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An innovative technique to improve heat transmission is the use of nanofluids. Nanofluids have a significant thermal conductivity for better heat transport. For the thermal behavior of a porous polymer sheet, activation energy assessment is a useful technique for the advancement of the thermal properties of polymers. The governing model is developed for the numerical and physical analysis of heat transfer of porous polymer sheets. The present model is converted into a smooth format for the accuracy of results. The Keller box and Newton–Raphson approaches are used to calculate the thermal properties numerically. The novelty of this research is the depiction of the temperature distributions and heat transfer of chemically reacting thermophoretic nanomaterials along porous polymer stretching sheets. It is noted that the velocity and temperature of thermophoretic nanoparticles decreases and nanoparticle concentration increases as activation energy increases. It is noted that the velocity of nanoparticles increases and concentration decreases as the temperature difference increases. The enhanced heating transfer with maximum thermophoretic transportation was depicted under maximum reaction and activation energy. It is observed that the mass transfer of nanomaterials increases as the Brownian motion of thermophoretic nanomaterials enhances. [ABSTRACT FROM AUTHOR]

Heat transport in two dimensions is fundamentally different from that in three dimensions. As a consequence, the thermal properties of 2D materials are of great interest, from both scientific and application points of view. However, few techniques are available for the accurate determination of these properties in ultrathin suspended membranes. Here, we present an optomechanical methodology for extracting the thermal expansion coefficient, specific heat, and thermal conductivity of ultrathin membranes made of 2H-TaS2, FePS3, polycrystalline silicon, MoS2, and WSe2. The obtained thermal properties are in good agreement with the values reported in the literature for the same materials. Our work provides an optomechanical method for determining the thermal properties of ultrathin suspended membranes, which are difficult to measure otherwise. It provides a route toward improving our understanding of heat transport in the 2D limit and facilitates engineering of 2D structures with a dedicated thermal performance. [ABSTRACT FROM AUTHOR]

For low-temperature thermoelectric applications, a bulk-phase inorganic/organic composite is prepared by introducing a conducting polymer, which is recognized as a potential organic thermoelectric material, into a representative inorganic thermoelectric material (n-type Bi2Te3). A conducting polymer, PEDOT:PSS, was chosen to prepare the Bi2Te3/PEDOT:PSS composite, wherein an intimate interface was formed between Bi2Te3 and PEDOT:PSS. The work function difference between Bi2Te3 and PEDOT:PSS created an energy barrier at the interface, possibly facilitating selective charge carrier transport depending on the energy levels of the carrier (i.e., energy filtering effect), thereby contributing to an enhancement in the Seebeck coefficient. The composite exhibited a completely different bipolar conduction tendency from pristine Bi2Te3, inducing a significant variation in the temperature dependence of the Seebeck coefficient. Furthermore, the interface may affect the carrier and phonon scattering probabilities, resulting in a considerable reduction in thermal conductivity. The composite adjustment was intensively studied to regulate the electrical and thermal properties using the energy filtering effect along with the carrier and phonon scattering probabilities, resulting in a noticeably enhanced thermoelectric performance. The temperature dependence of the performance was effectively adjusted using the bipolar conduction tendency, thereby affording the Bi2Te3/PEDOT:PSS composite exhibiting consistently high ZT values over the wide temperature range of 25–275 °C. The thermoelectric performance of Bi2Te3/PEDOT:PSS was competitive with that of previously reported high-performance n-type Bi2Te3-based analogs. The Bi2Te3/PEDOT:PSS composite is a promising n-type candidate for diverse low-temperature thermoelectric applications as a p-type Bi2Te3 counterpart. [ABSTRACT FROM AUTHOR]

Bulk crystals of β-Ga2O3 were successfully grown by the edge-defined film-fed growth method. The crystalline quality of the obtained crystals was analyzed by the method of x-ray diffractometry. The full width at half maximum of the rocking curve was about 72 arcsec. The optical bandgap was determined by analyzing the optical transmission spectra and amounted to 4.7 eV. The hot disk method was used to obtain the thermal conductivity of the sample along the [001] direction in the temperature range from 30 to 120 °C. The maximum value of thermal conductivity obtained at 30 °C was 9.25 W/(m K). [ABSTRACT FROM AUTHOR]

