Materials with ultrahigh or low thermal conductivity are desirable for many technological applications, such as thermal management of electronic and photonic devices, heat exchangers, energy ...converters and thermal insulation. Recent advances in simulation tools (first principles, the atomistic Green's function and molecular dynamics) and experimental techniques (pump-probe techniques and microfabricated platforms) have led to new insights on phonon transport and scattering in materials and the discovery of new thermal materials, and are enabling the engineering of phonons towards desired thermal properties. We review recent discoveries of both inorganic and organic materials with ultrahigh and low thermal conductivity, highlighting heat-conduction physics, strategies used to change thermal conductivity, and future directions to achieve extreme thermal conductivities in solid-state materials.
The enhancement of thermal conductivities of water in the presence of copper oxide and multiwalled carbon nanotubes is investigated for the first time. Hybrid nanofluid is a homogenous mixture of ...multiwalled carbon nanotubes-CuO particles suspended in water as the base fluid. The thermal conductivity of mixture is measured by KD2 Pro instrument. All thermal conductivity measurements are repeated three times in the range of 25–50 °C. A hot water bath is used to stabilize the temperature at 25, 30, 35, 40, 45 and 50 °C during the measurements. The results show that the thermal conductivity of the nanofluid increases at more solid concentration. Furthermore, the thermal conductivity of the nanofluid increases with the temperature; however, this increase is by far more noticeable in higher solid concentrations compared with the lower ones. Moreover, it is tried to propose a new correlation for predicting the thermal conductivity of the present nanofluid at different temperatures and volume fractions. The highest enhancement percentage was observed as 30.38% for the state of
T
= 50 °C and
φ
= 0.6%. However, the enhancement percentages were achieved as 25.57–30.38 for the state of
φ
= 0.6% at
T
= 25–50 °C, respectively.
From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing ...chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.
We measure the electrical resistivity of hcp iron up to ∼ 170 GPa and ∼ 3000 K using a four-probe van der Pauw method coupled with homogeneous flattop laser heating in a DAC, and compute its ...electrical and thermal conductivity by first-principles molecular dynamics including electron-phonon and electron-electron scattering. We find that the measured resistivity of hcp iron increases almost linearly with temperature, and is consistent with our computations. The results constrain the resistivity and thermal conductivity of hcp iron to ∼ 80 ± 5 μ Ω cm and ∼ 100 ± 10 W m−1 K−1, respectively, at conditions near the core-mantle boundary. Our results indicate an adiabatic heat flow of ∼ 10 ± 1 TW out of the core, supporting a present-day geodynamo driven by thermal and compositional convection.
Full text
Available for:
CMK, CTK, FMFMET, NUK, UL
Comparison of the other models to new model and experimental data for 47nm nanoparticles 17 and different nanoparticles volume of fractions.
Display omitted
•A dimensionless model is discussed to ...forecast thermal conductivity of nanofluids.•The proposed model considers knf, kbf, Φ, dp, Tnf, and t.•Proposed model has a good compatibility with experimental data of previous studies.
In this research, a dimensionless model is discussed to forecast effective thermal conductivity of nanofluids regarding the dimensionless groups. Nanofluids thermal conductivity is represented by this model as a function of thermal conductivity of nanoparticles and base liquid, nanoparticles size, volume fractions and interfacial shell properties. Moreover, temperature is considered as a most significant parameter for nanofluids thermal conductivity which influences even on the effective parameters. The results of modeling generate a non-linear correlation for thermal conductivity which demonstrates a good compatibility between present model and experimental data of Al2O3/H2O nanofluids compared to other models.
In this paper, the transport properties of a two-dimensional Lieb lattice that is a line-centered square lattice are investigated in the presence of magnetic field and spin-orbit coupling. Specially, ...we address the temperature dependence of electrical and thermal conductivities as well as Seebeck coefficient due to spin-orbit interaction. We have exploited Green's function approach in order to study thermoelectric and transport properties of Lieb lattice in the context of Kane-Mele model Hamiltonian. The results for Seebeck coefficient show the sign of thermopower is positive in the presence of spin-orbit coupling. Also the temperature dependence of transport properties indicates that the increase of spin-orbit coupling leads to decrease thermal conductivity however the decrease of gap parameter causes the reduction of thermal conductivity. There is a peak in temperature dependence of thermal conductivity for all values of magnetic fields and spin-orbit coupling strengths. Both electrical and thermal conductivities increase with increasing the temperature at low amounts of temperature due to the increasing of transition rate of charge carriers and excitation of them to the conduction bands. Also we have studied the temperature dependence of Seebeck coefficient of Lieb monolayer due to both spin orbit coupling and magnetic field factors in details.
