Thermal properties of borate crystals for high power optical parametric chirped-pulse amplification.

PubMed

Riedel, R; Rothhardt, J; Beil, K; Gronloh, B; Klenke, A; Höppner, H; Schulz, M; Teubner, U; Kränkel, C; Limpert, J; Tünnermann, A; Prandolini, M J; Tavella, F

2014-07-28

The potential of borate crystals, BBO, LBO and BiBO, for high average power scaling of optical parametric chirped-pulse amplifiers is investigated. Up-to-date measurements of the absorption coefficients at 515 nm and the thermal conductivities are presented. The measured absorption coefficients are a factor of 10-100 lower than reported by the literature for BBO and LBO. For BBO, a large variation of the absorption coefficients was found between crystals from different manufacturers. The linear and nonlinear absorption coefficients at 515 nm as well as thermal conductivities were determined for the first time for BiBO. Further, different crystal cooling methods are presented. In addition, the limits to power scaling of OPCPAs are discussed.

Experimental metrology to obtain thermal phonon transmission coefficients at solid interfaces

NASA Astrophysics Data System (ADS)

Hua, Chengyun; Chen, Xiangwen; Ravichandran, Navaneetha K.; Minnich, Austin J.

2017-05-01

Interfaces play an essential role in phonon-mediated heat conduction in solids, impacting applications ranging from thermoelectric waste heat recovery to heat dissipation in electronics. From the microscopic perspective, interfacial phonon transport is described by transmission coefficients that link vibrational modes in the materials composing the interface. However, direct experimental determination of these coefficients is challenging because most experiments provide a mode-averaged interface conductance that obscures the microscopic detail. Here, we report a metrology to extract thermal phonon transmission coefficients at solid interfaces using ab initio phonon transport modeling and a thermal characterization technique, time-domain thermoreflectance. In combination with transmission electron microscopy characterization of the interface, our approach allows us to link the atomic structure of an interface to the spectral content of the heat crossing it. Our work provides a useful perspective on the microscopic processes governing interfacial heat conduction.

Experimental metrology to obtain thermal phonon transmission coefficients at solid interfaces

DOE PAGES

Hua, Chengyun; Chen, Xiangwen; Ravichandran, Navaneetha K.; ...

2017-05-17

Interfaces play an essential role in phonon-mediated heat conduction in solids, impacting applications ranging from thermoelectric waste heat recovery to heat dissipation in electronics. From the microscopic perspective, interfacial phonon transport is described by transmission coefficients that link vibrational modes in the materials composing the interface. But, direct experimental determination of these coefficients is challenging because most experiments provide a mode-averaged interface conductance that obscures the microscopic detail. Here, we report a metrology to extract thermal phonon transmission coefficients at solid interfaces using ab initio phonon transport modeling and a thermal characterization technique, time-domain thermoreflectance. In combination with transmission electronmore » microscopy characterization of the interface, our approach allows us to link the atomic structure of an interface to the spectral content of the heat crossing it. This work provides a useful perspective on the microscopic processes governing interfacial heat conduction.« less

Measurements of thermal conductivity and the coefficient of thermal expansion for polysilicon thin films by using double-clamped beams

NASA Astrophysics Data System (ADS)

Liu, Haiyun; Wang, Lei

2018-01-01

In this paper, a test structure for simultaneously determining thermal conductivity and the coefficient of thermal expansion (CTE) of polysilicon thin film is proposed. The test structure consists of two double-clamped beams with different lengths. A theoretical model for extracting thermal conductivity and CTE based on electrothermal analysis and resonance frequency approach is developed. Both flat and buckled beams are considered in the theoretical model. The model is confirmed by finite element software ANSYS. The test structures are fabricated by surface micromachined fabrication process. Experiments are carried out in our atmosphere. Thermal conductivity and CTE of polysilicon thin film are obtained to be (29.96  ±  0.92) W · m · K-1 and (2.65  ±  0.03)  ×  10-6 K-1, respectively, with temperature ranging from 300-400 K.

High-pressure Seebeck coefficients and thermoelectric behaviors of Bi and PbTe measured using a Paris-Edinburgh cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Jason; Kumar, Ravhi S.; Park, Changyong

2016-01-01

A new sample cell assembly design for the Paris-Edinburgh type large-volume press for simultaneous measurements of X-ray diffraction, electrical resistance, Seebeck coefficient and relative changes in the thermal conductance at high pressures has been developed. The feasibility of performing in situ measurements of the Seebeck coefficient and thermal measurements is demonstrated by observing well known solid–solid phase transitions of bismuth (Bi) up to 3 GPa and 450 K. A reversible polarity flip has been observed in the Seebeck coefficient across the Bi-I to Bi-II phase boundary. Also, successful Seebeck coefficient measurements have been performed for the classical high-temperature thermoelectric materialmore » PbTe under high pressure and temperature conditions. In addition, the relative change in the thermal conductivity was measured and a relative change in ZT, the dimensionless figure of merit, is described. Furthermore, this new capability enables pressure-induced structural changes to be directly correlated to electrical and thermal properties.« less

High-pressure Seebeck coefficients and thermoelectric behaviors of Bi and PbTe measured using a Paris-Edinburgh cell.

PubMed

Baker, Jason; Kumar, Ravhi; Park, Changyong; Kenney-Benson, Curtis; Cornelius, Andrew; Velisavljevic, Nenad

2016-11-01

A new sample cell assembly design for the Paris-Edinburgh type large-volume press for simultaneous measurements of X-ray diffraction, electrical resistance, Seebeck coefficient and relative changes in the thermal conductance at high pressures has been developed. The feasibility of performing in situ measurements of the Seebeck coefficient and thermal measurements is demonstrated by observing well known solid-solid phase transitions of bismuth (Bi) up to 3 GPa and 450 K. A reversible polarity flip has been observed in the Seebeck coefficient across the Bi-I to Bi-II phase boundary. Also, successful Seebeck coefficient measurements have been performed for the classical high-temperature thermoelectric material PbTe under high pressure and temperature conditions. In addition, the relative change in the thermal conductivity was measured and a relative change in ZT, the dimensionless figure of merit, is described. This new capability enables pressure-induced structural changes to be directly correlated to electrical and thermal properties.

Identification of the Thermal Conductivity Coefficient for Quasi-Stationary Two-Dimensional Heat Conduction Equations

NASA Astrophysics Data System (ADS)

Matsevityi, Yu. M.; Alekhina, S. V.; Borukhov, V. T.; Zayats, G. M.; Kostikov, A. O.

2017-11-01

The problem of identifying the time-dependent thermal conductivity coefficient in the initial-boundary-value problem for the quasi-stationary two-dimensional heat conduction equation in a bounded cylinder is considered. It is assumed that the temperature field in the cylinder is independent of the angular coordinate. To solve the given problem, which is related to a class of inverse problems, a mathematical approach based on the method of conjugate gradients in a functional form is being developed.

Effect of silicide/silicon hetero-junction structure on thermal conductivity and Seebeck coefficient.

PubMed

Choi, Wonchul; Park, Young-Sam; Hyun, Younghoon; Zyung, Taehyoung; Kim, Jaehyeon; Kim, Soojung; Jeon, Hyojin; Shin, Mincheol; Jang, Moongyu

2013-12-01

We fabricated a thermoelectric device with a silicide/silicon laminated hetero-structure by using RF sputtering and rapid thermal annealing. The device was observed to have Ohmic characteristics by I-V measurement. The temperature differences and Seebeck coefficients of the proposed silicide/silicon laminated and bulk structure were measured. The laminated thermoelectric device shows suppression of heat flow from the hot to cold side. This is supported by the theory that the atomic mass difference between silicide and silicon creates a scattering center for phonons. The major impact of our work is that phonon transmission is suppressed at the interface between silicide and silicon without degrading electrical conductivity. The estimated thermal conductivity of the 3-layer laminated device is 126.2 +/- 3.7 W/m. K. Thus, by using the 3-layer laminated structure, thermal conductivity is reduced by around 16% compared to bulk silicon. However, the Seebeck coefficient of the thermoelectric device is degraded compared to that of bulk silicon. It is understood that electrical conductivity is improved by using silicide as a scattering center.

Thermal Conductivity and Expansion Coefficient of (Sm1- x Yb x )2Ce2O7 Ceramics for Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Xiaoge, Chen; Hongsong, Zhang; Kun, Sun; Xudan, Dang; Haoming, Zhang; Bo, Ren; An, Tang

2017-12-01

In the current paper, the (Sm1- x Yb x )2Ce2O7 ceramics were prepared via sol-gel and high-temperature solid reaction methods. The phase composition, microstructure, thermal conductivity, and expansion coefficient were investigated. Results indicate that pure (Sm1- x Yb x )2Ce2O7 ceramics with single defect-fluorite structure are synthesized successfully. Owing to the phonon scattering caused by Yb addition, the thermal conductivity of (Sm1- x Yb x )2Ce2O7 ceramics decreases with increasing Yb2O3 content at identical temperatures, which is lower than that of YSZ. Due to the relatively low ionic radius of Yb3+ ions, the addition of Yb2O3 decreases the thermal expansion coefficient of (Sm1- x Yb x )2Ce2O7 ceramics, which is higher than that of 8YSZ. The synthesized (Sm1- x Yb x )2Ce2O7 ceramics can be explored as candidate materials for thermal barrier coatings.

Advances in LED packaging and thermal management materials

NASA Astrophysics Data System (ADS)

Zweben, Carl

2008-02-01

Heat dissipation, thermal stresses and cost are key light-emitting diode (LED) packaging issues. Heat dissipation limits power levels. Thermal stresses affect performance and reliability. Copper, aluminum and conventional polymeric printed circuit boards (PCBs) have high coefficients of thermal expansion, which can cause high thermal stresses. Most traditional low-coefficient-of-thermal-expansion (CTE) materials like tungsten/copper, which date from the mid 20th century, have thermal conductivities that are no better than those of aluminum alloys, about 200 W/m-K. An OIDA LED workshop cited a need for better thermal materials. There are an increasing number of low-CTE materials with thermal conductivities ranging between that of copper (400 W/m-K) and 1700 W/m-K, and many other low-CTE materials with lower thermal conductivities. Some of these materials are low cost. Others have the potential to be low cost in high-volume production. High-thermal-conductivity materials enable higher power levels, potentially reducing the number of required LEDs. Advanced thermal materials can constrain PCB CTE and greatly increase thermal conductivity. This paper reviews traditional packaging materials and advanced thermal management materials. The latter provide the packaging engineer with a greater range of options than in the past. Topics include properties, status, applications, cost, using advanced materials to fix manufacturing problems, and future directions, including composites reinforced with carbon nanotubes and other thermally conductive materials.

Estimation of Phonon and Carrier Thermal Conductivities for Bulk Thermoelectric Materials Using Transport Properties

NASA Astrophysics Data System (ADS)

Otsuka, Mioko; Homma, Ryoei; Hasegawa, Yasuhiro

2017-05-01

The phonon and carrier thermal conductivities of thermoelectric materials were calculated using the Wiedemann-Franz law, Boltzmann equation, and a method we propose in this study called the Debye specific heat method. We prepared polycrystalline n-type doped bismuth telluride (BiTe) and bismuth antimony (BiSb) bulk alloy samples and measured six parameters (Seebeck coefficient, resistivity, thermal conductivity, thermal diffusivity, magneto-resistivity, and Hall coefficient). The carrier density and mobility were estimated for calculating the carrier thermal conductivity by using the Boltzmann equation. In the Debye specific heat method, the phonon thermal diffusivity, and thermal conductivity were calculated from the temperature dependence of the effective specific heat by using not only the measured thermal conductivity and Debye model, but also the measured thermal diffusivity. The carrier thermal conductivity was also evaluated from the phonon thermal conductivity by using the specific heat. The ratio of carrier thermal conductivity to thermal conductivity was evaluated for the BiTe and BiSb samples, and the values obtained using the Debye specific heat method at 300 K were 52% for BiTe and <5.5% for BiSb. These values are either considerably larger or smaller than those obtained using other methods. The Dulong-Petit law was applied to validate the Debye specific heat method at 300 K, which is significantly greater than the Debye temperature of the BiTe and BiSb samples, and it was confirmed that the phonon specific heat at 300 K has been accurately reproduced using our proposed method.

Electronic and thermal transport study of sinusoidally corrugated nanowires aiming to improve thermoelectric efficiency.

PubMed

Park, K H; Martin, P N; Ravaioli, U

2016-01-22

Improvement of thermoelectric efficiency has been very challenging in the solid-state industry due to the interplay among transport coefficients which measure the efficiency. In this work, we modulate the geometry of nanowires to interrupt thermal transport with causing only a minimal impact on electronic transport properties, thereby maximizing the thermoelectric power generation. As it is essential to scrutinize comprehensively both electronic and thermal transport behaviors for nano-scale thermoelectric devices, we investigate the Seebeck coefficient, the electrical conductance, and the thermal conductivity of sinusoidally corrugated silicon nanowires and eventually look into an enhancement of the thermoelectric figure-of-merit [Formula: see text] from the modulated nanowires over typical straight nanowires. A loss in the electronic transport coefficient is calculated with the recursive Green function along with the Landauer formalism, and the thermal transport is simulated with the molecular dynamics. In contrast to a small influence on the thermopower and the electrical conductance of the geometry-modulated nanowires, a large reduction of the thermal conductivity yields an enhancement of the efficiency by 10% to 35% from the typical nanowires. We find that this approach can be easily extended to various structures and materials as we consider the geometrical modulation as a sole source of perturbation to the system.

Calculating lattice thermal conductivity: a synopsis

NASA Astrophysics Data System (ADS)

Fugallo, Giorgia; Colombo, Luciano

2018-04-01

We provide a tutorial introduction to the modern theoretical and computational schemes available to calculate the lattice thermal conductivity in a crystalline dielectric material. While some important topics in thermal transport will not be covered (including thermal boundary resistance, electronic thermal conduction, and thermal rectification), we aim at: (i) framing the calculation of thermal conductivity within the general non-equilibrium thermodynamics theory of transport coefficients, (ii) presenting the microscopic theory of thermal conduction based on the phonon picture and the Boltzmann transport equation, and (iii) outlining the molecular dynamics schemes to calculate heat transport. A comparative and critical addressing of the merits and drawbacks of each approach will be discussed as well.

Advances in photonics thermal management and packaging materials

NASA Astrophysics Data System (ADS)

Zweben, Carl

2008-02-01

Heat dissipation, thermal stresses, and cost are key packaging design issues for virtually all semiconductors, including photonic applications such as diode lasers, light-emitting diodes (LEDs), solid state lighting, photovoltaics, displays, projectors, detectors, sensors and laser weapons. Heat dissipation and thermal stresses affect performance and reliability. Copper, aluminum and conventional polymeric printed circuit boards (PCBs) have high coefficients of thermal expansion, which can cause high thermal stresses. Most traditional low-coefficient-of-thermal-expansion (CTE) materials like tungsten/copper, which date from the mid 20 th century, have thermal conductivities that are no better than those of aluminum alloys, about 200 W/m-K. There are an increasing number of low-CTE materials with thermal conductivities ranging between that of copper (400 W/m-K) and 1700 W/m-K, and many other new low-CTE materials with lower thermal conductivities. An important benefit of low-CTE materials is that they allow use of hard solders. Some advanced materials are low cost. Others have the potential to be low cost in high-volume production. High-thermal-conductivity materials enable higher power levels, potentially reducing the number of required devices. Advanced thermal materials can constrain PCB CTE and greatly increase thermal conductivity. This paper reviews traditional packaging materials and advanced thermal management materials. The latter provide the packaging engineer with a greater range of options than in the past. Topics include properties, status, applications, cost, using advanced materials to fix manufacturing problems, and future directions, including composites reinforced with carbon nanotubes and other thermally conductive materials.

Effect of moisture content on the coefficient of thermal expansion of concrete.

DOT National Transportation Integrated Search

2007-09-01

The purpose of this report is to discuss a study conducted on twenty separate mix designs of concrete and the effects of : the aggregate type, moisture content, and temperature on the coefficient of thermal expansion(CTE). These results are to be use...

The effects of transverse magnetic field and local electronic interaction on thermoelectric properties of monolayer graphene

NASA Astrophysics Data System (ADS)

Rezania, Hamed; Azizi, Farshad

2018-02-01

We study the effects of a transverse magnetic field and electron doping on the thermoelectric properties of monolayer graphene in the context of Hubbard model at the antiferromagnetic sector. In particular, the temperature dependence of thermal conductivity and Seebeck coefficient has been investigated. Mean field approximation has been employed in order to obtain the electronic spectrum of the system in the presence of local electron-electron interaction. Our results show the peak in thermal conductivity moves to higher temperatures with increase of both chemical potential and Hubbard parameter. Moreover the increase of magnetic field leads to shift of peak in temperature dependence of thermal conductivity to higher temperatures. Finally the behavior of Seebeck coefficient in terms of temperature has been studied and the effects of magnetic field and Hubbard parameter on this coefficient have been investigated in details.

Task 6 : material thermal input for Iowa materials.

DOT National Transportation Integrated Search

2008-02-01

The present research project was designed to determine thermal properties, such as coefficient of thermal expansion : (CTE) and thermal conductivity, of Iowa concrete pavement materials. These properties are required as input values by : the Mechanis...

New Technique for TOC Estimation Based on Thermal Core Logging in Low-Permeable Formations (Bazhen fm.)

NASA Astrophysics Data System (ADS)

Popov, Evgeny; Popov, Yury; Spasennykh, Mikhail; Kozlova, Elena; Chekhonin, Evgeny; Zagranovskaya, Dzhuliya; Belenkaya, Irina; Alekseev, Aleksey

2016-04-01

A practical method of organic-rich intervals identifying within the low-permeable dispersive rocks based on thermal conductivity measurements along the core is presented. Non-destructive non-contact thermal core logging was performed with optical scanning technique on 4 685 full size core samples from 7 wells drilled in four low-permeable zones of the Bazhen formation (B.fm.) in the Western Siberia (Russia). The method employs continuous simultaneous measurements of rock anisotropy, volumetric heat capacity, thermal anisotropy coefficient and thermal heterogeneity factor along the cores allowing the high vertical resolution (of up to 1-2 mm). B.fm. rock matrix thermal conductivity was observed to be essentially stable within the range of 2.5-2.7 W/(m*K). However, stable matrix thermal conductivity along with the high thermal anisotropy coefficient is characteristic for B.fm. sediments due to the low rock porosity values. It is shown experimentally that thermal parameters measured relate linearly to organic richness rather than to porosity coefficient deviations. Thus, a new technique employing the transformation of the thermal conductivity profiles into continuous profiles of total organic carbon (TOC) values along the core was developed. Comparison of TOC values, estimated from the thermal conductivity values, with experimental pyrolytic TOC estimations of 665 samples from the cores using the Rock-Eval and HAWK instruments demonstrated high efficiency of the new technique for the organic rich intervals separation. The data obtained with the new technique are essential for the SR hydrocarbon generation potential, for basin and petroleum system modeling application, and estimation of hydrocarbon reserves. The method allows for the TOC richness to be accurately assessed using the thermal well logs. The research work was done with financial support of the Russian Ministry of Education and Science (unique identification number RFMEFI58114X0008).

High temperature XRD of Cu2.1Zn0.9SnSe4

NASA Astrophysics Data System (ADS)

Chetty, Raju; Mallik, Ramesh Chandra

2014-04-01

Quaternary compound with chemical composition Cu2.1Zn0.9SnSe4 is prepared by solid state synthesis. High temperature XRD (X-Ray Diffraction) of this compound is used in studying the effect of temperature on lattice parameters and thermal expansion coefficients. Thermal expansion coefficient is one of the important quantities in evaluating the Grüneisen parameter which further useful in determining the lattice thermal conductivity of the material. The high temperature XRD of the material revealed that the lattice parameters as well as thermal expansion coefficients of the material increased with increase in temperature which confirms the presence of anharmonicty.

Investigation of Thermal Conductivities and Expansion Coefficients of (Yb1 - x La x )2AlTaO7 Ceramics

NASA Astrophysics Data System (ADS)

Xiaoge, Chen; Hongsong, Zhang; Sai, Su; Yongde, Zhao; An, Tang; Haoming, Zhang

2017-12-01

The (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3, 0.5) ceramics were prepared by solid-state reaction method. The phase composition, microstructure, thermophysical properties of (Yb1 - x La x )2AlTaO7 ceramics were investigated. Results reveal that (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3) ceramics exhibit a single pyrochlore-type structure, and the (Yb0.5La0.5)2AlTaO7 has an orthorhombic weberite structure. The thermal conductivities of (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3) ceramics decrease with increasing Yb2O3 contents. (Yb0.5La0.5)2AlTaO7 has the highest thermal conductivity among all the ceramics studied, within the range of 1.48-1.75 W/m K (20-1200 °C). The thermal expansion coefficients of (Yb1 - x La x )2AlTaO7 ceramics decrease gradually with increasing La2O3 fractions, and the thermal expansion coefficients are close to those of YSZ.

Transparent athermal glass-ceramics in Li2O-Al2O3-SiO2 system

NASA Astrophysics Data System (ADS)

Himei, Yusuke; Nagakane, Tomohiro; Sakamoto, Akihiko; Kitamura, Naoyuki; Fukumi, Kohei; Nishii, Junji; Hirao, Kazuyuki

2005-04-01

An attempt has been conducted to develop multicomponent transparent glass-ceramics which have athermal property better than silica glass. Transparent Li2O-Al2O3-SiO2 (LAS) glass-ceramics with small thermal expansion coefficient was chosen as a candidate. Athermal property of the glass-ceramics was improved by the independent control of temperature coefficients of electronic polarizability and thermal expansion coefficient, both of which govern the temperature coefficient of optical path length. It was found that temperature coefficient of electronic polarizability and thermal expansion coefficient of the LAS glass-ceramics were controllable by the additives and crystallization conditions. The doping of B2O3 and the crystallization under a hydrostatic pressure of 196 MPa were very effective to reduce temperature coefficient of electronic polarizability without a remarkable increase in thermal expansion coefficient. It was deduced that the reduction in temperature coefficient of electronic polarizability by the crystallization under 196 MPa resulted from the inhibition of the precipitation of beta-spodumene solid solution. The relative temperature coefficients of optical path length of B2O3-doped glass-ceramic crystallized under 196 MPa was 11.7 x 10-6/°C, which was slightly larger than that of silica glass. Nevertheless, the thermal expansion coefficient of this glass-ceramic was smaller than that of silica glass.

High temperature XRD of Cu{sub 2.1}Zn{sub 0.9}SnSe{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chetty, Raju, E-mail: rcmallik@physics.iisc.ernet.in; Mallik, Ramesh Chandra, E-mail: rcmallik@physics.iisc.ernet.in

2014-04-24

Quaternary compound with chemical composition Cu{sub 2.1}Zn{sub 0.9}SnSe{sub 4} is prepared by solid state synthesis. High temperature XRD (X-Ray Diffraction) of this compound is used in studying the effect of temperature on lattice parameters and thermal expansion coefficients. Thermal expansion coefficient is one of the important quantities in evaluating the Grüneisen parameter which further useful in determining the lattice thermal conductivity of the material. The high temperature XRD of the material revealed that the lattice parameters as well as thermal expansion coefficients of the material increased with increase in temperature which confirms the presence of anharmonicty.

Ion conduction mechanisms and thermal properties of hydrated and anhydrous phosphoric acids studied with 1H, 2H, and 31P NMR.

PubMed

Aihara, Yuichi; Sonai, Atsuo; Hattori, Mineyuki; Hayamizu, Kikuko

2006-12-14

To understand the behaviors of phosphoric acids in fuel cells, the ion conduction mechanisms of phosphoric acids in condensed states without free water and in a monomer state with water were studied by measuring the ionic conductivity (sigma) using AC impedance, thermal properties, and self-diffusion coefficients (D) and spin-lattice relaxation times (T1) with multinuclear NMR. The self-diffusion coefficient of the protons (H+ or H3O+), H2O, and H located around the phosphate were always larger than the diffusion coefficients of the phosphates and the disparity increased with increasing phosphate concentration. The diffusion coefficients of the samples containing D2O paralleled those in the protonated samples. Since the 1H NMR T1 values exhibited a minimum with temperature, it was possible to determine the correlation times and they were found to be of nanosecond order for a distance of nanometer order for a flip. The agreement of the ionic conductivities measured directly and those calculated from the diffusion coefficients indicates that the ion conduction obeys the Nernst-Einstein equation in the condensed phosphoric acids. The proton diffusion plays a dominant role in the ion conduction, especially in the condensed phosphoric acids.

Anisotropy properties of the quartzite from Jegłowa, Poland

NASA Astrophysics Data System (ADS)

Marciniszyn, Tomasz; Sieradzki, Adam

2013-06-01

Marciniszyn, T. and Sieradzki, A. 2013. Anisotropy properties of the quartzite from Jegłowa, Poland. Acta Geologica Polonica, 63 (2), 265-269. Warszawa. Results of the dielectric spectroscopy, thermal and dilatometric measurements of the quartzite rock are presented. Based on the dielectric measurements performed in a wide range of the frequency (101 - 5 × 107 Hz) at temperature of 300K the piezoresonance in quartzite was found. A chemical composition of quartzite was examined by XRF. The anisotropy of the thermal conductivity was observed. The thermal conductivity coefficient changes from 13.2 [W/Km] to 5.6 [W/Km] for the [100] and [001] direction, respectively. Based on the thermal expansion measurement the thermal expansion coefficient of quartzite was estimated to be α Q = 8.0 × 10-6 [K-1 ] ±0.7 × 10-6 .

Pressurized electrolysis stack with thermal expansion capability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bourgeois, Richard Scott

The present techniques provide systems and methods for mounting an electrolyzer stack in an outer shell so as to allow for differential thermal expansion of the electrolyzer stack and shell. Generally, an electrolyzer stack may be formed from a material with a high coefficient of thermal expansion, while the shell may be formed from a material having a lower coefficient of thermal expansion. The differences between the coefficients of thermal expansion may lead to damage to the electrolyzer stack as the shell may restrain the thermal expansion of the electrolyzer stack. To allow for the differences in thermal expansion, themore » electrolyzer stack may be mounted within the shell leaving a space between the electrolyzer stack and shell. The space between the electrolyzer stack and the shell may be filled with a non-conductive fluid to further equalize pressure inside and outside of the electrolyzer stack.« less

High temperature XRD of Cu2GeSe3

NASA Astrophysics Data System (ADS)

Premkumar D., S.; Chetty, Raju; Malar, P.; Mallik, Ramesh Chandra

2015-06-01

The Cu2GeSe3 is prepared by solid state synthesis method. The high temperature XRD has been done at different temperature from 30 °C to 450 °C. The reitveld refinement confirms Cu2GeSe3 phase and orthorhombic crystal structure. The lattice constants are increasing with increase in the temperature and their rate of increase with respect to temperature are used for finding the thermal expansion coefficient. The calculation of the linear and volume coefficient of thermal expansion is done from 30 °C to 400 °C. Decrease in the values of linear expansion coefficients with temperature are observed along a and c axis. Since thermal expansion coefficient is the consequence of the distortion of atoms in the lattice; this can be further used to find the minimum lattice thermal conductivity at given temperature.

Design, Fabrication, Characterization and Modeling of Integrated Functional Materials

DTIC Science & Technology

2013-10-01

coated microwire to change the temperature of an FBG. We show below that the proposed sensor probe, with a relatively poor thermal coupling with FBG...Seebeck coefficient and decreased thermal conductivity due to the phenomenological properties of nanometer length scales, including enhanced...nanocomposites as compared to bulk polycrystalline materials, in addition to similar thermal conductivities , results in enhanced room temperature ZT as

Thermal Conductivity of Diamond Composites

PubMed Central

Kidalov, Sergey V.; Shakhov, Fedor M.

2009-01-01

A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K) and 400 W/(m·K), respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon); one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K). Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity.

Thermal Properties of Oxides With Magnetoplumbite Structure for Advanced Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Zhu, Dongming; Eslamloo-Grami, Maryam

2007-01-01

Oxides having magnetoplumbite structure are promising candidate materials for applications as high temperature thermal barrier coatings because of their high thermal stability, high thermal expansion, and low thermal conductivity. In this study, powders of LaMgAl11O19, GdMgAl11O19, SmMgAl11O19, and Gd0.7Yb0.3MgAl11O19 magnetoplumbite oxides were synthesized by citric acid sol-gel method and hot pressed into disk specimens. The thermal expansion coefficients (CTE) of these oxide materials were measured from room temperature to 1500 C. The average CTE value was found to be approx.9.6x10(exp -6)/C. Thermal conductivity of these magnetoplumbite-based oxide materials was also evaluated using steady-state laser heat flux test method. The effects of doping on thermal properties were also examined. Thermal conductivity of the doped Gd0.7Yb0.3MgAl11O19 composition was found to be lower than that of the undoped GdMgAl11O19. In contrast, thermal expansion coefficient was found to be independent of the oxide composition and appears to be controlled by the magnetoplumbite crystal structure. Thermal conductivity testing of LaMgAl11O19 and LaMnAl11O19 magnetoplumbite oxide coatings plasma sprayed on NiCrAlY/Rene N5 superalloy substrates indicated resistance of these coatings to sintering even at temperatures as high as 1600 C.

Apparatus for the measurement of electrical resistivity, Seebeck coefficient, and thermal conductivity of thermoelectric materials between 300 K and 12 K

NASA Astrophysics Data System (ADS)

Martin, Joshua; Nolas, George S.

2016-01-01

We have developed a custom apparatus for the consecutive measurement of the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of materials between 300 K and 12 K. These three transport properties provide for a basic understanding of the thermal and electrical properties of materials. They are of fundamental importance in identifying and optimizing new materials for thermoelectric applications. Thermoelectric applications include waste heat recovery for automobile engines and industrial power generators, solid-state refrigeration, and remote power generation for sensors and space probes. The electrical resistivity is measured using a four-probe bipolar technique, the Seebeck coefficient is measured using the quasi-steady-state condition of the differential method in a 2-probe arrangement, and the thermal conductivity is measured using a longitudinal, multiple gradient steady-state technique. We describe the instrumentation and the measurement uncertainty associated with each transport property, each of which is presented with representative measurement comparisons using round robin samples and/or certified reference materials. Transport properties data from this apparatus have supported the identification, development, and phenomenological understanding of novel thermoelectric materials.

Heat Transfer Performance of Functionalized Graphene Nanoplatelet Aqueous Nanofluids

PubMed Central

Agromayor, Roberto; Cabaleiro, David; Pardinas, Angel A.; Vallejo, Javier P.; Fernandez-Seara, Jose; Lugo, Luis

2016-01-01

The low thermal conductivity of fluids used in many industrial applications is one of the primary limitations in the development of more efficient heat transfer systems. A promising solution to this problem is the suspension of nanoparticles with high thermal conductivities in a base fluid. These suspensions, known as nanofluids, have great potential for enhancing heat transfer. The heat transfer enhancement of sulfonic acid-functionalized graphene nanoplatelet water-based nanofluids is addressed in this work. A new experimental setup was designed for this purpose. Convection coefficients, pressure drops, and thermophysical properties of various nanofluids at different concentrations were measured for several operational conditions and the results are compared with those of pure water. Enhancements in thermal conductivity and in convection heat transfer coefficient reach 12% (1 wt %) and 32% (0.5 wt %), respectively. New correlations capable of predicting the Nusselt number and the friction factor of this kind of nanofluid as a function of other dimensionless quantities are developed. In addition, thermal performance factors are obtained from the experimental convection coefficient and pressure drop data in order to assess the convenience of replacing the base fluid with designed nanofluids. PMID:28773578

Wittichenite Cu3BiS3: Synthesis and Physical Properties

NASA Astrophysics Data System (ADS)

Wei, Kaya; Hobbis, Dean; Wang, Hsin; Nolas, George S.

2018-04-01

Polycrystalline Cu3BiS3 was synthesized and densified using hot pressing in order to investigate the physical properties of this material. Both the thermal conductivity and the Seebeck coefficient of Cu3BiS3 are reported for the first time in order to investigate the thermoelectric properties of this material. The ultralow thermal conductivity coupled with the relatively high Seebeck coefficient, 0.17 W/m-K and 540 μV/K at room temperature, respectively, suggest Cu3BiS3 may show promise for thermoelectric applications.

Wittichenite Cu3BiS3: Synthesis and Physical Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Kaya; Hobbis, Dean; Wang, Hsin

Polycrystalline Cu 3BiS 3 was synthesized and densified using hot pressing in order to investigate the physical properties of this material. Both the thermal conductivity and the Seebeck coefficient of Cu 3BiS 3 are reported for the first time in order to investigate the thermoelectric properties of this material. The ultralow thermal conductivity coupled with the relatively high Seebeck coefficient, 0.17 W/m-K and 540 μV/K at room temperature, respectively, suggest Cu 3BiS 3 may show promise for thermoelectric applications.

Wittichenite Cu3BiS3: Synthesis and Physical Properties

DOE PAGES

Wei, Kaya; Hobbis, Dean; Wang, Hsin; ...

2018-01-18

Polycrystalline Cu 3BiS 3 was synthesized and densified using hot pressing in order to investigate the physical properties of this material. Both the thermal conductivity and the Seebeck coefficient of Cu 3BiS 3 are reported for the first time in order to investigate the thermoelectric properties of this material. The ultralow thermal conductivity coupled with the relatively high Seebeck coefficient, 0.17 W/m-K and 540 μV/K at room temperature, respectively, suggest Cu 3BiS 3 may show promise for thermoelectric applications.

Electrical and thermal transport through low densified copper doped PbSe for thermoelectric application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gayner, Chhatrasal; Malik, Iram; Das, Malay K.

2016-05-06

In this paper, Cu doped PbSe is successfully synthesized by solid state reaction. Theinfluence of porosity on thermal and electrical transport in Cu doped PbSe is investigated in this study. Low densified material significantly scatters the electrons as well as phonons through the high number of scattering sites (like pores, cracks, disorder, etc). As a result, the drastic reduction in thermal conductivity and electrical conductivity isnoticed. Additionally, Seebeck coefficient enhances in a low densified materials. Furthermore, Pb{sub 1-x}Cu{sub x}Se (x ∼ 0 to 0.06) has high Seebeck coefficient due to the energy filtering effect and lower charge carrier concentration.

Simulation and Experimental Study on Thermal Conductivity of [EMIM][DEP] + H_2 O + SWCNTs Nanofluids as a New Working Pairs

NASA Astrophysics Data System (ADS)

Li, Chang; Zhao, Zongchang; Zhang, Xiaodong; Li, Tianyu

2018-03-01

In this paper, the single-wall carbon nanotubes (SWCNTs) were dispersed into ionic liquid, 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and its aqueous solution [EMIM][DEP](1) + H2O(2) to enhance the thermal conductivity of base liquids, which will be the promising working pairs for absorption heat pumps and refrigerators. The enhancement effects on thermal conductivity were studied by experiment and molecular dynamic simulation (MD) methods. The thermal conductivities of [EMIM][DEP] + SWCNTs (INF) and [EMIM][DEP](1) + H2O(2) + SWCNT(SNF) both with SWCNT mass fraction of 0.5, 1, and 2 (wt%) were measured by transient hot-wire method. The results indicate that the enhancement ratio of thermal conductivity of INF, and SNF can approach 1.30 when SWCNT is 2 (wt%). Moreover, SWCNTs has a higher enhancement ratio than multi-wall carbon nanotubes (MWCNTs). Density and thermal conductivity of [EMIM][DEP], [EMIM][DEP](1) + H2O(2), INF and SNF systems, together with self-diffusion coefficients of [EMIM]+, [DEP]-, [EMIM][DEP] and water in solution [EMIM][DEP](1) + H2O(2), were investigated by MD simulations. The results indicate that the maximum relative error between the simulated and experimental densities is about 2 %, and the simulated self-diffusion coefficient of [EMIM][DEP] is in the order of magnitude of 10^{-11} m2\\cdot s^{-1}. The average relative deviation for the simulated thermal conductivity of [EMIM][DEP](1) + H2O(2), INF and SNF from experimental ones are 23.57 %, 5 %, and 5 %, respectively. In addition, the contributions of kinetic energy, potential energy, and virial and partial enthalpy terms to thermal conductivity were also calculated. The results indicate that virial term's contribution to thermal conductivity is the maximum, which accounts for 75 % to 80 % of total thermal conductivity.

Low Thermal Conductivity of RE-Doped SrO(SrTiO3)1 Ruddlesden Popper Phase Bulk Materials Prepared by Molten Salt Method

NASA Astrophysics Data System (ADS)

Putri, Yulia Eka; Said, Suhana Mohd; Refinel, Refinel; Ohtaki, Michitaka; Syukri, Syukri

2018-04-01

The SrO(SrTiO3)1 (Sr2TiO4) Ruddlesden Popper (RP) phase is a natural superlattice comprising of alternately stacking perovskite-type SrTiO3 layers and rock salt SrO layers along the crystallographic c direction. This paper discusses the properties of the Sr2TiO4 and (La, Sm)-doped Sr2TiO4 RP phase synthesized via molten salt method, within the context of thermoelectric applications. A good thermoelectric material requires high electrical conductivity, high Seebeck coefficient and low thermal conductivity. All three conditions have the potential to be fulfilled by the Sr2TiO4 RP phase, in particular, the superlattice structure allows a higher degree of phonon scattering hence resulting in lowered thermal conductivity. In this work, the Sr2TiO4 RP phase is doped with Sm and La respectively, which allows injection of charge carriers, modification of its electronic structure for improvement of the Seebeck coefficient, and most significantly, reduction of thermal conductivity. The particles with submicron size allows excessive phonon scattering along the boundaries, thus reduces the thermal conductivity by fourfold. In particular, the Sm-doped sample exhibited even lower lattice thermal conductivity, which is believed to be due to the mismatch in the ionic radius of Sr and Sm. This finding is useful as a strategy to reduce thermal conductivity of Sr2TiO4 RP phase materials as thermoelectric candidates, by employing dopants of differing ionic radius.

In vitro burn model illustrating heat conduction patterns using compressed thermal papers.

PubMed

Lee, Jun Yong; Jung, Sung-No; Kwon, Ho

2015-01-01

To date, heat conduction from heat sources to tissue has been estimated by complex mathematical modeling. In the present study, we developed an intuitive in vitro skin burn model that illustrates heat conduction patterns inside the skin. This was composed of tightly compressed thermal papers with compression frames. Heat flow through the model left a trace by changing the color of thermal papers. These were digitized and three-dimensionally reconstituted to reproduce the heat conduction patterns in the skin. For standardization, we validated K91HG-CE thermal paper using a printout test and bivariate correlation analysis. We measured the papers' physical properties and calculated the estimated depth of heat conduction using Fourier's equation. Through contact burns of 5, 10, 15, 20, and 30 seconds on porcine skin and our burn model using a heated brass comb, and comparing the burn wound and heat conduction trace, we validated our model. The heat conduction pattern correlation analysis (intraclass correlation coefficient: 0.846, p < 0.001) and the heat conduction depth correlation analysis (intraclass correlation coefficient: 0.93, p < 0.001) showed statistically significant high correlations between the porcine burn wound and our model. Our model showed good correlation with porcine skin burn injury and replicated its heat conduction patterns. © 2014 by the Wound Healing Society.

High temperature XRD of Cu{sub 2}GeSe{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Premkumar, D. S.; Malar, P.; Chetty, Raju

2015-06-24

The Cu{sub 2}GeSe{sub 3} is prepared by solid state synthesis method. The high temperature XRD has been done at different temperature from 30 °C to 450 °C. The reitveld refinement confirms Cu{sub 2}GeSe{sub 3} phase and orthorhombic crystal structure. The lattice constants are increasing with increase in the temperature and their rate of increase with respect to temperature are used for finding the thermal expansion coefficient. The calculation of the linear and volume coefficient of thermal expansion is done from 30 °C to 400 °C. Decrease in the values of linear expansion coefficients with temperature are observed along a andmore » c axis. Since thermal expansion coefficient is the consequence of the distortion of atoms in the lattice; this can be further used to find the minimum lattice thermal conductivity at given temperature.« less

Fabrication and thermophysical property characterization of UN/U 3Si 2 composite fuel forms

DOE PAGES

White, Joshua Taylor; Travis, Austin William; Dunwoody, John Tyler; ...

2017-09-21

High uranium density composite fuels composed of UN and U 3Si 2 have been fabricated using a liquid phase sintering route at temperatures between 1873 K and 1973 K and spanning compositions of 10 vol% to 40 vol% U 3Si 2. Microstructural analysis and phase characterization revealed the formation of an U-Si-N phase of unknown structure. Microcracking was observed in the U-Si portion of the composite microstructure that likely originates from the mismatched coefficient of thermal expansion between the UN and U 3Si 2 leading to stresses on heating and cooling of the composite. Thermal expansion coefficient, thermal diffusivity, andmore » thermal conductivity were characterized for each of the compositions as a function of temperature to 1673 K. Hysteresis is observed in the thermal diffusivity for the 20 vol% through 40 vol% specimens between room temperature and 1273 K, which is attributed to the microcracking in the U-Si phase. Thermal conductivity of the composites was modeled using the MOOSE framework based on the collected microstructure data. In conclusion, the impact of irradiation on thermal conductivity was also simulated for this class of composite materials.« less

Fabrication and thermophysical property characterization of UN/U 3Si 2 composite fuel forms

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, Joshua Taylor; Travis, Austin William; Dunwoody, John Tyler

High uranium density composite fuels composed of UN and U 3Si 2 have been fabricated using a liquid phase sintering route at temperatures between 1873 K and 1973 K and spanning compositions of 10 vol% to 40 vol% U 3Si 2. Microstructural analysis and phase characterization revealed the formation of an U-Si-N phase of unknown structure. Microcracking was observed in the U-Si portion of the composite microstructure that likely originates from the mismatched coefficient of thermal expansion between the UN and U 3Si 2 leading to stresses on heating and cooling of the composite. Thermal expansion coefficient, thermal diffusivity, andmore » thermal conductivity were characterized for each of the compositions as a function of temperature to 1673 K. Hysteresis is observed in the thermal diffusivity for the 20 vol% through 40 vol% specimens between room temperature and 1273 K, which is attributed to the microcracking in the U-Si phase. Thermal conductivity of the composites was modeled using the MOOSE framework based on the collected microstructure data. In conclusion, the impact of irradiation on thermal conductivity was also simulated for this class of composite materials.« less

THERMAL PROPERTIES AND HEATING AND COOLING DURABILITY OF REACTOR SHIELDING CONCRETE (in Japanese)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hosoi, J.; Chujo, K.; Saji, K.

1959-01-01

A study was made of the thermal properties of various concretes made of domestic raw materials for radiation shields of a power reactor and of a high- flux research reactor. The results of measurements of thermal expansion coefficient, specific heat, thermal diffusivity, thermal conductivity, cyclical heating, and cooling durability are described. Relationships between thermal properties and durability are discussed and several photographs of the concretes are given. It is shown that the heating and cooling durability of such a concrete which has a large thermal expansion coefficient or a considerable difference between the thermal expansion of coarse aggregate and themore » one of cement mortar part or aggregates of lower strength is very poor. The decreasing rates of bending strength and dynamical modulus of elasticity and the residual elongation of the concrete tested show interesting relations with the modified thermal stress resistance factor containing a ratio of bending strength and thermal expansion coefficient. The thermal stress resistance factor seems to depend on the conditions of heat transfer on the surface and on heat release in the concrete. (auth)« less

Ba6-3 x Nd8+2 x Ti18O54 Tungsten Bronze: A New High-Temperature n-Type Oxide Thermoelectric

NASA Astrophysics Data System (ADS)

Azough, Feridoon; Freer, Robert; Yeandel, Stephen R.; Baran, Jakub D.; Molinari, Marco; Parker, Stephen C.; Guilmeau, Emmanuel; Kepaptsoglou, Demie; Ramasse, Quentin; Knox, Andy; Gregory, Duncan; Paul, Douglas; Paul, Manosh; Montecucco, Andrea; Siviter, Jonathan; Mullen, Paul; Li, Wenguan; Han, Guang; Man, Elena A.; Baig, Hasan; Mallick, Tapas; Sellami, Nazmi; Min, Gao; Sweet, Tracy

2016-03-01

Semiconducting Ba6-3 x Nd8+2 x Ti18O54 ceramics (with x = 0.00 to 0.85) were synthesized by the mixed oxide route followed by annealing in a reducing atmosphere; their high-temperature thermoelectric properties have been investigated. In conjunction with the experimental observations, atomistic simulations have been performed to investigate the anisotropic behavior of the lattice thermal conductivity. The ceramics show promising n-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical conductivity, and temperature-stable, low thermal conductivity; For example, the composition with x = 0.27 (i.e., Ba5.19Nd8.54Ti18O54) exhibited a Seebeck coefficient of S 1000K = 210 µV/K, electrical conductivity of σ 1000K = 60 S/cm, and thermal conductivity of k 1000K = 1.45 W/(m K), leading to a ZT value of 0.16 at 1000 K.

Dynamical properties and transport coefficients of one-dimensional Lennard-Jones fluids: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Bazhenov, Alexiev M.; Heyes, David M.

1990-01-01

The thermodynamics, structure, and transport coefficients, as defined by the Green-Kubo integrals, of the one-dimensional Lennard-Jones fluid are evaluated for a wide range of state points by molecular dynamics computer simulation. These calculations are performed for the first time for thermal conductivity and the viscosity. We observe a transition from hard-rod behavior at low number density to harmonic-spring fluid behavior in the close-packed limit. The self-diffusion coefficient decays with increasing density to a finite limiting value. The thermal conductivity increases with density, tending to ∞ in the close-packed limit. The viscosity in contrast maximizes at intermediate density, tending to zero in the zero density and close-packed limits.

Theory of the dynamical thermal conductivity of metals

NASA Astrophysics Data System (ADS)

Bhalla, Pankaj; Kumar, Pradeep; Das, Nabyendu; Singh, Navinder

2016-09-01

The Mori's projection method, known as the memory function method, is an important theoretical formalism to study various transport coefficients. In the present work, we calculate the dynamical thermal conductivity in the case of metals using the memory function formalism. We introduce thermal memory functions for the first time and discuss the behavior of thermal conductivity in both the zero frequency limit and in the case of nonzero frequencies. We compare our results for the zero frequency case with the results obtained by the Bloch-Boltzmann kinetic approach and find that both approaches agree with each other. Motivated by some recent experimental advancements, we obtain several new results for the ac or the dynamical thermal conductivity.

Ceramic materials with low thermal conductivity and low coefficients of thermal expansion

DOEpatents

Brown, Jesse; Hirschfeld, Deidre; Liu, Dean-Mo; Yang, Yaping; Li, Tingkai; Swanson, Robert E.; Van Aken, Steven; Kim, Jin-Min

1992-01-01

Compositions having the general formula (Ca.sub.x Mg.sub.1-x)Zr.sub.4 (PO.sub.4).sub.6 where x is between 0.5 and 0.99 are produced by solid state and sol-gel processes. In a preferred embodiment, when x is between 0.5 and 0.8, the MgCZP materials have near-zero coefficients of thermal expansion. The MgCZPs of the present invention also show unusually low thermal conductivities, and are stable at high temperatures. Macrostructures formed from MgCZP are useful in a wide variety of high-temperature applications. In a preferred process, calcium, magnesium, and zirconium nitrate solutions have their pH adjusted to between 7 and 9 either before or after the addition of ammonium dihydrogen phosphate. After dehydration to a gel, and calcination at temperatures in excess of 850.degree. C. for approximately 16 hours, single phase crystalline MgCZP powders with particle sizes ranging from approximately 20 nm to 50 nm result. The MgCZP powders are then sintered at temperatures ranging from 1200.degree. C. to 1350.degree. C. to form solid macrostructures with near-zero bulk coefficients of thermal expansion and low thermal conductivities. Porous macrostructures of the MgCZP powders of the present invention are also formed by combination with a polymeric powder and a binding agent, and sintering at high temperatures. The porosity of the resulting macrostructures can be adjusted by varying the particle size of the polymeric powder used.