As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between "high-entropy" and "entropy-stabilized" phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O are investigated across this critical transition temperature via the transient plane-source method, temperature-dependent x-ray diffraction, and nano-indentation. The thermal conductivity remains constant within uncertainty across the multi-to-single phase transition at a value of ≈2.5 W/mK, while the linear coefficient of thermal expansion increases nearly 24% from 10.8 to 14.1 × 10−6 K−1. Mechanical softening is also observed across the transition. [ABSTRACT FROM AUTHOR]

Phonon transport properties of two-dimensional materials can play a crucial role in the thermal management of low-dimensional electronic devices and thermoelectric applications. In this study, both the empirical Stillinger–Weber (SW) and machine learning interatomic potentials are employed to investigate the lattice thermal conductivity of monolayer GeS and SnS through solving the phonon Boltzmann transport equation. The accuracy of the two types of interatomic potentials and their performance for the evaluation of thermal conductivity are verified by analyzing phonon harmonic and anharmonic properties. Our results indicate that the thermal conductivity can be predicted more accurately with a machine learning approach, while the SW potential gives rise to an overestimated value for both monolayers. In addition, the in-plane anisotropy of thermal transport properties existing in these monolayers can be confirmed by both potential models. Moreover, the origins of the deviation existing in calculated thermal conductivities, including both the effects of interatomic potential models and monolayer compositions, are elucidated through uncovering the underlying phonon transport mechanisms. This study highlights that in contrast to the machine learning approach, more careful verification is required for the simulation of thermal transport properties when empirical interatomic potential models are employed. [ABSTRACT FROM AUTHOR]

Back in 2008, Panofsky gave an empirical formula, T = 1 1.5 W 2 / 3 , for turkey baking time, T, in hours vs turkey weight, W, in pounds, the so-called Panofsky formula or Panofsky constant. Compared to the previously existed recipes that are based on the simple linear relationship between turkey weight and baking time, the Panofsky formula provides a more accurate estimate for the baking time. For instance, a general guideline of 13–20 min/lb was widely recommended in all previous turkey baking recipes. In this work, we conduct a comprehensive study of the turkey baking process that leads to a mathematical derivation of the Panofsky formula under some approximations. We also generalize the Panofsky formula to define a general Panofsky formula, T = 1 P W 2 / 3 , where P is defined as the Panofsky constant. Under spherical approximations, we then apply an accurate physical solution of the heat transfer equation and use the rigorous solution with numerical methods to study the generalized Panofsky formula and the Panofsky constant. We found that the generalized Panofsky formula can be perfectly applied to all turkey baking scenarios for baking time calculations. Furthermore, we did a careful analysis of the Panofsky constant, which equals 1.5 in the original Panofsky formula. The dependency of the new Panofsky constant on thermal properties of the turkeys and other initial parameters of baking, e.g., initial and final center temperature of the turkeys, oven temperature, thermal conductivity, specific heat, and turkey's density, was carefully analyzed and mapped out. The Panofsky constant, P, could vary from 1.1 to 1.9 depending on these thermal parameters. [ABSTRACT FROM AUTHOR]

We report systematic measurements of thermal transport properties of a Ni–Co-based superalloy at temperatures ranging from room temperature to around 800 K. In this temperature range, the thermal diffusivity and conductivity of the superalloy monotonically increase with an increase in the temperature, while the specific heat capacity is almost temperature-independent. We found that the observed thermal conductivity of the Ni–Co-based superalloy is higher than the electronic thermal conductivity expected from the Wiedemann–Franz law, indicating the substantial contribution of phonon thermal conductivity. The temperature dependence of the phonon thermal conductivity for the Ni–Co-based superalloy was observed to be weaker than that for other Ni-based alloys, which can be qualitatively explained by enhanced phonon scattering due to small γ′-phase precipitates in the superalloy. This result suggests possible tuning of the thermal conductivity of the superalloy based on phonon transport engineering. [ABSTRACT FROM AUTHOR]