Polymer‐based thermal management materials (TIMs) show great potentials as TIMs due to their excellent properties, such as high insulation, easy processing, and good flexibility. However, the limited ...thermal conductivity seriously hinders their practical applications in high heat generation devices. Herein, highly transparent, insulating, and super‐flexible cellulose reinforced polyvinyl alcohol/nylon12 modified hexagonal boron nitride nanosheet (PVA/(CNC/PA‐BNNS)) films with quasi‐isotropic thermal conductivity are successfully fabricated through a vacuum filtration and subsequent self‐assembly process. A special structure composed of horizontal stacked hexagonal boron nitride nanosheets (h‐BNNSs) connected by their warping edges in longitudinal direction, which is strengthened by cellulose nanocrystals, is formed in PVA matrix during self‐assembly process. This special structure makes the PVA/(CNC/PA‐BNNS) films show excellent thermal conductivity with an in‐plane thermal conductivity of 14.21 W m−1 K−1 and a through‐plane thermal conductivity of 7.29 W m−1 K−1. Additionally, the thermal conductive anisotropic constants of the as‐obtained PVA/(CNC/PA‐BNNS) films are in the range of 1 to 4 when the h‐BNNS contents change from 0 to 60 wt%, exhibiting quasi‐isotropic thermal conductivity. More importantly, the PVA/(CNC/PA‐BNNS) films exhibit excellent transparency, super flexibility, outstanding mechanical strength, and electric insulation, making them very promising as TIMs for highly efficient heat dissipation of diverse electronic devices.
Quasi‐isotropically thermal conductive cellulose reinforced polyvinyl alcohol/nylon12 modified hexagonal boron nitride nanosheet films with high transparency, good electrical insulation, and super‐flexibility are successfully fabricated through a vacuum filtration and subsequent self‐assembly process. These films are very promising as thermal interface management materials for highly efficient heat dissipation of diverse electronic devices.
Abstract
Thermal insulation under extreme conditions requires materials that can withstand complex thermomechanical stress and retain excellent thermal insulation properties at temperatures exceeding ...1,000 degrees Celsius
1–3
. Ceramic aerogels are attractive thermal insulating materials; however, at very high temperatures, they often show considerably increased thermal conductivity and limited thermomechanical stability that can lead to catastrophic failure
4–6
. Here we report a multiscale design of hypocrystalline zircon nanofibrous aerogels with a zig-zag architecture that leads to exceptional thermomechanical stability and ultralow thermal conductivity at high temperatures. The aerogels show a near-zero Poisson’s ratio (3.3 × 10
−4
) and a near-zero thermal expansion coefficient (1.2 × 10
−7
per degree Celsius), which ensures excellent structural flexibility and thermomechanical properties. They show high thermal stability with ultralow strength degradation (less than 1 per cent) after sharp thermal shocks, and a high working temperature (up to 1,300 degrees Celsius). By deliberately entrapping residue carbon species in the constituent hypocrystalline zircon fibres, we substantially reduce the thermal radiation heat transfer and achieve one of the lowest high-temperature thermal conductivities among ceramic aerogels so far—104 milliwatts per metre per kelvin at 1,000 degrees Celsius. The combined thermomechanical and thermal insulating properties offer an attractive material system for robust thermal insulation under extreme conditions.
Conventional theory predicts that ultrahigh lattice thermal conductivity can only occur in crystals composed of strongly bonded light elements, and that it is limited by anharmonic three-phonon ...processes. We report experimental evidence that departs from these long-held criteria. We measured a local room-temperature thermal conductivity exceeding 1000 watts per meter-kelvin and an average bulk value reaching 900 watts per meter-kelvin in bulk boron arsenide (BAs) crystals, where boron and arsenic are light and heavy elements, respectively. The high values are consistent with a proposal for phonon-band engineering and can only be explained by higher-order phonon processes. These findings yield insight into the physics of heat conduction in solids and show BAs to be the only known semiconductor with ultrahigh thermal conductivity.
PDF