Ceramic materials with low thermal conductivity and low coefficients of thermal expansion

DOEpatents

Brown, J.; Hirschfeld, D.; Liu, D.M.; Yang, Y.; Li, T.; Swanson, R.E.; Van Aken, S.; Kim, J.M.

1992-04-07

Compositions, having the general formula (Ca[sub x]Mg[sub 1[minus]x])Zr[sub 4](PO[sub 4])[sub 6] where x is between 0.5 and 0.99, are produced by solid state and sol-gel processes. In a preferred embodiment, when x is between 0.5 and 0.8, the MgCZP materials have near-zero coefficients of thermal expansion. The MgCZPs of the present invention also show unusually low thermal conductivities, and are stable at high temperatures. Macrostructures formed from MgCZP are useful in a wide variety of high-temperature applications. In a preferred process, calcium, magnesium, and zirconium nitrate solutions have their pH adjusted to between 7 and 9 either before or after the addition of ammonium dihydrogen phosphate. After dehydration to a gel, and calcination at temperatures in excess of 850 C for approximately 16 hours, single phase crystalline MgCZP powders with particle sizes ranging from approximately 20 nm to 50 nm result. The MgCZP powders are then sintered at temperatures ranging from 1200 C to 1350 C to form solid macrostructures with near-zero bulk coefficients of thermal expansion and low thermal conductivities. Porous macrostructures of the MgCZP powders of the present invention are also formed by combination with a polymeric powder and a binding agent, and sintering at high temperatures. The porosity of the resulting macrostructures can be adjusted by varying the particle size of the polymeric powder used. 7 figs.

Thermoelectric Properties of Nanograined Si-Ge-Au Thin Films Grown by Molecular Beam Deposition

NASA Astrophysics Data System (ADS)

Nishino, Shunsuke; Ekino, Satoshi; Inukai, Manabu; Omprakash, Muthusamy; Adachi, Masahiro; Kiyama, Makoto; Yamamoto, Yoshiyuki; Takeuchi, Tsunehiro

2018-06-01

Conditions to achieve extremely large Seebeck coefficient and extremely small thermal conductivity in Si-Ge-Au thin films formed of nanosized grains precipitated in amorphous matrix have been investigated. We employed molecular beam deposition to prepare Si1- x Ge x Au y thin films on sapphire substrate. The deposited films were annealed under nitrogen gas atmosphere at 300°C to 500°C for 15 min to 30 min. Nanocrystals dispersed in amorphous matrix were clearly observed by transmission electron microscopy. We did not observe anomalously large Seebeck coefficient, but very low thermal conductivity of nearly 1.0 W K-1 m-1 was found at around 0.2 < x < 0.6. The compositional dependence of the thermal conductivity was well accounted for by the compositional dependence of the mixing entropy. Some of these values agree exactly with the amorphous limit predicted by theoretical calculations. The smallest lattice thermal conductivity found for the present samples is lower than that of nanostructured Si-Ge bulk material for which dimensionless figure of merit of ZT ≈ 1 was reported at high temperature.

The influence of vibrational state-resolved transport coefficients on the wave propagation in diatomic gases

NASA Astrophysics Data System (ADS)

Kremer, Gilberto M.; Kunova, Olga V.; Kustova, Elena V.; Oblapenko, George P.

2018-01-01

A detailed kinetic-theory model for the vibrationally state-resolved transport coefficients is developed taking into account the dependence of the collision cross section on the size of vibrationally excited molecule. Algorithms for the calculation of shear and bulk viscosity, thermal conductivity, thermal diffusion and diffusion coefficients for vibrational states are proposed. The transport coefficients are evaluated for single-component diatomic gases N2, O2, NO, H2, Cl2 in the wide range of temperature, and the effects of molecular diameters and the number of accounted states are discussed. The developed model is applied to study wave propagation in diatomic gases. For the case of initial Boltzmann distribution, the influence of vibrational excitation on the phase velocity and attenuation coefficient is found to be weak. We expect more significant effect in the case of initial thermal non-equilibrium, for instance in gases with optically pumped selected vibrational states.

Thermophysical Properties and Temperature of the Start of Titanium Recrystallization in Different Structural States

NASA Astrophysics Data System (ADS)

Pavlenko, D. V.; Tkach, D. V.; Danilova-Tret'yak, S. M.; Evseeva, L. E.

2017-05-01

The results of measurements of the thermal diffusivity, thermal conductivity, and heat capacity of VT1-0-grade titanium samples in as-cast, deformed submicrocrystalline, and sintered states are presented. It has been established that the decrease in the thermal conductivity and thermal diffusivity of titanium in the submicrocrystalline and sintered states is associated with the increase in the quantity of defects in the material volume, whereas the increase in the temperature of polymorphic transformation of titanium is connected with the dissolution of oxygen in its lattice. The results of investigation of the coefficient of thermal linear expansion of titanium in the macrocrystalline and submicrocrystalline states are presented. The decrease in the coefficient of thermal linear expansion of titanium of submicrocrystalline structure has been established, which may point to the decrease in its melting temperature. It is shown that annealing of samples in a submicrocrystalline state leads to the growth of the temperature coefficient of linear expansion, bringing its value closer to the temperature coefficient of linear expansion of titanium in the equilibrium state. Studies by the method of back reflection photography in a KROS chamber made it possible to estimate the temperature of the start of VT1-0-grade titanium recrystallization after intense plastic deformation by the twist extrusion method. The decrease in the temperature of the start of recrystallization for titanium in the deformed submicrocrystalline state has been established. Based on the trends revealed, optimum regimes of thermal treatment of VT1-0-grade titanium for removing internal stresses and preserving the submicrocrystalline structure have been established.

Thermoelectric Figures of Merit of Zn4Sb3 and Zrnisn-based Half-heusler Compounds Influenced by Mev Ion-beam Bombardments

NASA Astrophysics Data System (ADS)

Budak, S.; Guner, S.; Muntele, C. I.; Ila, D.

Semiconducting β-Zn4Sb3 and ZrNiSn-based half-Heusler compound thin films with applications as thermoelectric (TE) materials were prepared using ion beam assisted deposition (IBAD). High-purity solid zinc (Zn) and antimony (Sb) were evaporated by electron beam to grow the β-Zn4Sb3 thin film while high-purity zirconium (Zr) powder and nickel (Ni) tin (Sn) powders were evaporated by electron beam to grow the ZrNiSn-based half-Heusler compound thin film. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of the thin films. The grown thin films were subjected to 5 MeV Si ions bombardment for generation of nanostructures in the films. We measured the thermal conductivity, Seebeck coefficient, and electrical conductivity of these two systems before and after 5 MeV Si ions beam bombardment. The two material systems have been identified as promising TE materials for the application of thermal-to-electrical energy conversion, but the efficiency still limits their applications. The electronic energy deposited due to ionization in the track of MeV ion beam couldcause localized crystallization. The nanostructures produced by MeV ion beam can cause significant change in both the electrical and the thermal conductivity of thin films, thereby improving the efficiency. We used the 3ω-method (3rd harmonic) measurement system to measure the cross-plane thermal conductivity, the van der Pauw measurement system to measure the electrical conductivity, and the Seebeck-coefficient measurement system to measure the cross-plane Seebeck coefficient. The thermoelectric figures of merit of the two material systems were then derived by calculations using the measurement results. The MeV ion-beam bombardment was found to decrease the thermal conductivity of thin films and increase the efficiency of thermal-to-electrical energy conversion.

Bus electrode having same thermal expansion coefficient as crystalline silicon solar cell

NASA Astrophysics Data System (ADS)

Kato, T.; Morita, H.; Nakano, H.; Washida, H.; Onoe, A.; Inomata, K.; Mori, F.; Sugai, S.

1982-01-01

It is well known that the bus electrode plays a main role in series resistance of solar cells. Bus electrodes composed of bare leads, were investigated for which thermal expansion coefficients are less than those of the cell and which are coated with highly conducting metals. These leads exhibited the lower expansion coefficient than expected by empirical law, and the origins of these phenomena were explained. Work hardening effect on the expansion coefficient was then measured. Solar cell fabrication with these leads and rigid solders rationalized assembly processing. Cell characteristics proved to be excellent compared with conventional ones. Finally, lead costs were compared for various materials.

Epitaxial Growth, Surface, and Electronic Properties of Unconventional Semiconductors: RE-V/III-V Nanocomposites and Semiconducting Half Heusler Alloys

DTIC Science & Technology

2014-09-01

with approximately 5 × 1018 Si atoms/cm3 to yield a conductive buffer for STM and photoemsission spectroscopy measurements. On some samples a 3 nm ErAs...where S is the Seebeck coefficient, σ is the electrical conductivity , and κ is the thermal conductivity . Here the electronic information is contained... conductivities (κ = κe + κlat). While the electronic component of thermal conductivity κe is inherently tied to electrical conductivity σ via Wiedemann

Thermoelectric properties of p-type perovskite compounds LaCoO3 systems containing the A-site vacancy

NASA Astrophysics Data System (ADS)

Anzai, Mayuka; Kawakami, Hiroshi; Saito, Miwa; Yamamura, Hiroshi

2011-05-01

Thermoelectric properties of Sr-doped LaCoO3 system which includes both La1-xSrxCoO3 and La0.95-xSrxsquare0.05CoO3 containing the A-site vacancy were prepared by solid state reaction. The crystal phases of the samples were investigated by X-ray diffraction method. The electrical conductivity, Seebeck coefficient, and thermal conductivity were investigated, focusing the effect of A-site vacancy. Doping of Sr to LaCoO3 improved the electrical conductivity but decreased the seebeck coefficient and increased the thermal conductivity. A-site vacancy of La0.95-xSrxsquare0.05CoO3 system, in comparison with La1-xSrxCoO3 system, increased electrical conductivity, and decreased lattice thermal conductivity. As a result, it was found that the thermoelectric properties of La0.95-xSrxsquare0.05CoO3 containing the A-site vacancy showed the higher values than those of La1-xSrxCoO3. The introduction of A-site vacancy was effective on the improvement of thermoelectric property.

Performance evaluation of Maxwell and Cercignani-Lampis gas-wall interaction models in the modeling of thermally driven rarefied gas transport.

PubMed

Liang, Tengfei; Li, Qi; Ye, Wenjing

2013-07-01

A systematic study on the performance of two empirical gas-wall interaction models, the Maxwell model and the Cercignani-Lampis (CL) model, in the entire Knudsen range is conducted. The models are evaluated by examining the accuracy of key macroscopic quantities such as temperature, density, and pressure, in three benchmark thermal problems, namely the Fourier thermal problem, the Knudsen force problem, and the thermal transpiration problem. The reference solutions are obtained from a validated hybrid DSMC-MD algorithm developed in-house. It has been found that while both models predict temperature and density reasonably well in the Fourier thermal problem, the pressure profile obtained from Maxwell model exhibits a trend that opposes that from the reference solution. As a consequence, the Maxwell model is unable to predict the orientation change of the Knudsen force acting on a cold cylinder embedded in a hot cylindrical enclosure at a certain Knudsen number. In the simulation of the thermal transpiration coefficient, although all three models overestimate the coefficient, the coefficient obtained from CL model is the closest to the reference solution. The Maxwell model performs the worst. The cause of the overestimated coefficient is investigated and its link to the overly constrained correlation between the tangential momentum accommodation coefficient and the tangential energy accommodation coefficient inherent in the models is pointed out. Directions for further improvement of models are suggested.

Coronal Seismology of Flare-Excited Standing Slow-Mode Waves Observed by SDO/AIA

NASA Astrophysics Data System (ADS)

Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.

2016-05-01

Flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 Å bandpasses. Based on the interpretation in terms of a slow-mode wave, quantitative evidence of thermal conduction suppression in hot (>9 MK) loops has been obtained for the first time from measurements of the polytropic index and phase shift between the temperature and density perturbations (Wang et al. 2015, ApJL, 811, L13). This result has significant implications in two aspects. One is that the thermal conduction suppression suggests the need of greatly enhanced compressive viscosity to interpret the observed strong wave damping. The other is that the conduction suppression provides a reasonable mechanism for explaining the long-duration events where the thermal plasma is sustained well beyond the duration of impulsive hard X-ray bursts in many flares, for a time much longer than expected by the classical Spitzer conductive cooling. In this study, we model the observed standing slow-mode wave in Wang et al. (2015) using a 1D nonlinear MHD code. With the seismology-derived transport coefficients for thermal conduction and compressive viscosity, we successfully simulate the oscillation period and damping time of the observed waves. Based on the parametric study of the effect of thermal conduction suppression and viscosity enhancement on the observables, we discuss the inversion scheme for determining the energy transport coefficients by coronal seismology.

Optimization and experimental validation of a thermal cycle that maximizes entropy coefficient fisher identifiability for lithium iron phosphate cells

NASA Astrophysics Data System (ADS)

Mendoza, Sergio; Rothenberger, Michael; Hake, Alison; Fathy, Hosam

2016-03-01

This article presents a framework for optimizing the thermal cycle to estimate a battery cell's entropy coefficient at 20% state of charge (SOC). Our goal is to maximize Fisher identifiability: a measure of the accuracy with which a parameter can be estimated. Existing protocols in the literature for estimating entropy coefficients demand excessive laboratory time. Identifiability optimization makes it possible to achieve comparable accuracy levels in a fraction of the time. This article demonstrates this result for a set of lithium iron phosphate (LFP) cells. We conduct a 24-h experiment to obtain benchmark measurements of their entropy coefficients. We optimize a thermal cycle to maximize parameter identifiability for these cells. This optimization proceeds with respect to the coefficients of a Fourier discretization of this thermal cycle. Finally, we compare the estimated parameters using (i) the benchmark test, (ii) the optimized protocol, and (iii) a 15-h test from the literature (by Forgez et al.). The results are encouraging for two reasons. First, they confirm the simulation-based prediction that the optimized experiment can produce accurate parameter estimates in 2 h, compared to 15-24. Second, the optimized experiment also estimates a thermal time constant representing the effects of thermal capacitance and convection heat transfer.

Transport coefficients of liquid CF4 and SF6 computed by molecular dynamics using polycenter Lennard-Jones potentials

NASA Astrophysics Data System (ADS)

Hoheisel, C.

1989-01-01

For several liquid states of CF4 and SF4, the shear and the bulk viscosity as well as the thermal conductivity were determined by equilibrium molecular dynamics (MD) calculations. Lennard-Jones four- and six-center pair potentials were applied, and the method of constraints was chosen for the MD. The computed Green-Kubo integrands show a steep time decay, and no particular longtime behavior occurs. The molecule number dependence of the results is found to be small, and 3×105 integration steps allow an accuracy of about 10% for the shear viscosity and the thermal conductivity coefficient. Comparison with experimental data shows a fair agreement for CF4, while for SF6 the transport coefficients fall below the experimental ones by about 30%.

Ab-initio study of thermal expansion in pure graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mann, Sarita; Kumar, Ranjan; Jindal, V. K., E-mail: jindal@pu.ac.in

Graphene is a zero band gap semiconductor with exceptionally high thermal conductivity. The electronic properties having been studied, therole of phonon in contributing to thermal expansion, thermal conductivity and other thermodynamic properties, is required to be investigated. This paper focuses more on thermal expansion. Some others results like phonon dispersion, Grüneisenparameters and bulk modulus,which are essential to estimation of thermal expansion, are also presented. The dynamical matrix was calculated using VASP code using both DFT and DFPT and the phonon frequencies were calculated using phonopy code under harmonic approximation. The linear thermal expansion coefficient of graphene is found to bemore » strongly dependent on temperature but remains negative upto 470 K and positive thereafter, with a room temperature value of −1.44×10{sup −6}. The negative expansion coefficient is very interesting and is found to be in conformity with experimental as well as with recent theoretical estimates. There is only qualitative agreement of our results with experimental data and motivates further investigation, primarily on the high negative values of Grüneisen parameters.« less

Creation of a Data Base on Energetic Materials

DTIC Science & Technology

1987-08-10

Examples of booster explosives are Tetryl, RDX , and HMX . Examples of bursting explosives are Amatols, TNT, Compositions A, B, & C, and Picatrol. Within...Test Thermal Shock Resistance Glass Transition Temperature Toxicity Grain Size Viscosity Hardness Volatility Heat Capacity Water Resistance Heat of...Tensile Strength Flammability Thermal Conductivity Flexural Strength Thermal Expansion Coefficient Gap Test Thermal Shock Resistance Glass Transition

Thermal properties of Pr2/3Sr1/3MnO3 manganites:PdO composites

NASA Astrophysics Data System (ADS)

Rao, Ashok; Manjunatha, S. O.; Bhatt, Ramesh Chandra; Awana, V. P. S.; Lin, C. F.; Kuo, Y. K.; Poornesh, P.

2017-10-01

In the present communication the results on thermal conductivity, Seebeck coefficient and specific heat of Pr2/3Sr1/3MnO3:PdO composites are reported. All the samples exhibit a pronounced anomaly in thermal conductivity (κ) at their respective Curie temperatures, TC of the samples. It is also observed that the overall magnitude of κ decreases with increasing Pd content. The observed reduction of the total k(T) is discussed with various thermal scattering mechanisms. The temperature-dependent Seebeck coefficient data S(T) in the high temperature region is analyzed within the framework of Mott's polaron hopping model. The analysis of low-temperature S(T) data reveals that the electron-magnon scattering contribution dominates the thermoelectric transport at low temperatures. The magnetic contribution for the CP and change in entropy (ΔS) during the magnetic phase transition is also evaluated.

Characterization of anisotropic thermal conductivity of suspended nm-thick black phosphorus with frequency-resolved Raman spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Tianyu; Han, Meng; Wang, Ridong; Yuan, Pengyu; Xu, Shen; Wang, Xinwei

2018-04-01

Frequency-resolved Raman spectroscopy (FR-Raman) is a new technique for nondestructive thermal characterization. Here, we apply this new technique to measure the anisotropic thermal conductivity of suspended nm-thick black phosphorus samples without the need of optical absorption and temperature coefficient. Four samples with thicknesses between 99.8 and 157.6 nm are studied. Based on steady state laser heating and Raman measurement of samples with a specifically designed thermal transport path, the thermal conductivity ratio (κZZ/κAC) is determined to be 1.86-3.06. Based on the FR-Raman measurements, the armchair thermal conductivity is measured as 14-22 W m-1 K-1, while the zigzag thermal conductivity is 40-63 W m-1 K-1. FR-Raman has great potential for studying the thermal properties of various nanomaterials. This study significantly advances our understanding of thermal transport in black phosphorus and facilitates the application of black phosphorus in novel devices.

Properties of air-aluminum thermal plasmas

NASA Astrophysics Data System (ADS)

Cressault, Y.; Gleizes, A.; Riquel, G.

2012-07-01

We present the calculation and the main results of the properties of air-aluminum thermal plasmas, useful for complete modelling of arc systems involving aluminum contacts. The properties are calculated assuming thermal equilibrium and correspond to the equilibrium composition, thermodynamic functions, transport coefficients including diffusion coefficients and net emission coefficient representing the divergence of the radiative flux in the hottest plasma regions. The calculation is developed in the temperature range between 2000 and 30 000 K, for a pressure range from 0.1 to 1 bar and for several metal mass proportions. As in the case of other metals, the presence of aluminum vapours has a strong influence on three properties at intermediate temperatures: the electron number density, the electrical conductivity and the net emission coefficient. Some comparisons with other metal vapour (Cu, Fe and Ag) properties are made and show the original behaviour for Al-containing mixtures: mass density at high temperatures is low due to the low Al atomic mass; high electrical conductivity at T < 10 000 K due to low ionization potential (around 2 V less for Al than for the other metals); very strong self-absorption of ionized aluminum lines, leading to a net emission coefficient lower than that of pure air when T > 10 000 K, in contrast to copper or iron radiation.

Thermal properties measurements in biodiesel oils using photothermal techniques

NASA Astrophysics Data System (ADS)

Castro, M. P. P.; Andrade, A. A.; Franco, R. W. A.; Miranda, P. C. M. L.; Sthel, M.; Vargas, H.; Constantino, R.; Baesso, M. L.

2005-08-01

In this Letter, thermal lens and open cell photoacoustic techniques are used to measure the thermal properties of biodiesel oils. The absolute values of the thermal effusivity, thermal diffusivity, thermal conductivity and the temperature coefficient of the refractive index were determined for samples obtained from soy, castor bean, sunflower and turnip. The results suggest that the employed techniques may be useful as complementary methods for biodiesel certification.

Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems.

PubMed

Khrustalyov, Yu V; Vaulina, O S

2012-04-01

Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed.

Thermal conductivity of microporous layers: Analytical modeling and experimental validation

NASA Astrophysics Data System (ADS)

Andisheh-Tadbir, Mehdi; Kjeang, Erik; Bahrami, Majid

2015-11-01

A new compact relationship is developed for the thermal conductivity of the microporous layer (MPL) used in polymer electrolyte fuel cells as a function of pore size distribution, porosity, and compression pressure. The proposed model is successfully validated against experimental data obtained from a transient plane source thermal constants analyzer. The thermal conductivities of carbon paper samples with and without MPL were measured as a function of load (1-6 bars) and the MPL thermal conductivity was found between 0.13 and 0.17 W m-1 K-1. The proposed analytical model predicts the experimental thermal conductivities within 5%. A correlation generated from the analytical model was used in a multi objective genetic algorithm to predict the pore size distribution and porosity for an MPL with optimized thermal conductivity and mass diffusivity. The results suggest that an optimized MPL, in terms of heat and mass transfer coefficients, has an average pore size of 122 nm and 63% porosity.

Influence of point defects on the thermal conductivity in FeSi

NASA Astrophysics Data System (ADS)

Stern, Robin; Wang, Tao; Carrete, Jesús; Mingo, Natalio; Madsen, Georg K. H.

2018-05-01

The unique transport properties of B20 FeSi have been investigated for decades. The progress in theoretical calculations allows the explanation and prediction of more and more of such properties. In this paper we investigate the lattice thermal conductivity of FeSi. Calculation for pristine FeSi severely overestimates the lattice thermal conductivity compared to experiment. We point out that the defect concentration can be considerably larger than indicated by the Hall coefficient. The defect formation energies are calculated and it is found that a substantial amount of iron vacancies can form at thermal equilibrium. These will lead to an increased phonon scattering. To explain the thermal conductivity of FeSi, we consider phonon-phonon, isotope, and phonon-defect scattering to assess possible scattering mechanisms. The calculated thermal conductivities indicate that phonon-defect scattering is important in order to explain the reported experimental values.

Applications of high thermal conductivity composites to electronics and spacecraft thermal design

NASA Technical Reports Server (NTRS)

Sharp, G. Richard; Loftin, Timothy A.

1990-01-01

Recently, high thermal conductivity continuous graphite fiber reinforced metal matrix composites (MMC's) have become available that can save much weight over present methods of heat conduction. These materials have two or three times higher thermal conductivity in the fiber direction than the pure metals when compared on a thermal conductivity to weight basis. Use of these materials for heat conduction purposes can result in weight savings of from 50 to 70 percent over structural aluminum. Another significant advantage is that these materials can be used without the plumbing and testing complexities that accompany the use of liquid heat pipes. A spinoff of this research was the development of other MMC's as electronic device heat sinks. These use particulates rather than fibers and are formulated to match the coefficient of thermal expansion of electronic substrates in order to alleviate thermally induced stresses. The development of both types of these materials as viable weight saving substitutes for traditional methods of thermal control for electronics packaging and also for spacecraft thermal control applications are the subject of this report.

Carbon nanotube-copper exhibiting metal-like thermal conductivity and silicon-like thermal expansion for efficient cooling of electronics.

PubMed

Subramaniam, Chandramouli; Yasuda, Yuzuri; Takeya, Satoshi; Ata, Seisuke; Nishizawa, Ayumi; Futaba, Don; Yamada, Takeo; Hata, Kenji

2014-03-07

Increasing functional complexity and dimensional compactness of electronic devices have led to progressively higher power dissipation, mainly in the form of heat. Overheating of semiconductor-based electronics has been the primary reason for their failure. Such failures originate at the interface of the heat sink (commonly Cu and Al) and the substrate (silicon) due to the large mismatch in thermal expansion coefficients (∼300%) of metals and silicon. Therefore, the effective cooling of such electronics demands a material with both high thermal conductivity and a similar coefficient of thermal expansion (CTE) to silicon. Addressing this demand, we have developed a carbon nanotube-copper (CNT-Cu) composite with high metallic thermal conductivity (395 W m(-1) K(-1)) and a low, silicon-like CTE (5.0 ppm K(-1)). The thermal conductivity was identical to that of Cu (400 W m(-1) K(-1)) and higher than those of most metals (Ti, Al, Au). Importantly, the CTE mismatch between CNT-Cu and silicon was only ∼10%, meaning an excellent compatibility. The seamless integration of CNTs and Cu was achieved through a unique two-stage electrodeposition approach to create an extensive and continuous interface between the Cu and CNTs. This allowed for thermal contributions from both Cu and CNTs, resulting in high thermal conductivity. Simultaneously, the high volume fraction of CNTs balanced the thermal expansion of Cu, accounting for the low CTE of the CNT-Cu composite. The experimental observations were in good quantitative concurrence with the theoretically described 'matrix-bubble' model. Further, we demonstrated identical in-situ thermal strain behaviour of the CNT-Cu composite to Si-based dielectrics, thereby generating the least interfacial thermal strain. This unique combination of properties places CNT-Cu as an isolated spot in an Ashby map of thermal conductivity and CTE. Finally, the CNT-Cu composite exhibited the greatest stability to temperature as indicated by its low thermal distortion parameter (TDP). Thus, this material presents a viable and efficient alternative to existing materials for thermal management in electronics.

Growth and anisotropic thermal properties of biaxial Ho:YAlO3 crystal

NASA Astrophysics Data System (ADS)

Dong, Qin; Zhao, Guangjun; Chen, Jianyu; Ding, Yuchong; Zhao, Chengchun

2010-07-01

Ho:YAlO3 (YAP) crystal with large size and good optical quality has been grown by the Czochralski method. Thermal properties of the as-grown Ho:YAP crystal have been investigated by measuring the temperature-dependent, anisotropic thermal expansion, specific heat, thermal diffusion, and thermal conductivity. The results show that Ho:YAP crystal possesses a large anisotropic thermal expansion and good thermal conductivity. The calculated average thermal expansion coefficients along a, b, and c axis are αa=9.18×10-6/K, αb=1.94×10-6/K, and αc=7.61×10-6/K from 293.15 to 770.15 K. The thermal conductivities along a, b, and c axis are up to 11.6, 9.9, and 12.3 W m-1 K-1 at 298.15 K. Compared with Ho: Y3Al5O12 (YAG), Ho:YAP crystal has a larger thermal conductivity along a axis from 298.15 to 568.15 K.

Multifunctional Lattices with Low Thermal Expansion and Low Thermal Conductivity

NASA Astrophysics Data System (ADS)

Xu, Hang; Liu, Lu; Pasini, Damiano

Systems in space are vulnerable to large temperature changes when travelling into and out of the Earth's shadow. Variations in temperature can lead to undesired geometric changes in susceptible applications requiring very fine precision. In addition, temperature-sensitive electronic equipment hosted in a satellite needs adequate thermal-control to guarantee a moderate ambient temperature. To address these specifications, materials with low coefficient of thermal expansion (CTE) and low coefficient of thermal conductivity (CTC) over a wide range of temperatures are often sought, especially for bearing components in satellites. Besides low CTE and low CTC, these materials should also provide desirable stiffness, strength and extraordinarily low mass. This work presents ultralightweight bi-material lattices with tunable CTE and CTC, besides high stiffness and strength. We show that the compensation of the thermal expansion and joint rotation at the lattice joints can be used as an effective strategy to tailor thermomechanical performance. Proof-of-concept lattices are fabricated from Al and Ti alloy sheets via a simple snap-fit technique and vacuum brazing, and their CTE and CTC are assessed via a combination of experiments and theory. Corresponding Author.

Thermal conductivity of III-V semiconductor superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, S., E-mail: song.mei@wisc.edu; Knezevic, I., E-mail: irena.knezevic@wisc.edu

2015-11-07

This paper presents a semiclassical model for the anisotropic thermal transport in III-V semiconductor superlattices (SLs). An effective interface rms roughness is the only adjustable parameter. Thermal transport inside a layer is described by the Boltzmann transport equation in the relaxation time approximation and is affected by the relevant scattering mechanisms (three-phonon, mass-difference, and dopant and electron scattering of phonons), as well as by diffuse scattering from the interfaces captured via an effective interface scattering rate. The in-plane thermal conductivity is obtained from the layer conductivities connected in parallel. The cross-plane thermal conductivity is calculated from the layer thermal conductivitiesmore » in series with one another and with thermal boundary resistances (TBRs) associated with each interface; the TBRs dominate cross-plane transport. The TBR of each interface is calculated from the transmission coefficient obtained by interpolating between the acoustic mismatch model (AMM) and the diffuse mismatch model (DMM), where the weight of the AMM transmission coefficient is the same wavelength-dependent specularity parameter related to the effective interface rms roughness that is commonly used to describe diffuse interface scattering. The model is applied to multiple III-arsenide superlattices, and the results are in very good agreement with experimental findings. The method is both simple and accurate, easy to implement, and applicable to complicated SL systems, such as the active regions of quantum cascade lasers. It is also valid for other SL material systems with high-quality interfaces and predominantly incoherent phonon transport.« less

Study on the Lattice Dynamics of the Argyrodite Ag8GeTe6

NASA Astrophysics Data System (ADS)

Hitchcock, Dale; Thompson, Emily; He, Jian; Bredesen, Isaac; Keppends, Veelre; Mandrus, David

2014-03-01

Ag8GeTe6 was initially studied as a super ionic-electronic mixed conductor in the 1970s, and more recently has attracted new interest for its thermoelectric performance. A key to the desirable thermoelectric performance of Ag8GeTe6 is its exceptionally low lattice thermal conductivity (~ 0.25W/m*K at 300K), which is intimately related to its structure, consecutive structural instabilities, and unusual lattice dynamics (e.g., anharmonicity). In this work, we have studied Ag8GeTe6 by means of thermal conductivity, electrical conductivity, Seebeck coefficient, Hall coefficient, magnetic susceptibility, resonant ultrasound spectroscopy (RUS), photoacoustic spectroscopy, and synchrotron x-ray diffraction at low temperatures in order to further understand the coexistence of mixed conduction and high thermoelectric performance at elevated temperatures. This work is supported by NSF DMR 1307740.

Theoretical and Experimental Investigation of Heat Conduction in Air, Including Effects of Oxygen Dissociation

NASA Technical Reports Server (NTRS)

Hansen, C. Frederick; Early, Richard A.; Alzofon, Frederick E.; Witteborn, Fred C.

1959-01-01

Solutions are presented for the conduction of beat through a semi-infinite gas medium having a uniform initial temperature and a constant boundary temperature. The coefficients of thermal conductivity and diffusivity are treated as variables, and the solutions are extended to the case of air at temperatures where oxygen dissociation occurs. These solutions are used together with shock-tube measurements to evaluate the integral of thermal conductivity for air as a function of temperature.

Design, fabrication and test of graphite/epoxy metering truss structure components, phase 3

NASA Technical Reports Server (NTRS)

1974-01-01

The design, materials, tooling, manufacturing processes, quality control, test procedures, and results associated with the fabrication and test of graphite/epoxy metering truss structure components exhibiting a near zero coefficient of thermal expansion are described. Analytical methods were utilized, with the aid of a computer program, to define the most efficient laminate configurations in terms of thermal behavior and structural requirements. This was followed by an extensive material characterization and selection program, conducted for several graphite/graphite/hybrid laminate systems to obtain experimental data in support of the analytical predictions. Mechanical property tests as well as the coefficient of thermal expansion tests were run on each laminate under study, the results of which were used as the selection criteria for the single most promising laminate. Further coefficient of thermal expansion measurement was successfully performed on three subcomponent tubes utilizing the selected laminate.

Thermal conductivity of freestanding single wall carbon nanotube sheet by Raman spectroscopy.

PubMed

Sahoo, Satyaprakash; Chitturi, Venkateswara Rao; Agarwal, Radhe; Jiang, Jin-Wu; Katiyar, Ram S

2014-11-26

Thermal properties of single wall carbon nanotube sheets (SWCNT-sheets) are of significant importance in the area of thermal management, as an isolated SWCNT possesses high thermal conductivity of the value about 3000 W m(-1) K(-1). Here we report an indirect method of estimating the thermal conductivity of a nanometer thick suspended SWCNT-sheet by employing the Raman scattering technique. Tube diameter size is examined by the transmissions electron microscopy study. The Raman analysis of the radial breathing modes predicts narrow diameter size distribution with achiral (armchair) symmetry of the constituent SWCNTs. From the first order temperature coefficient of the A1g mode of the G band along with the laser power dependent frequency shifting of this mode, the thermal conductivity of the suspended SWCNT-sheet is estimated to be about ∼18.3 W m(-1) K(-1). Our theoretical study shows that the thermal conductivity of the SWCNT-sheet has contributions simultaneously from the intratube and intertube thermal transport. The intertube thermal conductivity (with contributions from the van der Waals interaction) is merely around 0.7 W m(-1) K(-1), which is three orders smaller than the intratube thermal conductivity, leading to an abrupt decrease in the thermal conductivity of the SWCNT-sheet as compared to the reported value for isolated SWCNT.

Transport coefficients of Lennard-Jones fluids: A molecular-dynamics and effective-hard-sphere treatment

NASA Astrophysics Data System (ADS)

Heyes, David M.

1988-04-01

This study evaluates the shear viscosity, self-diffusion coefficient, and thermal conductivity of the Lennard-Jones (LJ) fluid over essentially the entire fluid range by molecular-dynamics (MD) computer simulation. The Green-Kubo (GK) method is mainly used. In addition, for shear viscosity, homogeneous shear nonequilibrium MD (NEMD) is also employed and compared with experimental data on argon along isotherms. Reasonable agreement between GK, NEMD, and experiment is found. Hard-sphere MD modified Chapman-Enskog expressions for these transport coefficients are tested with use of a temperature-dependent effective hard-sphere diameter. Excellent agreement is found for shear viscosity. The thermal conductivity and, more so, self-diffusion coefficient is less successful in this respect. This behavior is attributed to the attractive part to the LJ potential and its soft repulsive core. Expressions for the constant-volume and -pressure activation energies for these transport coefficients are derived solely in terms of the thermodynamic properties of the LJ fluid. Also similar expressions for the activation volumes are given, which should have a wider range of applications than just for the LJ system.

Thermal transport in boron nitride nanotorus—towards a nanoscopic thermal shield

NASA Astrophysics Data System (ADS)

Loh, G. C.; Baillargeat, D.

2013-11-01

Nanotori, or nanorings, are topological variants of nanotubes and are conceived to have different properties from their tubular form. In this study, the toroidal arrangement of boron nitride is introduced. Using classical molecular dynamics simulations, the thermal behaviour (thermal conductivity and thermal stability) of the boron nitride nanotorus and its relationship with the structural characteristics are investigated. Its circumferential thermal rectification strength displays a linear dependence on the bending coefficient of the nanostructure. Surface kinks are relatively inconsequential on its circumferential mode of conduction, as compared to its axial sense. The circumferential conductivity in the diffusive regime is calculated to be approximately 10 W/m K, while the axial conductivity is more than tenfold of this value. All nanotori with different toroidal characters show excellent thermal stability at extremely high temperatures approaching 3400 K. With consideration to its favourable properties, a thermal shield made up of a parallel row of nanotori is proposed as a nanoscale thermal insulation device.

Composites of aluminum alloy and magnesium alloy with graphite showing low thermal expansion and high specific thermal conductivity

NASA Astrophysics Data System (ADS)

Oddone, Valerio; Boerner, Benji; Reich, Stephanie

2017-12-01

High thermal conductivity, low thermal expansion and low density are three important features in novel materials for high performance electronics, mobile applications and aerospace. Spark plasma sintering was used to produce light metal-graphite composites with an excellent combination of these three properties. By adding up to 50 vol.% of macroscopic graphite flakes, the thermal expansion coefficient of magnesium and aluminum alloys was tuned down to zero or negative values, while the specific thermal conductivity was over four times higher than in copper. No degradation of the samples was observed after thermal stress tests and thermal cycling. Tensile strength and hardness measurements proved sufficient mechanical stability for most thermal management applications. For the production of the alloys, both prealloyed powders and elemental mixtures were used; the addition of trace elements to cope with the oxidation of the powders was studied.

Composites of aluminum alloy and magnesium alloy with graphite showing low thermal expansion and high specific thermal conductivity

PubMed Central

Oddone, Valerio; Boerner, Benji; Reich, Stephanie

2017-01-01

Abstract High thermal conductivity, low thermal expansion and low density are three important features in novel materials for high performance electronics, mobile applications and aerospace. Spark plasma sintering was used to produce light metal–graphite composites with an excellent combination of these three properties. By adding up to 50 vol.% of macroscopic graphite flakes, the thermal expansion coefficient of magnesium and aluminum alloys was tuned down to zero or negative values, while the specific thermal conductivity was over four times higher than in copper. No degradation of the samples was observed after thermal stress tests and thermal cycling. Tensile strength and hardness measurements proved sufficient mechanical stability for most thermal management applications. For the production of the alloys, both prealloyed powders and elemental mixtures were used; the addition of trace elements to cope with the oxidation of the powders was studied. PMID:28458742

Composites of aluminum alloy and magnesium alloy with graphite showing low thermal expansion and high specific thermal conductivity.

PubMed

Oddone, Valerio; Boerner, Benji; Reich, Stephanie

2017-01-01

High thermal conductivity, low thermal expansion and low density are three important features in novel materials for high performance electronics, mobile applications and aerospace. Spark plasma sintering was used to produce light metal-graphite composites with an excellent combination of these three properties. By adding up to 50 vol.% of macroscopic graphite flakes, the thermal expansion coefficient of magnesium and aluminum alloys was tuned down to zero or negative values, while the specific thermal conductivity was over four times higher than in copper. No degradation of the samples was observed after thermal stress tests and thermal cycling. Tensile strength and hardness measurements proved sufficient mechanical stability for most thermal management applications. For the production of the alloys, both prealloyed powders and elemental mixtures were used; the addition of trace elements to cope with the oxidation of the powders was studied.

Steady State Transportation Cooling in Porous Media Under Local, Non-Thermal Equilibrium Fluid Flow

NASA Technical Reports Server (NTRS)

Rodriquez, Alvaro Che

2002-01-01

An analytical solution to the steady-state fluid temperature for 1-D (one dimensional) transpiration cooling has been derived. Transpiration cooling has potential use in the aerospace industry for protection against high heating environments for re-entry vehicles. Literature for analytical treatments of transpiration cooling has been largely confined to the assumption of thermal equilibrium between the porous matrix and fluid. In the present analysis, the fundamental fluid and matrix equations are coupled through a volumetric heat transfer coefficient and investigated in non-thermal equilibrium. The effects of varying the thermal conductivity of the solid matrix and the heat transfer coefficient are investigated. The results are also compared to existing experimental data.

Investigation of heat and mass transfer under the influence of variable diffusion coefficient and thermal conductivity

NASA Astrophysics Data System (ADS)

Mohyud Din, S. T.; Zubair, T.; Usman, M.; Hamid, M.; Rafiq, M.; Mohsin, S.

2018-04-01

This study is devoted to analyze the influence of variable diffusion coefficient and variable thermal conductivity on heat and mass transfer in Casson fluid flow. The behavior of concentration and temperature profiles in the presence of Joule heating and viscous dissipation is also studied. The dimensionless conversation laws with suitable BCs are solved via Modified Gegenbauer Wavelets Method (MGWM). It has been observed that increase in Casson fluid parameter (β ) and parameter ɛ enhances the Nusselt number. Moreover, Nusselt number of Newtonian fluid is less than that of the Casson fluid. The phenomenon of mass transport can be increased by solute of variable diffusion coefficient rather than solute of constant diffusion coefficient. A detailed analysis of results is appropriately highlighted. The obtained results, error estimates, and convergence analysis reconfirm the credibility of proposed algorithm. It is concluded that MGWM is an appropriate tool to tackle nonlinear physical models and hence may be extended to some other nonlinear problems of diversified physical nature also.

Rigorous theory of graded thermoelectric converters including finite heat transfer coefficients

NASA Astrophysics Data System (ADS)

Gerstenmaier, York Christian; Wachutka, Gerhard

2017-11-01

Maximization of thermoelectric (TE) converter performance with an inhomogeneous material and electric current distribution has been investigated in previous literature neglecting thermal contact resistances to the heat reservoirs. The heat transfer coefficients (HTCs), defined as inverse thermal contact resistances per unit area, are thus infinite, whereas in reality, always parasitic thermal resistances, i.e., finite HTCs, are present. Maximization of the generated electric power and of cooling power in the refrigerator mode with respect to Seebeck coefficients and heat conductivity for a given profile of the material's TE figure of merit Z are mathematically ill-posed problems in the presence of infinite HTCs. As will be shown in this work, a fully self consistent solution is possible for finite HTCs, and in many respects, the results are fundamentally different. A previous theory for 3D devices will be extended to include finite HTCs and is applied to 1D devices. For the heat conductivity profile, an infinite number of solutions exist leading to the same device performance. Cooling power maximization for finite HTCs in 1D will lead to a strongly enhanced corresponding efficiency (coefficient of performance), whereas results with infinite HTCs lead to a non-monotonous temperature profile and coefficient of performance tending to zero for the prescribed heat conductivities. For maximized generated electric power, the corresponding generator efficiency is nearly a constant independent from the finite HTC values. The maximized efficiencies in the generator and cooling mode are equal to the efficiencies for the infinite HTC, provided that the corresponding powers approach zero. These and more findings are condensed in 4 theorems in the conclusions.

Micro thermal diode with glass thermal insulation structure embedded in a vapor chamber

NASA Astrophysics Data System (ADS)

Tsukamoto, Takashiro; Hirayanagi, Takashi; Tanaka, Shuji

2017-04-01

This paper reports a micro thermal diode based on one-way working fluid circulation driven by surface tension force. In forward mode, working fluid evaporates and condenses at a heated and cooled area, respectively, and the condensed liquid returns to the evaporation area due to the wettability difference. By this vapor-liquid phase change mechanism, the overall heat transfer coefficient becomes high. On the other hand, in reverse mode, no continuous evaporation-condensation cycle exists. The conductive heat loss in reverse mode was minimized by an embedded glass thermal isolation structure, which makes overall heat transfer coefficient low. The test device was made by a standard MEMS process combined with glass reflow and gold bump sealing. The overall heat transfer coefficients of 13 300 \\text{W}~{{\\text{m}}-2}~\\text{K} for forward mode and 4790 \\text{W}~{{\\text{m}}-2}~\\text{K} for reverse mode were measured. The performance index of the micro thermal diode was about 2.8.

Heat Diffusion in Gases, Including Effects of Chemical Reaction

NASA Technical Reports Server (NTRS)

Hansen, C. Frederick

1960-01-01

The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.

Experimental investigation of heat transfer of R134a in pool boiling on stainless steel and aluminum tubes

NASA Astrophysics Data System (ADS)

Wengler, C.; Addy, J.; Luke, A.

2018-03-01

Due to high energy demand required for chemical processes, refrigeration and process industries the increase of efficiency and performance of thermal systems especially evaporators is indispensable. One of the possibilities to meet this purpose are investigations in enhancement of the heat transfer in nucleate boiling where high heat fluxes at low superheat are transferred. In the present work, the heat transfer in pool boiling is investigated with pure R134a over wide ranges of reduced pressures and heat fluxes. The heating materials of the test tubes are aluminum and stainless steel. The influence of the thermal conductivity on the heat transfer coefficients is analysed by the surface roughness of sandblasted surfaces. The heat transfer coefficient increases with increasing thermal conductivity, surface roughness and reduced pressures. The experimental results show a small degradation of the heat transfer coefficients between the two heating materials aluminum and stainless steel. In correlation with the VDI Heat Atlas, the experimental results are matching well with the predictions but do not accurately consider the stainless steel material reference properties.

Heat-physical properties of lunar surface material returned to earth by the Luna 16 automatic station

NASA Technical Reports Server (NTRS)

Avduyevskiy, V. S.; Anfimov, N. A.; Marov, M. Y.; Treskin, Y. A.; Shalayev, S. P.; Ekonomov, A. P.

1974-01-01

Density, specific heat capacity, and coefficient of thermal conductivity were studied on a sample of lunar surface material returned by the Luna 16 automatic station. The study was carried out in a helium-filled chamber. The density of the surface material when freely heaped was 1.2 g/cu cm, and when shaken down -- 1.7 g/cu cm. The specific heat capacity was 0.177 + or - 0.010 cal x g/1 x deg/1. The coefficient of thermal conductivity in the material was 4.8 x 10/6 + or - 1.2 x 10/6 cal x cm/1 x sec/1 x deg/1.

The calculation of thermophysical properties of nickel plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Apfelbaum, E. M.

2015-09-15

The thermophysical properties of Nickel plasma have been calculated for the temperatures 10–60 kK and densities less than 1 g/cm{sup 3}. These properties are the pressure, internal energy, heat capacity, and the electronic transport coefficients (electrical conductivity, thermal conductivity, and thermal power). The thermodynamic values have been calculated by means of the chemical model, which also allows one to obtain the ionic composition of considered plasma. The composition has been used to calculate the electronic transport coefficients within the relaxation time approximation. The results of the present investigation have been compared with the calculations of other researchers and available data ofmore » measurements.« less

Linear Friction Welding Process Model for Carpenter Custom 465 Precipitation-Hardened Martensitic Stainless Steel

DTIC Science & Technology

2014-04-11

Fig. 9(a) and (b). In addition, the temperature dependencies of the true and room-temperature-based mean values of the linear thermal expansion ...Variation of (a) thermal conductivity, (b) specific heat, (c) true linear thermal expansion coefficient, and (d) room-temperature-based mean thermal ...defined as follows: (a) alloy-grade and thermal -mechanical treatment of the workpiece materials to be joined, (b) frequency of reciprocating motion

The features of the modeling the nanofluid flows

NASA Astrophysics Data System (ADS)

Rudyak, Valery; Minakov, Andrey

2018-05-01

The features of the nanofluid flows modeling are analyzed. In the first part the thermophysical properties (viscosity and thermal conductivity) of nanofluids are discussed in detailed. It was shown that the transport coefficients of nanofluids depend not only on the volume concentration of the particles but also on their size and material. The viscosity increases with decreasing the particle size while the thermal conductivity increases with increasing the particle size. The heat transfer of nanofluid in cylindrical channel and laminar-turbulent transition in some flows are considered. The heat transfer coefficient is determined by the flow mode (laminar or turbulent) of the nanofluid. However it was shown that adding nanoparticles to the coolant significantly influences the heat transfer coefficient. The laminar-turbulent transition begins in all cases earlier (at smaller Reynolds numbers) than for base fluid. In conclusion the possibility of the use of traditional similarity criteria are discussed.

Tuning Thermoelectric Properties of Type I Clathrate K 8–x Ba x Al 8+x Si 38–x through Barium Substitution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sui, Fan; Kauzlarich, Susan M.

2016-05-10

The thermal stability and thermoelectric properties of type I clathrate K8Al8Si38 up to 873 K are reported. K8Al8Si38 possesses a high absolute Seebeck coefficient value and high electrical resistivity in the temperature range of 323 to 873 K, which is consistent with previously reported low temperature thermoelectric properties. Samples with Ba partial substitution at the K guest atom sites were synthesized from metal hydride precursors. The samples with the nominal chemical formula of K8–xBaxAl8+xSi38–x (x = 1, 1.5, 2) possess type I clathrate structure (cubic, Pm3n), confirmed by X-ray diffraction. The guest atom site occupancies and thermal motions were investigatedmore » with Rietveld refinement of synchrotron powder X-ray diffraction. Transport properties of Ba-containing samples were characterized from 2 to 300 K. The K–Ba alloy phases showed low thermal conductivity and improved electrical conductivity compared to K8Al8Si38. Electrical resistivity and Seebeck coefficients were measured over the temperature range of 323 to 873 K. Thermal conductivity from 323 to 873 K was estimated from the Wiedemann–Franz relation and lattice thermal conductivity extrapolation from 300 to 873 K. K8–xBaxAl8+xSi38–x (x = 1, 1.5) synthesized with Al deficiency showed enhanced electrical conductivity, and the absolute Seebeck coefficients decrease with the increased carrier concentration. When x = 2, the Al content increases toward the electron balanced composition, and the electrical resistivity increases with the decreasing charge carrier concentration. Overall, K6.5Ba1.5Al9Si37 achieves an enhanced zT of 0.4 at 873 K.« less

Transport coefficients and heat fluxes in non-equilibrium high-temperature flows with electronic excitation

NASA Astrophysics Data System (ADS)

Istomin, V. A.; Kustova, E. V.