Using the first-principles calculations and combining with the phonon Boltzmann transport equation, we systematically investigated the phonon thermal transport properties of II–VI group graphenelike materials (BeO, MgO, CaO, SrS, and SrSe). The lattice thermal conductivities κ L 's of 118.68, 42.48, 11.13, 3.33, and 3.09 W/mK are obtained at 300 K in BeO, MgO, CaO, SrS, and SrSe, respectively, which is much lower than that of graphene. Strikingly, the κ L of SrS and SrSe is lower than most two-dimensional materials. Further analyses revealed that (i) the lower phonon group velocity of SrS and SrSe caused by a larger atomic mass reduces the κ L and (ii) strong anharmonicity and more available phonon scattering channels enhance phonon anharmonic scattering, resulting in lower κ L. By means of the relationship between κ L and the phonon mean-free path and the width of nanowires, the size dependence of lattice thermal conductivity is investigated as well, which provides a theoretical basis for the design of thermoelectric nanostructures. [ABSTRACT FROM AUTHOR]

The effects of the intercalated ion concentration on the cross-plane thermal conductivity and the thermal boundary conductance in the graphite/lithiated graphite interface are investigated from molecular dynamics simulations. At low ion concentration, the cross-plane thermal conductivity of the lithiated graphite is lower than that of the pristine graphite. However, as the intercalated ion concentration increases, the cross-plane thermal conductivity increases rapidly, even exceeding that of the pristine graphite at high ion concentration. By analyzing the variations of the cross-plane elastic constants and phonon dispersion relation with the intercalated ion concentration, it is found that the intercalated ions significantly increase the phonon irradiation heat flux along the cross-plane direction. Our study further shows that the variation of the intercalated ion concentrations can also modulate the thermal boundary conductance in the graphite/lithiated graphite interface. The non-equilibrium molecular dynamics simulations show that the thermal boundary conductance between graphite and lithiated graphite decreases as the lithiation level increases, which would worsen the thermal performance of Li-ion batteries. A one-dimensional atomic chain model is proposed to elaborate on how the effective spring stiffness of material influences the interfacial transmission of phonons with different frequencies. This work provides a quantitative calculation of the cross-plane thermal conductivity and thermal boundary conductance in intercalated graphite samples and is also extremely important for the thermal management and structural design of lithium-ion batteries. [ABSTRACT FROM AUTHOR]

A simple yet innovative approach has been made through a powder metallurgy route for the synthesis of aluminum–graphene (Al–Gr) composite materials for commercially viable solar thermal collectors. The Al–Gr composite (with 1 wt. % of graphene filler content) recorded an enhanced thermal conductivity of ∼280 W/mK, which is higher than that of pristine Al (∼124 W/mK), at room temperature. It has also been found that the prepared composite has a lower coefficient of thermal expansion. The structures and morphologies of the composites have been investigated in detail with the help of X-ray diffraction technique, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, etc. Furthermore, the density measurements showed that the composites retain ∼97.5% of the density of pristine aluminum even after the sintering treatment. X-ray micro-computed tomography revealed the structural integrity and non-porous nature of the samples, free from any defects and deformations. The thermal fusing of Al-based composite materials at 630 °C is found to be satisfactory with the required strength, and the composites showed at least ∼125% increase in the thermal conductivity than that of pristine Al. These results suggest that the Al–Gr composites can be deployed as solar thermal collectors and heat sink materials for thermal dissipation. [ABSTRACT FROM AUTHOR]

