ability of capacitive energy storage. The unit-length dependent thermal electric current manifests that the thermal electric current can be significantly decreased by slightly increase in length of copolymer. Overall, our research contributes to the understanding of the impact of TNI doping on the energy storage properties of the polymer and provides a valuable reference for future research focused on polymer energy storage.

Why is the thermal conductivity of Janus nanofluid larger? – From the perspective of aggregation morphology

The nanoparticle aggregation is a crucial factor for the thermal conductivity of nanofluids based on previous researches. Molecular dynamics simulations for the nanofluids involving 4–32 Janus nanoparticles (termed as Janus nanofluid) were conducted. The thermal conductivity of the Janus nanofluid was found to be larger than that of the ordinary nanofluid, approximately 0.3707 W/m.K for Janus, compared to 0.3521 W/m.K for Au and 0.3303 W/m.K for Cu nanofluid. Further analysis shows that the aggregation morphology in the Janus nanofluid is different from that in the ordinary one. For the better evaluation of the aggregation morphology, a term named degree of looseness was introduced to replace fractal dimension. The relationship between thermal conductivity and degree of looseness shows that the thermal conductivity of the Janus nanofluid first rises and then decreases with the degree of looseness. When 18 nanoparticles are included in the simulated system, the maximum thermal conductivity is 0.3249 W/m.K for a moderate degree of looseness of 10.841 at 4 vol%. Finally, the underlying mechanism why the Janus nanofluid has a larger thermal conductivity than the ordinary one is discussed. This can provide a useful reference for preparing Janus nanofluids with larger thermal conductivity and understanding the underlying mechanisms.

Alloying and Doping Control in the Layered Metal Phosphide Thermoelectric CaCuP.

We recently identified CaCuP as a potential low cost, low density thermoelectric material, achieving zT = 0.5 at 792 K. Its performance is limited by a large lattice thermal conductivity, κL, and by intrinsically large p-type doping levels. In this paper, we address the thermal and electronic tunability of CaCuP. Isovalent alloying with As is possible over the full solid solution range in the CaCuP1-xAsx series. This leads to a reduction in κL due to mass fluctuations but also to a detrimental increase in p-type doping due to increasing Cu vacancies, which prevents zT improvement. Phase boundary mapping, exploiting small deviations from 1:1:1 stoichiometry, was used to explore doping tunability, finding increasing p-type doping to be much easier than decreasing the doping level. Calculation of the Lorenz number within the single parabolic band approximation leads to an unrealistic low κL for highly doped samples consistent with the multiband behavior in these materials. Overall, CaCuP and slightly Cu-enriched CaCu1.02P yield the best performance, with zT approaching 0.6 at 873 K.

Nanoparticles and Their Application in Prosthetic Dentistry

In recent years, nanoparticles produced with nanotechnology have been widely used in many fields of medicine and dentistry such as prosthetic dental treatment. The advanced properties of nanoparticles such as biocompatibility, durability, solubility, large surface area, high stability, and thermal conductivity facilitate the development of dental materials. Compared to the traditional materials used, they can offer useful features, such as better diagnosis, treatment plans, improvement, and protection of oral health. Therefore, a better understanding of nanotechnology and nanoparticles is essential to appreciate how these materials can be utilised in our daily practice. This review provides an overview of nanoparticles and their applications in dentistry.

Volumetric solar carbon dioxide receiver designs with geometric parameters optimized in combination

Porous volumetric solar receivers with carbon dioxide as the working fluid can simultaneously harvest solar energy and utilize carbon dioxide. This means they hold promise for next-generation solar thermal power applications. The optimization of porous receivers has been performed in many works with their geometric parameters optimized using an exhaustive method. Such methods are computationally intensive and their deduced design guidelines are not consistent. This work presents a distinct design method where geometric parameters (porosity, pore size, and length) are combined into three heat transfer parameters (volumetric convection coefficient, effective solid-phase thermal conductivity and optical thickness), so that they are optimized in combination. The optimization objective is the combination of a large volumetric convection coefficient, a large effective solid-phase thermal conductivity and an optimal optical thickness. The corresponding combination of parameters is a small pore size, a small length and a moderate porosity. Guided by this criterion, the best combination is 0.4 mm pore size, 4 mm length and 0.85 porosity, which result in a corresponding thermal efficiency of 71.5%. This combination is consistent with that from the exhaustive method and the optimization complexity for the developed method is reduced by two dimensions.