2017-02-01

The influence of electronic excitation on transport processes in non-equilibrium high-temperature ionized mixture flows is studied. Two five-component mixtures, N 2 / N2 + / N / N + / e - and O 2 / O2 + / O / O + / e - , are considered taking into account the electronic degrees of freedom for atomic species as well as the rotational-vibrational-electronic degrees of freedom for molecular species, both neutral and ionized. Using the modified Chapman-Enskog method, the transport coefficients (thermal conductivity, shear viscosity and bulk viscosity, diffusion and thermal diffusion) are calculated in the temperature range 500-50 000 K. Thermal conductivity and bulk viscosity coefficients are strongly affected by electronic states, especially for neutral atomic species. Shear viscosity, diffusion, and thermal diffusion coefficients are not sensible to electronic excitation if the size of excited states is assumed to be constant. The limits of applicability for the Stokes relation are discussed; at high temperatures, this relation is violated not only for molecular species but also for electronically excited atomic gases. Two test cases of strongly non-equilibrium flows behind plane shock waves corresponding to the spacecraft re-entry (Hermes and Fire II) are simulated numerically. Fluid-dynamic variables and heat fluxes are evaluated in gases with electronic excitation. In inviscid flows without chemical-radiative coupling, the flow-field is weakly affected by electronic states; however, in viscous flows, their influence can be more important, in particular, on the convective heat flux. The contribution of different dissipative processes to the heat transfer is evaluated as well as the effect of reaction rate coefficients. The competition of diffusion and heat conduction processes reduces the overall effect of electronic excitation on the convective heating, especially for the Fire II test case. It is shown that reliable models of chemical reaction rates are of great importance for accurate predictions of the fluid dynamic variables and heat fluxes.

Development of Standardized Material Testing Protocols for Prosthetic Liners

PubMed Central

Cagle, John C.; Reinhall, Per G.; Hafner, Brian J.; Sanders, Joan E.

2017-01-01

A set of protocols was created to characterize prosthetic liners across six clinically relevant material properties. Properties included compressive elasticity, shear elasticity, tensile elasticity, volumetric elasticity, coefficient of friction (CoF), and thermal conductivity. Eighteen prosthetic liners representing the diverse range of commercial products were evaluated to create test procedures that maximized repeatability, minimized error, and provided clinically meaningful results. Shear and tensile elasticity test designs were augmented with finite element analysis (FEA) to optimize specimen geometries. Results showed that because of the wide range of available liner products, the compressive elasticity and tensile elasticity tests required two test maxima; samples were tested until they met either a strain-based or a stress-based maximum, whichever was reached first. The shear and tensile elasticity tests required that no cyclic conditioning be conducted because of limited endurance of the mounting adhesive with some liner materials. The coefficient of friction test was based on dynamic coefficient of friction, as it proved to be a more reliable measurement than static coefficient of friction. The volumetric elasticity test required that air be released beneath samples in the test chamber before testing. The thermal conductivity test best reflected the clinical environment when thermal grease was omitted and when liner samples were placed under pressure consistent with load bearing conditions. The developed procedures provide a standardized approach for evaluating liner products in the prosthetics industry. Test results can be used to improve clinical selection of liners for individual patients and guide development of new liner products. PMID:28233885

Pyroelectric effect and lattice thermal conductivity of InN/GaN heterostructures

NASA Astrophysics Data System (ADS)

Hansdah, Gopal; Sahoo, Bijay Kumar

2018-06-01

The built-in-polarization (BIP) of InN/GaN heterostructures enhances Debye temperature, phonon mean free path and thermal conductivity of the heterostructure at room temperature. The variation of thermal conductivities (kp: including polarization mechanism and k: without polarization mechanism) with temperature predicts the existence of a transition temperature (Tp) between primary and secondary pyroelectric effect. Below Tp, kp is lower than k; while above Tp, kp is significantly contributed from BIP mechanism due to thermal expansion. A thermodynamic theory has been proposed to explain the result. The room temperature thermal conductivity of InN/GaN heterostructure with and without polarization is respectively 32 and 48 W m-1 K-1. The temperature Tp and room temperature pyroelectric coefficient of InN has been predicted as 120 K and -8.425 μC m-2 K-1, respectively which are in line with prior literature studies. This study suggests that thermal conductivity measurement in InN/GaN heterostructures can help to understand the role of phonons in pyroelectricity.

Macro-Scale Strength and Microstructure of ZrW2O8 Cementitious Composites with Tunable Low Thermal Expansion

PubMed Central

Ouyang, Jianshu; Chen, Bo; Huang, Dahai

2018-01-01

Concretes with engineered thermal expansion coefficients, capable of avoiding failure or irreversible destruction of structures or devices, are important for civil engineering applications, such as dams, bridges, and buildings. In natural materials, thermal expansion usually cannot be easily regulated and an extremely low thermal expansion coefficient (TEC) is still uncommon. Here we propose a novel cementitious composite, doped with ZrW2O8, showing a wide range of tunable thermal expansion coefficients, from 8.65 × 10−6 °C−1 to 2.48 × 10−6 °C−1. Macro-scale experiments are implemented to quantify the evolution of the thermal expansion coefficients, compressive and flexural strength over a wide range of temperature. Scanning Electron Microscope (SEM) imaging was conducted to quantify the specimens’ microstructural characteristics including pores ratio and size. It is shown that the TEC of the proposed composites depends on the proportion of ZrW2O8 and the ambient curing temperature. Macro-scale experimental results and microstructures have a good agreement. The TEC and strength gradually decrease as ZrW2O8 increases from 0% to 20%, subsequently fluctuates until 60%. The findings reported here provide a new routine to design cementitious composites with tunable thermal expansion for a wide range of engineering applications. PMID:29735957

Emerging low-cost LED thermal management materials

NASA Astrophysics Data System (ADS)

Zweben, Carl H.

2004-10-01

As chip size and power levels continue to increase, thermal management, thermal stresses and cost have become key LED packaging issues. Until recently, low-coefficient-of-thermal-expansion (CTE) materials, which are needed to minimize thermal stresses, had thermal conductivities that are no better than those of aluminum alloys, about 200 W/m-K. Copper, which has a higher thermal conductivity (400 W/m-K), also has a high CTE, which can cause severe thermal stresses. We now have over a dozen low-CTE materials with thermal conductivities ranging between 400 and 1700 W/m-K, and almost a score with thermal conductivities at least 50% greater than that of aluminum. Some of these materials are low cost. Others have the potential to be low cost in high volume production. Emphasizing low cost, this paper reviews traditional packaging materials and the six categories of advanced materials: polymer matrix-, metal matrix-, ceramic matrix-, and carbon matrix composites; monolithic carbonaceous materials; and metal-metal composites/alloys. Topics include properties, status, applications, cost and likely future directions of new advanced materials, including carbon nanotubes and inexpensive graphite nanoplatelets.

Preparation and Thermoelectric Properties of the Skutterudite-Related Phase Ru(0.5)Pd(0.5)Sb3

NASA Technical Reports Server (NTRS)

Caillat, T.; Kulleck, J.; Borshchevsky, A.; Fleurial, J.-P.

1996-01-01

A new skutterudite phase Ru(0.5)Pd(0.5)Sb3 was prepared. This new phase adds to a large number of already known materials with the skutterudite structure which have shown good potential for thermoelectric applications. Single phase, polycrystalline samples were prepared and characterized by x-ray analysis, electron probe microanalysis, density, sound velocity, thermal-expansion coefficient, and differential thermal analysis measurements. Ru(0.5)Pd(0.5)Sb3 has a cubic lattice, space group Im3 (T(sup 5, sub h)), with a = 9.298 A and decomposes at about 920 K. The Seebeck coefficient, the electrical resistivity, the Hall effect, and the thermal conductivity were measured on hot-pressed samples over a wide range of temperatures. Preliminary results show that Ru(0.5)Pd(0.5)Sb3 behaves as a heavily doped semiconductor with an estimated band gap of about 0.6 eV. The lattice thermal conductivity of Ru(0.5)Pd(0.5)Sb3 is substantially lower than that of the binary isostructural compounds CoSb3 and IrSb3. The unusually low thermal conductivity might be explained by additional hole and charge transfer phonon scattering in this material. The potential of this material for thermoelectric applications is discussed.

High-Pressure Transport Properties Of Fluids: Theory And Data From Levitated Drops At Combustion-Relevant Temperatures

NASA Technical Reports Server (NTRS)

Bellan, Josette; Harstad, Kenneth; Ohsaka, Kenichi

2003-01-01

Although the high pressure multicomponent fluid conservation equations have already been derived and approximately validated for binary mixtures by this PI, the validation of the multicomponent theory is hampered by the lack of existing mixing rules for property calculations. Classical gas dynamics theory can provide property mixing-rules at low pressures exclusively. While thermal conductivity and viscosity high-pressure mixing rules have been documented in the literature, there is no such equivalent for the diffusion coefficients and the thermal diffusion factors. The primary goal of this investigation is to extend the low pressure mixing rule theory to high pressures and validate the new theory with experimental data from levitated single drops. The two properties that will be addressed are the diffusion coefficients and the thermal diffusion factors. To validate/determine the property calculations, ground-based experiments from levitated drops are being conducted.

Towards AlN optical cladding layers for thermal management in hybrid lasers

NASA Astrophysics Data System (ADS)

Mathews, Ian; Lei, Shenghui; Nolan, Kevin; Levaufre, Guillaume; Shen, Alexandre; Duan, Guang-Hua; Corbett, Brian; Enright, Ryan

2015-06-01

Aluminium Nitride (AlN) is proposed as a dual function optical cladding and thermal spreading layer for hybrid ridge lasers, replacing current benzocyclobutene (BCB) encapsulation. A high thermal conductivity material placed in intimate contact with the Multi-Quantum Well active region of the laser allows rapid heat removal at source but places a number of constraints on material selection. AlN is considered the most suitable due to its high thermal conductivity when deposited at low deposition temperatures, similar co-efficient of thermal expansion to InP, its suitable refractive index and its dielectric nature. We have previously simulated the possible reduction in the thermal resistance of a hybrid ridge laser by replacing the BCB cladding material with a material of higher thermal conductivity of up to 319 W/mK. Towards this goal, we demonstrate AlN thin-films deposited by reactive DC magnetron sputtering on InP.

Optimal Design of Functionally Graded Metallic Foam Insulations

NASA Technical Reports Server (NTRS)

Haftka, Raphael T.; Sankar, Bhavani; Venkataraman, Satchi; Zhu, Huadong

2002-01-01

The focus of our work has been on developing an insight into the physics that govern the optimum design of thermal insulation for use in thermal protection systems of launch vehicle. Of particular interest was to obtain optimality criteria for designing foam insulations that have density (or porosity) distributions through the thickness for optimum thermal performance. We investigate the optimum design of functionally graded thermal insulation for steady state heat transfer through the foam. We showed that the heat transfer in the foam has competing modes, of radiation and conduction. The problem assumed a fixed inside temperature of 400 K and varied the aerodynamic surface heating on the outside surface from 0.2 to 1.0 MW/sq m. The thermal insulation develops a high temperature gradient through the thickness. Investigation of the model developed for heat conduction in foams showed that at high temperatures (as on outside wall) intracellular radiation dominates the heat transfer in the foam. Minimizing radiation requires reducing the pore size, which increases the density of the foam. At low temperatures (as on the inside wall), intracellular conduction (of the metal and air) dominates the heat transfer. Minimizing conduction requires increasing the pore size. This indicated that for every temperature there was an optimum value of density that minimized the heat transfer coefficient. Two optimization studies were performed. One was to minimize the heat transmitted though a fixed thickness insulation by varying density profiles. The second was to obtain the minimum mass insulation for specified thickness. Analytical optimality criteria were derived for the cases considered. The optimality condition for minimum heat transfer required that at each temperature we find the density that minimizes the heat transfer coefficient. Once a relationship between the optimum heat transfer coefficient and the temperature was found, the design problem reduced to the solution of a simple nonlinear differential equation. Preliminary results of this work were presented at the American Society of Composites meeting, and the final version was submitted for publication in the AIAA Journal. In addition to minimizing the transmitted heat, we investigated the optimum design for minimum weight given an acceptable level of heat transmission through the insulation. The optimality criterion developed was different from that obtained for minimizing beat transfer coefficient. For minimum mass design, we had to find for a given temperature the optimum density, which minimized the logarithmic derivative of the insulation thermal conductivity with respect to its density. The logarithmic derivative is defined as the ratio of relative change in the dependent response (thermal conductivity) to the relative change in the independent variable (density). The results have been documented as a conference paper that will be presented at the upcoming AIAA.

Electronic and Transport Properties of LaNi4Sb12 Skutterudite: Modified Becke-Johnson Approach

NASA Astrophysics Data System (ADS)

Bhat, Tahir Mohiuddin; Singh, Srishti; Gupta, Dinesh C.

2018-05-01

We carried out an ab initio study of structural, electronic, thermodynamic, and thermoelectric properties of the lanthanum-filled skutterudite, LaNi4Sb12. Generalized gradient approximation and modified Becke-Johnson potentials were employed for the exchange-correlation potential. The electronic structure calculations display the metallic behavior of the compound. The alloy offers low lattice thermal conductivity along with a high Seebeck coefficient with a value of - 158 (μVK-1) at room temperature. The effect of high pressure and temperature on thermal properties like thermal expansion coefficient, heat capacity, and Grüneisen parameter are also investigated by means of a quasi-harmonic Debye model. The large Seebeck coefficient and high power factor exhibited by LaNi4Sb12 make it an attractive candidate for thermoelectric materials.

Stefan-Maxwell Relations and Heat Flux with Anisotropic Transport Coefficients for Ionized Gases in a Magnetic Field with Application to the Problem of Ambipolar Diffusion

NASA Astrophysics Data System (ADS)

Kolesnichenko, A. V.; Marov, M. Ya.

2018-01-01

The defining relations for the thermodynamic diffusion and heat fluxes in a multicomponent, partially ionized gas mixture in an external electromagnetic field have been obtained by the methods of the kinetic theory. Generalized Stefan-Maxwell relations and algebraic equations for anisotropic transport coefficients (the multicomponent diffusion, thermal diffusion, electric and thermoelectric conductivity coefficients as well as the thermal diffusion ratios) associated with diffusion-thermal processes have been derived. The defining second-order equations are derived by the Chapman-Enskog procedure using Sonine polynomial expansions. The modified Stefan-Maxwell relations are used for the description of ambipolar diffusion in the Earth's ionospheric plasma (in the F region) composed of electrons, ions of many species, and neutral particles in a strong electromagnetic field.

Step - wise transient method - Influence of heat source inertia

NASA Astrophysics Data System (ADS)

Malinarič, Svetozár; Dieška, Peter

2016-07-01

Step-wise transient (SWT) method is an experimental technique for measuring the thermal diffusivity and conductivity of materials. Theoretical models and experimental apparatus are presented and the influence of the heat source capacity are investigated using the experiment simulation. The specimens from low density polyethylene (LDPE) were measured yielding the thermal diffusivity 0.165 mm2/s and thermal conductivity 0.351 W/mK with the coefficient of variation less than 1.4 %. The heat source capacity caused the systematic error of the results smaller than 1 %.

Electrical and thermal transport properties of layered Bi{sub 2}YO{sub 4}Cu{sub 2}Se{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Yu; Pei, Yanling; Chang, Cheng

Bi{sub 2}YO{sub 4}Cu{sub 2}Se{sub 2} possesses a low thermal conductivity and high electrical conductivity at room temperature, which was considered as a potential thermoelectric material. In this work, we have investigated the electrical and thermal transport properties of Bi{sub 2}YO{sub 4}Cu{sub 2}Se{sub 2} system in the temperature range from 300 K to 873 K. We found that the total thermal conductivity decreases from ~1.8 W m{sup −1} K{sup −1} to ~0.9 W m{sup −1} K{sup −1}, and the electrical conductivity decreases from ~850 S/cm to ~163 S/cm in the measured temperature range. To investigate how potential of Bi{sub 2}YO{sub 4}Cu{submore » 2}Se{sub 2} system, we prepared the heavily Iodine doped samples to counter-dope intrinsically high carrier concentration and improve the electrical transport properties. Interestingly, the Seebeck coefficient could be enhanced to ~+80 μV/K at 873 K, meanwhile, we found that a low thermal conductivity of ~0.7 W m{sup −1} K{sup −1} could be achieved. The intrinsically low thermal conductivity in this system is related to the low elastic properties, such as Young's modulus of 70–72 GPa, and Grüneisen parameters of 1.55–1.71. The low thermal conductivity makes Bi{sub 2}YO{sub 4}Cu{sub 2}Se{sub 2} system to be a potential thermoelectric material, the ZT value ~0.06 at 873 K was obtained, a higher performance is expected by optimizing electrical transport properties through selecting suitable dopants, modifying band structures or by further reducing thermal conductivity through nanostructuring etc. - Highlights: • The total thermal conductivity decreases from 1.8 to 0.9 Wm{sup –1}K{sup –1} at 300–873K. • The electrical conductivity decreased from 850 to 163 S/cm at 300–873K. • The Seebeck coefficients were enhanced through heavily Iodine doping. • The ZT ~0.06 at 873K suggests that Bi{sub 2}YO{sub 4}Cu{sub 2}Se{sub 2} systems are potential thermoelectrical materials.« less

Thermoelectric Study of Copper Selenide

NASA Astrophysics Data System (ADS)

Yao, Mengliang; Liu, Weishu; Ren, Zhifeng; Opeil, Cyril

2014-03-01

Nanostructuring has been shown to be an effective approach in reducing lattice thermal conductivity and improving the figure of merit of thermoelectric materials. Copper selenide is a layered structure material, which has a low thermal conductivity and p-type Seebeck coefficient at low temperatures. We have evaluated several hot-pressed, nanostructured copper selenide samples with different dopants for their thermoelectric properties. The phenomenon of the charge-density wave observed in the nanocomposite, resistivity, Seebeck, thermal conductivity and carrier mobility will be discussed. Funding for this research was provided by the Solid State Solar - Thermal Energy Conversion Center (S3TEC), an Energy Frontier Research Center sponsored by the DOE, Office of Basic Energy Science, Award No. DE-SC0001299/ DE-FG02-09ER46577.

Transport properties of gases and binary liquids near the critical point

NASA Technical Reports Server (NTRS)

Sengers, J. V.

1972-01-01

A status report is presented on the anomalies observed in the behavior of transport properties near the critical point of gases and binary liquids. The shear viscosity exhibits a weak singularity near the critical point. An analysis is made of the experimental data for those transport properties, thermal conductivity and thermal diffusivity near the gas-liquid critical point and binary diffusion coefficient near the critical mixing point, that determine the critical slowing down of the thermodynamic fluctuations in the order parameter. The asymptotic behavior of the thermal conductivity appears to be closely related to the asymptotic behavior of the correlation length. The experimental data for the thermal conductivity and diffusivity are shown to be in substantial agreement with current theoretical predictions.

Refractory porcelain enamel passive-thermal-control coating for high-temperature superalloys

NASA Technical Reports Server (NTRS)

Levin, H.; Auker, B. H.; Gardos, M. N.

1973-01-01

Study was conducted to match thermal expansion coefficients thereby preventing enamels from cracking. Report discusses various enamel coatings that are applied to two different high-temperature superalloys. Study may be of interest to manufacturers of chemical equipment, furnaces, and metal components intended for high-temperature applications.

Experimental study of thermal conductivity of pyrolysised materials by means of a flat layer

NASA Astrophysics Data System (ADS)

Vaniushkin, V. D.; Popov, S. K.; Sidenkov, D. V.

2017-11-01

Recycling of tires is currently a very important task. One of the areas of recycling tires is their low-temperature pyrolysis to produce marketable products - liquid fraction and a solid coke residue. For the development of the pyrolysis installation it is important to know the thermal conductivity of the coke residue at different temperatures of pyrolysis of initial material. As a property of matter, thermal conductivity depends in general on temperature and pressure. For materials with some structure, such as porous materials, the thermal conductivity depends on the characteristics of the structure. The thermal conductivity of the porous coke residue at pyrolysis temperatures of 300 0C, 400 0C, 500 0C and atmospheric pressure was studied experimentally at the laboratory unit of the department of “Theoretical basis of heat engineering” using the method of the flat layer in the temperature range 5…100 0C. Experimentally proved temperature dependencies of the coefficient of thermal conductivity of the coke residue are built to improve the accuracy of calculations of constructive and regime parameters of the pyrolysis installation.

Electric Motor Thermal Management R&D. Annual Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bennion, Kevin

With the push to reduce component volumes, lower costs, and reduce weight without sacrificing performance or reliability, the challenges associated with thermal management increase for power electronics and electric motors. Thermal management for electric motors will become more important as the automotive industry continues the transition to more electrically dominant vehicle propulsion systems. The transition to more electrically dominant propulsion systems leads to higher-power duty cycles for electric drive systems. Thermal constraints place significant limitations on how electric motors ultimately perform, and as thermal management improves, there will be a direct trade-off between motor performance, efficiency, cost, and the sizingmore » of electric motors to operate within the thermal constraints. The goal of this research project is to support broad industry demand for data, analysis methods, and experimental techniques to improve and better understand motor thermal management. Work in FY15 focused on two areas related to motor thermal management: passive thermal performance and active convective cooling. Passive thermal performance emphasized the thermal impact of materials and thermal interfaces among materials within an assembled motor. The research tasks supported the publication of test methods and data for thermal contact resistances and direction-dependent thermal conductivity within an electric motor. Active convective cooling focused on measuring convective heat-transfer coefficients using automatic transmission fluid (ATF). Data for average convective heat transfer coefficients for direct impingement of ATF jets was published. Also, experimental hardware for mapping local-scale and stator-scale convective heat transfer coefficients for ATF jet impingement were developed.« less

Thermoelectric properties of FeAs based superconductors, with thick perovskite- and Sm-O fluorite-type blocking layers

NASA Astrophysics Data System (ADS)

Singh, S. J.; Shimoyama, J.; Ogino, H.; Kishio, K.

2015-11-01

The transport properties (electrical resistivity, Hall and Seebeck coefficient, and thermal conductivity) of iron based superconductors with thick perovskite-type oxide blocking layers and fluorine-doped SmFeAsO were studied to explore their possible potential for thermoelectric applications. The thermal conductivity of former compounds depicts the dominated role of phonon and its value decreases rapidly below the Tc, suggesting the addition of scattering of phonons. Both the Seebeck coefficient (S) and Hall coefficient (RH) of all samples were negative in the whole temperature region below 300 K, indicating that the major contribution to the normal state conductivity is by electrons. In addition, the profile of S(T) and RH(T) of all samples have similar behaviours as would be expected for a multi-band superconductors. Although the estimated thermoelectric figure of merit (ZT) of these compounds was much lower than that of practically applicable thermoelectric materials, however its improvement can be expected by optimizing microstructure of the polycrystalline materials, such as densification and grain orientation.

Transfer coefficients in ultracold strongly coupled plasma

NASA Astrophysics Data System (ADS)

Bobrov, A. A.; Vorob'ev, V. S.; Zelener, B. V.

2018-03-01

We use both analytical and molecular dynamic methods for electron transfer coefficients in an ultracold plasma when its temperature is small and the coupling parameter characterizing the interaction of electrons and ions exceeds unity. For these conditions, we use the approach of nearest neighbor to determine the average electron (ion) diffusion coefficient and to calculate other electron transfer coefficients (viscosity and electrical and thermal conductivities). Molecular dynamics simulations produce electronic and ionic diffusion coefficients, confirming the reliability of these results. The results compare favorably with experimental and numerical data from earlier studies.

Transport coefficients of hard-sphere mixtures. III. Diameter ratio 0. 4 and mass ratio 0. 03 at high fluid density

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erpenbeck, J.J.

1993-07-01

The equation of state and the transport coefficients of shear viscosity, thermal conductivity, thermal diffusion, and mutal diffusion are estimated for a binary, equimolar mixture of hard spheres having a diameter ratio of 0.4 and a mass ratio of 0.03 at volumes in the range 1.7[ital V][sub 0] to 3[ital V][sub 0] ([ital V][sub 0]=1/2 [radical]2 N[ital tsum][sub [ital a]x[ital a

Measurement of the thermal coefficient of electrical resistivity of a nonmagnetic metal

NASA Astrophysics Data System (ADS)

Lacsný, Boris; Králiková, Petra; Dudáková, Simona; Škorecová, Ivana; Teleki, Aba

2017-05-01

The experiment of a magnet falling through a conductive tube is well-known, and teachers often use it in their classrooms, not only in high schools, but also in undergraduate courses of physics. This article describes the measurement of the thermal coefficient of electrical resistivity of a nonmagnetic metal using this experiment. At room temperature, the experiments designed by the authors are suitable for high schools. For undergraduate courses, we present a set-up with liquid nitrogen to realize the measurement over a wider range of temperatures.

Materials and process optimization for dual-shell satellite antenna reflectors

NASA Astrophysics Data System (ADS)

Balaski, Darcy R.; van Oyen, Hans J.; Nissan, Sorin J.

A comprehensive, design-optimization test program was conducted for satellite antenna reflectors composed of two offset paraboloidal Kevlar-reinforced sandwich shells separated by a circular sandwich structure. In addition to standard mechanical properties testing, coefficient of thermal expansion and hygroscopic tests were conducted to predict reflector surface accuracy in the thermal cycling environment of orbital space. Attention was given to the relative placement of components during assembly, in view of reflector surface measurements.

Increasing the Thermal Conductivity and Thermal Diffusivity of Asbestos-Reinforced Laminates Through Modification of their Polymer Matrix with Carbon Nanomaterials

NASA Astrophysics Data System (ADS)

Danilova-Tret'yak, S. M.; Evseeva, L. E.; Tanaeva, S. A.

2014-11-01

Experimental investigations of the thermophysical properties of traditional and modified asbestos-reinforced laminates depending on the type of their carbon nanofiller have been carried out in the range of temperatures from -150 to 150°C. It has been shown that the largest (nearly twofold) increase in the thermal-conductivity and thermal-diffusivity coefficients of the indicated materials is observed when they are modified with a small-scale fraction of a nanofiller (carbon nanotubes). The specific heats of the modified and traditional asbestos-reinforced laminates turned out to be identical, in practice, within the measurement error.

Annular convective-radiative fins with a step change in thickness, and temperature-dependent thermal conductivity and heat transfer coefficient

NASA Astrophysics Data System (ADS)

Barforoush, M. S. M.; Saedodin, S.

2018-01-01

This article investigates the thermal performance of convective-radiative annular fins with a step reduction in local cross section (SRC). The thermal conductivity of the fin's material is assumed to be a linear function of temperature, and heat transfer coefficient is assumed to be a power-law function of surface temperature. Moreover, nonzero convection and radiation sink temperatures are included in the mathematical model of the energy equation. The well-known differential transformation method (DTM) is used to derive the analytical solution. An exact analytical solution for a special case is derived to prove the validity of the obtained results from the DTM. The model provided here is a more realistic representation of SRC annular fins in actual engineering practices. Effects of many parameters such as conduction-convection parameters, conduction-radiation parameter and sink temperature, and also some parameters which deal with step fins such as thickness parameter and dimensionless parameter describing the position of junction in the fin on the temperature distribution of both thin and thick sections of the fin are investigated. It is believed that the obtained results will facilitate the design and performance evaluation of SRC annular fins.

Observation and numerical modeling of chromospheric evaporation during the impulsive phase of a solar flare

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imada, Shinsuke, E-mail: shinimada@stelab.nagoya-u.ac.jp; Murakami, Izumi, E-mail: murakami.izumi@nifs.ac.jp; Department of Fusion Science, SOKENDAI

2015-10-15

We have studied the chromospheric evaporation flow during the impulsive phase of the flare by using the Hinode/EUV Imaging Spectrometer observation and 1D hydrodynamic numerical simulation coupled to the time-dependent ionization. The observation clearly shows that the strong redshift can be observed at the base of the flaring loop only during the impulsive phase. We performed two different numerical simulations to reproduce the strong downflows in FeXII and FeXV during the impulsive phase. By changing the thermal conduction coefficient, we carried out the numerical calculation of chromospheric evaporation in the thermal conduction dominant regime (conductivity coefficient κ{sub 0} = classical value) andmore » the enthalpy flux dominant regime (κ{sub 0} = 0.1 × classical value). The chromospheric evaporation calculation in the enthalpy flux dominant regime could reproduce the strong redshift at the base of the flare during the impulsive phase. This result might indicate that the thermal conduction can be strongly suppressed in some cases of flare. We also find that time-dependent ionization effect is important to reproduce the strong downflows in Fe XII and Fe XV.« less

Influence of Nano-Fluid and Receiver Modification in Solar Parabolic Trough Collector Performance

NASA Astrophysics Data System (ADS)

Dharani Kumar, M.; Yuvaraj, G.; Balaji, D.; Pravinraj, R.; shanmugasundaram, Prabhu

2018-02-01

Utilization of natural renewal sources in India is very high over the past decades. Solar power is a prime source of energy available plenty in the world. In this work solar energy is modified into thermal energy by using copper absorber tube with fins. Due to low heat transfer coefficient results leading to higher thermal losses and lower thermal efficiency. In order to increase the heat transfer coefficient copper receiver tube with fins is used and as well as solid has higher thermal conductivity compare to fluid (Tio2) nano fluid is used to improve the heat transfer rate. The analyses have been carried out and take the account of parameters such as solar radiation with time variation, mass flow rate of water, temperatures.

Tuning of the Seebeck Coefficient and the Electrical and Thermal Conductivity of Hybrid Materials Based on Polypyrrole and Bismuth Nanowires.

PubMed

Hnida, Katarzyna E; Pilarczyk, Kacper; Knutelski, Marcin; Marzec, Mateusz; Gajewska, Marta; Kosonowski, Artur; Chlebda, Damian; Lis, Bartłomiej; Przybylski, Marek

2018-04-06

The growing demand for clean energy catalyzes the development of new devices capable of generating electricity from renewable energy resources. One of the possible approaches focuses on the use of thermoelectric materials (TE), which may utilize waste heat, water, and solar thermal energy to generate electrical power. An improvement of the performance of such devices may be achieved through the development of composites made of an organic matrix filled with nanostructured thermoelectric materials working in a synergetic way. The first step towards such designs requires a better understanding of the fundamental interactions between available materials. In this paper, this matter is investigated and the questions regarding the change of electrical and thermal properties of nanocomposites based on low-conductive polypyrrole enriched with bismuth nanowires of well-defined geometry and morphology is answered. It is clearly demonstrated that the electrical conductivity and the Seebeck coefficient may be tuned either simultaneously or separately within particular Bi NWs content ranges, and that both parameters may be increased at the same time. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Performance evaluation of Mn and Fe doped SrCo0.9Nb0.1O3-δ cathode for IT-SOFC application

NASA Astrophysics Data System (ADS)

Bele, Lokesh; Lenka, R. K.; Patro, P. K.; Muhmood, L.; Mahata, T.; Sinha, P. K.

2018-02-01

Cathode materials of Mn and Fe doped SrCo0.9Nb0.1O3-δ, are synthesized by solid state route for intermediate temperature fuel cell applications. Phase pure material is obtained after calcining the precursors at 1100 °C. Phase compatibility is observed between this novel cathode material with gadolinia doped ceria (GDC) electrolyte material as reflected in the diffraction pattern. The state of art YSZ electrolyte is not compatible with this cathode material. Average thermal expansion coefficient of the material varies between 17 to 22 X 10-6 K-1 on doping, from room temperature to 800 °C. Increase in thermal expansion coefficient is observed with Mn and Fe doping associated with the loss of oxygen from the crystal. The electrical conductivity of the cathode material decreases with Fe and Mn doping. Mn doped samples show lowest conductivity. From the symmetric cell measurement lower area specific resistance (0.16 Ω-cm2) is obtained for un-doped samples, at 850 °C. From the initial results it can be inferred that Mn/Fe doping improves neither the thermal expansion co-efficient nor the electrochemical activity.

Characterisation of electrical resistance for CMC Materials up to 1200 °C

NASA Astrophysics Data System (ADS)

Stäbler, T.; Böhrk, H.; Voggenreiter, H.

2017-12-01

Damage to thermal protection systems (TPS) during atmospheric re-entry is a severe safety issue, especially when considering re-usability of space transportation systems. There is a need for structural health monitoring systems and non-destructive inspection methods. However, damages are hard to detect. When ceramic matrix composites, in this case carbon fibre reinforced silicon carbide (C/C-SiC), are used as a TPS, the electrical properties of the present semiconductor material can be used for health monitoring, since the resistivity changes with damage, strain and temperature. In this work the electrical resistivity as a function of the material temperature is analysed eliminating effects of thermal electricity and the thermal coefficient of electrical resistance is determined. A sensor network is applied for locally and time resolved monitoring of the 300 mm x 120 mm x 3 mm panel shaped samples. Since the material is used for atmospheric re-entry it needs to be characterised for a wide range of temperatures, in this case as high as 1200 °C. Therefore, experiments in an inductively heated test bench were conducted. Firstly, a reference sample was used with thermocouples for characterising the temperature distribution across the sample surface. Secondly, electrical resistance under heat load was measured, time and spatially resolved. Results will be shown and discussed in terms of resistance dependence on temperature, thermal coefficient of electrical resistance, thermal electricity and electrical path orientation including an analysis on effective conducting cross section. Conversely, the thermal coefficient can also be used to determine the material temperature as a function of electrical resistance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takaki, Hirokazu; Kobayashi, Kazuaki; Shimono, Masato

We present the thermoelectric properties of TiN/MgO superlattices employing first-principles calculation techniques. The Seebeck coefficients, the electrical conductances, the thermal conductances, and the figure of merit are investigated employing electrical and thermal transport calculations based on density functional theory combined with the nonequilibrium Green's function and nonequilibrium molecular dynamics simulation methods. The TiN/MgO superlattices with a small lattice mismatch at the interfaces are ideal systems to study the way for an enhancement of thermoelectric properties in artificial nanostructures. We find that the interfacial scattering between the two materials in the metal/insulator superlattices causes the electrical conductance to change rapidly, whichmore » enhances the Seebeck coefficient significantly. We show that the figure of merit for the artificial superlattice nanostructures has a much larger value compared with that of the bulk material and changes drastically with the superlattice configurations at the atomistic level.« less

High-performance thermoelectricity in edge-over-edge zinc-porphyrin molecular wires.

PubMed

Noori, Mohammed; Sadeghi, Hatef; Lambert, Colin J

2017-04-20

If high efficiency organic thermoelectric materials could be identified, then these would open the way to a range of energy harvesting technologies and Peltier coolers using flexible and transparent thin-film materials. We have compared the thermoelectric properties of three zinc porphyrin (ZnP) dimers and a ZnP monomer and found that the "edge-over-edge" dimer formed from stacked ZnP rings possesses a high electrical conductance, negligible phonon thermal conductance and a high Seebeck coefficient of the order of 300 μV K -1 . These combine to yield a predicted room-temperature figure of merit of ZT ≈ 4, which is the highest room-temperature ZT ever reported for a single organic molecule. This high value of ZT is a consequence of the low phonon thermal conductance arising from the stacked nature of the porphyrin rings, which hinders phonon transport through the edge-over-edge molecule and enhances the Seebeck coefficient.

Variational bounds on the temperature distribution

NASA Astrophysics Data System (ADS)

Kalikstein, Kalman; Spruch, Larry; Baider, Alberto

1984-02-01

Upper and lower stationary or variational bounds are obtained for functions which satisfy parabolic linear differential equations. (The error in the bound, that is, the difference between the bound on the function and the function itself, is of second order in the error in the input function, and the error is of known sign.) The method is applicable to a range of functions associated with equalization processes, including heat conduction, mass diffusion, electric conduction, fluid friction, the slowing down of neutrons, and certain limiting forms of the random walk problem, under conditions which are not unduly restrictive: in heat conduction, for example, we do not allow the thermal coefficients or the boundary conditions to depend upon the temperature, but the thermal coefficients can be functions of space and time and the geometry is unrestricted. The variational bounds follow from a maximum principle obeyed by the solutions of these equations.

High-temperature thermoelectric properties of the double-perovskite ruthenium oxide (Sr1-xLax)2ErRuO6

NASA Astrophysics Data System (ADS)

Takahashi, Ryohei; Okazaki, Ryuji; Yasui, Yukio; Terasaki, Ichiro; Sudayama, Takaaki; Nakao, Hironori; Yamasaki, Yuichi; Okamoto, Jun; Murakami, Youichi; Kitajima, Yoshinori

2012-10-01

We have prepared polycrystalline samples of (Sr1-xLax)2ErRuO6 and (Sr1-xLax)2YRuO6, and have measured the resistivity, Seebeck coefficient, thermal conductivity, susceptibility, and x-ray absorption in order to evaluate the electronic states and thermoelectric properties of the doped double-perovskite ruthenates. We have observed a large Seebeck coefficient of -160 μV/K and a low thermal conductivity of 7 mW/cmK for x = 0.1 at 800 K in air. These two values are suitable for efficient oxide thermoelectrics, although the resistivity is still as high as 1 Ω cm. From the susceptibility and x-ray absorption measurements, we find that the doped electrons exist as Ru4+ in the low spin state. On the basis of the measured results, the electronic states and the conduction mechanism are discussed.

Computational modeling and analysis of thermoelectric properties of nanoporous silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, H.; Yu, Y.; Li, G., E-mail: gli@clemson.edu

2014-03-28

In this paper, thermoelectric properties of nanoporous silicon are modeled and studied by using a computational approach. The computational approach combines a quantum non-equilibrium Green's function (NEGF) coupled with the Poisson equation for electrical transport analysis, a phonon Boltzmann transport equation (BTE) for phonon thermal transport analysis and the Wiedemann-Franz law for calculating the electronic thermal conductivity. By solving the NEGF/Poisson equations self-consistently using a finite difference method, the electrical conductivity σ and Seebeck coefficient S of the material are numerically computed. The BTE is solved by using a finite volume method to obtain the phonon thermal conductivity k{sub p}more » and the Wiedemann-Franz law is used to obtain the electronic thermal conductivity k{sub e}. The figure of merit of nanoporous silicon is calculated by ZT=S{sup 2}σT/(k{sub p}+k{sub e}). The effects of doping density, porosity, temperature, and nanopore size on thermoelectric properties of nanoporous silicon are investigated. It is confirmed that nanoporous silicon has significantly higher thermoelectric energy conversion efficiency than its nonporous counterpart. Specifically, this study shows that, with a n-type doping density of 10{sup 20} cm{sup –3}, a porosity of 36% and nanopore size of 3 nm × 3 nm, the figure of merit ZT can reach 0.32 at 600 K. The results also show that the degradation of electrical conductivity of nanoporous Si due to the inclusion of nanopores is compensated by the large reduction in the phonon thermal conductivity and increase of absolute value of the Seebeck coefficient, resulting in a significantly improved ZT.« less

Engineering and design properties of thallium-doped sodium iodide and selected properties of sodium-doped cesium iodide

NASA Technical Reports Server (NTRS)

Forrest, K.; Haehner, C.; Heslin, T.; Magida, M.; Uber, J.; Freiman, S.; Hicho, G.; Polvani, R.

1984-01-01

Mechanical and thermal properties, not available in the literature but necessary to structural design, using thallium doped sodium iodide and sodium doped cesium iodide were determined to be coefficient of linear thermal expansion, thermal conductivity, thermal shock resistance, heat capacity, elastic constants, ultimate strengths, creep, hardness, susceptibility to subcritical crack growth, and ingot variation of strength. These properties were measured for single and polycrystalline materials at room temperature.

Lifshitz black branes and DC transport coefficients in massive Einstein-Maxwell-dilaton gravity

NASA Astrophysics Data System (ADS)

Kuang, Xiao-Mei; Papantonopoulos, Eleftherios; Wu, Jian-Pin; Zhou, Zhenhua

2018-03-01

We construct analytical Lifshitz massive black brane solutions in massive Einstein-Maxwell-dilaton gravity theory. We also study the thermodynamics of these black brane solutions and obtain the thermodynamical stability conditions. On the dual nonrelativistic boundary field theory with Lifshitz symmetry, we analytically compute the DC transport coefficients, including the electric conductivity, thermoelectric conductivity, and thermal conductivity. The novel property of our model is that the massive term supports the Lifshitz black brane solutions with z ≠1 in such a way that the DC transport coefficients in the dual field theory are finite. We also find that the Wiedemann-Franz law in this dual boundary field theory is violated, which indicates that it may involve strong interactions.

Acoustic and thermal properties of tissue

NASA Astrophysics Data System (ADS)

Retat, L.; Rivens, I.; ter Haar, G. R.

2012-10-01

Differences in ultrasound (US) and thermal properties of abdominal soft tissues may affect the delivery of thermal therapies such as high intensity focused ultrasound and may provide a basis for US monitoring of such therapies. 21 rat livers were obtained, within one hour of surgical removal. For a single liver, 3 lobes were selected and each treated in one of 3 ways: maintained at room temperature, water bath heated to 50°C ± 1°C for 10 ± 0.5 minutes, or water bath heated to 60°C ± 1°C for 10 ± 0.6 minutes. The attenuation coefficient, speed of sound and thermal conductivity of fresh rat liver was measured. The attenuation coefficients and speed of sound were measured using the finite-amplitude insertion-substitution (FAIS) method. For each rat liver, the control and treated lobes were scanned using a pair of weakly focused 2.5 MHz Imasonic transducers over the range 1.8 to 3 MHz. The conductivity measurement apparatus was designed to provide one-dimensional heat flow through each specimen using a combination of insulation, heat source and heat sink. Using 35 MHz US images to determine the volume of air trapped in the system, the thermal conductivity was corrected using a simulation based on the Helmhotz bio-heat equation. The process of correlating these results with biological properties is discussed.

Enhancing thermoelectric properties of organic composites through hierarchical nanostructures

PubMed Central

Zhang, Kun; Zhang, Yue; Wang, Shiren

2013-01-01

Organic thermoelectric (TE) materials are very attractive due to easy processing, material abundance, and environmentally-benign characteristics, but their potential is significantly restricted by the inferior thermoelectric properties. In this work, noncovalently functionalized graphene with fullerene by π-π stacking in a liquid-liquid interface was integrated into poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate). Graphene helps to improve electrical conductivity while fullerene enhances the Seebeck coefficient and hinders thermal conductivity, resulting in the synergistic effect on enhancing thermoelectric properties. With the integration of nanohybrids, the electrical conductivity increased from ~10000 to ~70000 S/m, the thermal conductivity changed from 0.2 to 2 W·K−1m−1 while the Seebeck coefficient was enhanced by around 4-fold. As a result, nanohybrids-based polymer composites demonstrated the figure of merit (ZT) as high as 6.7 × 10−2, indicating an enhancement of more than one order of magnitude in comparison to single-phase filler-based polymer composites with ZT at the level of 10−3. PMID:24336319

Ambient temperature thermoelectric performance of thermally evaporated p-type Bi-Sb-Te thin films

NASA Astrophysics Data System (ADS)

Singh, Sukhdeep; Singh, Janpreet; Tripathi, S. K.

2018-04-01

Bismuth antimony telluride (BST) compounds have shown a promising performance in low to medium temperature thermoelectric (TE) conversion. One such composition, Bi1.2Sb0.8Te3, was synthesized by melting elemental entities and thin films of the as-synthesized material were deposited by thermal evaporation. X-Ray Diffraction analysis was conducted to study the crystallographic phases and other structural properties. Electrical conductivity and Seebeck coefficient measurements of as-prepared thin films were conducted in the temperature range from 303-363 K with a view to study ambient temperature application of the synthesized material for power generation in which an increasing trend was observed in the Seebeck coefficient. Electrical conductivity displayed a maximum value of 0.22 × 104 Sm-1 that was comparable to other Bi-Sb-Te compositions whereas power factor had its peak at 323 K. These trends observed in electrical properties indicate that synthesized material can be used for room temperature TE module fabrication.

Thermoelectric and phonon transport properties of two-dimensional IV-VI compounds.

PubMed

Shafique, Aamir; Shin, Young-Han

2017-03-30

We explore the thermoelectric and phonon transport properties of two-dimensional monochalcogenides (SnSe, SnS, GeSe, and GeS) using density functional theory combined with Boltzmann transport theory. We studied the electronic structures, Seebeck coefficients, electrical conductivities, lattice thermal conductivities, and figures of merit of these two-dimensional materials, which showed that the thermoelectric performance of monolayer of these compounds is improved in comparison compared to their bulk phases. High figures of merit (ZT) are predicted for SnSe (ZT = 2.63, 2.46), SnS (ZT = 1.75, 1.88), GeSe (ZT = 1.99, 1.73), and GeS (ZT = 1.85, 1.29) at 700 K along armchair and zigzag directions, respectively. Phonon dispersion calculations confirm the dynamical stability of these compounds. The calculated lattice thermal conductivities are low while the electrical conductivities and Seebeck coefficients are high. Thus, the properties of the monolayers show high potential toward thermoelectric applications.

Thermal transport properties of polycrystalline Pb2FeMoO6

NASA Astrophysics Data System (ADS)

Yuan, Xueping; Xu, Mingxiang

2018-06-01

Thermoelectric properties and specific heat of polycrystalline Pb2FeMoO6 have been systematically studied. The thermal conductivity increases monotonically with increasing of temperature, and reaches the maximum value 1.50 W m‑1 K‑1 at 350 K. The relatively low thermal conductivity is mainly attributed to the strong scattering effect of phonons at Fe/Mo sites. The negative Seebeck coefficient indicates the n-type conduction of the sample. The absolute value of S increases up to 20 μV K‑1 at 350 K. Due to the inhomogeneity resulting from Fe/Mo ions disorder, no distinct λ-type specific heat peak or anomaly typical for second-order transitions are observed.

Automated software to determine thermal diffusivity of oilgas mixture

NASA Astrophysics Data System (ADS)

Khismatullin, A. S.

2018-05-01

The paper presents automated software to determine thermal diffusivity of oil-gas mixture. A series of laboratory testscovering transformer oil cooling in a power transformer tank was conducted. The paper also describes diagrams of temperature-timedependence of bubbling. Thermal diffusivity coefficients are experimentally defined. The paper considers a mathematical task of heat flowdistribution in a rectangular parallelepiped, alongside with the solution of heat a conduction equation in a power transformer tank, which represents a rectangular parallelepiped. A device for temperature monitoring in the tank is described in detail. The relay control diagram, which ensures temperature monitoring againsttransformer overheating is described.

Marine Surface Condenser Design Using Vertical Tubes Which Are Enhanced.