Stability and duration of ultrasonic phantoms are still subjects of research. This work presents a tissue-mimicking material (TMM) to evaluate high-intensity therapeutic ultrasound (HITU) devices, composed of gellan gum (matrix), microparticles (scatterers), and chemicals. The ultrasonic velocity and attenuation coefficient were characterized as a function of temperature (range 20 °C–85 °C). The nonlinear parameter B/A was determined by the finite amplitude insertion substitution (FAIS) method, and the shear modulus was determined by a transient elastography technique. The thermal conductivity and specific heat were determined by the line source method. The attenuation was stable for 60 days, and in an almost linear frequency dependence (0.51f0.96 dB cm−1), at 20 °C (1–10 MHz). All other evaluated physical parameters are also close to typical soft tissue values. Longitudinal ultrasonic velocities were between 1.49 and 1.75 mm μs−1, the B/A parameter was 7.8 at 30 °C, and Young's modulus was 23.4 kPa. The thermal conductivity and specific heat values were 0.7 W(m K)−1 and 4.7 kJ(kg K)−1, respectively. Consistent temperature increases and thermal doses occurred under identical HITU exposures. Low cost, longevity, thermal stability, and thermal repeatability make TMM an excellent material for ultrasonic thermal applications. The TMM developed has the potential to assess the efficacy of hyperthermia devices and could be used to adjust the ultrasonic emission of HITU devices. [ABSTRACT FROM AUTHOR]

This study aims to observe the changes in the structural characterization and physical properties of calcium-praseodymium-cobalt oxide thermoelectric materials with graphene doping. Structural characterizations were examined via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), and Fourier Transformed Infrared Spectroscopy (FTIR) measurements. Temperature-dependent thermal conductivity and Seebeck coefficient were measured by Physical Properties Measurement System (PPMS). In the SEM images, the samples were observed to be crystalline and showed enhanced fusion with graphene doping. There were no impurities in the samples according to the EDX results and all sample components were observed in these results. The properties and structures of the bonds in the XRD results were also visible in the FTIR results. According to the PPMS results, it was determined by measurements and graphs that graphene doping provided a significant and changeable effect to the thermoelectric materials. [ABSTRACT FROM AUTHOR]

While over the past decade architected cellular materials have been shown to possess unique mechanical properties, their thermal properties have received relatively little attention. Here, we investigate thermal transport in hollow nickel microlattices as a function of temperature and mechanical loading using infrared thermography. The effective thermal conductivity of hollow nickel microlattices with 99.9% porosity and 1 µm layer thickness is as low as 0.049 W m−1 K−1 at 320 K and increases to 0.075 W m−1 K−1 at 480 K, an increase we attribute to internal thermal radiation. By measuring the emissivity and using the Stephan-Boltzmann law, we estimate the contribution of thermal radiation in the effective thermal conductivity to range from 20% at 320 K to 49% at 480 K. The high porosity of microlattices strongly limits solid conduction and makes surface radiation very important in thermal transport. We further explore the impact of the strut surface condition by comparing hollow doped nickel microlattices with a smooth surface to those with a rough surface: the emissivity increases from 0.24 to 0.43, leading to increased thermal radiation contributions of 41% at 320 K to 58% at 480 K. Under mechanical loading, as the strain increases from 0% to 50%, decreasing the angle between the struts and the horizontal plane from 60° to 38°, the effective thermal conductivity decreases from 0.049 W m−1 K−1 to 0.016 W m−1 K−1. These findings indicate that architected cellular materials provide an excellent platform to control thermal properties independently on mechanical properties and to potentially develop thermal and thermomechanical metamaterials. [ABSTRACT FROM AUTHOR]