Dispersion of InSb Nanoinclusions in Cu3SbS4 for Improved Stability and Thermoelectric Efficiency

Thermoelectric‐based waste heat recovery requires efficient materials to replace conventional non‐eco‐friendly Te‐ and Pb‐based commercial devices. Ternary copper chalcogenide‐based famatinite (Cu3SbS4) compound is one of the practical substitutes for traditional thermoelectric materials. However, the pristine Cu3SbS4 inherits poor structural complexion, large thermal conductivity, and low power conversion efficiency. To develop high‐efficiency Cu3SbS4, InSb nanoinclusions are incorporated via high‐energy ball milling followed by the hot‐press densification method. Incorporating InSb nanoinclusions to lower thermal conductivity via phonon scattering while increasing the thermopower via a carrier energy filtering process. The thermoelectric performance (ZT) of ≈0.4 at 623 K is obtained in Cu3SbS4‐3 mol% InSb nanocomposite, which is ≈140% higher than pure Cu3SbS4. Both mechanical and thermal stability are improved by grain boundary hardening and dispersion strengthening. Thus, a facile nanostructured Cu3SbS4 with added InSb nanoinclusions is delivered as a highly efficient, eco‐friendly, structurally‐, thermally‐, and mechanically‐stable material for next‐generation thermoelectric generators.

Multiple approaches of band engineering and mass fluctuation of solution-processed n-type Re-doped MoS2 nanosheets for enhanced thermoelectric power factor

The thermoelectric (TE) performance of Molybdenum disulpide (MoS2) can be improved by the incorporation of nanomaterials. MoS2 has been reported as promising thermoelectric materials due to their large bandgap and low thermal conductivity. In the present work, n-type MoS2 was successfully synthesized by facile hydrothermal route with an excellent thermoelectric performance by introducing rhenium (Re) dopant. The structural and morphological analyses confirmed the incorporation of Re into Mo (Molybdenum) lattice. The thermoelectric results showed that both the electrical conductivity (σ) and Seebeck coefficient (S) has been increased with the increase in Re content (2.5, 5, 7.5 and 10 at%) and temperature (303 K to 700 K), while the thermal conductivity (κ) was low. Doping with Re on MoS2 enhances the electrical conductivity through band engineering, improving carrier concentration and shifting the Fermi level to the conduction band. Introducing a heavy atomic element can reduce the total thermal conductivity by facilitating mass fluctuation. The maximum Seebeck coefficient was obtained as −100 μVK−1 at 500 K for Re 5 at% sample, which is 3.7 times greater than undoped MoS2. In addition, introducing electrons through Re doping induced bipolar conduction. These enhancements have increased the power factor of 8 μWm-1K−2 at 650 K.

Structural, elastic, anisotropic, electronic, thermal properties and tensile strength of AlTM2Ti (TM = Ni, Fe, Cu, Co, Au) studied by first-principles calculations

In the present work, we systematically studied the elastic properties, elastic anisotropy, electronic properties and thermal properties of ternary AlTM2Ti (TM = Ni, Fe, Cu, Co, Au) intermetallics by using first-principles calculations. The optimize the lattice parameters and phonon frequency confirm that the five intermetallics display dynamic stability. The elastic modulus of AlTM2Ti was calculated using the VRH approximation. On the one hand, according to the values of Poisson's ratio and G/B, AlTM2Ti intermetallics show the ductile behavior. In terms of density of states and electronic structure, AlTM2Ti (TM = Ni, Fe, Cu, Co, Au) show the metallic properties. Moreover, AlFe2Ti and AlCo2Ti show the magnetic properties. AlFe2Ti shows the strongest chemical bond, the largest hardness, the smallest anisotropy, the strongest deformation resistance and the largest thermal conductivity. The stress–strain curves are calculated and the ideal tensile strength follows the sequence: Al2FeTi > AlCo2Ti > AlNi2Ti > AlAu2Ti > AlCu2Ti.