DTIC Science & Technology

1981-06-01

hydraulic diameter. 2. Tube Wall. Heat transfer resistance through the tube wall is dependent upon tube material , wall thickness, and a scaling...B. Heat Transfer Coefficient for a Tube Wall For materials such as pure copper which have extremely high values for thermal conductivity, the...mandate the use of materials with relatively low thermal con- ductivities. The thermal resistance of the tube wall is the reciprocal of the heat

Experimental and theoretical investigation of thermal conductivity of ethylene glycol containing functionalized single walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Hemmat Esfe, Mohammad; Firouzi, Masoumeh; Afrand, Masoud

2018-01-01

In this paper, functionalized single walled carbon nanotubes (FSWCNTs) were suspended in Ethylene Glycol (EG) at different volume fractions. A KD2 pro thermal conductivity meter was used to measure the thermal conductivity in the temperature range from 30 to 50 °C. Nanofluids were prepared in solid volume fraction of 0.02, 0.05, 0.075, 0.1, 0.25, 0.5 and, 0.75%. Experimental results revealed that the thermal conductivity of the nanofluid is a non-linear function of temperature and SWCNTs volume fraction in the range of this investigation. Thermal conductivity increases with temperature and nanoparticles volume fraction as usual for this type of nanofluid. Maximum increment in thermal conductivity of the nanofluids was found to be about 45% at 0.75 vol fractions loading at 50 °C. Finally, a new correlation based on artificial neural network (ANN) approach has been proposed for SWCNT-EG thermal conductivity in terms of nanoparticles volume fraction and temperature using the experimental data. Used ANN approach has estimated the experimental values of thermal conductivity with the absolute average relative deviation lower than 0.9%, mean square error of 3.67 × 10-5 and regression coefficient of 0.9989. Comparison between the suggested techniques with various used correlation in the literatures established that the ANN approach is better to other presented methods and therefore can be proposed as a useful means for predicting of the nanofluids thermal conductivity.

Novel Application of Glass Fibers Recovered From Waste Printed Circuit Boards as Sound and Thermal Insulation Material

NASA Astrophysics Data System (ADS)

Sun, Zhixing; Shen, Zhigang; Ma, Shulin; Zhang, Xiaojing

2013-10-01

The aim of this study is to investigate the feasibility of using glass fibers, a recycled material from waste printed circuit boards (WPCB), as sound absorption and thermal insulation material. Glass fibers were obtained through a fluidized-bed recycling process. Acoustic properties of the recovered glass fibers (RGF) were measured and compared with some commercial sound absorbing materials, such as expanded perlite (EP), expanded vermiculite (EV), and commercial glass fiber. Results show that RGF have good sound absorption ability over the whole tested frequency range (100-6400 Hz). The average sound absorption coefficient of RGF is 0.86, which is prior to those of EP (0.81) and EV (0.73). Noise reduction coefficient analysis indicates that the absorption ability of RGF can meet the requirement of II rating for sound absorbing material according to national standard. The thermal insulation results show that RGF has a fair low thermal conductivity (0.046 W/m K), which is comparable to those of some insulation materials (i.e., EV, EP, and rock wool). Besides, an empirical dependence of thermal conductivity on material temperature was determined for RGF. All the results showed that the reuse of RGF for sound and thermal insulation material provided a promising way for recycling WPCB and obtaining high beneficial products.

Thermoelectric Properties of Dy-Doped SrTiO3 Ceramics

NASA Astrophysics Data System (ADS)

Liu, J.; Wang, C. L.; Peng, H.; Su, W. B.; Wang, H. C.; Li, J. C.; Zhang, J. L.; Mei, L. M.

2012-11-01

Sr1- x Dy x TiO3 ( x = 0.02, 0.05, 0.10) ceramics were prepared by the reduced solid-state reaction method, and their thermoelectric properties were investigated from room temperature to 973 K. The resistivity increases with temperature, showing metallic behavior. The Seebeck coefficients tend to saturate at high temperatures, presenting narrow-band behavior, as proved by ab initio calculations of the electronic structure. The magnitudes of the Seebeck coefficient and the electrical resistivity decrease with increasing Dy content. At the same time, the thermal conductivity decreases because the lattice thermal conductivity is reduced by Dy substitution. The maximum value of the figure of merit reaches 0.25 at 973 K for the Sr0.9Dy0.1TiO3 sample.

The effect of nanoparticles aggregation on the thermal conductivity of nanofluids at very low concentrations: Experimental and theoretical evaluations

NASA Astrophysics Data System (ADS)

Motevasel, Mohsen; Nazar, Ali Reza Solaimany; Jamialahmadi, Mohammad

2018-01-01

Nanoparticles suspended in a base fluid yield increased thermal conductivity, which in turn increases convection heat transfer rate. Prediction of suitable relations for determination of thermal conductivity results in heightened accuracy in the calculation of convection heat transfer coefficient and reduced costs. In the majority of studies performed on the prediction of thermal conductivity, some relations and models were used in which the effect of aggregation of particles, especially at low concentrations was ignored. In this research, the thermal conductivity of the nanofluid is measured experimentally at low volumetric concentrations, within the range of 0.02-0.2% for the nanoparticles of Al2O3, MgO, CuO, and SiC in the base fluid of distilled water. The results obtained from the models are compared by the available models considering and neglecting the effect of aggregation of particles. Within the range of the applied concentrations, the relative absolute average deviation ratio of the thermal conductivity models without considering the aggregation effect in relation with the models considering the aggregate, is observed to be between 2 and 6 times. Therefore, it is recommended that even at low concentrations, the effect of aggregation should be considered in the prediction of thermal conductivity.

Thermoelectric Properties of Bi2Te3: CuI and the Effect of Its Doping with Pb Atoms

PubMed Central

Han, Mi-Kyung; Lee, Da-Hee; Kim, Sung-Jin

2017-01-01

In order to understand the effect of Pb-CuI co-doping on the thermoelectric performance of Bi2Te3, n-type Bi2Te3 co-doped with x at % CuI and 1/2x at % Pb (x = 0, 0.01, 0.03, 0.05, 0.07, and 0.10) were prepared via high temperature solid state reaction and consolidated using spark plasma sintering. Electron and thermal transport properties, i.e., electrical conductivity, carrier concentration, Hall mobility, Seebeck coefficient, and thermal conductivity, of CuI-Pb co-doped Bi2Te3 were measured in the temperature range from 300 K to 523 K, and compared to corresponding x% of CuI-doped Bi2Te3 and undoped Bi2Te3. The addition of a small amount of Pb significantly decreased the carrier concentration, which could be attributed to the holes from Pb atoms, thus the CuI-Pb co-doped samples show a lower electrical conductivity and a higher Seebeck coefficient when compared to CuI-doped samples with similar x values. The incorporation of Pb into CuI-doped Bi2Te3 rarely changed the power factor because of the trade-off relationship between the electrical conductivity and the Seebeck coefficient. The total thermal conductivity(κtot) of co-doped samples (κtot ~ 1.4 W/m∙K at 300 K) is slightly lower than that of 1% CuI-doped Bi2Te3 (κtot ~ 1.5 W/m∙K at 300 K) and undoped Bi2Te3 (κtot ~ 1.6 W/m∙K at 300 K) due to the alloy scattering. The 1% CuI-Pb co-doped Bi2Te3 sample shows the highest ZT value of 0.96 at 370 K. All data on electrical and thermal transport properties suggest that the thermoelectric properties of Bi2Te3 and its operating temperature can be controlled by co-doping. PMID:29072613

Thermoelectric Properties of Bi₂Te₃: CuI and the Effect of Its Doping with Pb Atoms.

PubMed

Han, Mi-Kyung; Jin, Yingshi; Lee, Da-Hee; Kim, Sung-Jin

2017-10-26

In order to understand the effect of Pb-CuI co-doping on the thermoelectric performance of Bi₂Te₃, n -type Bi₂Te₃ co-doped with x at % CuI and 1/2 x at % Pb ( x = 0, 0.01, 0.03, 0.05, 0.07, and 0.10) were prepared via high temperature solid state reaction and consolidated using spark plasma sintering. Electron and thermal transport properties, i.e., electrical conductivity, carrier concentration, Hall mobility, Seebeck coefficient, and thermal conductivity, of CuI-Pb co-doped Bi₂Te₃ were measured in the temperature range from 300 K to 523 K, and compared to corresponding x % of CuI-doped Bi₂Te₃ and undoped Bi₂Te₃. The addition of a small amount of Pb significantly decreased the carrier concentration, which could be attributed to the holes from Pb atoms, thus the CuI-Pb co-doped samples show a lower electrical conductivity and a higher Seebeck coefficient when compared to CuI-doped samples with similar x values. The incorporation of Pb into CuI-doped Bi₂Te₃ rarely changed the power factor because of the trade-off relationship between the electrical conductivity and the Seebeck coefficient. The total thermal conductivity(κ tot ) of co-doped samples (κ tot ~ 1.4 W/m∙K at 300 K) is slightly lower than that of 1% CuI-doped Bi₂Te₃ (κ tot ~ 1.5 W/m∙K at 300 K) and undoped Bi₂Te₃ (κ tot ~ 1.6 W/m∙K at 300 K) due to the alloy scattering. The 1% CuI-Pb co-doped Bi₂Te 3 sample shows the highest ZT value of 0.96 at 370 K. All data on electrical and thermal transport properties suggest that the thermoelectric properties of Bi₂Te 3 and its operating temperature can be controlled by co-doping.

Characterization and optimization of polycrystalline Si70%Ge30% for surface micromachined thermopiles in human body applications

NASA Astrophysics Data System (ADS)

Wang, Ziyang; Fiorini, Paolo; Leonov, Vladimir; Van Hoof, Chris

2009-09-01

This paper presents the material characterization methods, characterization results and the optimization scheme for polycrystalline Si70%Ge30% (poly-SiGe) from the perspective of its application in a surface micromachined thermopile. Due to its comparative advantages, such as lower thermal conductivity and ease of processing, over other materials, poly-SiGe is chosen to fabricate a surface micromachined thermopile and eventually a wearable thermoelectric generator (TEG) to be used on a human body. To enable optimal design of advanced thermocouple microstructures, poly-SiGe sample materials prepared by two different techniques, namely low-pressure chemical vapor deposition (LPCVD) with in situ doping and rapid thermal chemical vapor deposition (RTCVD) with ion implantation, have been characterized. Relevant material properties, including electrical resistivity, Seebeck coefficient, thermal conductivity and specific contact resistance, have been reported. For the determination of thermal conductivity, a novel surface-micromachined test structure based on the Seebeck effect is designed, fabricated and measured. Compared to the traditional test structures, it is more advantageous for sample materials with a relatively large Seebeck coefficient, such as poly-SiGe. Based on the characterization results, a further optimization scheme is suggested to allow independent respective optimization of the figure of merit and the specific contact resistance.

Thermoelectric Properties of High-Doped Silicon from Room Temperature to 900 K

NASA Astrophysics Data System (ADS)

Stranz, A.; Kähler, J.; Waag, A.; Peiner, E.

2013-07-01

Silicon is investigated as a low-cost, Earth-abundant thermoelectric material for high-temperature applications up to 900 K. For the calculation of module design the Seebeck coefficient and the electrical as well as thermal properties of silicon in the high-temperature range are of great importance. In this study, we evaluate the thermoelectric properties of low-, medium-, and high-doped silicon from room temperature to 900 K. In so doing, the Seebeck coefficient, the electrical and thermal conductivities, as well as the resulting figure of merit ZT of silicon are determined.

Thermal Cycling of Thin and Thick Ply Composites

NASA Technical Reports Server (NTRS)

Tompkins, Stephen S.; Shen, James Y.; Lavoie, Andre J.

1994-01-01

An experimental study was conducted to determine the effects of ply thickness in composite laminates on thermally induced cracking and changes in the coefficient of thermal expansion (CTE). After a few thermal cycles, laminates with thick-plies cracked, resulting in large changes in CTE. CTE's of the thin-ply laminates were unaffected by microcracking during the first 500 thermal cycles, whereas, the CTE's of the thick-ply laminates changed significantly. After about 1500 cycles, microdamage had also reduced the CTE of the thin-ply laminates to a value of about half of their initial value.

Development of fly ash boards with thermal, acoustic and fire insulation properties.

PubMed

Leiva, C; Arenas, C; Vilches, L F; Alonso-Fariñas, B; Rodriguez-Galán, M

2015-12-01

This paper presents an experimental analysis on a new board composed of gypsum and fly ashes from coal combustion, which are mutually compatible. Physical and mechanical properties, sound absorption coefficient, thermal properties and leaching test have been obtained. The mechanical properties showed similar values to other commercial products. As far as the acoustic insulation characteristics are concerned, sound absorption coefficients of 0.3 and 0.8 were found. The board presents a low thermal conductivity and a fire resistance higher than 50 min (for 4 cm of thickness). The leaching of trace elements was below the leaching limit values. These boards can be considered as suitable to be used in building applications as partitions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Effect of Greenhouse Gases Dissolved in Seawater

PubMed Central

Matsunaga, Shigeki

2015-01-01

A molecular dynamics simulation has been performed on the greenhouse gases carbon dioxide and methane dissolved in a sodium chloride aqueous solution, as a simple model of seawater. A carbon dioxide molecule is also treated as a hydrogen carbonate ion. The structure, coordination number, diffusion coefficient, shear viscosity, specific heat, and thermal conductivity of the solutions have been discussed. The anomalous behaviors of these properties, especially the negative pressure dependence of thermal conductivity, have been observed in the higher-pressure region. PMID:26729101

Determination of thermal contact conductance in vacuum-bagged thermoplastic prepreg stacks using infrared thermography

NASA Astrophysics Data System (ADS)

Baumard, Théo; De Almeida, Olivier; Menary, Gary; Le Maoult, Yannick; Schmidt, Fabrice; Bikard, Jérôme

2016-10-01

The infrared heating of a vacuum-bagged, thermoplastic prepreg stack of glass/PA66 was studied to investigate the influence of vacuum level on thermal contact resistance between plies. A higher vacuum level was shown experimentally to decrease the transverse heat transfer efficiency, indicating that considering only the effect of heat conduction at the plies interfaces is not sufficient to predict the temperature distribution. An inverse analysis was used to retrieve the contact resistance coefficients as a function of vacuum pressure.

Mathematical Modeling of Ultraporous Nonmetallic Reticulated Materials

NASA Astrophysics Data System (ADS)

Alifanov, O. M.; Cherepanov, V. V.; Morzhukhina, A. V.

2015-01-01

We have developed an imitation statistical mathematical model reflecting the structure and the thermal, electrophysical, and optical properties of nonmetallic ultraporous reticulated materials. This model, in combination with a nonstationary thermal experiment and methods of the theory of inverse heat transfer problems, permits determining the little-studied characteristics of the above materials such as the radiative and conductive heat conductivities, the spectral scattering and absorption coefficients, the scattering indicatrix, and the dielectric constants, which are of great practical interest but are difficult to investigate.

Effect of Greenhouse Gases Dissolved in Seawater.

PubMed

Matsunaga, Shigeki

2015-12-30

A molecular dynamics simulation has been performed on the greenhouse gases carbon dioxide and methane dissolved in a sodium chloride aqueous solution, as a simple model of seawater. A carbon dioxide molecule is also treated as a hydrogen carbonate ion. The structure, coordination number, diffusion coefficient, shear viscosity, specific heat, and thermal conductivity of the solutions have been discussed. The anomalous behaviors of these properties, especially the negative pressure dependence of thermal conductivity, have been observed in the higher-pressure region.

Thermoelectric Properties of Cu-doped Bi2-xSbxTe3 Prepared by Encapsulated Melting and Hot Pressing

NASA Astrophysics Data System (ADS)

Jung, Woo-Jin; Kim, Il-Ho

2018-03-01

P-type Bi2-xSbxTe3:Cum (x = 1.5-1.7 and m = 0.002-0.003) solid solutions were synthesized using encapsulated melting and were consolidated using hot pressing. The effects of Sb substitution and Cu doping on the charge transport and thermoelectric properties were examined. The lattice constants decreased with increasing Sb and Cu contents. As the amount of Sb substitution and Cu doping was increased, the electrical conductivity increased, and the Seebeck coefficient decreased owing to the increase in the carrier concentration. All specimens exhibited degenerate semiconductor characteristics and positive Hall and Seebeck coefficients, indicating p-type conduction. The increased Sb substitution caused a shift in the onset temperature of the intrinsic transition and bipolar conduction to higher temperatures. The electronic thermal conductivity increased with increasing Sb and Cu contents owing to the increase in the carrier concentration, while the lattice thermal conductivity slightly decreased due to alloy scattering. A maximum figure of merit, ZTmax = 1.25, was achieved at 373 K for Bi0.4Sb1.6Te3:Cu0.003.

Fluid property measurements study

NASA Technical Reports Server (NTRS)

Devaney, W. E.

1976-01-01

Fluid properties of refrigerant-21 were investigated at temperatures from the freezing point to 423 Kelvin and at pressures to 1.38 x 10 to the 8th power N/sq m (20,000 psia). The fluid properties included were: density, vapor pressure, viscosity, specific heat, thermal conductivity, thermal expansion coefficient, freezing point and bulk modulus. Tables of smooth values are reported.

Effects of Doping on Thermal Conductivity of Pyrochlore Oxides for Advanced Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Zhu, Dongming; Eslamloo-Grami, Maryam

2006-01-01

Pyrochlore oxides of general composition, A2B2O7, where A is a 3(+) cation (La to Lu) and B is a 4(+) cation (Zr, Hf, Ti, etc.) have high melting point, relatively high coefficient of thermal expansion, and low thermal conductivity which make them suitable for applications as high-temperature thermal barrier coatings. The effect of doping at the A site on the thermal conductivity of a pyrochlore oxide La2Zr2O7, has been investigated. Oxide powders of various compositions La2Zr2O7, La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 were synthesized by the citric acid sol-gel method. These powders were hot pressed into discs and used for thermal conductivity measurements using a steady-state laser heat flux test technique. The rare earth oxide doped pyrochlores La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 had lower thermal conductivity than the un-doped La2Zr2O7. The Gd2O3 and Yb2O3 co-doped composition showed the lowest thermal conductivity.

Influential factors on thermoacoustic efficiency of multilayered graphene film loudspeakers for optimal design

NASA Astrophysics Data System (ADS)

Xing, Qianhe; Li, Shuang; Fan, Xueliang; Bian, Anhua; Cao, Shi-Jie; Li, Cheng

2017-09-01

Graphene thermoacoustic loudspeakers, composed of a graphene film on a substrate, generate sound with heat. Improving thermoacoustic efficiency of graphene speakers is a goal for optimal design. In this work, we first modified the existing TA model with respect to small thermal wavelengths, and then built an acoustic platform for model validation. Additionally, sensitivity analyses for influential factors on thermoacoustic efficiency were performed, including the thickness of multilayered graphene films, the thermal effusivity of substrates, and the characteristics of inserted gases. The higher sensitivity coefficients result in the stronger effects on thermoacoustic efficiency. We find that the thickness (5 nm-15 nm) of graphene films plays a trivial role in efficiency, resulting in the sensitivity coefficient less than 0.02. The substrate thermal effusivity, however, has significant effects on efficiency, with the sensitivity coefficient around 1.7. Moreover, substrates with a lower thermal effusivity show better acoustic performances. For influences of ambient gases, the sensitivity coefficients of density ρg, thermal conductivity κg, and specific heat cp,g are 2.7, 0.98, and 0.8, respectively. Furthermore, large magnitudes of both ρg and κg lead to a higher efficiency and the sound pressure level generated by graphene films is approximately proportional to the inverse of cp,g. These findings can refer to the optimal design for graphene thermoacoustic speakers.

Adaptive Green-Kubo estimates of transport coefficients from molecular dynamics based on robust error analysis.

PubMed

Jones, Reese E; Mandadapu, Kranthi K

2012-04-21

We present a rigorous Green-Kubo methodology for calculating transport coefficients based on on-the-fly estimates of: (a) statistical stationarity of the relevant process, and (b) error in the resulting coefficient. The methodology uses time samples efficiently across an ensemble of parallel replicas to yield accurate estimates, which is particularly useful for estimating the thermal conductivity of semi-conductors near their Debye temperatures where the characteristic decay times of the heat flux correlation functions are large. Employing and extending the error analysis of Zwanzig and Ailawadi [Phys. Rev. 182, 280 (1969)] and Frenkel [in Proceedings of the International School of Physics "Enrico Fermi", Course LXXV (North-Holland Publishing Company, Amsterdam, 1980)] to the integral of correlation, we are able to provide tight theoretical bounds for the error in the estimate of the transport coefficient. To demonstrate the performance of the method, four test cases of increasing computational cost and complexity are presented: the viscosity of Ar and water, and the thermal conductivity of Si and GaN. In addition to producing accurate estimates of the transport coefficients for these materials, this work demonstrates precise agreement of the computed variances in the estimates of the correlation and the transport coefficient with the extended theory based on the assumption that fluctuations follow a Gaussian process. The proposed algorithm in conjunction with the extended theory enables the calculation of transport coefficients with the Green-Kubo method accurately and efficiently.

Adaptive Green-Kubo estimates of transport coefficients from molecular dynamics based on robust error analysis

NASA Astrophysics Data System (ADS)

Jones, Reese E.; Mandadapu, Kranthi K.

2012-04-01

We present a rigorous Green-Kubo methodology for calculating transport coefficients based on on-the-fly estimates of: (a) statistical stationarity of the relevant process, and (b) error in the resulting coefficient. The methodology uses time samples efficiently across an ensemble of parallel replicas to yield accurate estimates, which is particularly useful for estimating the thermal conductivity of semi-conductors near their Debye temperatures where the characteristic decay times of the heat flux correlation functions are large. Employing and extending the error analysis of Zwanzig and Ailawadi [Phys. Rev. 182, 280 (1969)], 10.1103/PhysRev.182.280 and Frenkel [in Proceedings of the International School of Physics "Enrico Fermi", Course LXXV (North-Holland Publishing Company, Amsterdam, 1980)] to the integral of correlation, we are able to provide tight theoretical bounds for the error in the estimate of the transport coefficient. To demonstrate the performance of the method, four test cases of increasing computational cost and complexity are presented: the viscosity of Ar and water, and the thermal conductivity of Si and GaN. In addition to producing accurate estimates of the transport coefficients for these materials, this work demonstrates precise agreement of the computed variances in the estimates of the correlation and the transport coefficient with the extended theory based on the assumption that fluctuations follow a Gaussian process. The proposed algorithm in conjunction with the extended theory enables the calculation of transport coefficients with the Green-Kubo method accurately and efficiently.

Nanoscale Thermoelectrics: A Study of the Absolute Seebeck Coefficient of Thin Films

NASA Astrophysics Data System (ADS)

Mason, Sarah J.

The worlds demand for energy is ever increasing. Likewise, the environmental impact of climate change due generating that energy through combustion of fossil fuels is increasingly alarming. Due to these factors new sources of renewable energies are constantly being sought out. Thermoelectric devices have the ability to generate clean, renewable, energy out of waste heat. However promising that is, their inefficiency severely inhibits applicability and practical use. The usefulness of a thermoelectric material increases with the dimensionless quantity, ZT, which depends on the Seebeck coefficient and electrical and thermal conductivity. These characteristic material parameters have interdependent energy transport contributions that classically prohibit the optimization of one with out the detriment of another. Encouraging advancements of ZT have occurred in the past ten years due to the decoupling of the thermal and electrical conductivity. Further advancements are necessary in order to produce applicable devices. One auspicious way of decoupling or tuning energy transport properties, is through size reduction to the nanoscale. However, with reduced dimensions come complications in measuring material properties. Measurements of properties such as the Seebeck coefficient, S, are primarily contingent upon the measurement apparatus. The Seebeck coefficient is defined as the amount of voltage generated by a thermal gradient. Measuring a thermally generated voltage by traditional methods gives, the voltage measured as a linear function of the Seebeck coefficient of the leads and of the material being tested divided by the applied thermal gradient. If accurate values of the Seebeck coefficients of the leads are available, simple subtraction provides the answer. This is rarely the case in nanoscale measurement devices with leads exclusively made from thin film materials that do not have well known bulk-like thermopower values. We have developed a technique to directly measure, S, as a function of temperature using a micro-machined thermal isolation platform consisting of a suspended, patterned SiN membrane. By measuring a series of thicknesses of metallic films up to the infinitely thin film limit, in which the electrical resistivity is no longer decreasing with increasing film thickness, but still not at bulk values, along with the effective electron mean free path, we are able to show the contribution of the leads needed to measure this property. Having a comprehensive understanding of the background contribution we are able to determine the absolute Seebeck coefficient of a wide variety of thin films. The nature of the design of the SiN membrane also allows the ability to accurately and directly measure thermal and electrical transport of the thin films yielding a comprehensive measurement of the three quantities that characterize a material's efficiency. This can serve to further the development of thermoelectric materials through precise measurements of the material properties that dictate efficiency.

Effect of aerated concrete blockwork joints on the heat transfer performance uniformity

NASA Astrophysics Data System (ADS)

Pukhkal, Viktor; Murgul, Vera

2018-03-01

Analysis of data on the effect of joints of the aerated concrete blocks on the heat transfer uniformity of exterior walls was carried out. It was concluded, that the values of the heat transfer performance uniformity factor in the literature sources were obtained for the regular fragment of a wall construction by approximate addition of thermal conductivities. Heat flow patterns for the aerated concrete exterior walls amid different values of the thermal conductivity factors and design ambient air temperature of -26 °C were calculated with the use of "ELCUT" software for modelling of thermal patterns by finite element method. There were defined the values for the heat transfer performance uniformity factor, reduced total thermal resistance and heat-flux density for the exterior walls. The calculated values of the heat transfer performance uniformity factors, as a function of the coefficient of thermal conductivity of aerated concrete blocks, differ from the known data by a more rigorous thermal and physical substantiation.

Optimizing Thermoelectric Properties of In Situ Plasma-Spray-Synthesized Sub-stoichiometric TiO2-x Deposits

NASA Astrophysics Data System (ADS)

Lee, Hwasoo; Seshadri, Ramachandran Chidambaram; Pala, Zdenek; Sampath, Sanjay

2018-06-01

In this article, an attempt has been made to relate the thermoelectric properties of thermal spray deposits of sub-stoichiometric titania to process-induced phase and microstructural variances. The TiO2-x deposits were formed through the in situ reaction of the TiO1.9 or TiO1.7 feedstock within the high-temperature plasma flame and manipulated via varying the amounts of hydrogen fed into in the thermal plasma. Changes in the flow rates of H2 in the plasma plume greatly affected the in-flight particle behavior and composition of the deposits. For reference, a high-velocity oxy-fuel spray torch was also used to deposit the two varieties of feedstocks. Refinements to the representation of the in-flight particle characteristics derived via single particle and ensemble diagnostic methods are proposed using the group parameters (melting index and kinetic energy). The results show that depending on the value of the melting index, there is an inverse proportional relationship between electrical conductivity and Seebeck coefficient, whereas thermal conductivity has a directly proportional relationship with the electrical conductivity. Retention of the original phase and reduced decomposition is beneficial to retain the high Seebeck coefficient or the high electrical conductivity in the TiO2 system.

Fluctuation-enhanced electric conductivity in electrolyte solutions.

PubMed

Péraud, Jean-Philippe; Nonaka, Andrew J; Bell, John B; Donev, Aleksandar; Garcia, Alejandro L

2017-10-10

We analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson-Nernst-Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation-anion diffusion coefficient. Specifically, we predict a nonzero cation-anion Maxwell-Stefan coefficient proportional to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye-Huckel-Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Finally, we show that strong applied electric fields result in anisotropically enhanced "giant" velocity fluctuations and reduced fluctuations of salt concentration.

Fluctuation-enhanced electric conductivity in electrolyte solutions

PubMed Central

Péraud, Jean-Philippe; Nonaka, Andrew J.; Bell, John B.; Donev, Aleksandar; Garcia, Alejandro L.

2017-01-01

We analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson–Nernst–Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation–anion diffusion coefficient. Specifically, we predict a nonzero cation–anion Maxwell–Stefan coefficient proportional to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye–Huckel–Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Finally, we show that strong applied electric fields result in anisotropically enhanced “giant” velocity fluctuations and reduced fluctuations of salt concentration. PMID:28973890

Polarized Light Scanning Cryomacroscopy, Part II: Thermal Modeling and Analysis of Experimental Observations

PubMed Central

Feig, Justin S.G.; Solanki, Prem K.; Eisenberg, David P.; Rabin, Yoed

2016-01-01

This study aims at developing thermal analysis tools and explaining experimental observations made by means of polarized-light cryomacroscopy (Part I). Thermal modeling is based on finite elements analysis (FEA), where two model parameters are extracted from thermal measurements: (i) the overall heat transfer coefficient between the cuvette and the cooling chamber, and (ii) the effective thermal conductivity within the cryoprotective agent (CPA) at the upper part of the cryogenic temperature range. The effective thermal conductivity takes into account enhanced heat transfer due to convection currents within the CPA, creating the so-called Bénard cells. Comparison of experimental results with simulation data indicates that the uncertainty in simulations due to the propagation of uncertainty in measured physical properties exceeds the uncertainty in experimental measurements, which validates the modeling approach. It is shown in this study that while a cavity may form in the upper-center portion of the vitrified CPA, it has very little effect on estimating the temperature distribution within the domain. This cavity is driven by thermal contraction of the CPA, with the upper-center of the domain transitioning to glass last. Finally, it is demonstrated in this study that additional stresses may develop within the glass transition temperature range due to nonlinear behavior of the thermal expansion coefficient. This effect is reported here for the first time in the context of cryobiology, using the capabilities of polarized-light cryomacroscopy. PMID:27343139

Polarized light scanning cryomacroscopy, part II: Thermal modeling and analysis of experimental observations.

PubMed

Feig, Justin S G; Solanki, Prem K; Eisenberg, David P; Rabin, Yoed

2016-10-01

This study aims at developing thermal analysis tools and explaining experimental observations made by means of polarized-light cryomacroscopy (Part I). Thermal modeling is based on finite elements analysis (FEA), where two model parameters are extracted from thermal measurements: (i) the overall heat transfer coefficient between the cuvette and the cooling chamber, and (ii) the effective thermal conductivity within the cryoprotective agent (CPA) at the upper part of the cryogenic temperature range. The effective thermal conductivity takes into account enhanced heat transfer due to convection currents within the CPA, creating the so-called Bénard cells. Comparison of experimental results with simulation data indicates that the uncertainty in simulations due to the propagation of uncertainty in measured physical properties exceeds the uncertainty in experimental measurements, which validates the modeling approach. It is shown in this study that while a cavity may form in the upper-center portion of the vitrified CPA, it has very little effect on estimating the temperature distribution within the domain. This cavity is driven by thermal contraction of the CPA, with the upper-center of the domain transitioning to glass last. Finally, it is demonstrated in this study that additional stresses may develop within the glass transition temperature range due to nonlinear behavior of the thermal expansion coefficient. This effect is reported here for the first time in the context of cryobiology, using the capabilities of polarized-light cryomacroscopy. Copyright © 2016. Published by Elsevier Inc.

Crack propagation in functionally graded strip under thermal shock

NASA Astrophysics Data System (ADS)

Ivanov, I. V.; Sadowski, T.; Pietras, D.

2013-09-01

The thermal shock problem in a strip made of functionally graded composite with an interpenetrating network micro-structure of Al2O3 and Al is analysed numerically. The material considered here could be used in brake disks or cylinder liners. In both applications it is subjected to thermal shock. The description of the position-dependent properties of the considered functionally graded material are based on experimental data. Continuous functions were constructed for the Young's modulus, thermal expansion coefficient, thermal conductivity and thermal diffusivity and implemented as user-defined material properties in user-defined subroutines of the commercial finite element software ABAQUS™. The thermal stress and the residual stress of the manufacturing process distributions inside the strip are considered. The solution of the transient heat conduction problem for thermal shock is used for crack propagation simulation using the XFEM method. The crack length developed during the thermal shock is the criterion for crack resistance of the different graduation profiles as a step towards optimization of the composition gradient with respect to thermal shock sensitivity.

Electronic transport coefficients from ab initio simulations and application to dense liquid hydrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holst, Bastian; French, Martin; Redmer, Ronald

2011-06-15

Using Kubo's linear response theory, we derive expressions for the frequency-dependent electrical conductivity (Kubo-Greenwood formula), thermopower, and thermal conductivity in a strongly correlated electron system. These are evaluated within ab initio molecular dynamics simulations in order to study the thermoelectric transport coefficients in dense liquid hydrogen, especially near the nonmetal-to-metal transition region. We also observe significant deviations from the widely used Wiedemann-Franz law, which is strictly valid only for degenerate systems, and give an estimate for its valid scope of application toward lower densities.

An Initial Non-Equilibrium Porous-Media Model for CFD Simulation of Stirling Regenerators

NASA Technical Reports Server (NTRS)

Tew, Roy C.; Simon, Terry; Gedeon, David; Ibrahim, Mounir; Rong, Wei

2006-01-01

The objective of this paper is to define empirical parameters for an initial thermal non-equilibrium porous-media model for use in Computational Fluid Dynamics (CFD) codes for simulation of Stirling regenerators. The two codes currently used at Glenn Research Center for Stirling modeling are Fluent and CFD-ACE. The codes porous-media models are equilibrium models, which assume solid matrix and fluid are in thermal equilibrium. This is believed to be a poor assumption for Stirling regenerators; Stirling 1-D regenerator models, used in Stirling design, use non-equilibrium regenerator models and suggest regenerator matrix and gas average temperatures can differ by several degrees at a given axial location and time during the cycle. Experimentally based information was used to define: hydrodynamic dispersion, permeability, inertial coefficient, fluid effective thermal conductivity, and fluid-solid heat transfer coefficient. Solid effective thermal conductivity was also estimated. Determination of model parameters was based on planned use in a CFD model of Infinia's Stirling Technology Demonstration Converter (TDC), which uses a random-fiber regenerator matrix. Emphasis is on use of available data to define empirical parameters needed in a thermal non-equilibrium porous media model for Stirling regenerator simulation. Such a model has not yet been implemented by the authors or their associates.

Acousto-mechanical and thermal properties of clotted blooda)

PubMed Central

Nahirnyak, Volodymyr M.; Yoon, Suk Wang; Holland, Christy K.

2007-01-01

The efficacy of ultrasound-assisted thrombolysis as an adjunct treatment of ischemic stroke is being widely investigated. To determine the role of ultrasound hyperthermia in the process of blood clot disruption, the acousto-mechanical and thermal properties of clotted blood were measured in vitro, namely, density, speed of sound, frequency-dependent attenuation, specific heat, and thermal conductivity. The amplitude coefficient of attenuation of the clots was determined for 120 kHz, 1.0 MHz, and 3.5 MHz ultrasound at room temperature (20±2 °C). The attenuation coefficient ranged from 0.10 to 0.30 Np/cm in porcine clots and from 0.09 to 0.23 Np/cm in human clots. The experimentally determined values of specific heat and thermal conductivity for porcine clotted blood are (3.2±0.5)×103 J/kg·K and 0.55±0.13 W/m·K, respectively, and for human clotted blood are (3.5±0.8)×103 J/kg·K and 0.59±0.11 W/m·K, respectively. Measurements of the acousto-mechanical and thermal properties of clotted blood can be helpful in theoretical modeling of ultrasound hyperthermia in ultrasound-assisted thrombolysis and other high-intensity focused ultrasound applications. PMID:16838520

Effects of Mn Substitution on the Thermoelectric Properties and Thermal Excitations of the Electron-doped Perovskite Sr1-xLaxTiO3

NASA Astrophysics Data System (ADS)

Okuda, Tetsuji; Hata, Hiroto; Eto, Takahiro; Sobaru, Shogo; Oda, Ryosuke; Kaji, Hiroki; Nishina, Kousuke; Kuwahara, Hideki; Nakamura, Mitsutaka; Kajimoto, Ryoichi

2016-09-01

We studied how Mn substitution affects the thermoelectric properties and thermal excitations of the electron-doped perovskite Sr1-xLaxTiO3 by measuring its electrical and thermal transport properties, magnetization, specific heat, and inelastic neutron scattering. Slight Mn substitution with the lattice defects enhanced the Seebeck coefficient, perhaps because of coupling between itinerant electrons and localized spins or between itinerant electrons and local lattice distortion around Mn3+ ions, while it enhanced anharmonic lattice vibrations, which effectively suppressed thermal conductivity in a state of high electrical conductivity. Consequently, slight Mn substitution increased the dimensionless thermoelectric figure of merit for Sr1-xLaxTiO3 near room temperature.

Effective Thermal Conductivity of High Porosity Open Cell Nickel Foam

NASA Technical Reports Server (NTRS)

Sullins, Alan D.; Daryabeigi, Kamran

2001-01-01

The effective thermal conductivity of high-porosity open cell nickel foam samples was measured over a wide range of temperatures and pressures using a standard steady-state technique. The samples, measuring 23.8 mm, 18.7 mm, and 13.6 mm in thickness, were constructed with layers of 1.7 mm thick foam with a porosity of 0.968. Tests were conducted with the specimens subjected to temperature differences of 100 to 1000 K across the thickness and at environmental pressures of 10(exp -4) to 750 mm Hg. All test were conducted in a gaseous nitrogen environment. A one-dimensional finite volume numerical model was developed to model combined radiation/conduction heat transfer in the foam. The radiation heat transfer was modeled using the two-flux approximation. Solid and gas conduction were modeled using standard techniques for high porosity media. A parameter estimation technique was used in conjunction with the measured and predicted thermal conductivities at pressures of 10(exp -4) and 750 mm Hg to determine the extinction coefficient, albedo of scattering, and weighting factors for modeling the conduction thermal conductivity. The measured and predicted conductivities over the intermediate pressure values differed by 13%.

A Model to Couple Flow, Thermal and Reactive Chemical Transport, and Geo-mechanics in Variably Saturated Media

NASA Astrophysics Data System (ADS)

Yeh, G. T.; Tsai, C. H.

2015-12-01

This paper presents the development of a THMC (thermal-hydrology-mechanics-chemistry) process model in variably saturated media. The governing equations for variably saturated flow and reactive chemical transport are obtained based on the mass conservation principle of species transport supplemented with Darcy's law, constraint of species concentration, equation of states, and constitutive law of K-S-P (Conductivity-Degree of Saturation-Capillary Pressure). The thermal transport equation is obtained based on the conservation of energy. The geo-mechanic displacement is obtained based on the assumption of equilibrium. Conventionally, these equations have been implicitly coupled via the calculations of secondary variables based on primary variables. The mechanisms of coupling have not been obvious. In this paper, governing equations are explicitly coupled for all primary variables. The coupling is accomplished via the storage coefficients, transporting velocities, and conduction-dispersion-diffusion coefficient tensor; one set each for every primary variable. With this new system of equations, the coupling mechanisms become clear. Physical interpretations of every term in the coupled equations will be discussed. Examples will be employed to demonstrate the intuition and superiority of these explicit coupling approaches. Keywords: Variably Saturated Flow, Thermal Transport, Geo-mechanics, Reactive Transport.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nieroda, Pawel; Zybala, Rafal; Wojciechowski, Krzysztof T.

The aim of the study was to develop a fast and simple method for preparation of polycrystalline Mg{sub 2}Si. For this purpose a Spark Plasma Sintering (SPS) method was used and synthesis conditions were adjusted in such a manner that no excess Mg was required. Materials were synthesized by the direct reaction of Mg and Si raw powders. To determine the phase and chemical composition, the fabricated samples were studied by X-ray diffraction and SEM microscopy coupled with EDX chemical analysis. Thermoelectric properties of samples (thermal conductivity, electrical conductivity and Seebeck coefficient) were measured all over temperature range of 300-650more » K. The analysis by the scanning thermoelectric microprobe (STM) shows that samples have uniform distribution of Seebeck coefficient with mean value of about -405 {mu}VK{sup -1} and standard deviation of 94 {mu}VK{sup -1}. Prepared materials have intrinsic band gap of 0.45 eV and thermal conductivity {lambda}= 7.5 Wm{sup -1}K{sup -1} at room temperature.« less

Plasmachemical synthesis and evaluation of the thermal conductivity of metal-oxide compounds "Molybdenum-uranium dioxide"

NASA Astrophysics Data System (ADS)

Kotelnikova, Alexandra A.; Karengin, Alexander G.; Mendoza, Orlando

2018-03-01

The article represents possibility to apply oxidative and reducing plasma for plasma-chemical synthesis of metal-oxide compounds «Mo‒UO2» from water-salt mixtures «molybdic acid‒uranyl nitrate» and «molybdic acid‒ uranyl acetate». The composition of water-salt mixture was calculated and the conditions ensuring plasma-chemical synthesis of «Mo‒UO2» compounds were determined. Calculations were carried out at atmospheric pressure over a wide range of temperatures (300-4000 K), with the use of various plasma coolants (air, hydrogen). The heat conductivity coefficients of metal-oxide compounds «Mo‒UO2» consisting of continuous component (molybdenum matrix) are calculated. Inclusions from ceramics in the form of uranium dioxide were ordered in the matrix. Particular attention is paid to methods for calculating the coefficients of thermal conductivity of these compounds with the use of different models. Calculated results were compared with the experimental data.

Definition of the Mathematical Model Coefficients on the Weld Size of Butt Joint Without Edge Preparation

NASA Astrophysics Data System (ADS)

Sidorov, Vladimir P.; Melzitdinova, Anna V.

2017-10-01

This paper represents the definition methods for thermal constants according to the data of the weld width under the normal-circular heat source. The method is based on isoline contouring of “effective power - temperature conductivity coefficient”. The definition of coefficients provides setting requirements to the precision of welding parameters support with the enough accuracy for an engineering practice.

Nanofluids Containing γ-Fe2O3 Nanoparticles and Their Heat Transfer Enhancements

NASA Astrophysics Data System (ADS)

Guo, Shou-Zhu; Li, Yang; Jiang, Ji-Sen; Xie, Hua-Qing

2010-07-01

Homogeneous and stable magnetic nanofluids containing γ-Fe2O3 nanoparticles were prepared using a two-step method, and their thermal transport properties were investigated. Thermal conductivities of the nanofluids were measured to be higher than that of base fluid, and the enhanced values increase with the volume fraction of the nanoparticles. Viscosity measurements showed that the nanofluids demonstrated Newtonian behavior and the viscosity of the nanofluids depended strongly on the tested temperatures and the nanoparticles loadings. Convective heat transfer coefficients tested in a laminar flow showed that the coefficients increased with the augment of Reynolds number and the volume fraction.

Stepwise and Pulse Transient Methods of Thermophysical Parameters Measurement

NASA Astrophysics Data System (ADS)

Malinarič, Svetozár; Dieška, Peter

2016-12-01

Stepwise transient and pulse transient methods are experimental techniques for measuring the thermal diffusivity and conductivity of solid materials. Theoretical models and experimental apparatus are presented, and the influence of the heat source capacity and the heat transfer coefficient is investigated using the experiment simulation. The specimens from low-density polyethylene (LDPE) and polymethylmethacrylate (PMMA) were measured by both methods. Coefficients of variation were better than 0.9 % for LDPE and 2.8 % for PMMA measurements. The time dependence of the temperature response to the input heat flux showed a small drop, which was caused by thermoelastic wave generated by thermal expansions of the heat source.

Kapitza thermal resistance studied by high-frequency photothermal radiometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horny, Nicolas; Chirtoc, Mihai; Hamaoui, Georges

2016-07-18

Kapitza thermal resistance is determined using high-frequency photothermal radiometry (PTR) extended for modulation up to 10 MHz. Interfaces between 50 nm thick titanium coatings and silicon or stainless steel substrates are studied. In the used configuration, the PTR signal is not sensitive to the thermal conductivity of the film nor to its optical absorption coefficient, thus the Kapitza resistance is directly determined from single thermal parameter fits. Results of thermal resistances show the significant influence of the nature of the substrate, as well as of the presence of free electrons at the interface.

Thermal Cycling of Thin and Thick Ply Composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tompkins, S.S.; Shen, J.Y.; Lavoie, A.J.

1994-01-01

An experimental study was conducted to determine the effects of ply thickness in composite laminates on thermally induced cracking and changes in the coefficient of thermal expansion (CTE). After a few thermal cycles, laminates with thick-plies cracked, resulting in large changes in CTE. CTE`s of the thin-ply laminates were unaffected by microcracking during the first 500 thermal cycles, whereas, the CTE`s of the thick-ply laminates changed significantly. After about 1500 cycles, microdamage had also reduced the CTE of the thin-ply laminates to a value of about half of their initial value.

Electronic thermal transport in strongly correlated multilayered nanostructures

NASA Astrophysics Data System (ADS)

Freericks, J. K.; Zlatić, V.; Shvaika, A. M.

2007-01-01

The formalism for a linear-response many-body treatment of the electronic contributions to thermal transport is developed for multilayered nanostructures. By properly determining the local heat-current operator, it is possible to show that the Jonson-Mahan theorem for the bulk can be extended to inhomogeneous problems, so the various thermal-transport coefficient integrands are related by powers of frequency (including all effects of vertex corrections when appropriate). We illustrate how to use this formalism by showing how it applies to measurements of the Peltier effect, the Seebeck effect, and the thermal conductance.

Experimental Investigation on Thermal Physical Properties of an Advanced Polyester Material

NASA Astrophysics Data System (ADS)

Guangfa, Gao; Shujie, Yuan; Ruiyuan, Huang; Yongchi, Li

Polyester materials were applied widely in aircraft and space vehicles engineering. Aimed to an advanced polyester material, a series of experiments for thermal physical properties of this material were conducted, and the corresponding performance curves were obtained through statistic analyzing. The experimental results showed good consistency. And then the thermal physical parameters such as thermal expansion coefficient, engineering specific heat and sublimation heat were solved and calculated. This investigation provides an important foundation for the further research on the heat resistance and thermodynamic performance of this material.

An optimization method for the problems of thermal cloaking of material bodies

NASA Astrophysics Data System (ADS)

Alekseev, G. V.; Levin, V. A.

2016-11-01

Inverse heat-transfer problems related to constructing special thermal devices such as cloaking shells, thermal-illusion or thermal-camouflage devices, and heat-flux concentrators are studied. The heatdiffusion equation with a variable heat-conductivity coefficient is used as the initial heat-transfer model. An optimization method is used to reduce the above inverse problems to the respective control problem. The solvability of the above control problem is proved, an optimality system that describes necessary extremum conditions is derived, and a numerical algorithm for solving the control problem is proposed.

Thermal Expansion Behavior of Hot-Pressed Engineered Matrices

NASA Technical Reports Server (NTRS)

Raj, S. V.

2016-01-01

Advanced engineered matrix composites (EMCs) require that the coefficient of thermal expansion (CTE) of the engineered matrix (EM) matches those of the fiber reinforcements as closely as possible in order to reduce thermal compatibility strains during heating and cooling of the composites. The present paper proposes a general concept for designing suitable matrices for long fiber reinforced composites using a rule of mixtures (ROM) approach to minimize the global differences in the thermal expansion mismatches between the fibers and the engineered matrix. Proof-of-concept studies were conducted to demonstrate the validity of the concept.

Synthetic thermoelectric materials comprising phononic crystals

DOEpatents

El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang

2013-08-13

Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heimann, Stefan; Schulz, Stephan; Schaumann, Julian

We report on the synthesis of Sb 2Te 3 nanoparticles with record-high figure of merit values of up to 1.5. The central thermoelectric parameters, electrical conductivity, thermal conductivity and Seebeck coefficient, were independently optimized. Critical influence of porosity for the fabrication of highly efficient thermoelectric materials is firstly demonstrated, giving a strong guidance for the optimization of other thermoelectric materials.

Numerical model of thermo-mechanical coupling for the tensile failure process of brittle materials

NASA Astrophysics Data System (ADS)

Fu, Yu; Wang, Zhe; Ren, Fengyu; Wang, Daguo

2017-10-01

A numerical model of thermal cracking with a thermo-mechanical coupling effect was established. The theory of tensile failure and heat conduction is used to study the tensile failure process of brittle materials, such as rock and concrete under high temperature environment. The validity of the model is verified by thick-wall cylinders with analytical solutions. The failure modes of brittle materials under thermal stresses caused by temperature gradient and different thermal expansion coefficient were studied by using a thick-wall cylinder model and an embedded particle model, respectively. In the thick-wall cylinder model, different forms of cracks induced by temperature gradient were obtained under different temperature boundary conditions. In the embedded particle model, radial cracks were produced in the medium part with lower tensile strength when temperature increased because of the different thermal expansion coefficient. Model results are in good agreement with the experimental results, thereby providing a new finite element method for analyzing the thermal damage process and mechanism of brittle materials.