Creating micro/nanoscale systems with one dimension substantially larger than the others is relatively straightforward, and convenient for studying thermal energy transport. This paper reports the theory for a novel noncontact micro/nanoscale temperature measurement technique named Suspended ThermoReflectance (STR). Here, the heat diffusion equation is applied to a cantilever beam of micro and nanoscale dimensions with Neumann and Dirichlet Boundary Conditions. The Neumann condition takes on constant, decaying, and periodic forms leading to steady-state, transient and harmonic solutions, respectively. Though general solutions are presented for multiple length to width ratios (L/w) in terms of geometry as well as thermal properties, silicon is studied due to its continued technological importance. The analytical solutions are compared to a 3D Finite Element Model to determine at what L/w ratio the analytical solutions accurately represent a 3D microcantilever beam. Thermal conductivity is determined using the steady-state solution. The transient solution yields the overall thermal diffusivity of the system irrespective of any frequency change, while the harmonic solution provides the phase difference along the length of the cantilever beam leading to a thermal diffusivity and the frequency dependent heat capacity. The analytical model can be used to analyze the aforementioned thermal properties for STR measurement at 4% accuracy for the system with length to width ratio of 20 and at 1% accuracy for length to width ratio of 100. [ABSTRACT FROM AUTHOR]

Controlling and tuning thermal conductivities of composites, including changing the direction of heat flux and thermal energy distribution, possesses significantly meaningful potential in many applications such as heat cloak, heat invisibility, heat protection and so on. In this paper, a novel design of composite metamaterial with periodic lattice structure, consisting of metal lattice layer (copper) and stretchable polymer matrix (Ecoflex), owns the ability to tune the anisotropic thermal conductivity through external strains. The parameters (such as geometric arrangement of metal lattice, loading strains), which can effectively influence the thermal properties of this metamaterial, have been investigated through finite element method considering large deformation. This new design may be helpful for designing and controlling heat flow and temperature distribution in the applications. [ABSTRACT FROM AUTHOR]

Bond transition of sp2 to sp3 in carbon nanotube can be realized through bending operation at buckling location, which affects the electronic, mechanical and thermal properties of buckled carbon nanotube. In this work, thermal properties of buckled tri-walled carbon nanotube with sp3 bonds are explored using molecular dynamics. Our results reveal that interfacial thermal conductance at buckling location is sensitive to the bending angle, which decreases exponentially with increasing bending angle until 90 degree because of increasing the number of interlayer sp3 bonds. When the bending angle is beyond 90 degree, there are sp3 bonds formed on the outer-tube walls which provide new paths for heat transfer. The insight of mechanism of thermal properties is analyzed by determining atomic micro-heat flux scattering. Our findings provide a flexible and applicable method to design thermal management device. This unusual phenomenon is explained by the micro-heat flux migration and stress distributions. [ABSTRACT FROM AUTHOR]

This paper contains new, representative reference equations for the thermal conductivity of carbon dioxide. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. In the case of the dilute-gas thermal conductivity, we incorporated recent theoretical calculations to extend the temperature range of the experimental data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlation is applicable for the temperature range from the triple point to 1100 K and pressures up to 200 MPa. The overall uncertainty (at the 95% confidence level) of the proposed correlation varies depending on the state point from a low of 1% at very low pressures below 0.1 MPa between 300 and 700 K, to 5% at the higher pressures of the range of validity. [ABSTRACT FROM AUTHOR]

The thermal conductivity, electrical conductivity, and Seebeck coefficient of a vaporgrown CdTe and two melt-grown Cd0.8Zn0.2Te crystals, including In-doped CZT-30 and un-doped CZT-34 samples, were measured from room temperature to 780#176;C. The measured thermal conductivity of CdTe was higher than the two CdZnTe samples in the low temperature range and the three sets of data merged together at temperature above 750#176;C. The measured electrical conductivities of CdTe and CZT-30 were close to be intrinsic from 190#176;C to 780#176;C. The CZT-34 sample showed higher electrical conductivity value at 290#176;C and merged with the data of CZT-30 at temperatures above 650#176;C. The measured Seebeck coefficients for all three samples showed high positive values, between 0.9 and 1.1mV/K, in the intermediate temperature range between 350 and 550#176;C and, as temperature increased, decreased slowly and converted to n-type. The Figure of Merit for the thermoelectric application, zT, calculated for the three samples were orders of magnitude lower than the state-of-the-art p-type thermoelectric materials mainly due to the low values of the electrical conductivity. A rough estimate was made on the hole concentration needed to improve the value of zT for CdTe to 1.0 at 500#176;C. A simple interpolation and extrapolation of the present data gives the value of zT for the n-type intrinsic CdTe to be 1.2±0.4 at 1050#176;C. [ABSTRACT FROM AUTHOR]