Study of physical and sound absorbing property of epoxy blended coir dust biocomposite

NASA Astrophysics Data System (ADS)

Nath, G.; Mishra, S. P.

2016-09-01

Reinforcement biocomposite has gained more attention recently due to its low cost, abundantly availability, low density, specific properties, easy method of separation, enhanced energy recovery, CO2 neutrality, biodegradability and recyclable in nature. As a waste product of coconut fruit, the coconut coir dust (CCD) obtained from the coconut husk. The biocomposite material prepared from the CCD modified with the proper blended solution with the help of ultrasonic technique. The study of adiabatic compressibility of acetone / water (70/30) worth its blending property for bleaching of CCD. The biocomposite material of CCD was prepared with epoxy resin. The different physical properties such as sound absorption coefficient, thermal conductivity and electrical conductivity were measured. The morphological study of biocomposite and measurement of sound absorption coefficient shows good evidence of sound absorbing characteristics of biocomposite of CCD. The sound absorption property of composite material shows a significant result where as the thermal conductivity and electrical conductivity executes a weak result. Thus biocomposite of CCD can acts as a good sound absorber and band conductor of heat and electric current.

Transient plane source (tps) sensors for simultaneous measurements of thermal conductivity and thermal diffusivity of insulators, fluids and conductors

NASA Astrophysics Data System (ADS)

Maqsood, Asghari; Anis-ur-Rehman, M.

2013-12-01

Thermal conductivity and thermal diffusivity are two important physical properties for designing any food engineering processes1. The knowledge of thermal properties of the elements, compounds and different materials in many industrial applications is a requirement for their final functionality. Transient plane source (tps) sensors are reported2 to be useful for the simultaneous measurement of thermal conductivity, thermal diffusivity and volumetric heat capacity of insulators, conductor liquids3 and high-TC superconductors4. The tps-sensor consists of a resistive element in the shape of double spiral made of 10 micrometer thick Ni-foils covered on both sides with 25 micrometer thick Kapton. This sensor acts both as a heat source and a resistance thermometer for recording the time dependent temperature increase. From the knowledge of the temperature co-efficient of the metal spiral, the temperature increase of the sensor can be determined precisely by placing the sensor in between two surfaces of the same material under test. This temperature increase is then related to the thermal conductivity, thermal diffusivity and volumetric heat capacity by simple relations2,5. The tps-sensor has been used to measure thermal conductivities from 0.001 Wm-1K-1to 600 Wm-1K-1 and temperature ranges covered from 77K- 1000K. This talk gives the design, advantages and limitations of the tpl-sensor along with its applications to the measurementof thermal properties in a variety of materials.

Viscothermal Coupling Effects on Sound Attenuation in Concentrated Colloidal Dispersions.

NASA Astrophysics Data System (ADS)

Han, Wei

1995-11-01

This thesis describes a Unified Coupled Phase Continuum (UCPC) model to analyze sound propagation through aerosols, emulsions and suspensions in terms of frequency dependent attenuation coefficient and sound speed. Expressions for the viscous and thermal coupling coefficients explicitly account for the effects of particle size, shape factor, orientation as well as concentration and the sound frequency. The UCPC model also takes into account the intrinsic acoustic absorption within the fluid medium due to its viscosity and heat conductivity. The effective complex wave number as a function of frequency is derived. A frequency- and concentration-dependent complex Nusselt number for the interfacial thermal coupling coefficient is derived using an approximate similarity between the 'viscous skin drag' and 'heat conduction flux' associated with the discontinuous suspended phase, on the basis of a cell model. The theoretical predictions of attenuation spectra provide satisfactory agreement with reported experimental data on two concentrated suspensions (polystyrene latex and kaolin pigment), two concentrated emulsions (toluene -in-water, n-hexadecane-in-water), and two aerosols (oleic acid droplets-in-nitrogen, alumina-in-air), covering a wide range of relative magnitudes (from 10^ {-3} to 10^{3}) of thermal versus viscous contributions, for dispersed phase volume fractions as high as 50%. The relative differences between the additive result of separate viscous and thermal loss estimates and combined viscothermal absorption results are also presented. Effects of particle shape on viscous attenuation of sound in concentrated suspensions of non-spherical clay particles are studied. Attenuation spectra for 18 frequencies from 3 to 100 MHz are measured and analyzed for eleven kaolin clay slurries with solid concentrations ranging from 0.6% to 35% (w/w). A modified viscous drag coefficient that considers frequency, concentration, particle size, shape and orientation of spheroids, is developed and applied to estimate the viscous attenuation coefficients. With incorporation of particle size and shape distributions (PSSD), predictions agree quantitatively with observed attenuation coefficients. The effects of particle aspect ratio and orientation become more evident as particle concentrations and frequencies are increased. The UCPC model combined with the ultrasonic spectroscopy techniques can provide for theoretical and experimental frameworks in characterization of concentrated colloidal dispersions.

Thermodynamic properties and transport coefficients of air thermal plasmas mixed with ablated vapors of Cu and polytetrafluoroethylene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, JunMin, E-mail: jmzhang@buaa.edu.cn, E-mail: guanyg@tsinghua.edu.cn; Lu, ChunRong; Guan, YongGang, E-mail: jmzhang@buaa.edu.cn, E-mail: guanyg@tsinghua.edu.cn

2015-10-15

Because the fault arc in aircraft electrical system often causes a fire, it is particularly important to analyze its energy and transfer for aircraft safety. The calculation of arc energy requires the basic parameters of the arc. This paper is mainly devoted to the calculations of equilibrium composition, thermodynamic properties (density, molar weight, enthalpy, and specific heat at constant pressure) and transport coefficients (thermal conductivity, electrical conductivity, and viscosity) of plasmas produced by a mixture of air, Cu, and polytetrafluoroethylene under the condition of local thermodynamic equilibrium. The equilibrium composition is determined by solving a system of equations around themore » number densities of each species. The thermodynamic properties are obtained according to the standard thermodynamic relationships. The transport coefficients are calculated using the Chapman-Enskog approximations. Results are presented in the temperature range from 3000 to 30 000 K for pressures of 0.08 and 0.1 MPa, respectively. The results are more accurate and are reliable reference data for theoretical analysis and computational simulation of the behavior of fault arc.« less

Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion.

PubMed

Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S; Chen, Gang

2015-12-01

Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect--a coupling phenomenon between electrons and nonequilibrium phonons--in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼ 0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons.

Deposition and thermal characterization of nano-structured aluminum nitride thin film on Cu-W substrate for high power light emitting diode package.

PubMed

Cho, Hyun Min; Kim, Min-Sun

2014-08-01

In this study, we developed AlN thick film on metal substrate for hybrid type LED package such as chip on board (COB) using metal printed circuit board (PCB). Conventional metal PCB uses ceramic-polymer composite as electrical insulating layer. Thermal conductivities of such type dielectric film are typically in the range of 1~4 W/m · K depending on the ceramic filler. Also, Al or Cu alloy are mainly used for metal base for high thermal conduction to dissipate heat from thermal source mounted on metal PCB. Here we used Cu-W alloy with low thermal expansion coefficient as metal substrate to reduce thermal stress between insulating layer and base metal. AlN with polyimide (PI) powder were used as starting materials for deposition. We could obtain very high thermal conductivity of 28.3 W/m · K from deposited AlN-PI thin film by AlN-3 wt% PI powder. We made hybrid type high power LED package using AlN-PI thin film. We tested thermal performance of this film by thermal transient measurement and compared with conventional metal PCB substrate.

A simple method for characterizing and engineering thermal relaxation of an optical microcavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Weijian; Zhu, Jiangang; Özdemir, Şahin Kaya

2016-08-08

Thermal properties of a photonic resonator are determined not only by intrinsic properties of materials, such as thermo-optic coefficient, but also by the geometry and structure of the resonator. Techniques for characterization and measurement of thermal properties of individual photonic resonator will benefit numerous applications. In this work, we demonstrate a method to optically measure the thermal relaxation time and effective thermal conductance of a whispering gallery mode microcavity using optothermal effect. Two nearby optical modes within the cavity are optically probed, which allows us to quantify the thermal relaxation process of the cavity by analyzing changes in the transmissionmore » spectra induced by optothermal effect. We show that the effective thermal conductance can be experimentally deduced from the thermal relaxation measurement, and it can be tailored by changing the geometric parameters of the cavity. The experimental observations are in good agreement with the proposed analytical modeling. This method can be applied to various resonators in different forms.« less

Comparative study of the thermal properties of mud and peat solutions applied in clinical practice.

PubMed

Beer, A M; Grozeva, A; Sagorchev, P; Lukanov, J

2003-11-01

Different peloids as e.g. mud and peat have been traditionally used for therapeutic purposes successfully, especially of there thermal actions. It was the aim of the experimental study to compare the thermal properties of two peloids, mud and peat, with a view to assessing their thermal effects when they are applied in clinical practice. The studies were carried out using peat of the marsh type of peats (Hochmoor), and curative Pomorie (Bulgaria) mud. As important parameters were determined the specific thermal capacity at constant pressure (Cp), the density of solutions (rho), the cooling rate (m), the coefficient of temperature transfer (a) of solutions and the coefficient of thermal conductivity (lambda) of solutions of peat and curative mud, compared to water bath. The comparative studies of the thermal properties of water and water solutions of peat and curative mud show that the thermal effect of the water bath is substantially smaller than that of the peat and mud applications. This difference is due to a greater extent to the high values of the dynamic viscosity, not allowing cooling by convection and protecting the surface of the skin upon applications of peloid solutions with a higher temperature.

Achieving high thermoelectric performance of Cu1.8S composites with WSe2 nanoparticles.

PubMed

Qin, Peng; Ge, Zhen-Hua; Chen, Yue-Xing; Chong, Xiaoyu; Feng, Jing; He, Jiaqing

2018-08-24

Polycrystalline p-type Cu 1.8 S composites with WSe 2 nanoparticles were fabricated by the mechanical alloying method combined with the spark plasma sintering technique. The Seebeck coefficient was significantly enhanced by the optimized carrier concentration, while the thermal conductivity was simultaneously decreased due to the refined grain and WSe 2 nanoparticles. An enhanced Seebeck coefficient of 110 μV K -1 and a reduced thermal conductivity of 0.68 W m -1 K -1 were obtained for the Cu 1.8 S + 1 wt% WSe 2 sample at 773 K, resulting in a remarkably enhanced peak ZT of 1.22 at 773 K, which is 2.5 times higher than that (0.49 at 773 K) of a pristine Cu 1.8 S sample. The cheap and environmentally friendly Cu 1.8 S-based materials with enhanced properties may find promising applications in thermoelectric devices.

Evaluation of Temperature-Dependent Effective Material Properties and Performance of a Thermoelectric Module

NASA Astrophysics Data System (ADS)

Chien, Heng-Chieh; Chu, En-Ting; Hsieh, Huey-Lin; Huang, Jing-Yi; Wu, Sheng-Tsai; Dai, Ming-Ji; Liu, Chun-Kai; Yao, Da-Jeng

2013-07-01

We devised a novel method to evaluate the temperature-dependent effective properties of a thermoelectric module (TEM): Seebeck coefficient ( S m), internal electrical resistance ( R m), and thermal conductance ( K m). After calculation, the effective properties of the module are converted to the average material properties of a p- n thermoelectric pillar pair inside the module: Seebeck coefficient ( S TE), electrical resistivity ( ρ TE), and thermal conductivity ( k TE). For a commercial thermoelectric module (Altec 1091) chosen to verify the novel method, the measured S TE has a maximum value at bath temperature of 110°C; ρ TE shows a positive linear trend dependent on the bath temperature, and k TE increases slightly with increasing bath temperature. The results show the method to have satisfactory measurement performance in terms of practicability and reliability; the data for tests near 23°C agree with published values.

Thermophysical properties of Apollo 14 fines

NASA Technical Reports Server (NTRS)

Cremers, C. J.

1974-01-01

The vacuum thermal conductivity of lunar fines sample 14163 was measured for the approximate temperature range of 100 to 400 K. Sample densities of 1500 kg/cu m and 1800 kg/cu m were used. The temperature dependence of the conductivity was found to be well represented by the relation k = A + BT-cubed, which is predicted by elementary theory. The coefficients A and B were obtained by least-squares analysis of the data. The thermal diffusivity was calculated for the various densities using specific heat data from the literature along with the measured conductivities. The results are compared with those obtained for Apollo 11, Apollo 12, and terrestrial basalt samples.

Effective conductivity of a periodic dilute composite with perfect contact and its series expansion

NASA Astrophysics Data System (ADS)

Pukhtaievych, Roman

2018-06-01

We study the asymptotic behavior of the effective thermal conductivity of a periodic two-phase dilute composite obtained by introducing into an infinite homogeneous matrix a periodic set of inclusions of a different material, each of them of size proportional to a positive parameter ɛ . We assume a perfect thermal contact at constituent interfaces, i.e., a continuity of the normal component of the heat flux and of the temperature. For ɛ small, we prove that the effective conductivity can be represented as a convergent power series in ɛ and we determine the coefficients in terms of the solutions of explicit systems of integral equations.

Exact Thermal Transport Properties of Gray-Arsenic using Electon-Phonon Coupling

NASA Astrophysics Data System (ADS)

Kang, Seoung-Hun; Kwon, Young-Kyun

Using various theoretical methods, we investigate the thermoelectric property of gray arsenic. Thermoelectric devices that utilize the Seebeck effect convert heat flow into electrical energy. The conversion efficiency of such a device is determined by its figure of merit or ZT value, which is related to various transport coefficients, such as Seebeck coefficient and the ratio of its electrical conductivity to its thermal counterpart for given temperature. To calculate various transport coefficients and thus the ZT values of gray arsenic, we apply the Boltzmann transport theory to its electronic and phononic structures obtained by density functional theory and density functional perturbation theory together with maximally locallized Wannier functions. During this procedure, we evaluate its relaxation time accurately by explicitly considering electron-phonon coupling. Our result reveals that gray arsenic may be used for a good p-type thermoelectric devices.

Measurement setup for the simultaneous determination of diffusivity and Seebeck coefficient in a multi-anvil apparatus

NASA Astrophysics Data System (ADS)

Jacobsen, M. K.; Liu, W.; Li, B.

2012-09-01

In this paper, a high pressure setup is presented for performing simultaneous measurements of Seebeck coefficient and thermal diffusivity in multianvil apparatus for the purpose of enhancing the study of transport phenomena. Procedures for the derivation of Seebeck coefficient and thermal diffusivity/conductivity, as well as their associated sources of errors, are presented in detail, using results obtained on the filled skutterudite, Ce0.8Fe3CoSb12, up to 12 GPa at ambient temperature. Together with recent resistivity and sound velocity measurements in the same apparatus, these developments not only provide the necessary data for a self-consistent and complete characterization of the figure of merit of thermoelectric materials under pressure, but also serve as an important tool for furthering our knowledge of the dynamics and interplay between these transport phenomena.

Measurement setup for the simultaneous determination of diffusivity and Seebeck coefficient in a multi-anvil apparatus.

PubMed

Jacobsen, M K; Liu, W; Li, B

2012-09-01

In this paper, a high pressure setup is presented for performing simultaneous measurements of Seebeck coefficient and thermal diffusivity in multianvil apparatus for the purpose of enhancing the study of transport phenomena. Procedures for the derivation of Seebeck coefficient and thermal diffusivity/conductivity, as well as their associated sources of errors, are presented in detail, using results obtained on the filled skutterudite, Ce(0.8)Fe(3)CoSb(12,) up to 12 GPa at ambient temperature. Together with recent resistivity and sound velocity measurements in the same apparatus, these developments not only provide the necessary data for a self-consistent and complete characterization of the figure of merit of thermoelectric materials under pressure, but also serve as an important tool for furthering our knowledge of the dynamics and interplay between these transport phenomena.

Electrical and thermal transport properties of layered Bi2YO4Cu2Se2

NASA Astrophysics Data System (ADS)

Xiao, Yu; Pei, Yanling; Chang, Cheng; Zhang, Xiao; Tan, Xing; Ye, Xinxin; Gong, Shengkai; Lin, Yuanhua; He, Jiaqing; Zhao, Li-Dong

2016-07-01

Bi2YO4Cu2Se2 possesses a low thermal conductivity and high electrical conductivity at room temperature, which was considered as a potential thermoelectric material. In this work, we have investigated the electrical and thermal transport properties of Bi2YO4Cu2Se2 system in the temperature range from 300 K to 873 K. We found that the total thermal conductivity decreases from 1.8 W m-1 K-1 to 0.9 W m-1 K-1, and the electrical conductivity decreases from 850 S/cm to 163 S/cm in the measured temperature range. To investigate how potential of Bi2YO4Cu2Se2 system, we prepared the heavily Iodine doped samples to counter-dope intrinsically high carrier concentration and improve the electrical transport properties. Interestingly, the Seebeck coefficient could be enhanced to +80 μV/K at 873 K, meanwhile, we found that a low thermal conductivity of 0.7 W m-1 K-1 could be achieved. The intrinsically low thermal conductivity in this system is related to the low elastic properties, such as Young's modulus of 70-72 GPa, and Grüneisen parameters of 1.55-1.71. The low thermal conductivity makes Bi2YO4Cu2Se2 system to be a potential thermoelectric material, the ZT value 0.06 at 873 K was obtained, a higher performance is expected by optimizing electrical transport properties through selecting suitable dopants, modifying band structures or by further reducing thermal conductivity through nanostructuring etc.

Heat transfer in fish: are short excursions between habitats a thermoregulatory behaviour to exploit resources in an unfavourable thermal environment?

PubMed

Pépino, Marc; Goyer, Katerine; Magnan, Pierre

2015-11-01

Temperature is the primary environmental factor affecting physiological processes in ectotherms. Heat-transfer models describe how the fish's internal temperature responds to a fluctuating thermal environment. Specifically, the rate coefficient (k), defined as the instantaneous rate of change in body temperature in relation to the difference between ambient and body temperature, summarizes the combined effects of direct thermal conduction through body mass, passive convection (intracellular and intercellular fluids) and forced convective heat transfer (cardiovascular system). The k-coefficient is widely used in fish ecology to understand how body temperature responds to changes in water temperature. The main objective of this study was to estimate the k-coefficient of brook charr equipped with internal temperature-sensitive transmitters in controlled laboratory experiments. Fish were first transferred from acclimation tanks (10°C) to tanks at 14, 19 or 23°C (warming experiments) and were then returned to the acclimation tanks (10°C; cooling experiments), thus producing six step changes in ambient temperature. We used non-linear mixed models to estimate the k-coefficient. Model comparisons indicated that the model incorporating the k-coefficient as a function of absolute temperature difference (dT: 4, 9 and 13°C) best described body temperature change. By simulating body temperature in a heterogeneous thermal environment, we provide theoretical predictions of maximum excursion duration between feeding and resting areas. Our simulations suggest that short (i.e. <60 min) excursions could be a common thermoregulatory behaviour adopted by cold freshwater fish species to sustain body temperature below a critical temperature threshold, enabling them to exploit resources in an unfavourable thermal environment. © 2015. Published by The Company of Biologists Ltd.

Thermoelectric transport coefficients in mono-layer MoS{sub 2} and WSe{sub 2}: Role of substrate, interface phonons, plasmon, and dynamic screening

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Krishnendu, E-mail: kghosh3@buffalo.edu; Singisetti, Uttam, E-mail: uttamsin@buffalo.edu

2015-10-07

The thermoelectric transport coefficients of electrons in two recently emerged transition metal di-chalcogenides (TMD), MoS{sub 2} and WSe{sub 2}, are calculated by solving Boltzmann transport equation using Rode's iterative technique in the diffusive transport regime and the coupled current (electrical and heat) equations. Scattering from remote phonons along with the hybridization of TMD plasmon with remote phonon modes and dynamic screening under linear polarization response are investigated in TMDs sitting on a dielectric environment. The transport coefficients are obtained for a varying range of temperature and doping density for three different types of substrates—SiO{sub 2}, Al{sub 2}O{sub 3}, and HfO{submore » 2}. The Seebeck co-efficient for MoS{sub 2} and WSe{sub 2} is found to be higher than 3D semiconductors even with diffusive transport. The electronic thermal conductivity is found to be low, however, the thermoelectric figure of merit is limited by the high phonon thermal conductivity. It is found that judicious selection of a dielectric environment based on temperature of operation and carrier density is crucial to optimize the thermoelectric performance of TMD materials.« less

Fluctuation-enhanced electric conductivity in electrolyte solutions

DOE PAGES

Péraud, Jean-Philippe; Nonaka, Andrew J.; Bell, John B.; ...

2017-09-26

In this work, we analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson–Nernst–Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation–anion diffusion coefficient. Specifically, we predict a nonzero cation–anion Maxwell– Stefan coefficient proportionalmore » to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye–Huckel–Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Lastly, we show that strong applied electric fields result in anisotropically enhanced “giant” velocity fluctuations and reduced fluctuations of salt concentration.« less

Fluctuation-enhanced electric conductivity in electrolyte solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Péraud, Jean-Philippe; Nonaka, Andrew J.; Bell, John B.

In this work, we analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson–Nernst–Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation–anion diffusion coefficient. Specifically, we predict a nonzero cation–anion Maxwell– Stefan coefficient proportionalmore » to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye–Huckel–Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Lastly, we show that strong applied electric fields result in anisotropically enhanced “giant” velocity fluctuations and reduced fluctuations of salt concentration.« less

High temperature insulation materials for reradiative thermal protection systems

NASA Technical Reports Server (NTRS)

Hughes, T. A.

1972-01-01

Results are presented of a two year program to evaluate packaged thermal insulations for use under a metallic radiative TPS of a shuttle orbiter vehicle. Evaluations demonstrated their survival for up to 100 mission reuse cycles under shuttle acoustic and thermal loads with peak temperatures of 1000 F, 1800 F, 2000 F, 2200 F and 2500 F. The specimens were composed of low density refractory fiber felts, packaged in thin gage metal foils. In addition, studies were conducted on the venting requirements of the packages, salt spray resistance of the metal foils, and the thermal conductivity of many of the insulations as a function of temperature and ambient air pressure. Data is also presented on the radiant energy transport through insulations, and back-scattering coefficients were experimentally determined as a function of source temperature.

Modeling and Ab initio Calculations of Thermal Transport in Si-Based Clathrates and Solar Perovskites

NASA Astrophysics Data System (ADS)

He, Yuping

2015-03-01

We present calculations of the thermal transport coefficients of Si-based clathrates and solar perovskites, as obtained from ab initio calculations and models, where all input parameters derived from first principles. We elucidated the physical mechanisms responsible for the measured low thermal conductivity in Si-based clatherates and predicted their electronic properties and mobilities, which were later confirmed experimentally. We also predicted that by appropriately tuning the carrier concentration, the thermoelectric figure of merit of Sn and Pb based perovskites may reach values ranging between 1 and 2, which could possibly be further increased by optimizing the lattice thermal conductivity through engineering perovskite superlattices. Work done in collaboration with Prof. G. Galli, and supported by DOE/BES Grant No. DE-FG0206ER46262.

Inverse problem to constrain the controlling parameters of large-scale heat transport processes: The Tiberias Basin example

NASA Astrophysics Data System (ADS)

Goretzki, Nora; Inbar, Nimrod; Siebert, Christian; Möller, Peter; Rosenthal, Eliyahu; Schneider, Michael; Magri, Fabien

2015-04-01

Salty and thermal springs exist along the lakeshore of the Sea of Galilee, which covers most of the Tiberias Basin (TB) in the northern Jordan- Dead Sea Transform, Israel/Jordan. As it is the only freshwater reservoir of the entire area, it is important to study the salinisation processes that pollute the lake. Simulations of thermohaline flow along a 35 km NW-SE profile show that meteoric and relic brines are flushed by the regional flow from the surrounding heights and thermally induced groundwater flow within the faults (Magri et al., 2015). Several model runs with trial and error were necessary to calibrate the hydraulic conductivity of both faults and major aquifers in order to fit temperature logs and spring salinity. It turned out that the hydraulic conductivity of the faults ranges between 30 and 140 m/yr whereas the hydraulic conductivity of the Upper Cenomanian aquifer is as high as 200 m/yr. However, large-scale transport processes are also dependent on other physical parameters such as thermal conductivity, porosity and fluid thermal expansion coefficient, which are hardly known. Here, inverse problems (IP) are solved along the NW-SE profile to better constrain the physical parameters (a) hydraulic conductivity, (b) thermal conductivity and (c) thermal expansion coefficient. The PEST code (Doherty, 2010) is applied via the graphical interface FePEST in FEFLOW (Diersch, 2014). The results show that both thermal and hydraulic conductivity are consistent with the values determined with the trial and error calibrations. Besides being an automatic approach that speeds up the calibration process, the IP allows to cover a wide range of parameter values, providing additional solutions not found with the trial and error method. Our study shows that geothermal systems like TB are more comprehensively understood when inverse models are applied to constrain coupled fluid flow processes over large spatial scales. References Diersch, H.-J.G., 2014. FEFLOW Finite Element Modeling of Flow, Mass and Heat Transport in Porous and Fractured Media. Springer- Verlag Berlin Heidelberg ,996p. Doherty J., 2010, PEST: Model-Independent Parameter Estimation. user manual 5th Edition. Watermark, Brisbane, Australia Magri, F., Inbar, N., Siebert C., Rosenthal, E., Guttman, J., Möller, P., 2015. Transient simulations of large-scale hydrogeological processes causing temperature and salinity anomalies in the Tiberias Basin. Journal of Hydrology, 520(0), 342-355.

Transport Coefficients from Large Deviation Functions

NASA Astrophysics Data System (ADS)

Gao, Chloe; Limmer, David

2017-10-01

We describe a method for computing transport coefficients from the direct evaluation of large deviation function. This method is general, relying on only equilibrium fluctuations, and is statistically efficient, employing trajectory based importance sampling. Equilibrium fluctuations of molecular currents are characterized by their large deviation functions, which is a scaled cumulant generating function analogous to the free energy. A diffusion Monte Carlo algorithm is used to evaluate the large deviation functions, from which arbitrary transport coefficients are derivable. We find significant statistical improvement over traditional Green-Kubo based calculations. The systematic and statistical errors of this method are analyzed in the context of specific transport coefficient calculations, including the shear viscosity, interfacial friction coefficient, and thermal conductivity.

Tuning conductivity in boron nanowire by edge geometry

NASA Astrophysics Data System (ADS)

Bhuyan, Prabal Dev; Gupta, Sanjeev K.; Sonvane, Yogesh; Gajjar, P. N.

2018-04-01

In present study, we have investigated electronic and temperature dependent transport properties of carbyne like linear chain and ribbon like zigzag structures of Boron (B) nanowire. The linear chain structure showed higher electric and thermal conductivity, as it is sp-hybridized, than its counterpart ribbon (R) structure. However the conductivity of ribbon structure increases with increases in width due to edge geometry effect. The ribbon (3R) structure showed high electric and thermal conductivity of 8.0×1019 1/Ω m s and 0.59×1015 W/ m K respectively. Interestingly we have observed that B linear chain showed higher thermal conductivity of 0.23×1015 W/ m K than its ribbon R and 2R structure above 600K. Because of high Seebeck co-efficient of boron chain and ribbon (R) structures at low temperature, they could find applications in thermoelectric sensors. Our results show that tuning conductivity property of boron nanowire could be of great interest in research for future electric connector in nanodevices.

Study of heat generation and cutting force according to minimization of grain size (500 nm to 180 nm) of WC ball endmill using FEM

NASA Astrophysics Data System (ADS)

Byeon, J. H.; Ahmed, F.; Ko, T. J.; lee, D. K.; Kim, J. S.

2018-03-01

As the industry develops, miniaturization and refinement of products are important issues. Precise machining is required for cutting, which is a typical method of machining a product. The factor determining the workability of the cutting process is the material of the tool. Tool materials include carbon tool steel, alloy tool steel, high-speed steel, cemented carbide, and ceramics. In the case of a carbide material, the smaller the particle size, the better the mechanical properties with higher hardness, strength and toughness. The specific heat, density, and thermal diffusivity are also changed through finer particle size of the material. In this study, finite element analysis was performed to investigate the change of heat generation and cutting power depending on the physical properties (specific heat, density, thermal diffusivity) of tool material. The thermal conductivity coefficient was obtained by measuring the thermal diffusivity, specific heat, and density of the material (180 nm) in which the particle size was finer and the particle material (0.05 μm) in the conventional size. The coefficient of thermal conductivity was calculated as 61.33 for 180nm class material and 46.13 for 0.05μm class material. As a result of finite element analysis using this value, the average temperature of exothermic heat of micronized particle material (180nm) was 532.75 °C and the temperature of existing material (0.05μm) was 572.75 °C. Cutting power was also compared but not significant. Therefore, if the thermal conductivity is increased through particle refinement, the surface power can be improved and the tool life can be prolonged by lowering the temperature generated in the tool during machining without giving a great influence to the cutting power.

Experimental and Theoretical Study of Heat Conduction for Air up to 5000 K

NASA Technical Reports Server (NTRS)

Peng, Tzy-Cheng; Ahtye, Warren F.

1961-01-01

The theoretical value of the integral of thermal conductivity is compared with the experimental values from shock-tube measurements. The particular case considered is the one-dimensional nonsteady flow of heat through air at constant pressure. This approach has been previously described in NASA TR R-27. experiment was uncertain because of the large scatter in the experimental data. In this paper, an attempt is made to improve the correlation by use of a more refined calculation of the integral of thermal conductivity, and by use of improved experimental techniques and instrumentation. As a result of these changes, a much closer correlation is shown between the experimental and theoretical heat-flux potentials. This indicates that the predicted values of the coefficient of thermal conductivity for high-temperature air may be suitably accurate for many engineering needs, up to the limits of the test (4600 K).

Investigation of thermoelectricity in KScSn half-Heusler compound

NASA Astrophysics Data System (ADS)

Shrivastava, Deepika; Acharya, Nikita; Sanyal, Sankar P.

2018-05-01

The electronic and transport properties of KScSn half-Heusler (HH) compound have been investigated using first-principles density functional theory and semi classical Boltzmann transport theory. The electronic band structure and density of states (total and partial) show semiconducting nature of KScSn with band gap 0.48 eV which agree well with previously reported results. The transport coefficient such as electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor as a function of chemical potential are evaluated. KScSn has high power factor for p-type doping and is a potential candidate for thermoelectric applications.

Thickness dependence of optical properties of amorphous indium oxide thin films deposited by reactive evaporation

NASA Astrophysics Data System (ADS)

Uluta, K.; Deer, D.; Skarlatos, Y.

2006-08-01

The electrical conductivity and absorption coefficient of amorphous indium oxide thin films, thermally evaporated on glass substrates at room temperature, were evaluated. For direct transitions the variation of the optical band gap with thickness was determined and this variation was supposed to appear due to the variation of localized gap states, whereas the variation of conductivity with thickness was supposed to be due to the variation of carrier concentration. We attribute the variation of absorption coefficient with thickness to the variation of optical band gap energy rather than optical interference.

Modeling of the heat transfer performance of plate-type dispersion nuclear fuel elements

NASA Astrophysics Data System (ADS)

Ding, Shurong; Huo, Yongzhong; Yan, XiaoQing

2009-08-01

Considering the mutual actions between fuel particles and the metal matrix, the three-dimensional finite element models are developed to simulate the heat transfer behaviors of dispersion nuclear fuel plates. The research results indicate that the temperatures of the fuel plate might rise more distinctly with considering the particle swelling and the degraded surface heat transfer coefficients with increasing burnup; the local heating phenomenon within the particles appears when their thermal conductivities are too low. With rise of the surface heat transfer coefficients, the temperatures within the fuel plate decrease; the temperatures of the fuel plate are sensitive to the variations of the heat transfer coefficients whose values are lower, but their effects are weakened and slight when the heat transfer coefficients increase and reach a certain extent. Increasing the heat generation rate leads to elevating the internal temperatures. The temperatures and the maximum temperature differences within the plate increase along with the particle volume fractions. The surface thermal flux goes up along with particle volume fractions and heat generation rates, but the effects of surface heat transfer coefficients are not evident.

Thermoelectric transport properties of BaBiTe{sub 3}-based materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Yiming; Zhao, Li-Dong, E-mail: zhaolidong@buaa.edu.cn

BaBiTe{sub 3}, a material with low thermal conductivity, is an inferior thermoelectric material due to the poor electrical properties originated from its narrow band gap. We choose two types of dopants, K and La, trying to optimize its electrical transport properties. The minority carriers, which harm the Seebeck coefficient in this system, are suppressed by La doping. With the increase of both electrical conductivity and Seebeck coefficient, the power factor of 3% La doped BaBiTe{sub 3} reaches 3.7 μW cm{sup −1} K{sup −2} which increased by 40% from undoped BaBiTe{sub 3}. Besides high power factor, the thermal conductivity is alsomore » reduced in it. Eventually, a high ZT value, 0.25 at 473 K, for n-type BaBiTe{sub 3} is achieved in 3% La doped BaBiTe{sub 3}. - Graphical abstract: BaBiTe{sub 3} possesses a low thermal conductivity. However, it is an inferior thermoelectric material due to the poor electrical properties originated from its narrow band gap. A high ZT value of 0.25 at 473 K for n-type BaBiTe{sub 3} can be achieved through optimizing electrical transport properties via La doping. - Highlights: • BaBiTe{sub 3} is an analogue of these promising thermoelectric materials: such as CsBi{sub 4}Te{sub 6} and K{sub 2}Bi{sub 8}Se{sub 13}, etc. • BaBiTe{sub 3} possesses a low thermal conductivity. • La is an effective dopant to enhance electrical transport properties. • A high ZT value of 0.25 at 473 K can be achieved in n-type La-doped BaBiTe{sub 3}.« less

Characterization of Lorenz number with Seebeck coefficient measurement

DOE PAGES

Kim, Hyun -Sik; Gibbs, Zachary M.; Tang, Yinglu; ...

2015-04-01

In analyzing zT improvements due to lattice thermal conductivity (κ L ) reduction, electrical conductivity (σ) and total thermal conductivity (κ Total ) are often used to estimate the electronic component of the thermal conductivity (κ E ) and in turn κ L from κ L = ~ κ Total - LσT. The Wiedemann-Franz law, κ E = LσT, where L is Lorenz number, is widely used to estimate κ E from σ measurements. It is a common practice to treat L as a universal factor with 2.44 × 10⁻⁸ WΩK⁻² (degenerate limit). However, significant deviations from the degenerate limitmore » (approximately 40% or more for Kane bands) are known to occur for non-degenerate semiconductors where L converges to 1.5 × 10⁻⁸ WΩK⁻² for acoustic phonon scattering. The decrease in L is correlated with an increase in thermopower (absolute value of Seebeck coefficient (S)). Thus, a first order correction to the degenerate limit of L can be based on the measured thermopower, |S|, independent of temperature or doping. We propose the equation: (where L is in 10⁻⁸ WΩK⁻² and S in μV/K) as a satisfactory approximation for L. This equation is accurate within 5% for single parabolic band/acoustic phonon scattering assumption and within 20% for PbSe, PbS, PbTe, Si₀.₈Ge₀.₂ where more complexity is introduced, such as non-parabolic Kane bands, multiple bands, and/or alternate scattering mechanisms. The use of this equation for L rather than a constant value (when detailed band structure and scattering mechanism is not known) will significantly improve the estimation of lattice thermal conductivity. L = 1.5 + exp [-|S|116]« less

Microstructure and thermal properties of copper–diamond composites with tungsten carbide coating on diamond particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Qiping; He, Xinbo, E-mail: xb_he@163.com; Ren, Shubin

2015-07-15

An effective method for preparing tungsten carbide coating on diamond surfaces was proposed to improve the interface bonding between diamond and copper. The WC coating was formed on the diamond surfaces with a reaction medium of WO{sub 3} in mixed molten NaCl–KCl salts and the copper–diamond composites were obtained by vacuum pressure infiltration of WC-coated diamond particles with pure copper. The microstructure of interface bonding between diamond and copper was discussed. Thermal conductivity and thermal expansion behavior of the obtained copper–diamond composites were investigated. Results indicated that the thermal conductivity of as-fabricated composite reached 658 W m{sup −} {sup 1}more » K{sup −} {sup 1}. Significant reduction in coefficient of thermal expansion of the composite compared with that of pure copper was obtained. - Highlights: • WC coating was successfully synthesized on diamond particles in molten salts. • WC coating obviously promoted the wettability of diamond and copper matrix. • WC coating greatly enhanced the thermal conductivity of Cu–diamond composite. • The composites are suitable candidates for heat sink applications.« less

CarbAl Heat Transfer Material

NASA Technical Reports Server (NTRS)

Fink, Richard

2015-01-01

The increasing use of power electronics, such as high-current semiconductor devices and modules, within space vehicles is driving the need to develop specialty thermal management materials in both the packaging of these discrete devices and the packaging of modules consisting of these device arrays. Developed by Applied Nanotech, Inc. (ANI), CarbAl heat transfer material is uniquely characterized by its low density, high thermal diffusivity, and high thermal conductivity. Its coefficient of thermal expansion (CTE) is similar to most power electronic materials, making it an effective base plate substrate for state-of-the-art silicon carbide (SiC) super junction transistors. The material currently is being used to optimize hybrid vehicle inverter packaging. Adapting CarbAl-based substrates to space applications was a major focus of the SBIR project work. In Phase I, ANI completed modeling and experimentation to validate its deployment in a space environment. Key parameters related to cryogenic temperature scaling of CTE, thermal conductivity, and mechanical strength. In Phase II, the company concentrated on improving heat sinks and thermally conductive circuit boards for power electronic applications.

Measurement of CO 2, CO, SO 2, and NO emissions from coal-based thermal power plants in India

NASA Astrophysics Data System (ADS)

Chakraborty, N.; Mukherjee, I.; Santra, A. K.; Chowdhury, S.; Chakraborty, S.; Bhattacharya, S.; Mitra, A. P.; Sharma, C.

Measurements of CO 2 (direct GHG) and CO, SO 2, NO (indirect GHGs) were conducted on-line at some of the coal-based thermal power plants in India. The objective of the study was three-fold: to quantify the measured emissions in terms of emission coefficient per kg of coal and per kWh of electricity, to calculate the total possible emission from Indian thermal power plants, and subsequently to compare them with some previous studies. Instrument IMR 2800P Flue Gas Analyzer was used on-line to measure the emission rates of CO 2, CO, SO 2, and NO at 11 numbers of generating units of different ratings. Certain quality assurance (QA) and quality control (QC) techniques were also adopted to gather the data so as to avoid any ambiguity in subsequent data interpretation. For the betterment of data interpretation, the requisite statistical parameters (standard deviation and arithmetic mean) for the measured emissions have been also calculated. The emission coefficients determined for CO 2, CO, SO 2, and NO have been compared with their corresponding values as obtained in the studies conducted by other groups. The total emissions of CO 2, CO, SO 2, and NO calculated on the basis of the emission coefficients for the year 2003-2004 have been found to be 465.667, 1.583, 4.058, and 1.129 Tg, respectively.

Thermal conductivity of electron-irradiated graphene

NASA Astrophysics Data System (ADS)

Weerasinghe, Asanka; Ramasubramaniam, Ashwin; Maroudas, Dimitrios

2017-10-01

We report results of a systematic analysis of thermal transport in electron-irradiated, including irradiation-induced amorphous, graphene sheets based on nonequilibrium molecular-dynamics simulations. We focus on the dependence of the thermal conductivity, k, of the irradiated graphene sheets on the inserted irradiation defect density, c, as well as the extent of defect passivation with hydrogen atoms. While the thermal conductivity of irradiated graphene decreases precipitously from that of pristine graphene, k0, upon introducing a low vacancy concentration, c < 1%, in the graphene lattice, further reduction of the thermal conductivity with the increasing vacancy concentration exhibits a weaker dependence on c until the amorphization threshold. Beyond the onset of amorphization, the dependence of thermal conductivity on the vacancy concentration becomes significantly weaker, and k practically reaches a plateau value. Throughout the range of c and at all hydrogenation levels examined, the correlation k = k0(1 + αc)-1 gives an excellent description of the simulation results. The value of the coefficient α captures the overall strength of the numerous phonon scattering centers in the irradiated graphene sheets, which include monovacancies, vacancy clusters, carbon ring reconstructions, disorder, and a rough nonplanar sheet morphology. Hydrogen passivation increases the value of α, but the effect becomes very minor beyond the amorphization threshold.

Symmetric flows for compressible heat-conducting fluids with temperature dependent viscosity coefficients

NASA Astrophysics Data System (ADS)

Wan, Ling; Wang, Tao

2017-06-01

We consider the Navier-Stokes equations for compressible heat-conducting ideal polytropic gases in a bounded annular domain when the viscosity and thermal conductivity coefficients are general smooth functions of temperature. A global-in-time, spherically or cylindrically symmetric, classical solution to the initial boundary value problem is shown to exist uniquely and converge exponentially to the constant state as the time tends to infinity under certain assumptions on the initial data and the adiabatic exponent γ. The initial data can be large if γ is sufficiently close to 1. These results are of Nishida-Smoller type and extend the work (Liu et al. (2014) [16]) restricted to the one-dimensional flows.

Ba-filled Ni–Sb–Sn based skutterudites with anomalously high lattice thermal conductivity

DOE PAGES

Paschinger, W.; Rogl, Gerda; Grytsiv, A.; ...

2016-06-21

Here, in this study, novel filled skutterudites Ba yNi 4Sb 12-xSn x (y max = 0.93) have been prepared by arc melting followed by annealing at 250, 350 and 450°C up to 30 days in vacuum-sealed quartz vials. Extension of the homogeneity region, solidus temperatures and structural investigations were performed for the skutterudite phase in the ternary Ni–Sn–Sb and in the quaternary Ba–Ni–Sb–Sn systems. Phase equilibria in the Ni–Sn–Sb system at 450°C were established by means of Electron Probe Microanalysis (EPMA) and X-ray Powder Diffraction (XPD). With rather small cages Ni 4(Sb,Sn) 12, the Ba–Ni–Sn–Sb skutterudite system is perfectly suitedmore » to study the influence of filler atoms on the phonon thermal conductivity. Single-phase samples with the composition Ni 4Sb 8.2Sn 3.8, Ba 0.42Ni 4Sb 8.2Sn 3.8 and Ba 0.92Ni 4Sb 6.7Sn 5.3 were used to measure their physical properties, i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. The resistivity data demonstrate a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from the maxima in the Seebeck coefficient data as a function of temperature. Single crystal X-ray structure analyses at 100, 200 and 300 K revealed the thermal expansion coefficients as well as Einstein and Debye temperatures for Ba 0.73Ni 4Sb 8.1Sn 3.9 and Ba 0.95Ni 4Sb 6.1Sn 5.9. These data were in accordance with the Debye temperatures obtained from the specific heat (4.4 K < T < 140 K) and Mössbauer spectroscopy (10 K < T < 290 K). Rather small atom displacement parameters for the Ba filler atoms indicate a severe reduction in the “rattling behaviour” consistent with the high levels of lattice thermal conductivity. The elastic moduli, collected from Resonant Ultrasonic Spectroscopy ranged from 100 GPa for Ni 4Sb 8.2Sn 3.8 to 116 GPa for Ba 0.92Ni 4Sb 6.7Sn 5.3. The thermal expansion coefficients were 11.8 × 10 -6 K -1 for Ni 4Sb 8.2Sn 3.8 and 13.8 × 10 -6 K -1 for Ba 0.92Ni 4Sb 6.7Sn 5.3. The room temperature Vickers hardness values vary within the range from 2.6 GPa to 4.7 GPa. Lastly, severe plastic deformation via high-pressure torsion was used to introduce nanostructuring; however, the physical properties before and after HPT showed no significant effect on the materials thermoelectric behaviour.« less

Investigation of nitrate salts for solar latent heat storage

NASA Astrophysics Data System (ADS)

Kamimoto, M.; Tanaka, T.; Tani, T.; Horigome, T.

1980-01-01

The properties of heat transfer in the discharging of a model solar latent heat storage unit based on various nitrate salts and salt mixtures are investigated. A shell-and-tube-type passive heat exchanger containing NaNO3 or eutectic or off-eutectic mixtures of NaNO3 with KNO3 and Ca(NO3)2 was heated to 40 K above the melting temperature of the salt, when air was made to flow through a heat transfer tube at a constant flow rate, and heat transfer material and air temperatures were monitored. Thermal conductivity and the apparent heat transfer coefficient are estimated from the heat extraction rate and temperature profiles, and it is found that although the thermal conductivities of the materials are similar, the off-eutectic salts exhibit higher heat transfer coefficients. Temperature distributions in the NaNO3-KNO3 mixtures are found to be in fairly good agreement with those predicted by numerical solutions of a one-dimensional finite difference equation, and with approximate analytical solutions. It is observed that the temperature of the heat transfer surface drops rapidly after the appearance of a solid phase, due to the low thermal conductivity of the salts, and means of avoiding this temperature drop are considered.

Thermal measurements of short-duration CO2 laser resurfacing

NASA Astrophysics Data System (ADS)

Harris, David M.; Fried, Daniel; Reinisch, Lou; Bell, Thomas; Lyver, Rex

1997-05-01

The thermal consequences of a 100 microsecond carbon-dioxide laser used for skin resurfacing were examined with infrared radiometry. Human skin was evaluated in a cosmetic surgery clinic and extirpated rodent skin was measured in a research laboratory. Thermal relaxation following single pulses of in vivo human and ex vivo animal skin were quantitatively similar in the 30 - 1000 msec range. The thermal emission from the area of the irradiated tissue increased monotonically with increasing incident laser fluence. Extremely high peak temperatures during the 100 microsecond pulse are attributed to plume incandescence. Ejecta thermal emission may also contribute to our measurements during the first several msecs. The data are combined into a thermal relaxation model. Given known coefficients, and adjusting tissue absorption to reflect a 50% water content, and thermal conductivity of 2.3 times that of water, the measured (both animal back and human forearm) and calculated values coincide. The high thermal conductance suggests preferential thermal conduction along the protein matrix. The clinical observation of a resurfacing procedure clearly shows thermal overlap and build-up is a result of sequential, adjacent pulses. A decrease of 4 - 6 degrees Celsius in surface temperature at the treatment site that appeared immediately post-Tx and gradually diminished over several days is possibly a sign of dermal convective and/or evaporative cooling.

Mathematical model for thermal and entropy analysis of thermal solar collectors by using Maxwell nanofluids with slip conditions, thermal radiation and variable thermal conductivity

NASA Astrophysics Data System (ADS)

Aziz, Asim; Jamshed, Wasim; Aziz, Taha

2018-04-01

In the present research a simplified mathematical model for the solar thermal collectors is considered in the form of non-uniform unsteady stretching surface. The non-Newtonian Maxwell nanofluid model is utilized for the working fluid along with slip and convective boundary conditions and comprehensive analysis of entropy generation in the system is also observed. The effect of thermal radiation and variable thermal conductivity are also included in the present model. The mathematical formulation is carried out through a boundary layer approach and the numerical computations are carried out for Cu-water and TiO2-water nanofluids. Results are presented for the velocity, temperature and entropy generation profiles, skin friction coefficient and Nusselt number. The discussion is concluded on the effect of various governing parameters on the motion, temperature variation, entropy generation, velocity gradient and the rate of heat transfer at the boundary.

Power electronics cooling apparatus

DOEpatents

Sanger, Philip Albert; Lindberg, Frank A.; Garcen, Walter

2000-01-01

A semiconductor cooling arrangement wherein a semiconductor is affixed to a thermally and electrically conducting carrier such as by brazing. The coefficient of thermal expansion of the semiconductor and carrier are closely matched to one another so that during operation they will not be overstressed mechanically due to thermal cycling. Electrical connection is made to the semiconductor and carrier, and a porous metal heat exchanger is thermally connected to the carrier. The heat exchanger is positioned within an electrically insulating cooling assembly having cooling oil flowing therethrough. The arrangement is particularly well adapted for the cooling of high power switching elements in a power bridge.