AgSbTe2 is a thermoelectric semiconductor with an intrinsically low thermal conductivity and a valence band structure that is favorable to obtaining a high thermoelectric figure of merit zT. It also has a very small energy gap Eg ~ 7.6 ± 3 meV. As this gap is less than the thermal excitation energy at room temperature, near-intrinsic AgSbTe2 is a two carrier system having both holes (concentration p) and electrons (n). Good thermoelectric performance requires heavy p-type doping (p >> n). This can be achieved with native defects or with extrinsic doping, e.g. with transition metal element. The use of defect doping is complicated by the fact that many of the ternary Ag-Sb-Te and pseudo-binary Sb2Te3-Ag2Te phase diagrams are contradictory. This paper determines the compositional region most favorable to creating a single phase material. Through a combination of intrinsic and extrinsic doping, values of zT > 1 are achieved, though not on single-phased material. Additionally, we show that thermal conductivity is not affected by defects, further demonstrating that the low lattice thermal conductivity of I-V-VI2 materials is due to an intrinsic mechanism, insensitive to changes in defect structure. [ABSTRACT FROM AUTHOR]

Since the thermal conduction equation has form invariance under coordinate transformation, one can design thermal metamaterials with novel functions by tailoring materials' thermal conductivities. In this work, we establish a different transformation theory, and propose a layered device with anisotropic thermal conductivities. The device is able to convert heat flux from parallel patterns into non-parallel patterns and vice versa. In the mean time, the heat flux pattern outside the device keeps undisturbed as if this device is absent. We perform finite-element simulations to confirm the converting behavior. This work paves a different way to manipulate the flow of heat at will. [ABSTRACT FROM AUTHOR]

Thermal transport in suspended graphene samples has been measured in prior works and this work with the use of a suspended electro-thermal micro-bridge method. These measurement results are analyzed here to evaluate and eliminate the errors caused by the extrinsic thermal contact resistance. It is noted that the roomtemperature thermal resistance measured in a recent work increases linearly with the suspended length of the single-layer graphene samples synthesized by chemical vapor deposition (CVD), and that such a feature does not reveal the failure of Fourier's law despite the increase in the reported apparent thermal conductivity with length. The re-analyzed apparent thermal conductivity of a single-layer CVD graphene sample reaches about 1680 ± 180 W m-1 K-1 at room temperature, which is close to the highest value reported for highly oriented pyrolytic graphite. In comparison, the apparent thermal conductivity values measured for two suspended exfoliated bi-layer graphene samples are about 880 ± 60 and 730 ± 60 Wm-1 K-1 at room temperature, and approach that of the natural graphite source above room temperature. However, the low-temperature thermal conductivities of these suspended graphene samples are still considerably lower than the graphite values, with the peak thermal conductivities shifted to much higher temperatures. Analysis of the thermal conductivity data reveals that the low temperature behavior is dominated by phonon scattering by polymer residue instead of by the lateral boundary. [ABSTRACT FROM AUTHOR]