Experimental Investigation on Thermal Physical Properties of an Advanced Glass Fiber Composite Material

NASA Astrophysics Data System (ADS)

Guangfa, Gao; Yongchi, Li; Zheng, Jing; Shujie, Yuan

Fiber reinforced composite materials were applied widely in aircraft and space vehicles engineering. Aimed to an advanced glass fiber reinforced composite material, a series of experiments for measuring thermal physical properties of this material were conducted, and the corresponding performance curves were obtained through statistic analyzing. The experimental results showed good consistency. And then the thermal physical parameters such as thermal expansion coefficient, engineering specific heat and sublimation heat were solved and calculated. This investigation provides an important foundation for the further research on the heat resistance and thermodynamic performance of this material.

Phonon-interface scattering in multilayer graphene on an amorphous support

PubMed Central

Sadeghi, Mir Mohammad; Jo, Insun; Shi, Li

2013-01-01

The recent studies of thermal transport in suspended, supported, and encased graphene just began to uncover the richness of two-dimensional phonon physics, which is relevant to the performance and reliability of graphene-based functional materials and devices. Among the outstanding questions are the exact causes of the suppressed basal-plane thermal conductivity measured in graphene in contact with an amorphous material, and the layer thickness needed for supported or embedded multilayer graphene (MLG) to recover the high thermal conductivity of graphite. Here we use sensitive in-plane thermal transport measurements of graphene samples on amorphous silicon dioxide to show that full recovery to the thermal conductivity of the natural graphite source has yet to occur even after the MLG thickness is increased to 34 layers, considerably thicker than previously thought. This seemingly surprising finding is explained by long intrinsic scattering mean free paths of phonons in graphite along both basal-plane and cross-plane directions, as well as partially diffuse scattering of MLG phonons by the MLG-amorphous support interface, which is treated by an interface scattering model developed for highly anisotropic materials. Based on the phonon transmission coefficient calculated from reported experimental thermal interface conductance results, phonons emerging from the interface consist of a large component that is scattered across the interface, making rational choice of the support materials a potential approach to increasing the thermal conductivity of supported MLG. PMID:24067656

Thermoelectric properties of Sn doped BiCuSeO

NASA Astrophysics Data System (ADS)

Das, Sayan; Chetty, Raju; Wojciechowski, Krzysztof; Suwas, Satyam; Mallik, Ramesh Chandra

2017-10-01

BiCuSeO and Bi1-xSnxCuSeO (x = 0.02, 0.04, 0.06, 0.08) were prepared by a two-step solid state synthesis. The phase purity and the crystal structure were investigated by the X-Ray Diffraction (XRD) and confirmed by Energy Dispersive Spectroscopy (EDS). The volatilization of Bi and Bi2O3 lead to off-stoichiometry of the main phase and the formation of CuSe2 secondary phase in the undoped sample. SnO2 secondary phases were found in the doped samples. Both the Seebeck coefficient and the electrical resistivity, measured from the room temperature to 773 K linearly increases with the temperature, which indicates that the sample have metallic like behavior. The origin of such a behavior is due to high hole concentration originating from the Bi and the O vacancies. The Sn +4 valence state was confirmed from the X-Ray Photoelectron Spectroscopy (XPS) and from the reduction of lattice parameter 'a' with doping. The substitution of Sn+4 in the place of Bi+3 leads to the higher Seebeck coefficient and electrical resistivity in the doped samples. Highest power-factor (∼1 mW/m-K2 at 773 K), was obtained for the undoped sample and the 4% Sn doped sample (Bi0.96Sn0.04CuSeO). The lowest thermal conductivity was obtained for the undoped sample, from the room temperature to 773 K. The presence of thermally-conducting SnO2 secondary phases in the doped samples increases the thermal conductivity in comparison with the undoped sample. The zTs of the doped samples were lower compared to the undoped sample, owing to their higher thermal conductivity. The oxygen vacancies as well as the all-length scale phonon scattering, lowers the thermal conductivity of the undoped sample and, as a result, a maximum zT of 1.09 was achieved at 773 K.

On the transport coefficients of hydrogen in the inertial confinement fusion regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lambert, Flavien; Recoules, Vanina; Decoster, Alain

2011-05-15

Ab initio molecular dynamics is used to compute the thermal and electrical conductivities of hydrogen from 10 to 160 g cm{sup -3} and temperatures up to 800 eV, i.e., thermodynamical conditions relevant to inertial confinement fusion (ICF). The ionic structure is obtained using molecular dynamics simulations based on an orbital-free treatment for the electrons. The transport properties were computed using ab initio simulations in the DFT/LDA approximation. The thermal and electrical conductivities are evaluated using Kubo-Greenwood formulation. Particular attention is paid to the convergence of electronic transport properties with respect to the number of bands and atoms. These calculations aremore » then used to check various analytical models (Hubbard's, Lee-More's and Ichimaru's) widely used in hydrodynamics simulations of ICF capsule implosions. The Lorenz number, which is the ratio between thermal and electrical conductivities, is also computed and compared to the well-known Wiedemann-Franz law in different regimes ranging from the highly degenerate to the kinetic one. This allows us to deduce electrical conductivity from thermal conductivity for analytical model. We find that the coupling of Hubbard and Spitzer models gives a correct description of the behavior of electrical and thermal conductivities in the whole thermodynamic regime.« less

Further elucidation of nanofluid thermal conductivity measurement using a transient hot-wire method apparatus

NASA Astrophysics Data System (ADS)

Yoo, Donghoon; Lee, Joohyun; Lee, Byeongchan; Kwon, Suyong; Koo, Junemo

2018-02-01

The Transient Hot-Wire Method (THWM) was developed to measure the absolute thermal conductivity of gases, liquids, melts, and solids with low uncertainty. The majority of nanofluid researchers used THWM to measure the thermal conductivity of test fluids. Several reasons have been suggested for the discrepancies in these types of measurements, including nanofluid generation, nanofluid stability, and measurement challenges. The details of the transient hot-wire method such as the test cell size, the temperature coefficient of resistance (TCR) and the sampling number are further investigated to improve the accuracy and consistency of the measurements of different researchers. It was observed that smaller test apparatuses were better because they can delay the onset of natural convection. TCR values of a coated platinum wire were measured and statistically analyzed to reduce the uncertainty in thermal conductivity measurements. For validation, ethylene glycol (EG) and water thermal conductivity were measured and analyzed in the temperature range between 280 and 310 K. Furthermore, a detailed statistical analysis was conducted for such measurements, and the results confirmed the minimum number of samples required to achieve the desired resolution and precision of the measurements. It is further proposed that researchers fully report the information related to their measurements to validate the measurements and to avoid future inconsistent nanofluid data.

Thermophysical Properties of 60-NITINOL for Mechanical Component Applications

NASA Technical Reports Server (NTRS)

Stanford, Malcolm K.

2012-01-01

The linear thermal expansion coefficient, specific heat capacity, electrical resistivity and thermal conductivity of 60- NITINOL were studied over a range of temperatures representing the operating environment of an oil-lubricated bearing. The behavior of this material appears to follow wellestablished theories applicable to either metal alloys, in general, or to intermetallic compounds, more specifically and the measured data were found to be comparable to those for conventional bearing alloys.

Thermophysical and radiation properties of high-temperature C4F8-CO2 mixtures to replace SF6 in high-voltage circuit breakers

NASA Astrophysics Data System (ADS)

Zhong, Linlin; Cressault, Yann; Teulet, Philippe

2018-03-01

C4F8-CO2 mixtures are one of the potential substitutes to SF6 in high-voltage circuit breakers. However, the arc quenching ability of C4F8-CO2 mixtures is still unknown. In order to provide the necessary basic data for the further investigation of arc quenching performance, the compositions, thermodynamic properties, transport coefficients, and net emission coefficients (NEC) of various C4F8-CO2 mixtures are calculated at temperatures of 300-30 000 K in this work. The thermodynamic properties are presented as the product of mass density and specific heat, i.e., ρCp. The transport coefficients include electrical conductivity, viscosity, and thermal conductivity. The atomic and molecular radiation are both taken into account in the calculation of NEC. The comparison of the properties between SF6 and C4F8-CO2 mixtures is also discussed to find their differences. The results of compositions show that C4F8-CO2 mixtures have a distinctive advantage over other alternative gases e.g., CF3I and C3F8, because the dissociative product (i.e., C4F6) of C4F8 at low temperatures has a very high dielectric strength. This is good for an arc quenching medium to endure the arc recovery phase. Compared with SF6, C4F8-CO2 mixtures present lower ρCp at temperatures below 2800 K and larger thermal conductivity above 2800 K. Based on the position of peaks in thermal conductivity, we predict that the cooling of C4F8-CO2 arc will be slowed down at higher temperatures than that of SF6 arc. It is also found that the mixing of CO2 shows slight effects on the electrical conductivity and NEC of C4F8-CO2 mixtures.

Large anisotropic thermoelectricity in perovskite related layered structure: SrnNbnO3n+2 (n=4,5)

NASA Astrophysics Data System (ADS)

Sakai, Akihiro; Kanno, Tsutomu; Takahashi, Kouhei; Yamada, Yuka; Adachi, Hideaki

2010-11-01

We measured the thermal and charge transport properties of perovskite-related layered structures. Strontium-Niobates, which were expressed as SrnNbnO3n+2 (n =4: Sr1.8La0.2Nb2O7, n =5: Sr5Nb5O17), to explore their thermoelectricities and thermal anisotropies. The behaviors of the thermoelectric parameters (thermal conductivity, Seebeck coefficient, resistivity) were strongly anisotropic in all crystallographic axes (a, b, and c) and large anisotropy exists even in the in-plane direction of the layered structure. Especially, along the a-axis in which corner-sharing NbO6 octahedra aligned straightly, contrastive properties were observed between Sr1.8La0.2Nb2O7 and Sr5Nb5O17. For Sr1.8La0.2Nb2O7, a thermally activated charge conduction is pronounced in the temperature dependence of Seebeck coefficient and resistivity, on the other hand, it was a metallic nature for Sr5Nb5O17. In both compounds, ZT results in anisotropic due to the anisotropic properties of thermoelectric parameters, the best performance is commonly observed in the a-axis. The respective ZT values at room temperature are 3.5×10-2 and 3.6×10-3.

Thermal and Electrical Transport in Oxide Heterostructures

NASA Astrophysics Data System (ADS)

Ravichandran, Jayakanth

This dissertation presents a study of thermal and electrical transport phenomena in heterostructures of transition metal oxides, with specific interest in understanding and tailoring thermoelectricity in these systems. Thermoelectric energy conversion is a promising method for waste heat recovery and the efficiency of such an engine is directly related to a material dependent figure of merit, Z, given as S2sigma/kappa, where S is thermopower and sigma and kappa are electrical and thermal conductivity respectively. Achieving large figure of merit has been hampered by the coupling between these three thermoelectric coefficients, and the primary aim of this study is to understand the nature of thermoelectricity in complex oxides and identify mechanisms which can allow tuning of one or more thermoelectric coefficients in a favorable manner. Unlike the heavily studied conventional thermoelectric semiconductors, transition metals based complex oxides show conduction band characteristics dominated by d-bands, with much larger effective masses and varying degrees of electron correlations. These systems provide for exotic thermoelectric effects which are typically not explained by conventional theories and hence provide an ideal platform for exploring the limits of thermoelectricity. Meanwhile, oxides are composed of earth abundant elements and have excellent high temperature stability, thus providing compelling technological possibilities for thermoelectrics based power generation. In this dissertation, we address specific aspects of thermoelectricity in model complex oxide systems such as perovskite titanates and layered cobaltates to understand thermal and thermoelectric behavior and explore the tunability of thermoelectricity in these systems. The demonstration of band engineering as a viable method to tune physical properties of materials is explored. The model system used for this case is strontium titanate, where two dopants such as La on the Sr-site and oxygen vacancies are employed to achieve band engineering. This method was used to obtain tunable transparent conducting properties and thermoelectric properties for heavily doped strontium titanate. The second aspect investigated is the use of strongly correlated materials for thermoelectricity. The cobaltates, specifically layered cobaltates, show large thermopower even at very large carrier densities. The coupling of thermopower and electrical conductivity is shown to be weaker for a strongly correlated material such as cobaltate, which opens up possibilities of complete decoupling of all three thermoelectric coefficients. Finally, the thermal properties of complex oxides, specifically in perovskite titanates, is addressed in detail. Thermal conductivity is demonstrated to be a sensitive probe for defects in a system, where processing conditions play a significant role in modulating the crystallinity of the material. The perovskite titanate superlattice system of strontium titanate and calcium titanate is used beat alloy limit. It also shows interesting period thickness dependent thermal properties. The possible origin of this effect is briefly discussed and future directions for this research is also elaborated in detail.

Effects of transport coefficients on excitation of flare-induced standing slow-mode waves

NASA Astrophysics Data System (ADS)

Wang, Tongjiang; Ofman, Leon; Davila, Joseph

2017-08-01

The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA, and interpreted as the slow-mode standing waves. By means of the seismology technique we have, for the first time, determined the transport coefficients in the hot (>9 MK) flare plasma, and found that thermal conductivity is suppressed by at least 3 times and viscosity coefficient is enhanced by a factor of 15 as the upper limit (Wang et al. 2015, ApJL, 811, L13). In this presentation, we first discuss possible causes for conduction suppression and viscosity enhancements. Then we use the nonlinear MHD simulations to validate the seismology method that is based on linear analytical analysis, and demonstrate the inversion scheme for determining transport coefficients using numerical parametric study. Finally, we show how the seismologically-determined transport coefficients are crucial for understanding the excitation of the observed standing slow-mode waves in coronal loops and the heating of the loop plasma by a footpoint flare.

Nonlinear effects on composite laminate thermal expansion

NASA Technical Reports Server (NTRS)

Hashin, Z.; Rosen, B. W.; Pipes, R. B.

1979-01-01

Analyses of Graphite/Polyimide laminates shown that the thermomechanical strains cannot be separated into mechanical strain and free thermal expansion strain. Elastic properties and thermal expansion coefficients of unidirectional Graphite/Polyimide specimens were measured as a function of temperature to provide inputs for the analysis. The + or - 45 degrees symmetric Graphite/Polyimide laminates were tested to obtain free thermal expansion coefficients and thermal expansion coefficients under various uniaxial loads. The experimental results demonstrated the effects predicted by the analysis, namely dependence of thermal expansion coefficients on load, and anisotropy of thermal expansion under load. The significance of time dependence on thermal expansion was demonstrated by comparison of measured laminate free expansion coefficients with and without 15 day delay at intermediate temperature.

Enhanced Thermoelectric Properties of Polycrystalline SnSe via LaCl₃ Doping.

PubMed

Li, Fu; Wang, Wenting; Ge, Zhen-Hua; Zheng, Zhuanghao; Luo, Jingting; Fan, Ping; Li, Bo

2018-01-28

LaCl₃ doped polycrystalline SnSe was synthesized by combining mechanical alloying (MA) process with spark plasma sintering (SPS). It is found that the electrical conductivity is enhanced after doping due to the increased carrier concentration and carrier mobility, resulting in optimization of the power factor at 750 K combing with a large Seebeck coefficient over 300 Μvk -1 . Meanwhile, all the samples exhibit lower thermal conductivity below 1.0 W/mK in the whole measured temperature. The lattice thermal conductivity for the doped samples was reduced, which effectively suppressed the increscent of the total thermal conductivity because of the improved electrical conductivity. As a result, a ZT value of 0.55 has been achieved for the composition of SnSe-1.0 wt % LaCl₃ at 750 K, which is nearly four times higher than the undoped one and reveals that rare earth element is an effective dopant for optimization of the thermoelectric properties of SnSe.

Preparation and characterization of self-crosslinked organic/inorganic proton exchange membranes

NASA Astrophysics Data System (ADS)

Zhong, Shuangling; Cui, Xuejun; Dou, Sen; Liu, Wencong

A series of silicon-containing sulfonated polystyrene/acrylate (Si-sPS/A) nanoparticles are successfully synthesized via simple emulsion polymerization method. The Si-sPS/A latexes show good film-forming capability and the self-crosslinked organic/inorganic proton exchange membranes are prepared by pouring the Si-sPS/A nanoparticle latexes into glass plates and drying at 60 °C for 10 h and 120 °C for 2 h. The potential of the membranes in direct methanol fuel cells (DMFCs) is characterized preliminarily by studying their thermal stability, ion-exchange capacity, water uptake, methanol diffusion coefficient, proton conductivity and selectivity (proton conductivity/methanol diffusion coefficient). The results indicate that these membranes possess excellent thermal stability and methanol barrier due to the existence of self-crosslinked silica network. In addition, the proton conductivity of the membranes is in the range of 10 -3-10 -2 S cm -1 and all the membranes show much higher selectivity in comparison with Nafion ® 117. These results suggest that the self-crosslinked organic/inorganic proton exchange membranes are particularly promising in DMFC applications.

Thermal effects in two-phase flow through face seals. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Basu, Prithwish

1988-01-01

When liquid is sealed at high temperature, it flashes inside the seal due to pressure drop and/or viscous heat dissipation. Two-phase seals generally exhibit more erratic behavior than their single phase counterparts. Thermal effects, which are often neglected in single phase seal analyses, play an important role in determining seal behavior under two-phase operation. It is necessary to consider the heat generation due to viscous shear, conduction into the seal rings and convection with the leakage flow. Analytical models developed work reasonably well at the two extremes - for low leakage rates when convection is neglected and for higher leakage rates when conduction is neglected. A preliminary model, known as the Film Coefficient Model, is presented which considers conduction and convection both, and allows continuous boiling over an extended region unlike the previous low-leakage rate model which neglects convection and always forces a discrete boiling interface. Another simplified, semi-analytical model, based on the assumption of isothermal conditions along the seal interafce, has been developed for low leakage rates. The Film Coefficient Model may be used for more accurate and realistic description.

Cross-plane thermoelectric transport in p-type La0.67Sr0.33MnO3/LaMnO3 oxide metal/semiconductor superlattices

NASA Astrophysics Data System (ADS)

Jha, Pankaj; Sands, Timothy D.; Jackson, Philip; Bomberger, Cory; Favaloro, Tela; Hodson, Stephen; Zide, Joshua; Xu, Xianfan; Shakouri, Ali

2013-05-01

The cross-plane thermoelectric transport properties of La0.67Sr0.33MnO3 (LSMO)/LaMnO3 (LMO) oxide metal/semiconductor superlattices were investigated. The LSMO and LMO thin-film depositions were performed using pulsed laser deposition to achieve low resistivity constituent materials for LSMO/LMO superlattice heterostructures on (100)-strontium titanate substrates. X-ray diffraction and high-resolution reciprocal space mapping indicate that the superlattices are epitaxial and pseudomorphic. Cross-plane devices were fabricated by etching cylindrical pillar structures in superlattices using inductively, this coupled-plasma reactive-ion etching. The cross-plane electrical conductivity data for LSMO/LMO superlattices reveal a lowering of the effective barrier height to 223 meV as well as an increase in cross-plane conductivity by an order of magnitude compared to high resistivity superlattices. These results suggest that controlling the oxygen deficiency in the constituent materials enables modification of the effective barrier height and increases the cross-plane conductivity in oxide superlattices. The cross-plane LSMO/LMO superlattices showed a giant Seebeck coefficient of 2560 μV/K at 300 K that increases to 16 640 μV/K at 360 K. The giant increase in the Seebeck coefficient with temperature may include a collective contribution from the interplay of charge, spin current, and phonon drag. The low resistance oxide superlattices exhibited a room temperature cross-plane thermal conductivity of 0.92 W/m K, this indicating that the suppression of thermal conductivities due to the interfaces is preserved in both low and high resistivity superlattices. The high Seebeck coefficient, the order of magnitude improvement in cross-plane conductivity, and the low thermal conductivity in LSMO/LMO superlattices resulted in a two order of magnitude increase in cross-plane power factor and thermoelectric figure of merit (ZT), compared to the properties of superlattices with higher resistivity that were reported previously. The temperature dependence of the cross-plane power factor in low resistance superlattices suggests a direction for further investigations of the potential LSMO/LMO oxide superlattices for thermoelectric devices.

Thermophysical properties of U 3 Si 2 to 1773K

DOE PAGES

White, Joshua Taylor; Nelson, Andrew Thomas; Dunwoody, John Tyler; ...

2015-05-08

Use of U 3Si 2 in nuclear reactors requires accurate thermophysical property data to capture heat transfer within the core. Compilation of the limited previous research efforts focused on the most critical property, thermal conductivity, reveals extensive disagreement. Assessment of this data is challenged by the fact that the critical structural and chemical details of the material used to provide historic data is either absent or confirms the presence of significant impurity phases. This study was initiated to fabricate high purity U 3Si 2 to quantify the coefficient of thermal expansion, heat capacity, thermal diffusivity, and thermal conductivity from roommore » temperature to 1773 K. Here, the datasets provided in this manuscript will facilitate more detailed fuel performance modeling to assess both current and proposed reactor designs that incorporate U 3Si 2.« less

Thermal Properties of SiOC Glasses and Glass Ceramics at Elevated Temperatures

PubMed Central

Stabler, Christina; Reitz, Andreas; Stein, Peter; Albert, Barbara; Riedel, Ralf

2018-01-01

In the present study, the effect of the chemical and phase composition on the thermal properties of silicon oxide carbides (SiOC) has been investigated. Dense monolithic SiOC materials with various carbon contents were prepared and characterized with respect to their thermal expansion, as well as thermal conductivity. SiOC glass has been shown to exhibit low thermal expansion (e.g., ca. 3.2 × 10−6 K−1 for a SiOC sample free of segregated carbon) and thermal conductivity (ca. 1.5 W/(m∙K)). Furthermore, it has been observed that the phase separation, which typically occurs in SiOC exposed to temperatures beyond 1000–1200 °C, leads to a decrease of the thermal expansion (i.e., to 1.83 × 10−6 K−1 for the sample above); whereas the thermal conductivity increases upon phase separation (i.e., to ca. 1.7 W/(m∙K) for the sample mentioned above). Upon adjusting the amount of segregated carbon content in SiOC, its thermal expansion can be tuned; thus, SiOC glass ceramics with carbon contents larger than 10–15 vol % exhibit similar coefficients of thermal expansion to that of the SiOC glass. Increasing the carbon and SiC content in the studied SiOC glass ceramics leads to an increase in their thermal conductivity: SiOC with relatively large carbon and silicon carbides (SiC) volume fractions (i.e., 12–15 and 20–30 vol %, respectively) were shown to possess thermal conductivities in the range from 1.8 to 2.7 W/(m∙K). PMID:29439441

Thermoelectric properties of V2O5 thin films deposited by thermal evaporation

NASA Astrophysics Data System (ADS)

Santos, R.; Loureiro, J.; Nogueira, A.; Elangovan, E.; Pinto, J. V.; Veiga, J. P.; Busani, T.; Fortunato, E.; Martins, R.; Ferreira, I.

2013-10-01

This work reports the structural, optical, electrical and thermoelectric properties of vanadium pentoxide (V2O5) thin films deposited at room temperature by thermal evaporation on Corning glass substrates. A post-deposition thermal treatment up to 973 K under atmospheric conditions induces the crystallization of the as-deposited amorphous films with an orthorhombic V2O5 phase with grain sizes around 26 nm. As the annealing temperature rises up to 773 K the electrical conductivity increases. The films exhibit thermoelectric properties with a maximum Seebeck coefficient of -218 μV/K and electrical conductivity of 5.5 (Ω m)-1. All the films show NIR-Vis optical transmittance above 60% and optical band gap of 2.8 eV.

Thermally stimulated processes in samarium-modified lead titanate ferroelectric ceramics

NASA Astrophysics Data System (ADS)

Peláiz-Barranco, A.; García-Wong, A. C.; González-Abreu, Y.; Gagou, Y.; Saint-Grégoire, P.

2013-08-01

The thermally stimulated processes in a samarium-modified lead titanate ferroelectric system are analyzed from the thermally stimulated depolarization discharge current. The discharge due to the space charge injected during the poling process, the pyroelectric response and a conduction process related to oxygen vacancies are evaluated considering a theoretical decomposition by using a numerical method. The pyroelectric response is separated from other components to evaluate the polarization behavior and some pyroelectric parameters. High remanent polarization, pyroelectric coefficient and merit figure values are obtained at room temperature.

First-principles study of lattice thermal conductivity in ZrTe5 and HfTe5

NASA Astrophysics Data System (ADS)

Wang, Cong; Wang, Haifeng; Chen, Y. B.; Yao, Shu-Hua; Zhou, Jian

2018-05-01

Recently, the layered transition-metal pentatellurides ZrTe5 and HfTe5 have attracted increasing attention because of their interesting topological electronic properties. Nevertheless, some of their other good physical properties seem to be ignored now. Actually, both ZrTe5 and HfTe5 have high electric conductivities (>105 Ω-1 m-1) and Seebeck coefficients (> 100 μV/K) at room temperature, thus making them promising thermoelectric materials. However, the disadvantage is that the thermal conductivities of the two materials are relatively high according to the few available experiments; meanwhile, the detailed mechanism of the intrinsic thermal conductivity has not been studied yet. Based on the density functional theory and the Boltzmann transport theory, we present here the theoretical study of the intrinsic lattice thermal conductivities of ZrTe5 and HfTe5, which are found to be in the range of 5-8 W/mṡK at room temperature and well consistent with the experimental results. We also find that the thermal conductivities of the two materials are anisotropic, which are mainly caused by their anisotropic crystal structures. Based on the detailed analysis, we proposed that the thermal conductivities of the two materials could possibly be reduced by different kinds of structural engineering at the atomic and mesoscopic scales, such as alloying, doping, nano-structuring, and polycrystalline structuring, which could make ZrTe5 and HfTe5 good thermoelectric materials for room temperature thermoelectric applications.

Quantifying Uncertainties in the Thermo-Mechanical Properties of Particulate Reinforced Composites

NASA Technical Reports Server (NTRS)

Mital, Subodh K.; Murthy, Pappu L. N.

1999-01-01

The present paper reports results from a computational simulation of probabilistic particulate reinforced composite behavior. The approach consists use of simplified micromechanics of particulate reinforced composites together with a Fast Probability Integration (FPI) technique. Sample results are presented for a Al/SiC(sub p)(silicon carbide particles in aluminum matrix) composite. The probability density functions for composite moduli, thermal expansion coefficient and thermal conductivities along with their sensitivity factors are computed. The effect of different assumed distributions and the effect of reducing scatter in constituent properties on the thermal expansion coefficient are also evaluated. The variations in the constituent properties that directly effect these composite properties are accounted for by assumed probabilistic distributions. The results show that the present technique provides valuable information about the scatter in composite properties and sensitivity factors, which are useful to test or design engineers.

Large Reduction of Hot Spot Temperature in Graphene Electronic Devices with Heat-Spreading Hexagonal Boron Nitride.

PubMed

Choi, David; Poudel, Nirakar; Park, Saungeun; Akinwande, Deji; Cronin, Stephen B; Watanabe, Kenji; Taniguchi, Takashi; Yao, Zhen; Shi, Li

2018-04-04

Scanning thermal microscopy measurements reveal a significant thermal benefit of including a high thermal conductivity hexagonal boron nitride (h-BN) heat-spreading layer between graphene and either a SiO 2 /Si substrate or a 100 μm thick Corning flexible Willow glass (WG) substrate. At the same power density, an 80 nm thick h-BN layer on the silicon substrate can yield a factor of 2.2 reduction of the hot spot temperature, whereas a 35 nm thick h-BN layer on the WG substrate is sufficient to obtain a factor of 4.1 reduction. The larger effect of the h-BN heat spreader on WG than on SiO 2 /Si is attributed to a smaller effective heat transfer coefficient per unit area for three-dimensional heat conduction into the thick, low-thermal conductivity WG substrate than for one-dimensional heat conduction through the thin oxide layer on silicon. Consequently, the h-BN lateral heat-spreading length is much larger on WG than on SiO 2 /Si, resulting in a larger degree of temperature reduction.

Bandgap tuning and enhancement of seebeck coefficient in one dimensional GeSe

NASA Astrophysics Data System (ADS)

Kagdada, Hardik L.; Dabhi, Shweta D.; Jha, Prafulla K.

2018-04-01

The first principles based density functional theory is used for tuning the electronic bandgap and thermoelectric properties of bulk, two dimensional (2D) and one dimensional (1D) GeSe. There is an increase in the bandgap going from bulk to 1D with indirect to direct bandgap transition. There is a dramatic change in Seebeck coefficient (S) for GeSe going from bulk to 1D at 300 K. The electrical conductivity and electronic thermal conductivity are lower for 1D GeSe compared to the bulk GeSe due to larger bandgap in the case of 1D GeSe.

Nonlinear, Incremental Structural Analysis of Olmsted Locks and Dams. Volume 1: Main Text

DTIC Science & Technology

1992-12-01

dependent functions, which are supplied as algebraic functions of time or as data arrays in ABAQUS user subroutines (Hibbitt, Karlsson, and Sorenson 1988...143.0 Thermal Prouerties 9. The heat transfer capability of ABAQUS uses the finite element method to numerically solve the governing differential...coefficient of linear thermal expansion which were conducted at WES for Olmsted mixtures 6 and 11 (Hammons et al. 1991). The different concrete mixture

Certain physical properties of cobalt and nickel borides

NASA Technical Reports Server (NTRS)

Kostetskiy, I. I.; Lvov, S. N.

1981-01-01

The temperature dependence of the electrical resistivity, the thermal conductivity, and the thermal emf of cobalt and nickel borides were studied. In the case of the nickel borides the magnetic susceptibility and the Hall coefficient were determined at room temperature. The results are discussed with allowance for the current carrier concentration, the effect of various mechanisms of current-carrier scattering and the location of the Fermi level in relation to the 3d band.

Determination of thermal wave reflection coefficient to better estimate defect depth using pulsed thermography

NASA Astrophysics Data System (ADS)

Sirikham, Adisorn; Zhao, Yifan; Mehnen, Jörn

2017-11-01

Thermography is a promising method for detecting subsurface defects, but accurate measurement of defect depth is still a big challenge because thermographic signals are typically corrupted by imaging noise and affected by 3D heat conduction. Existing methods based on numerical models are susceptible to signal noise and methods based on analytical models require rigorous assumptions that usually cannot be satisfied in practical applications. This paper presents a new method to improve the measurement accuracy of subsurface defect depth through determining the thermal wave reflection coefficient directly from observed data that is usually assumed to be pre-known. This target is achieved through introducing a new heat transfer model that includes multiple physical parameters to better describe the observed thermal behaviour in pulsed thermographic inspection. Numerical simulations are used to evaluate the performance of the proposed method against four selected state-of-the-art methods. Results show that the accuracy of depth measurement has been improved up to 10% when noise level is high and thermal wave reflection coefficients is low. The feasibility of the proposed method in real data is also validated through a case study on characterising flat-bottom holes in carbon fibre reinforced polymer (CFRP) laminates which has a wide application in various sectors of industry.

Calculation of Thermal Conductivity Coefficients of Electrons in Magnetized Dense Matter

NASA Astrophysics Data System (ADS)

Bisnovatyi-Kogan, G. S.; Glushikhina, M. V.

2018-04-01

The solution of Boltzmann equation for plasma in magnetic field with arbitrarily degenerate electrons and nondegenerate nuclei is obtained by Chapman-Enskog method. Functions generalizing Sonine polynomials are used for obtaining an approximate solution. Fully ionized plasma is considered. The tensor of the heat conductivity coefficients in nonquantized magnetic field is calculated. For nondegenerate and strongly degenerate plasma the asymptotic analytic formulas are obtained and compared with results of previous authors. The Lorentz approximation with neglecting of electron-electron encounters is asymptotically exact for strongly degenerate plasma. For the first time, analytical expressions for the heat conductivity tensor for nondegenerate electrons in the presence of a magnetic field are obtained in the three-polynomial approximation with account of electron-electron collisions. Account of the third polynomial improved substantially the precision of results. In the two-polynomial approximation, the obtained solution coincides with the published results. For strongly degenerate electrons, an asymptotically exact analytical solution for the heat conductivity tensor in the presence of a magnetic field is obtained for the first time. This solution has a considerably more complicated dependence on the magnetic field than those in previous publications and gives a several times smaller relative value of the thermal conductivity across the magnetic field at ωτ * 0.8.

A strategy to optimize the thermoelectric performance in a spark plasma sintering process

PubMed Central

Chiu, Wan-Ting; Chen, Cheng-Lung; Chen, Yang-Yuan

2016-01-01

Spark plasma sintering (SPS) is currently widely applied to existing alloys as a means of further enhancing the alloys’ figure of merit. However, the determination of the optimal sintering condition is challenging in the SPS process. This report demonstrates a systematic way to independently optimize the Seebeck coefficient S and the ratio of electrical to thermal conductivity (σ/κ) and thus achieve the maximum figure of merit zT = S2(σ/κ)T. Sb2−xInxTe3 (x = 0–0.2) were chosen as examples to validate the method. Although high sintering temperature and pressure are helpful in enhancing the compactness and electrical conductivity of pressed samples, the resultant deteriorated Seebeck coefficient and increasing thermal conductivity eventually offset the benefit. We found that the optimal sintering temperature coincides with temperatures at which the maximum Seebeck coefficient begins to degrade, whereas the optimal sintering pressure coincided with the pressure at which the σ/κ ratio reaches a maximum. Based on this principle, the optimized sintering conditions were determined, and the zT of Sb1.9In0.1Te3 is raised to 0.92 at 600 K, showing an approximately 84% enhancement. This work develops a facile strategy for selecting the optimal SPS sintering condition to further enhance the zT of bulk specimens. PMID:26975209

Transport properties of carbon dioxide and methane from molecular dynamics simulations.

PubMed

Aimoli, C G; Maginn, E J; Abreu, C R A

2014-10-07

Transport properties of carbon dioxide and methane are predicted for temperatures between (273.15 and 573.15) K and pressures up to 800 MPa by molecular dynamics simulations. Viscosities and thermal conductivities were obtained through the Green-Kubo formalism, whereas the Einstein relation was used to provide self-diffusion coefficient estimates. The differences in property predictions due to the force field nature and parametrization were investigated by the comparison of seven different CO2 models (two single-site models, three rigid three-site models, and two fully flexible three-site models) and three different CH4 models (two single-site models and one fully flexible five-site model). The simulation results show good agreement with experimental data, except for thermal conductivities at low densities. The molecular structure and force field parameters play an important role in the accuracy of the simulations, which is within the experimental deviations reported for viscosities and self-diffusion coefficients considering the most accurate CO2 and CH4 models studied. On the other hand, the molecular flexibility does not seem to improve accuracy, since the explicit account of vibrational and bending degrees of freedom in the CO2 flexible models leads to slightly less accurate results. Nonetheless, the use of a correctional term to account for vibrational modes in rigid models generally improves estimations of thermal conductivity values. At extreme densities, the caging effect observed with single-site representations of the molecules restrains mobility and leads to an unphysical overestimation of viscosities and, conversely, to the underestimation of self-diffusion coefficients. This result may help to better understand the limits of applicability of such force fields concerning structural and transport properties of dense systems.

Thermoelectric Properties of Bi Doped Tetrahedrite

NASA Astrophysics Data System (ADS)

Prem Kumar, D. S.; Chetty, R.; Femi, O. E.; Chattopadhyay, K.; Malar, P.; Mallik, R. C.

2017-05-01

Bi doped tetrahedrites with nominal compositions of Cu12Sb4- x Bi x S13 ( x = 0, 0.2, 0.4, 0.6, 0.8) were synthesized by the solid state reaction method. Powder x-ray diffraction patterns confirmed that Cu12Sb4S13 (tetrahedrite structure) was the main phase, along with Cu3SbS4 and Cu3SbS3 as the secondary phases. Electron probe microanalysis provided the elemental composition of all the samples. It was confirmed that the main phase is the tetrahedrite phase with slight deviations in the stoichiometry. All the transport properties were measured between 423 K and 673 K. The electrical resistivity increased with an increase in Bi content for all the samples, possibly induced by the variation in the carrier concentration, which may be due to the influence of impurity phases. The increase in electrical resistivity with an increase in temperature indicates the degenerate semiconducting nature of the samples. The absolute Seebeck coefficient is positive throughout the temperature range indicating the p-type nature of the samples. The Seebeck coefficient for all the samples increased with an increase in Bi content as electrical resistivity. The variation of electrical resistivity and the Seebeck coefficient with doping can be attributed to the changes in the carrier concentration of the samples. The total thermal conductivity increases with an increase in temperature and decreases with an increase in the Bi content that could be due to the reduction in carrier thermal conductivity. The highest thermoelectric figure of merit ( zT) 0.84 at 673 K was obtained for the sample with x = 0.2 due to lower thermal conductivity (1.17 W/m K).

Cross-plane electrical and thermal transport in oxide metal/semiconductor superlattices

NASA Astrophysics Data System (ADS)

Jha, Pankaj

Perovskite oxides display a rich variety of electronic properties as metals, ferroelectrics, ferromagnetics, multiferroics, and thermoelectrics. Cross-plane electron filtering transport in metal/semiconductor superlattices provides a potential approach to increase the thermoelectric figure of merit (ZT). La0.67Sr0.33MnO3 (LSMO) and LaMnO3 (LMO) thin-film depositions were optimized using pulsed laser deposition (PLD) to achieve low resistivity constituent materials for LSMO/LMO superlattice heterostructures on (100)-strontium titanate (STO) substrates. X-ray diffraction and high-resolution reciprocal space mapping (RSM) indicate that the superlattices are epitaxial and pseudomorphic. Cross-plane devices were fabricated by etching cylindrical pillar structures in superlattices using inductively-coupled-plasma reactive-ion etching. The cross-plane electrical conductivity data for LSMO/LMO superlattices reveal an effective barrier height of 220 meV. The cross-plane LSMO/LMO superlattices showed a giant Seebeck coefficient of 2560 microV/K at 300K that increases to 16640 microV/K at 360K. The large Seebeck coefficient may arise due to hot electron and spin filtering as LSMO/LMO superlattice constituent materials exhibit spintronic properties where charges and spin current are intertwined and can generate a spin-Seebeck effect. The room temperature thermal conductivity achieved in low resistivity superlattices was 0.92 W/mK, which indicates that cross-plane phonon scattering at interfaces reduces the lattice contribution to the thermal conductivity. The giant contribution of spin-Seebeck, the large temperature dependence of the cross-plane power factor, and the low thermal conductivity in low resistance LSMO/LMO superlattices may offer opportunities to realize spin-magnetic thermoelectric devices, and suggests a direction for further investigations of the potential of LSMO/LMO oxide superlattices for thermoelectric devices.

Thermal conductivity investigation of adhesive-free bond laser components

NASA Astrophysics Data System (ADS)

Li, Da; Hong, Pengda; Vedula, MahaLakshmi; Meissner, Helmuth E.

2017-02-01

An interferometric method has been developed and employed at Onyx Optics, Inc. to accurately measure the thermal conductivity of laser-active crystals as function of dopant concentration or inactive materials such as single crystals, optical ceramics and glasses relative to a standard of assumed to be known thermal conductivity [1]. This technique can also provide information on heat transfer resistance at the interface between two materials in close thermal contact. While the technique appears generally applicable to composites between optically homogeneous materials, we report on thermal conductivities and heat transfer coefficients of selected adhesive-free bond (AFB®) laser composites. Single crystal bars and AFB bonded crystal doublets with the combinations of various rare-earth (Nd3+, Yb3+, Er3+, and Tm3+ trivalent ion doped YAG, and un-doped YAG have been fabricated with the AFB technique. By loading the test sample in a vacuum cryostat, with a precisely controlled heat load at one end of the doublets, the temperature distribution inside the single crystal or the composite samples can been precisely mapped by measuring the optical path difference interferometrically, given the material's thermal-optical properties. No measurable heat transfer resistance can be identified for the AFB interfaces between low-concentration doped YAG and un-doped YAG. For the heavily doped RE3+:YAG, for example, 10% Yb:YAG, the thermal conductivity measured in our experiment is 8.3 W/m•K, using the thermal conductivity of undoped YAG reported in [1] as basis. The thermal transfer resistance of the AFB interface with un-doped YAG, if there is any at the AFB interface, could be less than 1.29×10-6 m2•K/W.

Thermoelectric Properties of Complex Zintl Phases

NASA Astrophysics Data System (ADS)

Snyder, G. Jeffrey

2008-03-01

Complex Zintl phases make ideal thermoelectric materials because they can exhibit the necessary ``electron-crystal, phonon-glass'' properties required for high thermoelectric efficiency. Complex crystal structures can lead to high thermoelectric figure of merit (zT) by having extraordinarily low lattice thermal conductivity. A recent example is the discovery that Yb14MnSb11, a complex Zintl compound, has twice the zT as the SiGe based material currently in use at NASA. The high temperature (300K - 1300K) electronic properties of Yb14MnSb11 can be understood using models for heavily doped semiconductors. The free hole concentration, confirmed by Hall effect measurements, is set by the electron counting rules of Zintl and the valence of the transition metal (Mn^+2). Substitution of nonmagnetic Zn^+2 for the magnetic Mn^+2 reduces the spin-disorder scattering and leads to increased zT (10%). The reduction of spin-disorder scattering is consistent with the picture of Yb14MnSb11 as an underscreened Kondo lattice as derived from low temperature measurements. The hole concentration can be reduced by the substitution of Al^+3 for Mn^+2, which leads to an increase in the Seebeck coefficient and electrical resistivity consistent with models for degenerate semiconductors. This leads to further improvements (about 25%) in zT and a reduction in the temperature where the zT peaks. The peak in zT is due to the onset of minority carrier conduction and can be correlated with reduction in Seebeck coefficient, increase in electrical conductivity and increase in thermal conductivity due to bipolar thermal conduction.

New methodology for the thermal characterization of thermoelectric liquids

NASA Astrophysics Data System (ADS)

Touati, Karim; Depriester, Michael; Kuriakose, Maju; Hadj Sahraoui, Abdelhak

2015-09-01

A new and accurate method for the thermal characterization of thermoelectric liquids is proposed. The experiment is based on a self-generated voltage due to the Seebeck effect. This voltage is provided by the sample when one of its two faces is thermally excited using a modulated laser. The sample used is tetradodecylammonium nitrate salt/1-octanol mixture, with high Seebeck coefficient. The thermal properties of the used sample (thermal diffusivity, effusivity, and conductivity) are found and compared to those obtained by other photothermal techniques. In addition to this, a study of the electrolyte thermal parameters with the variation of tetradodecylammonium nitrate concentration was also carried out. This new method is promising due to its accuracy and its simplicity.

A method of measuring the effective thermal conductivity of thermoplastic foams

NASA Astrophysics Data System (ADS)

Asséko, André Chateau Akué; Cosson, Benoit; Chaki, Salim; Duborper, Clément; Lacrampe, Marie-France; Krawczak, Patricia

2017-10-01

An inverse method for determining the in-plane effective thermal conductivity of porous thermoplastics was implemented by coupling infrared thermography experiments and numerical solution of heat transfer in straight fins having temperature-dependent convective heat transfer coefficient. The obtained effective thermal conductivity values were compared with previous results obtained using a numerical solution based on periodic homogenization techniques (NSHT) in which the microstructure heterogeneity of extruded polymeric polyethylene (PE) foam in which pores are filled with air with different levels of open and closed porosity was taken into account and Transient Plane Source Technique (TPS) in order to verify the accuracy of the proposed method. The new method proposed in the present study is in good agreement with both NSHT and TPS. It is also applicable to structural materials such as composites, e.g. unidirectional fiber-reinforced plastics, where heat transfer is very different according to the fiber direction (parallel or transverse to the fibers).

Enhanced thermoelectric performance of defected silicene nanoribbons

NASA Astrophysics Data System (ADS)

Zhao, W.; Guo, Z. X.; Zhang, Y.; Ding, J. W.; Zheng, X. J.

2016-02-01

Based on non-equilibrium Green's function method, we investigate the thermoelectric performance for both zigzag (ZSiNRs) and armchair (ASiNRs) silicene nanoribbons with central or edge defects. For perfect silicene nanoribbons (SiNRs), it is shown that with its width increasing, the maximum of ZT values (ZTM) decreases monotonously while the phononic thermal conductance increases linearly. For various types of edges and defects, with increasing defect numbers in longitudinal direction, ZTM increases monotonously while the phononic thermal conductance decreases. Comparing with ZSiNRs, defected ASiNRs possess higher thermoelectric performance due to higher Seebeck coefficient and lower thermal conductance. In particular, about 2.5 times enhancement to ZT values is obtained in ASiNRs with edge defects. Our theoretical simulations indicate that by controlling the type and number of defects, ZT values of SiNRs could be enhanced greatly which suggests their very appealing thermoelectric applications.

Role of grain and grain boundary on the electrical and thermal conductivity of Bi0.9Y0.1Fe0.9Mn0.1O3 ceramics

NASA Astrophysics Data System (ADS)

Pandey, Rabichandra; Panda, Chandrakanta; Kumar, Pawan; Pradhan, Lagen Kumar; Kar, Manoranjan

2017-05-01

Role of grain and grain boundary on electrical and thermal conductivity of Bi0.9Y0.1Fe0.9Mn0.1O3 ceramic was investigated systematically. Tartaric acid modified sol gel method was used to synthesize the compound. X-ray diffraction technique was used to confirm the formation of single phase orthorhombic (Pbnm) structure. Electrical properties of the sample were measured with a wide frequency range from 100Hz to 10MHz at different temperature from 40°C to 250°C. AC impedance studies indicate the presence of grain and grain boundary effect. The negative temperature coefficient of resistance (NTCR) behaviour of the compound has been confirmed by the cole-cole plot. DC electrical and thermal conductivities of the compound were explained on the basis of grain and grain boundaries.

The time and temperature dependence of the thermoelectric properties of silicon-germanium alloy

NASA Technical Reports Server (NTRS)

Raag, V.

1975-01-01

Experimental data on the electrical resistivity and Seebeck coefficient of n-type and p-type silicon-germanium alloys are analyzed in terms of a solid-state dopant precipitation model proposed by Lifshitz and Slyozov (1961). Experimental findings on the time and temperature dependence of the thermal conductivity of these two types of alloy indicate that the thermal conductivity of silicon-germanium alloys changes with time, contrary to previous hypothesis. A preliminary model is presented which stipulates that the observed thermal conductivity decrease in silicon-germanium alloys is due partly to dopant precipitation underlying the electrical property changes and partly to enhanced alloying of the material. It is significant that all three properties asymptotically approach equilibrium values with time. Total characterization of these properties will enable the time change to be fully compensated in the design of a thermoelectric device employing silicon-germanium alloys.

Electric Motor Thermal Management Research: Annual Progress Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bennion, Kevin S.

Past work in the area of active convective cooling provided data on the average convective heat transfer coefficients of circular orifice automatic transmission fluid (ATF) jets impinging on stationary targets intended to represent the wire bundle surface of the motor end-winding. Work during FY16 focused on the impact of alternative jet geometries that could lead to improved cooling over a larger surface of the motor winding. Results show that the planar jet heat transfer coefficients over a small (12.7-mm-diameter) target surface are not too much lower than for the circular orifice jet in which all of the ATF from themore » jet impinges on the target surface. The planar jet has the potential to achieve higher heat transfer over a larger area of the motor end winding. A new test apparatus was constructed to measure the spatial dependence of the heat transfer relative to the jet nozzle over a larger area representative of a motor end-winding. The tested planar flow geometry has the potential to provide more uniform cooling over the full end-winding surface versus the conventional jet configuration. The data will be used by motor designers to develop thermal management strategies to improve motor power density. Work on passive thermal design in collaboration with Oak Ridge National Laboratory to measure the thermal conductivity of wire bundle samples representative of end-winding and slot-winding materials was completed. Multiple measurement techniques were compared to determine which was most suitable for measuring composite wire bundle samples. NREL used a steady-state thermal resistance technique to measure the direction-dependent thermal conductivity. The work supported new interactions with industry to test new materials and reduce passive-stack thermal resistance in motors, leading to motors with increased power density. NREL collaborated with Ames Laboratory in the area of material characterization. The work focused on measuring the transverse rupture strength of new magnet materials developed at Ames. The impact of the improved transverse rupture strength is a mechanically stronger magnet that is easier for manufacturers to implement into motor designs. The thermal conductivity of the new magnet materials was also measured in comparison to two commercially available AlNiCo magnet materials. The impact of the thermal conductivity of the magnet material will need to be analyzed in the context of a motor application.« less

Forced and natural convection in aggregate-laden nanofluids

NASA Astrophysics Data System (ADS)

Thajudeen, Thaseem; Hogan, Christopher J.

2011-12-01

A number of experimental and theoretical studies of convective heat transfer in nanofluids (liquid suspensions of nanoparticles, typically with features below 100 nm in size) reveal contrasting results; nanoparticles can either enhance or reduce the convective heat transfer coefficient. These disparate conclusions regarding the influence of nanoparticles on convective heat transfer may arise due to the aggregation of nanoparticles, which is often not considered in studies of nanofluids. Here, we examine theoretically forced and natural convective heat transfer of aggregate-laden nanofluids using Monte Carlo-based models to determine how the aggregate morphology influences the convective heat transfer coefficient. Specifically, in this study, it is first shown that standard heat transfer correlations should apply to nanofluids, and the main influence of the nanoparticles is to alter suspension thermal conductivity, dynamic viscosity, density, specific heat, and thermal expansion coefficient. Aggregated particles in suspension are modeled as quasi-fractal aggregates composed of individual primary particles described by the primary particle radius, number of primary particles, fractal (Hausdorff) dimension, pre-exponential factor, and degree of coalescence between primary particles. A sequential algorithm is used to computationally generate aggregates with prescribed morphological descriptors. Four types of aggregates are considered; spanning the range of aggregate morphologies observed in nanofluids. For each morphological type, the influences of aggregates on nanofluid dynamic viscosity and thermal conductivity are determined via first passage-based Brownian dynamics calculations. It is found that depending on both the material properties of the nanoparticles as well as the nanoparticle morphology, the addition of nanoparticles to a suspension can either increase or decrease both the forced and natural convective heat transfer coefficients, with both a 51% increase and a 32% decrease in the heat transfer coefficient achievable at particle volume fractions of 0.05. This study shows clearly that the influence of particle morphology needs to be accounted for in all studies of heat transfer in nanofluids.

Thermoelectric Properties and Thermal Tolerance of Indium Tin Oxide Nanowires.

PubMed

Hernandez, Jose A; Carpena Nunez, Jennifer; Fonseca, Luis F; Pettes, Michael Thompson; Yacaman, Miguel Jose; Benitez, Alfredo

2018-06-14

Single-crystalline indium tin oxide (ITO) nanowires were grown via a vapor-liquid-solid (VLS) method, with thermal tolerance up to ~1300°C. We report the electric and thermoelectric properties of the ITO nanowires before and after heat treatments and draw conclusions about their applicability as thermoelectric building blocks in nanodevices that can operate in high temperature conditions. The Seebeck coefficient and the thermal and electrical conductivities were measured in each individual nanowire by means of specialized micro-bridge thermometry devices. Measured data was analyzed and explained in terms of changes in charge carrier density, impurities and vacancies due to the thermal treatments. © 2018 IOP Publishing Ltd.

Thermophysical properties of gas phase uranium tetrafluoride

NASA Technical Reports Server (NTRS)

Watanabe, Yoichi; Anghaie, Samim

1993-01-01

Thermophysical data of gaseous uranium tetrafluoride (UF4) are theoretically obtained by taking into account dissociation of molecules at high temperatures (2000-6000 K). Determined quantities include specific heat, optical opacity, diffusion coefficient, viscosity, and thermal conductivity. A computer program is developed for the calculation.

Mechanical properties of neat polymer matrix materials and their unidirectional carbon fiber-reinforced composites

NASA Technical Reports Server (NTRS)

Zimmerman, Richard S.; Adams, Donald F.

1988-01-01

The mechanical properties of two neat resin systems for use in carbon fiber epoxy composites were characterized. This included tensile and shear stiffness and strengths, coefficients of thermal and moisture expansion, and fracture toughness. Tests were conducted on specimens in the dry and moisture-saturated states, at temperatures of 23, 82 and 121 C. The neat resins tested were American Cyanamid 1806 and Union Carbide ERX-4901B(MPDA). Results were compared to previously tested neat resins. Four unidirectional carbon fiber reinforced composites were mechanically characterized. Axial and transverse tension and in-plane shear strengths and stiffness were measured, as well as transverse coefficients of thermal and moisture expansion. Tests were conducted on dry specimens only at 23 and 100 C. The materials tested were AS4/3502, AS6/5245-C, T300/BP907, and C6000/1806 unidirectional composites. Scanning electron microscopic examination of fracture surfaces was performed to permit the correlation of observed failure modes with the environmental test conditions.

Electronic transport properties of intermediately coupled superconductors: PdTe2 and Cu0.04PdTe2

NASA Astrophysics Data System (ADS)

Hooda, M. K.; Yadav, C. S.

2018-01-01

We have investigated the electrical resistivity (1.8-480 K), Seebeck coefficient (2.5-300 K) and thermal conductivity (2.5-300 K) of PdTe2 and 4% Cu intercalated PdTe2 compounds. The electrical resistivity for the compounds shows a Bloch-Gruneisen-type linear temperature (T) dependence for 100 \\text{K}, and Fermi liquid behavior (ρ (T) \\propto T2) for T<50 \\text{K} . Seebeck coefficient data exhibit a strong competition between Normal (N) and Umklapp (U) scattering processes at low T. The low-T, thermal conductivity (κ) of the compounds is strongly dominated by the electronic contribution, and exhibits a rare linear T-dependence below 10 K. However, high-T, κ (T) shows the usual 1/T -dependence, dominated by the U-scattering process. The electron-phonon coupling parameters, estimated from the low-T, specific-heat data and first-principle electronic structure calculations suggest that PdTe2 and Cu0.04PdTe2 are intermediately coupled superconductors.

Monte Carlo Study on Carbon-Gradient-Doped Silica Aerogel Insulation.

PubMed

Zhao, Y; Tang, G H

2015-04-01

Silica aerogel is almost transparent for wavelengths below 8 µm where significant energy is transferred by thermal radiation. The radiative heat transfer can be restricted at high temperature if doped with carbon powder in silica aerogel. However, different particle sizes of carbon powder doping have different spectral extinction coefficients and the doped carbon powder will increase the solid conduction of silica aerogel. This paper presents a theoretical method for determining the optimal carbon doping in silica aerogel to minimize the energy transfer. Firstly we determine the optimal particle size by combining the spectral extinction coefficient with blackbody radiation and then evaluate the optimal doping amount between heat conduction and radiation. Secondly we develop the Monte Carlo numerical method to study radiative properties of carbon-gradient-doped silica aerogel to decrease the radiative heat transfer further. The results indicate that the carbon powder is able to block infrared radiation and thus improve the thermal insulating performance of silica aerogel effectively.

Thermoelectric Properties in the TiO2/SnO2 System

NASA Technical Reports Server (NTRS)

Dynys, F.; Sayir, A.; Sehirlioglu, A.; Berger, M.

2009-01-01

Nanotechnology has provided a new interest in thermoelectric technology. A thermodynamically driven process is one approach in achieving nanostructures in bulk materials. TiO2/SnO2 system exhibits a large spinodal region with exceptional stable phase separated microstructures up to 1400 C. Fabricated TiO2/SnO2 nanocomposites exhibit n-type behavior with Seebeck coefficients greater than -300 .V/K. Composites exhibit good thermal conductance in the range of 7 to 1 W/mK. Dopant additions have not achieved high electrical conductivity (<1000 S/m). Formation of oxygen deficient composites, TixSn1-xO2-y, can change the electrical conductivity by four orders of magnitude. Achieving higher thermoelectric ZT by oxygen deficiency is being explored. Seebeck coeffcient, thermal conductivity, electrical conductance and microstructure will be discussed in relation to composition and doping.

Thermoelectric properties of nanostructured porous silicon

NASA Astrophysics Data System (ADS)

Martín-Palma, R. J.; Cabrera, H.; Martín-Adrados, B.; Korte, D.; Pérez-Cappe, E.; Mosqueda, Y.; Frutis, M. A.; Danguillecourt, E.

2018-01-01

In this work we report on the thermoelectric properties of nanostructured porous silicon (nanoPS) layers grown onto silicon substrates. More specifically, nanoPS layers of different porosity, nanocrystal size, and thickness were fabricated and their electrical conductivities, Seebeck coefficients, and thermal conductivities were subsequently measured. It was found that these parameters show a strong dependence on the characteristics of the nanoPS layers and thus can be controlled.

Impact of internal crystalline boundaries on lattice thermal conductivity: Importance of boundary structure and spacing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aghababaei, Ramin, E-mail: ramin.aghababaei@epfl.ch; Anciaux, Guillaume; Molinari, Jean-François

2014-11-10

The low thermal conductivity of nano-crystalline materials is commonly explained via diffusive scattering of phonons by internal boundaries. In this study, we have quantitatively studied phonon-crystalline boundaries scattering and its effect on the overall lattice thermal conductivity of crystalline bodies. Various types of crystalline boundaries such as stacking faults, twins, and grain boundaries have been considered in FCC crystalline structures. Accordingly, the specularity coefficient has been determined for different boundaries as the probability of the specular scattering across boundaries. Our results show that in the presence of internal boundaries, the lattice thermal conductivity can be characterized by two parameters: (1)more » boundary spacing and (2) boundary excess free volume. We show that the inverse of the lattice thermal conductivity depends linearly on a non-dimensional quantity which is the ratio of boundary excess free volume over boundary spacing. This shows that phonon scattering across crystalline boundaries is mainly a geometrically favorable process rather than an energetic one. Using the kinetic theory of phonon transport, we present a simple analytical model which can be used to evaluate the lattice thermal conductivity of nano-crystalline materials where the ratio can be considered as an average density of excess free volume. While this study is focused on FCC crystalline materials, where inter-atomic potentials and corresponding defect structures have been well studied in the past, the results would be quantitatively applicable for semiconductors in which heat transport is mainly due to phonon transport.« less

Transport properties of partially ionized and unmagnetized plasmas.

PubMed

Magin, Thierry E; Degrez, Gérard

2004-10-01

This work is a comprehensive and theoretical study of transport phenomena in partially ionized and unmagnetized plasmas by means of kinetic theory. The pros and cons of different models encountered in the literature are presented. A dimensional analysis of the Boltzmann equation deals with the disparity of mass between electrons and heavy particles and yields the epochal relaxation concept. First, electrons and heavy particles exhibit distinct kinetic time scales and may have different translational temperatures. The hydrodynamic velocity is assumed to be identical for both types of species. Second, at the hydrodynamic time scale the energy exchanged between electrons and heavy particles tends to equalize both temperatures. Global and species macroscopic fluid conservation equations are given. New constrained integral equations are derived from a modified Chapman-Enskog perturbative method. Adequate bracket integrals are introduced to treat thermal nonequilibrium. A symmetric mathematical formalism is preferred for physical and numerical standpoints. A Laguerre-Sonine polynomial expansion allows for systems of transport to be derived. Momentum, mass, and energy fluxes are associated to shear viscosity, diffusion coefficients, thermal diffusion coefficients, and thermal conductivities. A Goldstein expansion of the perturbation function provides explicit expressions of the thermal diffusion ratios and measurable thermal conductivities. Thermal diffusion terms already found in the Russian literature ensure the exact mass conservation. A generalized Stefan-Maxwell equation is derived following the method of Kolesnikov and Tirskiy. The bracket integral reduction in terms of transport collision integrals is presented in Appendix for the thermal nonequilibrium case. A simple Eucken correction is proposed to deal with the internal degrees of freedom of atoms and polyatomic molecules, neglecting inelastic collisions. The authors believe that the final expressions are readily usable for practical applications in fluid dynamics.

Characterization of microstructural, mechanical and thermophysical properties of Th-52U alloy

NASA Astrophysics Data System (ADS)

Das, Santanu; Kaity, S.; Kumar, R.; Banerjee, J.; Roy, S. B.; Chaudhari, G. P.; Daniel, B. S. S.

2016-11-01

Th-52 wt.% U alloy has a microstructure featuring interspersed networks of uranium rich and thorium rich phases. Room temperature hardness of the alloy is more than twice that of unalloyed thorium. The alloy age hardens (550 °C) only slightly (peak hardness/hardness of solution heated and quenched = 1.05). Room temperature thermal conductivity (25.6 W m-1 °C-1) is close to that of uranium and most of the binary and ternary metallic alloy fuel materials. Average linear coefficient of thermal expansion (CTE) of Th-52 wt.% U alloy [11.2 × 10-06 °C-1 (27-290 °C) and 16.75 × 10-06 °C-1 (27-600 °C)] are comparable with that of many metallic alloy fuel candidates. Th-52 wt.% U alloy with non-age hardenable microstructure, appreciable thermal conductivity, moderate thermal expansion may find metallic fuel applications in nuclear reactors.

CaMn(1-x)Nb(x)O3 (x < or = 0.08) perovskite-type phases as promising new high-temperature n-type thermoelectric materials.

PubMed

Bocher, L; Aguirre, M H; Logvinovich, D; Shkabko, A; Robert, R; Trottmann, M; Weidenkaff, A

2008-09-15

Perovskite-type CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) compounds were synthesized by applying both a "chimie douce" (SC) synthesis and a classical solid state reaction (SSR) method. The crystallographic parameters of the resulting phases were determined from X-ray, electron, and neutron diffraction data. The manganese oxidations states (Mn(4+)/Mn(3+)) were investigated by X-ray photoemission spectroscopy. The orthorhombic CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) phases were studied in terms of their high-temperature thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Differences in electrical transport and thermal properties can be correlated with different microstructures obtained by the two synthesis methods. In the high-temperature range, the electron-doped manganate phases exhibit large absolute Seebeck coefficient and low electrical resistivity values, resulting in a high power factor, PF (e.g., for x = 0.05, S(1000K) = -180 microV K(-1), rho(1000K) = 16.8 mohms cm, and PF > 1.90 x 10(-4) W m(-1) K(-2) for 450 K < T < 1070 K). Furthermore, lower thermal conductivity values are achieved for the SC-derived phases (kappa < 1 W m(-1) K(-1)) compared to the SSR compounds. High power factors combined with low thermal conductivity (leading to ZT values > 0.3) make these phases the best perovskitic candidates as n-type polycrystalline thermoelectric materials operating in air at high temperatures.

Hybrid Heat Exchangers

NASA Technical Reports Server (NTRS)

Tu, Jianping Gene; Shih, Wei

2010-01-01

A hybrid light-weight heat exchanger concept has been developed that uses high-conductivity carbon-carbon (C-C) composites as the heat-transfer fins and uses conventional high-temperature metals, such as Inconel, nickel, and titanium as the parting sheets to meet leakage and structural requirements. In order to maximize thermal conductivity, the majority of carbon fiber is aligned in the fin direction resulting in 300 W/m.K or higher conductivity in the fin directions. As a result of this fiber orientation, the coefficient of thermal expansion (CTE) of the C-C composite in both non-fiber directions matches well with the CTE of various high-temperature metal alloys. This allows the joining of fins and parting sheets by using high-temperature braze alloys.

Energy-absorption spectroscopy of unitary Fermi gases in a uniform potential

NASA Astrophysics Data System (ADS)

Zhang, Pengfei; Yu, Zhenhua

2018-04-01

We propose to use the energy absorption spectroscopy to measure the kinetic coefficients of unitary Fermi gases in a uniform potential. We show that, in our scheme, the energy absorption spectrum is proportional to the dynamic structure factor of the system. The profile of the spectrum depends on the shear viscosity η , the thermal conductivity κ , and the superfluid bulk viscosity ξ3. We show that extraction of these coefficients from the spectrum is achievable in present experiments.

High Thermal Conductivity Polymer Matrix Composites (PMC) for Advanced Space Radiators

NASA Technical Reports Server (NTRS)

Shin, E. Eugene; Bowman, Cheryl; Beach, Duane

2007-01-01

High temperature polymer matrix composites (PMC) reinforced with high thermal conductivity (approx. 1000 W/mK) pitch-based carbon fibers are evaluated for a facesheet/fin structure of large space radiator systems. Significant weight reductions along with improved thermal performance, structural integrity and space durability toward its metallic counterparts were envisioned. Candidate commercial resin systems including Cyanate Esters, BMIs, and polyimide were selected based on thermal capabilities and processability. PMC laminates were designed to match the thermal expansion coefficient of various metal heat pipes or tubes. Large, but thin composite panels were successfully fabricated after optimizing cure conditions. Space durability of PMC with potential degradation mechanisms was assessed by simulated thermal aging tests in high vacuum, 1-3 x 10(exp -6) torr, at three temperatures, 227 C, 277 C, and 316 C for up to one year. Nanocomposites with vapor-grown carbon nano-fibers and exfoliated graphite flakes were attempted to improve thermal conductivity (TC) and microcracking resistance. Good quality nanocomposites were fabricated and evaluated for TC and durability including radiation resistance. TC was measured in both in-plan and thru-the-thickness directions, and the effects of microcracks on TC are also being evaluated. This paper will discuss the systematic experimental approaches, various performance-durability evaluations, and current subcomponent design and fabrication/manufacturing efforts.

“Glass-like” thermal conductivity gradually induced in thermoelectric Sr{sub 8}Ga{sub 16}Ge{sub 30} clathrate by off-centered guest atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christensen, Sebastian; Schmøkel, Mette Stokkebro; Borup, Kasper Andersen

The origin of the “glass-like” plateau in thermal conductivity of inorganic type I clathrates has been debated for more than a decade. Here, it is demonstrated that the low temperature thermal conductivity of Sr{sub 8}Ga{sub 16}Ge{sub 30} can be controlled by the synthesis method: A flux-grown sample has a “glass-like” plateau in thermal conductivity at low temperature, while a zone-melted sample instead has a crystalline peak. A combination of flux-growth and zone-melting produces an intermediate thermal conductivity. In a comprehensive study of three single crystal samples, it is shown by neutron diffraction that the transition from crystalline peak to “glass-like”more » plateau is related to an increase in Sr guest atom off-centering distance from 0.24 Å to 0.43 Å. By modifying ab initio calculated force constants for the guest atom to an isotropic model, we reproduce both measured heat capacity and inelastic neutron scattering data. The transition from peak to plateau in the thermal conductivity can be modeled by a combined increase of Rayleigh and disorder scattering. Measurement of heat capacity refutes simple models for tunneling of Sr between off-center sites. Furthermore, the electronic properties of the same samples are characterized by Hall carrier density, Seebeck coefficient, and resistivity. The present comprehensive analysis excludes tunneling and charge carrier scattering as dominant contributors to the “glass-like” plateau. The increased guest atom off-centering distance controlled by synthesis provides a possible microscopic mechanism for reducing the low temperature thermal conductivity of clathrates.« less

Hybrid Exhaust Component

NASA Technical Reports Server (NTRS)

Pelletier, Gerard D. (Inventor); Logan, Charles P. (Inventor); McEnerney, Bryan William (Inventor); Haynes, Jeffrey D. (Inventor)

2015-01-01

An exhaust includes a wall that has a first composite material having a first coefficient of thermal expansion and a second composite material having a second coefficient of the thermal expansion that is less than the first coefficient of thermal expansion.

Ceramic matrix composite turbine engine vane

NASA Technical Reports Server (NTRS)

Prill, Lisa A. (Inventor); Schaff, Jeffery R. (Inventor); Shi, Jun (Inventor)

2012-01-01

A vane has an airfoil shell and a spar within the shell. The vane has an outboard shroud at an outboard end of the shell and an inboard platform at an inboard end of the shell. The shell includes a region having a depth-wise coefficient of thermal expansion and a second coefficient of thermal expansion transverse thereto, the depth-wise coefficient of thermal expansion being greater than the second coefficient of thermal expansion.

Unsteady Convection Flow and Heat Transfer over a Vertical Stretching Surface

PubMed Central

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient. PMID:25264737

Unsteady convection flow and heat transfer over a vertical stretching surface.

PubMed

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.

Long-time tails of the green-kubo integrands for a binary mixture

NASA Astrophysics Data System (ADS)

Wood, W. W.

1989-11-01

The long-time tails for the mutual diffusion coefficient, the thermal diffusivity, the thermal conductivity, and the shear and longitudinal viscosities (from which the tail of the bulk viscosity can be calculated) of a nonreactive binary mixture are calculated from mode-coupling theory, and compared with a prior calculation by Pomeau. Three different choices of the thermal forces and currents are considered, with the results found to take their simplest form in the case of the de Groot "double-primed set". The decompositions into the kinetic, potential, and cross terms are given.

Improved Gas Metal Arc Welding Multi-Physics Process Model and Its Application to MIL A46100 Armor-Grade Steel Butt-welds

DTIC Science & Technology

2014-01-01

expansion a 1/K 11e–6-12e–6 Specific heat C p J/kg K 440-520 Thermal conductivity k W/m K 35-50 Heat transfer coefficient h W/m2 K 45 Sink temperature...filler-metal consumable electrode to the weld; third, prediction of the temporal evolution and the spatial distribution of thermal and mechanical...the thermal The current issue and full text archive of this journal is available at www.emeraldinsight.com/1573-6105.htm Received 20 May 2013 Revised 13

The Observed Properties of Liquid Helium at the Saturated Vapor Pressure

NASA Astrophysics Data System (ADS)

Donnelly, Russell J.; Barenghi, Carlo F.

1998-11-01

The equilibrium and transport properties of liquid 4He are deduced from experimental observations at the saturated vapor pressure. In each case, the bibliography lists all known measurements. Quantities reported here include density, thermal expansion coefficient, dielectric constant, superfluid and normal fluid densities, first, second, third, and fourth sound velocities, specific heat, enthalpy, entropy, surface tension, ion mobilities, mutual friction, viscosity and kinematic viscosity, dispersion curve, structure factor, thermal conductivity, latent heat, saturated vapor pressure, thermal diffusivity and Prandtl number of helium I, and displacement length and vortex core parameter in helium II.

Hoberman-sphere-inspired lattice metamaterials with tunable negative thermal expansion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yangbo; Chen, Yanyu; Li, Tiantian

Materials with engineered thermal expansion coefficients, capable of avoiding failure or irreversible destruction of structures and devices, are important for aerospace, civil, biomedical, optics, and semiconductor applications. In natural materials, thermal expansion usually cannot be adjusted easily and a negative thermal expansion coefficient is still uncommon. Here we propose a novel architected lattice bi-material system, inspired by the Hoberman sphere, showing a wide range of tunable thermal expansion coefficient from negative to positive, -1.04 x 10 -3 degrees C-1 to 1.0 x 10 -5 degrees C-1. Numerical simulations and analytical formulations are implemented to quantify the evolution of the thermalmore » expansion coefficients and reveal the underlying mechanisms responsible for this unusual behavior. We show that the thermal expansion coefficient of the proposed metamaterials depends on the thermal expansion coefficient ratio and the axial stiffness ratio of the constituent materials, as well as the bending stiffness and the topological arrangement of the constitutive elements. The finding reported here provides a new routine to design architected metamaterial systems with tunable negative thermal expansion for a wide range of potential applications.« less

Hoberman-sphere-inspired lattice metamaterials with tunable negative thermal expansion

DOE PAGES

Li, Yangbo; Chen, Yanyu; Li, Tiantian; ...

2018-02-02

Materials with engineered thermal expansion coefficients, capable of avoiding failure or irreversible destruction of structures and devices, are important for aerospace, civil, biomedical, optics, and semiconductor applications. In natural materials, thermal expansion usually cannot be adjusted easily and a negative thermal expansion coefficient is still uncommon. Here we propose a novel architected lattice bi-material system, inspired by the Hoberman sphere, showing a wide range of tunable thermal expansion coefficient from negative to positive, -1.04 x 10 -3 degrees C-1 to 1.0 x 10 -5 degrees C-1. Numerical simulations and analytical formulations are implemented to quantify the evolution of the thermalmore » expansion coefficients and reveal the underlying mechanisms responsible for this unusual behavior. We show that the thermal expansion coefficient of the proposed metamaterials depends on the thermal expansion coefficient ratio and the axial stiffness ratio of the constituent materials, as well as the bending stiffness and the topological arrangement of the constitutive elements. The finding reported here provides a new routine to design architected metamaterial systems with tunable negative thermal expansion for a wide range of potential applications.« less

Evaluation of Computational Fluid Dynamics and Coupled Fluid-Solid Modeling for a Direct Transfer Preswirl System.

PubMed

Javiya, Umesh; Chew, John; Hills, Nick; Dullenkopf, Klaus; Scanlon, Timothy

2013-05-01

The prediction of the preswirl cooling air delivery and disk metal temperature are important for the cooling system performance and the rotor disk thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady computation fluid dynamics (CFD), and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer preswirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disk previously obtained from a rotor disk heat conduction solution. Considering the modeling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disk from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution.

Metallic Junction Thermoelectric Device Simulations

NASA Technical Reports Server (NTRS)

Duzik, Adam J.; Choi, Sang H.

2017-01-01

Thermoelectric junctions made of semiconductors have existed in radioisotope thermoelectric generators (RTG) for deep space missions, but are currently being adapted for terrestrial energy harvesting. Unfortunately, these devices are inefficient, operating at only 7% efficiency. This low efficiency has driven efforts to make high-figure-of-merit thermoelectric devices, which require a high electrical conductivity but a low thermal conductivity, a combination that is difficult to achieve. Lowered thermal conductivity has increased efficiency, but at the cost of power output. An alternative setup is to use metallic junctions rather than semiconductors as thermoelectric devices. Metals have orders of magnitude more electrons and electronic conductivities higher than semiconductors, but thermal conductivity is higher as well. To evaluate the viability of metallic junction thermoelectrics, a two dimensional heat transfer MATLAB simulation was constructed to calculate efficiency and power output. High Seebeck coefficient alloys, Chromel (90%Ni-10%Cr) and Constantan (55%Cu-45%Ni), produced efficiencies of around 20-30%. Parameters such as the number of layers of junctions, lateral junction density, and junction sizes for both series- and parallel-connected junctions were explored.

Characterization of Lorenz number with Seebeck coefficient measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Hyun-Sik; Materials Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Suwon 443-803; Gibbs, Zachary M.

2015-04-01

In analyzing zT improvements due to lattice thermal conductivity (κ{sub L}) reduction, electrical conductivity (σ) and total thermal conductivity (κ{sub Total}) are often used to estimate the electronic component of the thermal conductivity (κ{sub E}) and in turn κ{sub L} from κ{sub L} = ∼ κ{sub Total} − LσT. The Wiedemann-Franz law, κ{sub E} = LσT, where L is Lorenz number, is widely used to estimate κ{sub E} from σ measurements. It is a common practice to treat L as a universal factor with 2.44 × 10{sup −8} WΩK{sup −2} (degenerate limit). However, significant deviations from the degenerate limit (approximatelymore » 40% or more for Kane bands) are known to occur for non-degenerate semiconductors where L converges to 1.5 × 10{sup −8} WΩK{sup −2} for acoustic phonon scattering. The decrease in L is correlated with an increase in thermopower (absolute value of Seebeck coefficient (S)). Thus, a first order correction to the degenerate limit of L can be based on the measured thermopower, |S|, independent of temperature or doping. We propose the equation: L=1.5+exp[−(|S|)/(116) ] (where L is in 10{sup −8} WΩK{sup −2} and S in μV/K) as a satisfactory approximation for L. This equation is accurate within 5% for single parabolic band/acoustic phonon scattering assumption and within 20% for PbSe, PbS, PbTe, Si{sub 0.8}Ge{sub 0.2} where more complexity is introduced, such as non-parabolic Kane bands, multiple bands, and/or alternate scattering mechanisms. The use of this equation for L rather than a constant value (when detailed band structure and scattering mechanism is not known) will significantly improve the estimation of lattice thermal conductivity.« less

Numerical Simulation of Heat Transfer in Porous Metals for Cooling Applications

NASA Astrophysics Data System (ADS)

Gauna, Edgar Avalos; Zhao, Yuyuan

2017-08-01

Porous metals have low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Hence, they have attracted a large amount of interest over the last few decades. One of their applications is for thermal management in the electronics industry because of their fluid permeability and thermal conductivity. The heat transfer capability is achieved by the interaction between the internal channels within the porous metal and the coolant flowing through them. This paper studies the fluid flow and heat transfer in open-cell porous metals manufactured by space holder methods by numerical simulation using software ANSYS Fluent. A 3D geometric model of the porous structure was created based on the face-centered-cubic arrangement of spheres linked by cylinders. This model allows for different combinations of pore parameters including a wide range of porosity (50 to 80 pct), pore size (400 to 1000 µm), and metal particle size (10 to 75 µm). In this study, water was used as the coolant and copper was selected as the metal matrix. The flow rate was varied in the Darcian and Forchheimer's regimes. The permeability, form drag coefficient, and heat transfer coefficient were calculated under a range of conditions. The numerical results showed that permeability increased whereas the form drag coefficient decreased with porosity. Both permeability and form drag coefficient increased with pore size. Increasing flow rate and decreasing porosity led to better heat transfer performance.

Thermal/structural analyses of several hydrogen-cooled leading-edge concepts for hypersonic flight vehicles

NASA Technical Reports Server (NTRS)

Gladden, Herbert J.; Melis, Matthew E.; Mockler, Theodore T.; Tong, Mike

1990-01-01

The aerodynamic heating at high flight Mach numbers, when shock interference heating is included, can be extremely high and can exceed the capability of most conventional metallic and potential ceramic materials available. Numerical analyses of the heat transfer and thermal stresses are performed on three actively cooled leading-edge geometries (models) made of three different materials to address the issue of survivability in a hostile environment. These analyses show a mixture of results from one configuration to the next. Results for each configuration are presented and discussed. Combinations of enhanced internal film coefficients and high material thermal conductivity of copper and tungsten are predicted to maintain the maximum wall temperature for each concept within acceptable operating limits. The exception is the TD nickel material which is predicted to melt for most cases. The wide range of internal impingement film coefficients (based on correlations) for these conditions can lead to a significant uncertainty in expected leading-edge wall temperatures. The equivalent plastic strain, inherent in each configuration which results from the high thermal gradients, indicates a need for further cyclic analysis to determine component life.

Portable Oxygen Generation for Medical Applications.

DTIC Science & Technology

1997-07-01

stabilized zirconia; these include scandia- stabilized zirconia, lanthanum gallate , ceria, and bismuth oxide. Scandia-stabilized zirconia [1] exhibits...uncertainty of using doped ceria is its high thermal expansion coefficient (ceria -13-14 ppm/°C, YSZ -10.5 ppm/°C). Lanthanum gallate (LaGa03) [2-4...the conductivity of lanthanum gallate approximately 2-3 times that of YSZ in the 600- 1000°C temperature range. The enhanced conductivity in lanthanum

Enhanced Thermoelectric Performance of n-type Bi2O2Se Ceramics Induced by Ge Doping

NASA Astrophysics Data System (ADS)

Ruleova, P.; Plechacek, T.; Kasparova, J.; Vlcek, M.; Benes, L.; Lostak, P.; Drasar, C.

2018-02-01

Ceramic samples with the composition Bi2- x Ge x O2Se1.01 ( x = 0, 0.05, 0.075, and 0.1) were synthesized by solid-state reaction and compacted using a hot-pressing technique. The prepared materials were characterized by x-ray diffraction analysis, electron microscopy, and measurements of electrical conductivity σ, Seebeck coefficient S, and thermal conductivity in the temperature range 300-780 K. Ge in the Bi2O2Se host structure led to an increase of the free electron concentration compared to pristine Bi2O2Se1.01. The donor effect is attributed to point substitutional defects in the Bi sublattice— {Ge}_{{Bi}}^{ + }, and oxygen vacancies {V}_{{O}}^{ + 2} producing free electrons. As a result, we observe an increase in the electrical conductivity and decrease in Seebeck coefficient while thermal conductivity κ changes slightly. The highest value of the dimensionless figure of merit ZT = σS 2 T/ κ reaches 0.25 for the composition Bi1.95Ge0.05O2Se1.01 at T = 723 K, which is, to date, the highest ZT value reported for Bi2O2Se ceramics. Our results suggest that Bi2O2Se is still worth exploring.

Switch on the high thermal conductivity of graphene paper.

PubMed

Xie, Yangsu; Yuan, Pengyu; Wang, Tianyu; Hashemi, Nastaran; Wang, Xinwei

2016-10-14

This work reports on the discovery of a high thermal conductivity (κ) switch-on phenomenon in high purity graphene paper (GP) when its temperature is reduced from room temperature down to 10 K. The κ after switch-on (1732 to 3013 W m -1 K -1 ) is 4-8 times that before switch-on. The triggering temperature is 245-260 K. The switch-on behavior is attributed to the thermal expansion mismatch between pure graphene flakes and impurity-embedded flakes. This is confirmed by the switch behavior of the temperature coefficient of resistance. Before switch-on, the interactions between pure graphene flakes and surrounding impurity-embedded flakes efficiently suppress phonon transport in GP. After switch-on, the structure separation frees the pure graphene flakes from the impurity-embedded neighbors, leading to a several-fold κ increase. The measured κ before and after switch-on is consistent with the literature reported κ values of supported and suspended graphene. By conducting comparison studies with pyrolytic graphite, graphene oxide paper and partly reduced graphene paper, the whole physical picture is illustrated clearly. The thermal expansion induced switch-on is feasible only for high purity GP materials. This finding points out a novel way to switch on/off the thermal conductivity of graphene paper based on substrate-phonon scattering.

A small-plane heat source method for measuring the thermal conductivities of anisotropic materials

NASA Astrophysics Data System (ADS)

Cheng, Liang; Yue, Kai; Wang, Jun; Zhang, Xinxin

2017-07-01

A new small-plane heat source method was proposed in this study to simultaneously measure the in-plane and cross-plane thermal conductivities of anisotropic insulating materials. In this method the size of the heat source element is smaller than the sample size and the boundary condition is thermal insulation due to no heat flux at the edge of the sample during the experiment. A three-dimensional model in a rectangular coordinate system was established to exactly describe the heat transfer process of the measurement system. Using the Laplace transform, variable separation, and Laplace inverse transform methods, the analytical solution of the temperature rise of the sample was derived. The temperature rises calculated by the analytical solution agree well with the results of numerical calculation. The result of the sensitivity analysis shows that the sensitivity coefficients of the estimated thermal conductivities are high and uncorrelated to each other. At room temperature and in a high-temperature environment, experimental measurements of anisotropic silica aerogel were carried out using the traditional one-dimensional plane heat source method and the proposed method, respectively. The results demonstrate that the measurement method developed in this study is effective and feasible for simultaneously obtaining the in-plane and cross-plane thermal conductivities of the anisotropic materials.

Thermal Characterization of Nanostructures and Advanced Engineered Materials

NASA Astrophysics Data System (ADS)

Goyal, Vivek Kumar

Continuous downscaling of Si complementary metal-oxide semiconductor (CMOS) technology and progress in high-power electronics demand more efficient heat removal techniques to handle the increasing power density and rising temperature of hot spots. For this reason, it is important to investigate thermal properties of materials at nanometer scale and identify materials with the extremely large or extremely low thermal conductivity for applications as heat spreaders or heat insulators in the next generation of integrated circuits. The thin films used in microelectronic and photonic devices need to have high thermal conductivity in order to transfer the dissipated power to heat sinks more effectively. On the other hand, thermoelectric devices call for materials or structures with low thermal conductivity because the performance of thermoelectric devices is determined by the figure of merit Z=S2sigma/K, where S is the Seebeck coefficient, K and sigma are the thermal and electrical conductivity, respectively. Nanostructured superlattices can have drastically reduced thermal conductivity as compared to their bulk counterparts making them promising candidates for high-efficiency thermoelectric materials. Other applications calling for thin films with low thermal conductivity value are high-temperature coatings for engines. Thus, materials with both high thermal conductivity and low thermal conductivity are technologically important. The increasing temperature of the hot spots in state-of-the-art chips stimulates the search for innovative methods for heat removal. One promising approach is to incorporate materials, which have high thermal conductivity into the chip design. Two suitable candidates for such applications are diamond and graphene. Another approach is to integrate the high-efficiency thermoelectric elements for on-spot cooling. In addition, there is strong motivation for improved thermal interface materials (TIMs) for heat transfer from the heat-generating chip to heat-sinking units. This dissertation presents results of the experimental investigation and theoretical interpretation of thermal transport in the advanced engineered materials, which include thin films for thermal management of nanoscale devices, nanostructured superlattices as promising candidates for high-efficiency thermoelectric materials, and improved TIMs with graphene and metal particles as fillers providing enhanced thermal conductivity. The advanced engineered materials studied include chemical vapor deposition (CVD) grown ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films on Si substrates, directly integrated nanocrystalline diamond (NCD) films on GaN, free-standing polycrystalline graphene (PCG) films, graphene oxide (GOx) films, and "pseudo-superlattices" of the mechanically exfoliated Bi2Te3 topological insulator films, and thermal interface materials (TIMs) with graphene fillers.

Effects of Mev Si Ions and Thermal Annealing on Thermoelectric and Optical Properties of SiO2/SiO2+Ge Multi-nanolayer thin Films

NASA Astrophysics Data System (ADS)

Budak, S.; Alim, M. A.; Bhattacharjee, S.; Muntele, C.

Thermoelectric generator devices have been prepared from 200 alternating layers of SiO2/SiO2+Ge superlattice films using DC/RF magnetron sputtering. The 5 MeV Si ionsbombardmenthasbeen performed using the AAMU Pelletron ion beam accelerator to formquantum dots and / or quantum clusters in the multi-layer superlattice thin films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient and increase the cross-plane electrical conductivity to increase the figure of merit, ZT. The fabricated devices have been annealed at the different temperatures to tailor the thermoelectric and optical properties of the superlattice thin film systems. While the temperature increased, the Seebeck coefficient continued to increase and reached the maximum value of -25 μV/K at the fluenceof 5x1013 ions/cm2. The decrease in resistivity has been seen between the fluence of 1x1013 ions/cm2 and 5x1013 ions/cm2. Transport properties like Hall coefficient, density and mobility did not change at all fluences. Impedance spectroscopy has been used to characterize the multi-junction thermoelectric devices. The loci obtained in the C*-plane for these data indicate non-Debye type relaxation displaying the presence of the depression parameter.

Properties of binary transition-metal arsenides (TAs)

NASA Astrophysics Data System (ADS)

Saparov, Bayrammurad; Mitchell, Jonathan E.; Sefat, Athena S.

2012-08-01

We present thermodynamic and transport properties of transition-metal (T) arsenides, TAs, with T = Sc to Ni (3d), Zr, Nb, Ru (4d), Hf and Ta (5d). Characterization of these binaries is carried out with powder x-ray diffraction, temperature- and field-dependent magnetization and resistivity, temperature-dependent heat capacity, Seebeck coefficient, and thermal conductivity. All binaries show metallic behavior except TaAs and RuAs. TaAs, NbAs, ScAs and ZrAs are diamagnetic, while CoAs, VAs, TiAs, NiAs and RuAs show approximately Pauli paramagnetic behavior. FeAs and CrAs undergo antiferromagnetic ordering below TN ≈ 71 K and TN ≈ 260 K, respectively. MnAs is a ferromagnet below TC ≈ 317 K and undergoes hexagonal-orthorhombic-hexagonal transitions at TS ≈ 317 K and 384 K, respectively. For TAs, Seebeck coefficients vary between + 40 and - 40 μV K-1 in the 2-300 K range, whereas thermal conductivity values stay below 18 W m-1 K-1. The Sommerfeld coefficients γ are less than 10 mJ K-2 mol-1. At room temperature with application of 8 T magnetic field, large positive magnetoresistance is found for TaAs (˜25%), MnAs (˜90%) and NbAs (˜75%).

Material Properties of Three Candidate Elastomers for Space Seals Applications

NASA Technical Reports Server (NTRS)

Bastrzyk, Marta B.; Daniels, Christopher C.; Oswald, Jay J.; Dunlap, Patrick H., Jr.; Steinetz, Bruce M.

2010-01-01

A next-generation docking system is being developed by the National Aeronautics and Space Administration (NASA) to support Constellation Space Exploration Missions to low Earth orbit (LEO), to the Moon, and to Mars. A number of investigations were carried out to quantify the properties of candidate elastomer materials for use in the main interface seal of the Low Impact Docking System (LIDS). This seal forms the gas pressure seal between two mating spacecraft. Three candidate silicone elastomer compounds were examined: Esterline ELA-SA-401, Parker Hannifin S0383-70, and Parker Hannifin S0899-50. All three materials were characterized as low-outgassing compounds, per ASTM E595, so as to minimize the contamination of optical and solar array systems. Important seal properties such as outgas levels, durometer, tensile strength, elongation to failure, glass transition temperature, permeability, compression set, Yeoh strain energy coefficients, coefficients of friction, coefficients of thermal expansion, thermal conductivity and diffusivity were measured and are reported herein.

Thermal analysis of insulated north-wall greenhouse with solar collector under passive mode

NASA Astrophysics Data System (ADS)

Chauhan, Prashant Singh; Kumar, Anil

2018-04-01

An insulated north wall greenhouse dryer has been fabricated and tested for no-load condition under passive mode. Testing has been conducted in two different cases. Case-I is considered for solar collector kept inside the dryer and Case-II is dryer without solar collector. Convective heat transfer coefficient and various heat transfer dimensionless numbers with have been calculated for thermal analysis. The maximum convective heat transfer coefficient is found 52.18 W/m2°C at 14 h during the first day for Case-I. The difference of the highest convective heat transfer coefficient of both cases was 8.34 W/m2°C. Net heat gain inside room curves are uniform and smooth for Case-I, which shows the steady heat generation process due to presence of solar collector inside the dryer. Above results depicts the effectiveness of solar collector and insulated north wall. The selection of suitable crop for drying can be done by analysing article's result.

In-situ Observation of Size and Irradiation Effects on Thermoelectric Properties of Bi-Sb-Te Nanowire in FIB Trimming

PubMed Central

Chien, Chia-Hua; Lee, Ping-Chung; Tsai, Wei-Han; Lin, Chien-Hung; Lee, Chih-Hao; Chen, Yang-Yuan

2016-01-01

In this report, the thermoelectric properties of a Bi0.8Sb1.2Te2.9 nanowire (NW) were in-situ studied as it was trimmed from 750 down to 490 and 285 nm in diameter by a focused ion beam. While electrical and thermal conductivities both indubitably decrease with the diameter reduction, the two physical properties clearly exhibit different diameter dependent behaviors. For 750 and 490 nm NWs, much lower thermal conductivities (0.72 and 0.69 W/m-K respectively) were observed as compared with the theoretical prediction of Callaway model. The consequence indicates that in addition to the size effect, extra phonon scattering of defects created by Ga ion irradiation was attributed to the reduction of thermal conductivities. As the NW was further trimmed down to 285 nm, both the electrical and thermal conductivities exhibited a dramatic reduction which was ascribed to the formation of amorphous structure due to Ga ion irradiation. The size dependence of Seebeck coefficient and figure of merit (ZT) show the maximum at 750 nm, then decrease linearly with size decrease. The study not only provides the thoroughly understanding of the size and defect effects on the thermoelectric properties but also proposes a possible method to manipulate the thermal conductivity of NWs via ion irradiation. PMID:27030206

Crystal Lattice Controlled SiGe Thermoelectric Materials with High Figure of Merit

NASA Technical Reports Server (NTRS)

Kim, Hyun-Jung; Park, Yeonjoon; King, Glen C.; Lee, Kunik; Choi, Sang H.

2010-01-01

Direct energy conversion between thermal and electrical energy, based on thermoelectric (TE) effect, has the potential to recover waste heat and convert it to provide clean electric power. The energy conversion efficiency is related to the thermoelectric figure of merit ZT expressed as ZT=S(exp 2)(sigma)T/Kappa, T is temperature, S is the Seebeck coefficient, sigma is conductance and Kappa is thermal conductivity. For a lower thermal conductivity Kappa and high power factor (S(exp 2)(sigma)), our current strategy is the development of rhombohedrally strained single crystalline SiGe materials that are highly [111]-oriented twinned. The development of a SiGe "twin lattice structure (TLS)" plays a key role in phonon scattering. The TLS increases the electrical conductivity and decreases thermal conductivity due to phonon scattering at stacking faults generated from the 60 X rotated primary twin structure. To develop high performance materials, the substrate temperature, chamber working pressure, and DC sputtering power are controlled for the aligned growth production of SiGe layer and TLS on a c-plane sapphire. Additionally, a new elevated temperature thermoelectric characterization system, that measures the thermal diffusivity and Seebeck effect nondestructively, was developed. The material properties were characterized at various temperatures and optimized process conditions were experimentally determined. The present paper encompasses the technical discussions toward the development of thermoelectric materials and the measurement techniques.

Simulation of abuse tolerance of lithium-ion battery packs

NASA Astrophysics Data System (ADS)

Spotnitz, Robert M.; Weaver, James; Yeduvaka, Gowri; Doughty, D. H.; Roth, E. P.

A simple approach for using accelerating rate calorimetry data to simulate the thermal abuse resistance of battery packs is described. The thermal abuse tolerance of battery packs is estimated based on the exothermic behavior of a single cell and an energy balance than accounts for radiative, conductive, and convective heat transfer modes of the pack. For the specific example of a notebook computer pack containing eight 18650-size cells, the effects of cell position, heat of reaction, and heat-transfer coefficient are explored. Thermal runaway of the pack is more likely to be induced by thermal runaway of a single cell when that cell is in good contact with other cells and is close to the pack wall.

Thermal-hydraulic performance of metal foam heat exchangers under dry operating conditions

DOE PAGES

Nawaz, Kashif; Bock, Jessica; Jacobi, Anthony M.

2017-03-14

High porosity metal foams with novel thermal, mechanical, electrical, and acoustic properties are being more widely adopted for application. Due to their large surface-area-to-volume ratio and complex structure which induces better fluid mixing, boundary layer restarting and wake destruction, they hold promise for heat transfer applications. In this study, the thermal-hydraulic performance of open-cell aluminum metal foam heat exchanger has been evaluated. The impact of flow conditions and metal foam geometry on the heat transfer coefficient and gradient have been investigated. Metal foam heat exchanger with same geometry (face area, flow depth and fin dimensions) consisting of four different typemore » of metal foams have been built for the study. Experiments are conducted in a closed-loop wind tunnel at different flow rate under dry operating condition. Metal foams with a smaller pore size (40 PPI) have a larger heat transfer coefficient compared to foams with a larger pore size (5 PPI). However, foams with larger pores result in relatively smaller pressure gradients. Current thermal-hydraulic modeling practices have been reviewed and potential issues have been identified. Permeability and inertia coefficients are determined and compared to data reported in open literature. Finally, on the basis of the new experimental results, correlations are developed relating the foam characteristics and flow conditions through the friction factor f and the Colburn j factor.« less

Thermal-hydraulic performance of metal foam heat exchangers under dry operating conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nawaz, Kashif; Bock, Jessica; Jacobi, Anthony M.