Probing length-dependent thermal conductivity of a given material has been considered as an important experimental method to determine the length of ballistic thermal conduction, or equivalently, the averaged phonon mean free path (l). However, many previous thermal transport measurements have focused on varying the lateral dimensions of samples, rendering the experimental interpretation indirect. Moreover, deducing l is model-dependent in many optical measurement techniques. In addition, finite contact thermal resistances and variations of sample qualities are very likely to obscure the effect in practice, leading to an overestimation of l. We point out that directly investigating one-dimensional length-dependent (normalized) thermal resistance is a better experimental method to determine l. In this regard, we find that no clear experimental data strongly support ballistic thermal conduction of Si or Ge at room temperature. On the other hand, data of both homogeneously-alloyed SiGe nanowires and heterogeneously-interfaced Si-Ge core-shell nanowires provide undisputed evidence for ballistic thermal conduction over several micrometers at room temperature. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are performed to evaluate the effect of van der Waals forces among single-wall carbon nanotubes (SWNTs) on the interfacial thermal conductance between a SWNT array and silicon substrate. First, samples of SWNTs vertically aligned on silicon substrate are simulated, where both the number and arrangement of SWNTs are varied. Results reveal that the interfacial thermal conductance of a SWNT array/Si with van der Waals forces present is higher than when they are absent. To better understand how van der Waals forces affect heat transfer through the interface between SWNTs and silicon, further constructs of one SWNT surrounded by different numbers of other ones are studied, and the results show that the interfacial thermal conductance of the central SWNT increases with increasing van der Waals forces. Through analysis of the covalent bonds and vibrational density of states at the interface, we find that heat transfer across the interface is enhanced with a greater number of chemical bonds and that improved vibrational coupling of the two sides of the interface results in higher interfacial thermal conductance. Van der Waals forces stimulate heat transfer at the interface. [ABSTRACT FROM AUTHOR]

We discuss the textbook presentation of the concept of umklapp vs normal phonon-phonon scattering processes in the context of lattice thermal conductivity. A simplistic picture, in which the "momentum conservation" in a normal process leads to the conservation of the heat flux, is only valid within the single-velocity Debye model of phonon dispersion. Outside this model, the simple "momentum conservation" argument is demonstrably inaccurate and leads to conceptual confusion. Whether or not an individual scattering event changes the direction of the energy flow is determined by the phonon group velocity, which, unlike the quasimomentum, is a uniquely defined quantity independent of the choice of the primitive cell in reciprocal space. Furthermore, the statement that normal processes do not lead to a finite thermal conductivity when umklapp processes are absent is a statistical statement that applies to a phonon distribution rather than to individual scattering events. It is also important to understand that once umklapp processes are present, both normal and umklapp processes contribute to thermal resistance. A nuanced explanation of the subject would help avoid confusion of the student and establish a connection with cutting edge research. [ABSTRACT FROM AUTHOR]

We theoretically predict some thermal properties versus temperature dependence of one dimensional (1D) material nanowire systems. A known method is used to provide an efficient and reliable analytical procedure for wide temperature range. Predicted formulas are expressed in terms of Bloch-Grüneisen functions and Debye functions. Computing results has proved that the expressions are in excellent agreement with the results reported in the literature even if it is in very low dimension limits of nanowire systems. Therefore the calculation method is a fully predictive approach to calculate thermal conductivity and heat capacities of nanowire material systems. [ABSTRACT FROM AUTHOR]

Phonon dispersions for graphene nanoribbons (GNRs) have been derived from the first-principles calculations, and ballistic phonon thermal conductances have been evaluated using the Landauer theory. The phonon thermal conductance per unit width for GNR is larger than that for graphene and increases with decreasing ribbon width. The normalized thermal conductance with a unit of thermal quantum for the zigzag GNR is higher than that for the single-walled carbon nanotube that has a circumferential length corresponding to the width of GNR. [ABSTRACT FROM AUTHOR]

This paper contains new, representative reference equations for the thermal conductivity of ethanol. The equations are based in part upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory whenever possible. In the case of the dilute-gas thermal conductivity, a theoretically based correlation was adopted in order to extend the temperature range of the experimental data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 600 K and pressures up to 245 MPa. The overall uncertainty (at the 95% confidence level) of the proposed correlation is estimated to be less than 4.6%. [ABSTRACT FROM AUTHOR]

This paper contains new, representative reference equations for the thermal conductivity of n-hexane. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. In the case of the dilute-gas thermal conductivity, a theoretically based correlation was adopted in order to extend the temperature range of the experimental data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 600 K and pressures up to 500 MPa. The overall uncertainty (considered to be estimates of a combined expanded uncertainty with a coverage factor of 2) of the proposed correlation is estimated, for pressures less than 500 MPa and temperatures less than 600 K, to be less than 6%. [ABSTRACT FROM AUTHOR]