High porosity metal foams with novel thermal, mechanical, electrical, and acoustic properties are being more widely adopted for application. Due to their large surface-area-to-volume ratio and complex structure which induces better fluid mixing, boundary layer restarting and wake destruction, they hold promise for heat transfer applications. In this study, the thermal-hydraulic performance of open-cell aluminum metal foam heat exchanger has been evaluated. The impact of flow conditions and metal foam geometry on the heat transfer coefficient and gradient have been investigated. Metal foam heat exchanger with same geometry (face area, flow depth and fin dimensions) consisting of four different typemore » of metal foams have been built for the study. Experiments are conducted in a closed-loop wind tunnel at different flow rate under dry operating condition. Metal foams with a smaller pore size (40 PPI) have a larger heat transfer coefficient compared to foams with a larger pore size (5 PPI). However, foams with larger pores result in relatively smaller pressure gradients. Current thermal-hydraulic modeling practices have been reviewed and potential issues have been identified. Permeability and inertia coefficients are determined and compared to data reported in open literature. Finally, on the basis of the new experimental results, correlations are developed relating the foam characteristics and flow conditions through the friction factor f and the Colburn j factor.« less

Potentialities of silicon nanowire forests for thermoelectric generation

NASA Astrophysics Data System (ADS)

Dimaggio, Elisabetta; Pennelli, Giovanni

2018-04-01

Silicon is a material with very good thermoelectric properties, with regard to Seebeck coefficient and electrical conductivity. Low thermal conductivities, and hence high thermal to electrical conversion efficiencies, can be achieved in nanostructures, which are smaller than the phonon mean free path but large enough to preserve the electrical conductivity. We demonstrate that it is possible to fabricate a leg of a thermoelectric generator based on large collections of long nanowires, placed perpendicularly to the two faces of a silicon wafer. The process exploits the metal assisted etching technique which is simple, low cost, and can be easily applied to large surfaces. Copper can be deposited by electrodeposition on both faces, so that contacts can be provided, on top of the nanowires. Thermal conductivity of silicon nanowire forests with more than 107 nanowires mm-2 have been measured; the result is comparable with that achieved by several groups on devices based on few nanowires. On the basis of the measured parameters, numerical calculations of the efficiency of silicon-based thermoelectric generators are reported, and the potentialities of these devices for thermal to electrical energy conversion are shown. Criteria to improve the conversion efficiency are suggested and described.

Thermal Modeling and Performance Measurements of Radiometric Arrays for Near Space Propulsion

DTIC Science & Technology

2012-07-16

radiometer vane dimensions for maximum force production. Square vanes with an edge thickness of 1.57 mm and thickness of 0.5 mm were modeled as aerogel ...materials evaluated include aerogel , Teflon, silicon dioxide, type 304 stainless steel, aluminum, and pure copper (thermal conductivity = 0.017, 0.25...front face 0.5 1 0.1 Absorptivity of aerogel 0.1 0.5 0.1 Convection coefficient across vanes (W/m^2*K) 5 40 5 Vane thickness (mm) 0.5 2 0.25

Thermal Analysis of Nanofluids Using Modeling and Molecular Dynamics Simulation

NASA Astrophysics Data System (ADS)

Namboori, P. K. Krishnan; Vasavi, C. S.; Gopal, K. Varun; Gopakumar, Deepa; Ramachandran, K. I.; Narayanan, B. Sabarish

2010-10-01

Nanofluids are nanotechnology-based heat transfer fluids obtained by suspending nanometer-sized particles in conventional heat transfer fluids in a stable manner. In many of the physical phenomena such as boiling and properties such as latent heat, thermal conductivity and heat transfer coefficient, there is significant change on addition of nanoparticles. These exceptional qualities of Nanofluids mainly depend on the atomic level mechanisms, which in turn govern all mechanical properties like strength, Young's modulus, Poisson's ratio, compressibility etc. Control over the fundamental thermo physical properties of the working medium will help to understand these unique phenomena of nanofluids to a great extent. Macroscopic modeling approaches, which are based on conventional relations of thermodynamics, have been proved to be incompetent to explain this difference. Atomistic `modeling and simulation' has been emerged out as an efficient alternative for this. The enhancement of thermal conductivity of water by suspending nanoparticle inclusions has been experimented and proved to be an effective method of enhancing convective heat dissipation. This work mainly deals with characterization of the thermal conductivity of nanofluids. Nano particle sized aluminium oxide; copper oxide and titanium dioxide have been taken in this work for the analysis of thermal conductivity. The effect of thermal conductivity on parameters like volume concentration of the fluid, nature of particle material and size of the particle has been computationally formulated. It has been found that there is an increase in effective thermal conductivity of the fluid by the addition of nanomaterials ascertaining an improvement in the heat transfer behavior of nanofluids. This facilitates the reduction in size of such heat transfer systems (radiators) and lead to increased energy and fuel efficiency, lower pollution and improved reliability.

Thermal sensitivity of elastic coefficients of langasite and langatate.

PubMed

Bourquin, Roger; Dulmet, Bernard

2009-10-01

Thermal coefficients of elastic constants of langasite and langatate crystals have been determined from frequency-temperature curves of contoured resonators operating in thickness modes. The effect of the trapping of the vibration has been taken into account to improve the accuracy. In a first step, the thermal sensitivities of stiffness coefficients in Lagrangian description are obtained. Thermal sensitivities of the usual elastic constants are further deduced. Predictions of thermally compensated cuts are given.

The glass-like thermal conductivity in ZrO2-Dy3TaO7 ceramic for promising thermal barrier coating application

NASA Astrophysics Data System (ADS)

Wu, Peng; Hu, Ming Yu; Chong, Xiao Yu; Feng, Jing

2018-03-01

Using the solid-state reaction method, the (ZrO2)x-(Dy3TaO7)1-x (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) ceramics are synthesized in this work. The identification of the crystal structures indicates that the (ZrO2)x-(Dy3TaO7)1-x ceramics belong to the orthorhombic system, and the space group is C2221 in spite of the value of x increasing to 0.1. The thermal conductivities of the (ZrO2)x-(Dy3TaO7)1-x ceramics range from 1.3 W/(m K) to 1.8 W/(m K), and this value is much lower than that of 7-8 YSZ (yttria-stabilized zirconia). Besides, the (ZrO2)x-(Dy3TaO7)1-x ceramics possess the glass-like thermal conductivity caused by intrinsic oxygen vacancies existing in the lattice of Dy3TaO7. Moreover, the results of thermal expansion rates demonstrate that the (ZrO2)x-(Dy3TaO7)1-x ceramics possess excellent high temperature phase stability, and the thermal expansion coefficients [(9.7-11) × 10-6 K-1] are comparable to that of 7-8 YSZ.

Effect of Cattaneo-Christov heat flux on Jeffrey fluid flow with variable thermal conductivity

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Javed, Mehwish; Imtiaz, Maria; Alsaedi, Ahmed

2018-03-01

This paper presents the study of Jeffrey fluid flow by a rotating disk with variable thickness. Energy equation is constructed by using Cattaneo-Christov heat flux model with variable thermal conductivity. A system of equations governing the model is obtained by applying boundary layer approximation. Resulting nonlinear partial differential system is transformed to ordinary differential system. Homotopy concept leads to the convergent solutions development. Graphical analysis for velocities and temperature is made to examine the influence of different involved parameters. Thermal relaxation time parameter signifies that temperature for Fourier's heat law is more than Cattaneo-Christov heat flux. A constitutional analysis is made for skin friction coefficient and heat transfer rate. Effects of Prandtl number on temperature distribution and heat transfer rate are scrutinized. It is observed that larger Reynolds number gives illustrious temperature distribution.

Frequency-resolved Raman for transient thermal probing and thermal diffusivity measurement

DOE PAGES

Wang, Tianyu; Xu, Shen; Hurley, David H.; ...

2015-12-18

Steady state Raman has been widely used for temperature probing and thermal conductivity/conductance measurement in combination with temperature coefficient calibration. In this work, a new transient Raman thermal probing technique: frequency-resolved Raman (FR-Raman) is developed for probing the transient thermal response of materials and measuring their thermal diffusivity. The FR-Raman uses an amplitude modulated square-wave laser for simultaneous material heating and Raman excitation. The evolution profile of Raman properties: intensity, Raman wavenumber, and emission, against frequency are measured experimentally and reconstructed theoretically. They are used for fitting to determine the thermal diffusivity of the material under test. A Si cantilevermore » is used to investigate the capacity of this new technique. The cantilever’s thermal diffusivity is determined as 9.57 × 10 -5 m 2/s, 11.00 × 10 -5 m 2/s and 9.02 × 10 -5 m 2/s by fitting the Raman intensity, wavenumber and emission. The deviation from the reference value is largely attributed to thermal stress-induced material deflection and Raman drift, which could be significantly suppressed by using a higher sensitivity Raman spectrometer with lower laser energy. As a result, the FR-Raman provides a novel way for transient thermal characterization of materials with a ?m spatial resolution.« less

Effects of interdot hopping and Coulomb blockade on the thermoelectric properties of serially coupled quantum dots

PubMed Central

2012-01-01

We have theoretically studied the thermoelectric properties of serially coupled quantum dots (SCQDs) embedded in an insulator connected to metallic electrodes. In the framework of Keldysh Green’s function technique, the Landauer formula of transmission factor is obtained using the equation of motion method. Based on such analytical expressions of charge and heat currents, we calculate the electrical conductance, Seebeck coefficient, electron thermal conductance, and figure of merit (ZT) of SCQDs in the linear response regime. The effects of interdot hopping and electron Coulomb interactions on ZT are analyzed. We demonstrate that ZT is not a monotonic increasing function of interdot electron hopping strength (tc). We also show that in the absence of phonon thermal conductance, SCQD can reach the Carnot efficiency as tcapproaches zero. PMID:22591807

Theory of interparticle correlations in dense, high-temperature plasmas. V - Electric and thermal conductivities

NASA Technical Reports Server (NTRS)

Ichimaru, S.; Tanaka, S.

1985-01-01

Ichimaru et al. (1985) have developed a general theory in which the interparticle correlations in dense, high-temperature multicomponent plasmas were formulated systematically over a wide range of plasma parameters. The present paper is concerned with an extension of this theory, taking into account the problems of the electronic transport in such high-density plasmas. It is shown that the resulting theory is capable of describing the transport coefficients accurately over a wide range of the density and temperature parameters. Attention is given to electric and thermal conductivities, generalized Coulomb logarithms, a comparison of the considered theory with other theories, and a comparison of the theory with experimental results.

Prospects for Engineering Thermoelectric Properties in La1/3NbO3 Ceramics Revealed via Atomic-Level Characterization and Modeling.

PubMed

Kepaptsoglou, Demie; Baran, Jakub D; Azough, Feridoon; Ekren, Dursun; Srivastava, Deepanshu; Molinari, Marco; Parker, Stephen C; Ramasse, Quentin M; Freer, Robert

2018-01-02

A combination of experimental and computational techniques has been employed to explore the crystal structure and thermoelectric properties of A-site-deficient perovskite La 1/3 NbO 3 ceramics. Crystallographic data from X-ray and electron diffraction confirmed that the room temperature structure is orthorhombic with Cmmm as a space group. Atomically resolved imaging and analysis showed that there are two distinct A sites: one is occupied with La and vacancies, and the second site is fully unoccupied. The diffuse superstructure reflections observed through diffraction techniques are shown to originate from La vacancy ordering. La 1/3 NbO 3 ceramics sintered in air showed promising high-temperature thermoelectric properties with a high Seebeck coefficient of S 1 = -650 to -700 μV/K and a low and temperature-stable thermal conductivity of k = 2-2.2 W/m·K in the temperature range of 300-1000 K. First-principles electronic structure calculations are used to link the temperature dependence of the Seebeck coefficient measured experimentally to the evolution of the density of states with temperature and indicate possible avenues for further optimization through electron doping and control of the A-site occupancies. Moreover, lattice thermal conductivity calculations give insights into the dependence of the thermal conductivity on specific crystallographic directions of the material, which could be exploited via nanostructuring to create high-efficiency compound thermoelectrics.

Thermally Conductive Metal-Tube/Carbon-Composite Joints

NASA Technical Reports Server (NTRS)

Copeland, Robert J.

2004-01-01

An improved method of fabricating joints between metal and carbon-fiber-based composite materials in lightweight radiators and heat sinks has been devised. Carbon-fiber-based composite materials have been used in such heat-transfer devices because they offer a combination of high thermal conductivity and low mass density. Metal tubes are typically used to carry heat-transfer fluids to and from such heat-transfer devices. The present fabrication method helps to ensure that the joints between the metal tubes and the composite-material parts in such heat-transfer devices have both (1) the relatively high thermal conductances needed for efficient transfer of heat and (2) the flexibility needed to accommodate differences among thermal expansions of dissimilar materials in operation over wide temperature ranges. Techniques used previously to join metal tubes with carbon-fiber-based composite parts have included press fitting and bonding with epoxy. Both of these prior techniques have been found to yield joints characterized by relatively high thermal resistances. The present method involves the use of a solder (63 percent Sn, 37 percent Pb) to form a highly thermally conductive joint between a metal tube and a carbon-fiber-based composite structure. Ordinarily, the large differences among the coefficients of thermal expansion of the metal tube, solder, and carbon-fiber-based composite would cause the solder to pull away from the composite upon post-fabrication cooldown from the molten state. In the present method, the structure of the solder is modified (see figure) to enable it to deform readily to accommodate the differential thermal expansion.

Estimated Viscosities and Thermal Conductivities of Gases at High Temperatures

NASA Technical Reports Server (NTRS)

Svehla, Roger A.

1962-01-01

Viscosities and thermal conductivities, suitable for heat-transfer calculations, were estimated for about 200 gases in the ground state from 100 to 5000 K and 1-atmosphere pressure. Free radicals were included, but excited states and ions were not. Calculations for the transport coefficients were based upon the Lennard-Jones (12-6) potential for all gases. This potential was selected because: (1) It is one of the most realistic models available and (2) intermolecular force constants can be estimated from physical properties or by other techniques when experimental data are not available; such methods for estimating force constants are not as readily available for other potentials. When experimental viscosity data were available, they were used to obtain the force constants; otherwise the constants were estimated. These constants were then used to calculate both the viscosities and thermal conductivities tabulated in this report. For thermal conductivities of polyatomic gases an Eucken-type correction was made to correct for exchange between internal and translational energies. Though this correction may be rather poor at low temperatures, it becomes more satisfactory with increasing temperature. It was not possible to obtain force constants from experimental thermal conductivity data except for the inert atoms, because most conductivity data are available at low temperatures only (200 to 400 K), the temperature range where the Eucken correction is probably most in error. However, if the same set of force constants is used for both viscosity and thermal conductivity, there is a large degree of cancellation of error when these properties are used in heat-transfer equations such as the Dittus-Boelter equation. It is therefore concluded that the properties tabulated in this report are suitable for heat-transfer calculations of gaseous systems.

Versatile apparatus for thermoelectric characterization of oxides at high temperatures

NASA Astrophysics Data System (ADS)

Schrade, Matthias; Fjeld, Harald; Norby, Truls; Finstad, Terje G.

2014-10-01

An apparatus for measuring the Seebeck coefficient and electrical conductivity is presented and characterized. The device can be used in a wide temperature range from room temperature to 1050 °C and in all common atmospheres, including oxidizing, reducing, humid, and inert. The apparatus is suitable for samples with different geometries (disk-, bar-shaped), allowing a complete thermoelectric characterization (including thermal conductivity) on a single sample. The Seebeck coefficient α can be measured in both sample directions (in-plane and cross-plane) simultaneously. Electrical conductivity is measured via the van der Pauw method. Perovskite-type CaMnO3 and the misfit cobalt oxide (Ca2CoO3)q(CoO2) are studied to demonstrate the temperature range and to investigate the variation of the electrical properties as a function of the measurement atmosphere.

Versatile apparatus for thermoelectric characterization of oxides at high temperatures.

PubMed

Schrade, Matthias; Fjeld, Harald; Norby, Truls; Finstad, Terje G

2014-10-01

An apparatus for measuring the Seebeck coefficient and electrical conductivity is presented and characterized. The device can be used in a wide temperature range from room temperature to 1050 °C and in all common atmospheres, including oxidizing, reducing, humid, and inert. The apparatus is suitable for samples with different geometries (disk-, bar-shaped), allowing a complete thermoelectric characterization (including thermal conductivity) on a single sample. The Seebeck coefficient α can be measured in both sample directions (in-plane and cross-plane) simultaneously. Electrical conductivity is measured via the van der Pauw method. Perovskite-type CaMnO3 and the misfit cobalt oxide (Ca2CoO3)q(CoO2) are studied to demonstrate the temperature range and to investigate the variation of the electrical properties as a function of the measurement atmosphere.

Low temperature thermoelectric properties of hot pressed composite samples of CrSb2: evidence for possible phonon-drag effect.

NASA Astrophysics Data System (ADS)

Pokharel, Mani; Koirala, Machhindra; Ren, Zhifeng; Opeil, Cyril

We present on the thermoelectric transport properties of CrSb2 samples prepared by hot-press densification in the temperature range of 2 - 350 K. At around 10 K, the thermal conductivity of CrSb2 decreases dramatically by three orders of magnitude compared to the single crystal counterpart. Analysis shows that the reduced thermal conductivity results from increased scattering of the phonons off the grain-boundaries within the samples. A strong interrelationship between the thermal conductivity and the Seebeck coefficient is observed; indicating a significant presence of phonon-drag effect in this system. With ZT = 0.018 at 310 K for the sample hot pressed at 600 oC, an increase in ZT by 80 % over the previously reported values for polycrystalline samples is achieved. We gratefully acknowledge funding for this work by the Department of Defense, United States Air Force Office of Scientific Researchs MURI program under contract FA9550-10-1-0533.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yan; Cai, Lu; Liu, Zengcai

Our letter reports the correlation of anisotropy and directional conduction in the fast Li + conductor β-Li 3PS 4, one of the low-symmetry crystalline electrolyte candidates. The material has both high conductivity and good stability that serves well for the large-scale energy storage applications of all-solid-state lithium ion batteries. The anisotropic physical properties, demonstrated here by the thermal expansion coefficients, are crucial for compatibility in the solid-state system and battery performance. Neutron and X-ray powder diffraction measurements were done to determine the crystal structure and thermal stability. Moreover, the crystallographic b-axis was revealed as a fast expansion direction, while negligiblemore » thermal expansion was observed along the a-axis around the battery operating temperatures. The anisotropic behavior has its structural origin from the Li + conduction channels with incomplete Li occupancy and a flexible connection of LiS 4 and PS 4 tetrahedra within the framework. This indicates a strong correlation in the direction of the ionic transport in the low-symmetry Li + conductor.« less

Prediction of thermal conductivity of polyvinylpyrrolidone (PVP) electrospun nanocomposite fibers using artificial neural network and prey-predator algorithm.

PubMed

Khan, Waseem S; Hamadneh, Nawaf N; Khan, Waqar A

2017-01-01

In this study, multilayer perception neural network (MLPNN) was employed to predict thermal conductivity of PVP electrospun nanocomposite fibers with multiwalled carbon nanotubes (MWCNTs) and Nickel Zinc ferrites [(Ni0.6Zn0.4) Fe2O4]. This is the second attempt on the application of MLPNN with prey predator algorithm for the prediction of thermal conductivity of PVP electrospun nanocomposite fibers. The prey predator algorithm was used to train the neural networks to find the best models. The best models have the minimal of sum squared error between the experimental testing data and the corresponding models results. The minimal error was found to be 0.0028 for MWCNTs model and 0.00199 for Ni-Zn ferrites model. The predicted artificial neural networks (ANNs) responses were analyzed statistically using z-test, correlation coefficient, and the error functions for both inclusions. The predicted ANN responses for PVP electrospun nanocomposite fibers were compared with the experimental data and were found in good agreement.

Effective Thermal Property Estimation of Unitary Pebble Beds Based on a CFD-DEM Coupled Method for a Fusion Blanket

NASA Astrophysics Data System (ADS)

Chen, Lei; Chen, Youhua; Huang, Kai; Liu, Songlin

2015-12-01

Lithium ceramic pebble beds have been considered in the solid blanket design for fusion reactors. To characterize the fusion solid blanket thermal performance, studies of the effective thermal properties, i.e. the effective thermal conductivity and heat transfer coefficient, of the pebble beds are necessary. In this paper, a 3D computational fluid dynamics discrete element method (CFD-DEM) coupled numerical model was proposed to simulate heat transfer and thereby estimate the effective thermal properties. The DEM was applied to produce a geometric topology of a prototypical blanket pebble bed by directly simulating the contact state of each individual particle using basic interaction laws. Based on this geometric topology, a CFD model was built to analyze the temperature distribution and obtain the effective thermal properties. The current numerical model was shown to be in good agreement with the existing experimental data for effective thermal conductivity available in the literature. supported by National Special Project for Magnetic Confined Nuclear Fusion Energy of China (Nos. 2013GB108004, 2015GB108002, 2014GB122000 and 2014GB119000), and National Natural Science Foundation of China (No. 11175207)

All-optical beam deflection method for simultaneous thermal conductivity and thermo-optic coefficient ( d n / d T ) measurements

NASA Astrophysics Data System (ADS)

Putnam, Shawn A.; Fairchild, Steven B.; Arends, Armando A.; Urbas, Augustine M.

2016-05-01

This work describes an all-optical beam deflection method to simultaneously measure the thermal conductivity ( Λ) and thermo-optic coefficient ( d n / d T ) of materials that are absorbing at λ = 10.6 μm and are transparent to semi-transparent at λ = 632.8 nm. The technique is based on the principle of measuring the beam deflection of a probe beam (632.8 nm) in the frequency-domain due to a spatially and temporally varying index gradient that is thermally induced by 50:50 split pump beam from a CO2 laser (10.6 μm). The technique and analysis methods are validated with measurements of 10 different optical materials having Λ and d n / d T properties ranging between 0.7 W/m K ≲ Λ ≲ 33.5 W/m K and -12 × 10-6 K-1 ≲ d n / d T ≲ 14 × 10-6 K-1, respectively. The described beam deflection technique is highly related to other well-established, all-optical materials characterization methods, namely, thermal lensing and photothermal deflection spectroscopy. Likewise, due to its all-optical, pump-probe nature, it is applicable to materials characterization in extreme environments with minimal errors due to black-body radiation. In addition, the measurement principle can be extended over a broad range of electromagnetic wavelengths (e.g., ultraviolet to THz) provided the required sources, detectors, and focusing elements are available.

Calculation of thermal expansion coefficient of glasses based on topological constraint theory

NASA Astrophysics Data System (ADS)

Zeng, Huidan; Ye, Feng; Li, Xiang; Wang, Ling; Yang, Bin; Chen, Jianding; Zhang, Xianghua; Sun, Luyi

2016-10-01

In this work, the thermal expansion behavior and the structure configuration evolution of glasses were studied. Degree of freedom based on the topological constraint theory is correlated with configuration evolution; considering the chemical composition and the configuration change, the analytical equation for calculating the thermal expansion coefficient of glasses from degree of freedom was derived. The thermal expansion of typical silicate and chalcogenide glasses was examined by calculating their thermal expansion coefficients (TEC) using the approach stated above. The results showed that this approach was energetically favorable for glass materials and revealed the corresponding underlying essence from viewpoint of configuration entropy. This work establishes a configuration-based methodology to calculate the thermal expansion coefficient of glasses that, lack periodic order.

Thermal-Interaction Matrix For Resistive Test Structure

NASA Technical Reports Server (NTRS)

Buehler, Martin G.; Dhiman, Jaipal K.; Zamani, Nasser

1990-01-01

Linear mathematical model predicts increase in temperature in each segment of 15-segment resistive structure used to test electromigration. Assumption of linearity based on fact: equations that govern flow of heat are linear and coefficients in equations (heat conductivities and capacities) depend only weakly on temperature and considered constant over limited range of temperature.

Thermoelectric transport properties in graphene connected molecular junctions

NASA Astrophysics Data System (ADS)

Rodriguez, S. T.; Grosu, I.; Crisan, M.; Ţifrea, I.

2018-02-01

We study the electronic contribution to the main thermoelectric properties of a molecular junction consisting of a single quantum dot coupled to graphene external leads. The system electrical conductivity (G), Seebeck coefficient (S), and the thermal conductivity (κ), are numerically calculated based on a Green's function formalism that includes contributions up to the Hartree-Fock level. We consider the system leads to be made either of pure or gapped-graphene. To describe the free electrons in the gapped-graphene electrodes we used two possible scenarios, the massive gap scenario, and the massless gap scenario, respectively. In all cases, the Fano effect is responsible for a strong violation of the Wiedemann-Franz law and we found a substantial increase of the system figure of merit ZT due to a drastic reduction of the system thermal coefficient. In the case of gapped-graphene electrodes, the system figure of merit presents a maximum at an optimal value of the energy gap of the order of Δ / D ∼ 0.002 (massive gap scenario) and Δ / D ∼ 0.0026 (massless gap scenario). Additionally, for all cases, the system figure of merit is temperature dependent.

Unravelling the magnetism, high spin polarization and thermoelectric efficiency of ZrFeSi half-Heusler

NASA Astrophysics Data System (ADS)

Yousuf, Saleem; Gupta, D. C.

2018-04-01

We report the systematic investigation of structural properties, occupancy of density of states, nature of bonding and thermoelectric efficiency of half-Heusler ZrFeSi. The band structure analysis predicts the hybridization of Zr-d and Fe-d metal atoms resulting in occupation of density of states above the Fermi level (EF) while Fe-p and Si-p occupy the lower energy states below the EF. Thermoelectric transport coefficients are predicted using the Boltzmann transport theory under constant relaxation approximation, where Seebeck coefficient (S), total thermal conductivity and figure of merit are calculated. The negative value of total S as -14.02 μV/K predicts the material as n-type with thermoelectric figure of merit (zT) of 0.5 at 800 K. The lattice thermal conductivity decreases with increasing temperature with room temperature value of 4.18 W/mK and shows a significant reduction towards higher temperatures. In view of above elements, structural stability, high zT, ZrFeSi alloy have the capabilities to stimulate experimental verification as a promising materials for high temperature power generation and spintronic device fabrications.

The Effects of Excess Co on the Phase Composition and Thermoelectric Properties of Half-Heusler NbCoSb.

PubMed

Huang, Lihong; Wang, Junchen; Chen, Xi; He, Ran; Shuai, Jing; Zhang, Jianjun; Zhang, Qinyong; Ren, Zhifeng

2018-05-11

NbCoSb with nominal 19 valence electrons, and is supposed to be metallic, has recently been reported to also exhibit the thermoelectric properties of a heavily doped n-type semiconductor. In this study, we prepared Co-rich NbCo 1+ x Sb samples ( x = 0, 0.2, 0.3, 0.4, 0.5), and their phase compositions, microstructures and thermoelectric properties were investigated. The Seebeck coefficient increased a great deal with increasing x , due to decreasing carrier concentration, and the total thermal conductivity reduced mainly because of declining κ e . Finally, a peak thermoelectric figure of merit, ZT , was about 0.46 for NbCo 1.3 Sb at 973 K. This enhancement was mainly attributed to the reduction of electric thermal conductivity and the increase of Seebeck coefficient. The excess Co had effects on the carrier concentration, deformation potential E def and DOS effective mass m * . Adding an excessive amount of Co leads to a very high E def , which was detrimental for transport characteristics.

Nonlinear thermotics: nonlinearity enhancement and harmonic generation in thermal metasurfaces

NASA Astrophysics Data System (ADS)

Dai, Gaole; Shang, Jin; Wang, Ruizhe; Huang, Jiping

2018-03-01

We propose and investigate a class of structural surfaces (metasurfaces). We develop the perturbation theory and the effective medium theory to study the thermal properties of the metasurface. We report that the coefficient of temperature-dependent (nonlinear) item in thermal conductivity can be enhanced under certain conditions. Furthermore, the existence of nonlinear item helps to generate high-order harmonic frequencies of heat flux in the presence of a heat source with periodic temperature. This work paves a different way to control and manipulate the transfer of heat, and it also makes it possible to develop nonlinear thermotics in the light of nonlinear optics.

A similarity solution of time dependent MHD liquid film flow over stretching sheet with variable physical properties

NASA Astrophysics Data System (ADS)

Idrees, M.; Rehman, Sajid; Shah, Rehan Ali; Ullah, M.; Abbas, Tariq

2018-03-01

An analysis is performed for the fluid dynamics incorporating the variation of viscosity and thermal conductivity on an unsteady two-dimensional free surface flow of a viscous incompressible conducting fluid taking into account the effect of a magnetic field. Surface tension quadratically vary with temperature while fluid viscosity and thermal conductivity are assumed to vary as a linear function of temperature. The boundary layer partial differential equations in cartesian coordinates are transformed into a system of nonlinear ordinary differential equations (ODEs) by similarity transformation. The developed nonlinear equations are solved analytically by Homotopy Analysis Method (HAM) while numerically by using the shooting method. The Effects of natural parameters such as the variable viscosity parameter A, variable thermal conductivity parameter N, Hartmann number Ma, film Thickness, unsteadiness parameter S, Thermocapillary number M and Prandtl number Pr on the velocity and temperature profiles are investigated. The results for the surface skin friction coefficient f″ (0) , Nusselt number (heat flux) -θ‧ (0) and free surface temperature θ (1) are presented graphically and in tabular form.

Correlation of anisotropy and directional conduction in β-Li 3PS 4 fast Li + conductor

DOE PAGES

Chen, Yan; Cai, Lu; Liu, Zengcai; ...

2015-07-06

Our letter reports the correlation of anisotropy and directional conduction in the fast Li + conductor β-Li 3PS 4, one of the low-symmetry crystalline electrolyte candidates. The material has both high conductivity and good stability that serves well for the large-scale energy storage applications of all-solid-state lithium ion batteries. The anisotropic physical properties, demonstrated here by the thermal expansion coefficients, are crucial for compatibility in the solid-state system and battery performance. Neutron and X-ray powder diffraction measurements were done to determine the crystal structure and thermal stability. Moreover, the crystallographic b-axis was revealed as a fast expansion direction, while negligiblemore » thermal expansion was observed along the a-axis around the battery operating temperatures. The anisotropic behavior has its structural origin from the Li + conduction channels with incomplete Li occupancy and a flexible connection of LiS 4 and PS 4 tetrahedra within the framework. This indicates a strong correlation in the direction of the ionic transport in the low-symmetry Li + conductor.« less

Thermoelectric Properties of Highly-Crystallized Ge-Te-Se Glasses Doped with Cu/Bi.

PubMed

Srinivasan, Bhuvanesh; Boussard-Pledel, Catherine; Dorcet, Vincent; Samanta, Manisha; Biswas, Kanishka; Lefèvre, Robin; Gascoin, Franck; Cheviré, François; Tricot, Sylvain; Reece, Michael; Bureau, Bruno

2017-03-23

Chalcogenide semiconducting systems are of growing interest for mid-temperature range (~500 K) thermoelectric applications. In this work, Ge 20 Te 77 Se₃ glasses were intentionally crystallized by doping with Cu and Bi. These effectively-crystallized materials of composition (Ge 20 Te 77 Se₃) 100- x M x (M = Cu or Bi; x = 5, 10, 15), obtained by vacuum-melting and quenching techniques, were found to have multiple crystalline phases and exhibit increased electrical conductivity due to excess hole concentration. These materials also have ultra-low thermal conductivity, especially the heavily-doped (Ge 20 Te 77 Se₃) 100- x Bi x ( x = 10, 15) samples, which possess lattice thermal conductivity of ~0.7 Wm -1 K -1 at 525 K due to the assumable formation of nano-precipitates rich in Bi, which are effective phonon scatterers. Owing to their high metallic behavior, Cu-doped samples did not manifest as low thermal conductivity as Bi-doped samples. The exceptionally low thermal conductivity of the Bi-doped materials did not, alone, significantly enhance the thermoelectric figure of merit, zT. The attempt to improve the thermoelectric properties by crystallizing the chalcogenide glass compositions by excess doping did not yield power factors comparable with the state of the art thermoelectric materials, as these highly electrically conductive crystallized materials could not retain the characteristic high Seebeck coefficient values of semiconducting telluride glasses.

Thermoelectric Properties of Highly-Crystallized Ge-Te-Se Glasses Doped with Cu/Bi

PubMed Central

Srinivasan, Bhuvanesh; Boussard-Pledel, Catherine; Dorcet, Vincent; Samanta, Manisha; Biswas, Kanishka; Lefèvre, Robin; Gascoin, Franck; Cheviré, François; Tricot, Sylvain; Reece, Michael; Bureau, Bruno

2017-01-01

Chalcogenide semiconducting systems are of growing interest for mid-temperature range (~500 K) thermoelectric applications. In this work, Ge20Te77Se3 glasses were intentionally crystallized by doping with Cu and Bi. These effectively-crystallized materials of composition (Ge20Te77Se3)100−xMx (M = Cu or Bi; x = 5, 10, 15), obtained by vacuum-melting and quenching techniques, were found to have multiple crystalline phases and exhibit increased electrical conductivity due to excess hole concentration. These materials also have ultra-low thermal conductivity, especially the heavily-doped (Ge20Te77Se3)100−xBix (x = 10, 15) samples, which possess lattice thermal conductivity of ~0.7 Wm−1 K−1 at 525 K due to the assumable formation of nano-precipitates rich in Bi, which are effective phonon scatterers. Owing to their high metallic behavior, Cu-doped samples did not manifest as low thermal conductivity as Bi-doped samples. The exceptionally low thermal conductivity of the Bi-doped materials did not, alone, significantly enhance the thermoelectric figure of merit, zT. The attempt to improve the thermoelectric properties by crystallizing the chalcogenide glass compositions by excess doping did not yield power factors comparable with the state of the art thermoelectric materials, as these highly electrically conductive crystallized materials could not retain the characteristic high Seebeck coefficient values of semiconducting telluride glasses. PMID:28772687

Theoretical performance of liquid hydrogen and liquid fluorine as a rocket propellant

NASA Technical Reports Server (NTRS)

Gordon, Sanford; Huff, Vearl N

1953-01-01

Theoretical values of performance parameters for liquid hydrogen and liquid fluorine as a rocket propellant were calculated on the assumption of equilibrium composition during the expansion process for a wide range of fuel-oxidant and expansion ratios. The parameters included were specific impulse, combustion-chamber temperature, nozzle-exit temperature, equilibrium composition, mean molecular weight, characteristic velocity, coefficient of thrust, ration of nozzle-exit area to throat area, specific heat at constant pressure, coefficient of viscosity, and coefficient of thermal conductivity. The maximum value of specific impulse was 364.6 pound-seconds per pound for a chamber pressure of 300 pounds per square inch absolute (20.41 atm) and an exit pressure of 1 atmosphere.

Theoretical performance of liquid ammonia and liquid fluorine as a rocket propellant

NASA Technical Reports Server (NTRS)

Gordon, Sanford; Huff, Vearl N

1953-01-01

Theoretical values of performance parameters for liquid ammonia and liquid fluorine as a rocket propellant were calculated on the assumption of equilibrium composition during the expansion process for a wide range of fuel-oxidant and expansion ratios. The parameters included were specific impulse, combustion chamber temperature, nozzle-exit temperature, equilibrium composition, mean molecular weight, characteristic velocity, coefficient of thrust, ratio of nozzle-exit area to throat area, specific heat at constant pressure, coefficient of viscosity, and coefficient of thermal conductivity. The maximum value of specific impulse was 311.5 pound-seconds per pound for a chamber pressure of 300 pounds per square inch absolute (20.41 atm) and an exit pressure of 1 atmosphere.

Thermal transport in strongly correlated multilayered nanostructures

NASA Astrophysics Data System (ADS)

Freericks, James; Zlatic, Veljko

2006-03-01

The formalism for thermal transport in strongly correlated multilayered nanostructures is developed. We employ inhomogeneous dynamical mean-field theory and the Kubo formula to derive relevant thermal transport coefficients, which take the form of matrices with respect to the planar indices. We show how to define the local versions of the current and heat current operators so that heat-current correlation functions can be easily evaluated via the Jonson-Mahan theorem. Thermal transport in nanostructures is complicated by the fact that the thermal current need not be conserved through the device, and a given experimental set-up determines both how the thermal current can change through the device and how the steady-state temperature profile can be determined. Formulae to analyze classic experiments such as the Peltier and Seebeck effects, the thermal conductivity, and for running a thermoelectric cooler or power generator are also discussed.

Magnetism, optical, and thermoelectric response of CdFe2O4 by using DFT scheme

NASA Astrophysics Data System (ADS)

Mahmood, Q.; Yaseen, M.; Bhamu, K. C.; Mahmood, Asif; Javed, Y.; Ramay, Shahid M.

2018-03-01

Comparative analysis of electronic, magnetic, optical, and thermoelectric properties of CdFe2O4, calculated by employing PBEsol + mBJ has been done. The PBEsol reveals metallic nature, while TB-mBJ illustrates ferromagnetic semiconducting behavior. The reasons behind the origin of ferromagnetism are explored by observing the exchange, crystal field, and John–Teller energies. The optical nature is investigated by analyzing dielectric constants, refraction, absorption coefficient, reflectivity, and optical conductivity. Finally, thermoelectric properties are elaborated by describing the electrical and thermal conductivities, Seebeck coefficient, and power factor. The strong absorption for the visible energy and high power factor suggest CdFe2O4 as the potential candidate for renewable energy applications.

Prediction of coefficients of thermal expansion for unidirectional composites

NASA Technical Reports Server (NTRS)

Bowles, David E.; Tompkins, Stephen S.

1989-01-01

Several analyses for predicting the longitudinal, alpha(1), and transverse, alpha(2), coefficients of thermal expansion of unidirectional composites were compared with each other, and with experimental data on different graphite fiber reinforced resin, metal, and ceramic matrix composites. Analytical and numerical analyses that accurately accounted for Poisson restraining effects in the transverse direction were in consistently better agreement with experimental data for alpha(2), than the less rigorous analyses. All of the analyses predicted similar values of alpha(1), and were in good agreement with the experimental data. A sensitivity analysis was conducted to determine the relative influence of constituent properties on the predicted values of alpha(1), and alpha(2). As would be expected, the prediction of alpha(1) was most sensitive to longitudinal fiber properties and the prediction of alpha(2) was most sensitive to matrix properties.

Discrete component bonding and thick film materials study

NASA Technical Reports Server (NTRS)

Kinser, D. L.

1975-01-01

The results are summarized of an investigation of discrete component bonding reliability and a fundamental study of new thick film resistor materials. The component bonding study examined several types of solder bonded components with some processing variable studies to determine their influence upon bonding reliability. The bonding reliability was assessed using the thermal cycle: 15 minutes at room temperature, 15 minutes at +125 C 15 minutes at room temperature, and 15 minutes at -55 C. The thick film resistor materials examined were of the transition metal oxide-phosphate glass family with several elemental metal additions of the same transition metal. These studies were conducted by preparing a paste of the subject composition, printing, drying, and firing using both air and reducing atmospheres. The resulting resistors were examined for adherence, resistance, thermal coefficient of resistance, and voltage coefficient of resistance.

Stability and thermal behavior of molybdenum disulfide nanotubes: Nonequilibrium molecular dynamics simulation using REBO potential

NASA Astrophysics Data System (ADS)

Ahadi, Zohreh; Shadman Lakmehsari, Muhammad; Kumar Singh, Sandeep; Davoodi, Jamal

2017-12-01

This study is an attempt to perform equilibrium molecular dynamics and non-equilibrium molecular dynamics (NEMD) to evaluate the stability and thermal behavior of molybdenum disulfide nanotubes (MoS2NTs) by reactive empirical bond order potential. The stability of nanotubes, cohesive energy, isobaric heat capacity, and enthalpies of fusion in armchair and zigzag structures with different radii were calculated. The observed results illustrate that SWMoS2NTs, which have larger diameters, are more stable with more negative energy than the smaller ones. Moreover, it was found that the melting point is increased with an increase in the nanotube's radius. During the melting process, the structural transformation of nanotubes was investigated using a mean-square displacement and radial distribution function diagrams. Afterwards, using a NEMD simulation, the thermal conductivity of nanotubes with various diameters was calculated at a constant nanotube length. The obtained results show that the thermal conductivity coefficient increases with increasing nanotube diameters when the nanotube length is constant.

Impact of generalized Fourier's and Fick's laws on MHD 3D second grade nanofluid flow with variable thermal conductivity and convective heat and mass conditions

NASA Astrophysics Data System (ADS)

Ramzan, M.; Bilal, M.; Chung, Jae Dong; Lu, Dian Chen; Farooq, Umer

2017-09-01

A mathematical model has been established to study the magnetohydrodynamic second grade nanofluid flow past a bidirectional stretched surface. The flow is induced by Cattaneo-Christov thermal and concentration diffusion fluxes. Novel characteristics of Brownian motion and thermophoresis are accompanied by temperature dependent thermal conductivity and convective heat and mass boundary conditions. Apposite transformations are betrothed to transform a system of nonlinear partial differential equations to nonlinear ordinary differential equations. Analytic solutions of the obtained nonlinear system are obtained via a convergent method. Graphs are plotted to examine how velocity, temperature, and concentration distributions are affected by varied physical involved parameters. Effects of skin friction coefficients along the x- and y-direction versus various parameters are also shown through graphs and are well debated. Our findings show that velocities along both the x and y axes exhibit a decreasing trend for the Hartmann number. Moreover, temperature and concentration distributions are decreasing functions of thermal and concentration relaxation parameters.

Ceramic joints

DOEpatents

Miller, Bradley J.; Patten, Jr., Donald O.

1991-01-01

Butt joints between materials having different coefficients of thermal expansion are prepared having a reduced probability of failure of stress facture. This is accomplished by narrowing/tapering the material having the lower coefficient of thermal expansion in a direction away from the joint interface and not joining the narrow-tapered surface to the material having the higher coefficient of thermal expansion.

Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices

NASA Astrophysics Data System (ADS)

Jha, Pankaj; Sands, Timothy D.; Cassels, Laura; Jackson, Philip; Favaloro, Tela; Kirk, Benjamin; Zide, Joshua; Xu, Xianfan; Shakouri, Ali

2012-09-01

Lanthanum strontium manganate (La0.67Sr0.33MnO3, i.e., LSMO)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated as a potential p-type thermoelectric material. Growth was performed using pulsed laser deposition to achieve epitaxial LSMO (metal)/LMO (p-type semiconductor) superlattices on (100)-strontium titanate (STO) substrates. The magnitude of the in-plane Seebeck coefficient of LSMO thin films (<20 μV/K) is consistent with metallic behavior, while LMO thin films were p-type with a room temperature Seebeck coefficient of 140 μV/K. Thermal conductivity measurements via the photo-acoustic (PA) technique showed that LSMO/LMO superlattices exhibit a room temperature cross-plane thermal conductivity (0.89 W/m.K) that is significantly lower than the thermal conductivity of individual thin films of either LSMO (1.60 W/m.K) or LMO (1.29 W/m.K). The lower thermal conductivity of LSMO/LMO superlattices may help overcome one of the major limitations of oxides as thermoelectrics. In addition to a low cross-plane thermal conductivity, a high ZT requires a high power factor (S2σ). Cross-plane electrical transport measurements were carried out on cylindrical pillars etched in LSMO/LMO superlattices via inductively coupled plasma reactive ion etching. Cross-plane electrical resistivity data for LSMO/LMO superlattices showed a magnetic phase transition temperature (TP) or metal-semiconductor transition at ˜330 K, which is ˜80 K higher than the TP observed for in-plane resistivity of LSMO, LMO, or LSMO/LMO thin films. The room temperature cross-plane resistivity (ρc) was found to be greater than the in-plane resistivity by about three orders of magnitude. The magnitude and temperature dependence of the cross-plane conductivity of LSMO/LMO superlattices suggests the presence of a barrier with the effective barrier height of ˜300 meV. Although the magnitude of the cross-plane power factor is too low for thermoelectric applications by a factor of approximately 10-4—in part because the growth conditions chosen for this study yielded relatively high resistivity films—the temperature dependence of the resistivity and the potential for tuning the power factor by engineering strain, oxygen stoichiometry, and electronic band structure suggest that these epitaxial metal/semiconductor superlattices are deserving of further investigation.

Effect of titanium addition on the thermal properties of diamond/cu-ti composites fabricated by pressureless liquid-phase sintering technique.

PubMed

Chung, Chih-Yu; Chu, Chao-Hung; Lee, Mu-Tse; Lin, Chun-Ming; Lin, Su-Jien

2014-01-01

In this study, minor-addition elements such as Si, Co, Cr, W, Mo, and Ti were added to matrix to improve the wettability between the diamonds and Cu matrix. The pressureless liquid-phase sintering technique adopted in this study provides a low-cost method for producing diamond/Cu composites with high potential for industrial mass production. Thermal properties of the diamond/Cu-Ti composites fabricated by pressureless liquid-phase sintering at 1373 K with variation in Ti contents were thoroughly investigated. XRD and TEM analysis show that TiC layer formed in the interface between Cu and diamond. The composites exhibited thermal conductivity as high as 620 W/m · K for 50 vol% diamond/Cu-0.6 at % Ti composite with diamond particle size of 300 µm. This value comes up to 85% of the thermal conductivity calculated by the Hasselman and Johnson (H-J) theoretical analysis. Under these conditions, a suitable coefficient of thermal expansion of 6.9 ppm/K was obtained.

Effect of Titanium Addition on the Thermal Properties of Diamond/Cu-Ti Composites Fabricated by Pressureless Liquid-Phase Sintering Technique

PubMed Central

Chung, Chih-Yu; Chu, Chao-Hung; Lee, Mu-Tse; Lin, Chun-Ming; Lin, Su-Jien

2014-01-01

In this study, minor-addition elements such as Si, Co, Cr, W, Mo, and Ti were added to matrix to improve the wettability between the diamonds and Cu matrix. The pressureless liquid-phase sintering technique adopted in this study provides a low-cost method for producing diamond/Cu composites with high potential for industrial mass production. Thermal properties of the diamond/Cu-Ti composites fabricated by pressureless liquid-phase sintering at 1373 K with variation in Ti contents were thoroughly investigated. XRD and TEM analysis show that TiC layer formed in the interface between Cu and diamond. The composites exhibited thermal conductivity as high as 620 W/m·K for 50 vol% diamond/Cu-0.6  at % Ti composite with diamond particle size of 300 µm. This value comes up to 85% of the thermal conductivity calculated by the Hasselman and Johnson (H-J) theoretical analysis. Under these conditions, a suitable coefficient of thermal expansion of 6.9 ppm/K was obtained. PMID:24715816

Seal assembly for materials with different coefficients of thermal expansion

DOEpatents

Minford, Eric [Laurys Station, PA

2009-09-01

Seal assembly comprising (a) two or more seal elements, each element having having a coefficient of thermal expansion; and (b) a clamping element having a first segment, a second segment, and a connecting segment between and attached to the first and second segments, wherein the two or more seal elements are disposed between the first and second segments of the clamping element. The connecting segment has a central portion extending between the first segment of the clamping element and the second segment of the clamping element, and the connecting segment is made of a material having a coefficient of thermal expansion. The coefficient of thermal expansion of the material of the connecting segment is intermediate the largest and smallest of the coefficients of thermal expansion of the materials of the two or more seal elements.

A Selected Library of Transport Coefficients for Combustion and Plasma Physics Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cloutman, L.D.

2000-08-01

COYOTE and similar combustion programs based on the multicomponent Navier-Stokes equations require the mixture viscosity, thermal conductivity, and species transport coefficients as input. This report documents a model of these molecular transport coefficients that is simpler than the general theory, but which provides adequate accuracy for many purposes. This model leads to a computationally convenient, self-contained, and easy-to-use source of such data in a format suitable for use by such programs. We present the data for various neutral species in two forms. The first form is a simple functional fit to the transport coefficients. The second form is the usemore » of tabulated Lennard-Jones parameters in simple theoretical expressions for the gas-phase transport coefficients. The model then is extended to the case of a two-temperature plasma. Lennard-Jones parameters are given for a number of chemical species of interest in combustion research.« less

Fiber laser welding of austenitic steel and commercially pure copper butt joint

NASA Astrophysics Data System (ADS)

Kuryntsev, S. V.; Morushkin, A. E.; Gilmutdinov, A. Kh.

2017-03-01

The fiber laser welding of austenitic stainless steel and commercially pure copper in butt joint configuration without filler or intermediate material is presented. In order to melt stainless steel directly and melt copper via heat conduction a defocused laser beam was used with an offset to stainless steel. During mechanical tests the weld seam was more durable than heat affected zone of copper so samples without defects could be obtained. Three process variants of offset of the laser beam were applied. The following tests were conducted: tensile test of weldment, intermediate layer microhardness, optical metallography, study of the chemical composition of the intermediate layer, fractography. Measurements of electrical resistivity coefficients of stainless steel, copper and copper-stainless steel weldment were made, which can be interpreted or recalculated as the thermal conductivity coefficient. It shows that electrical resistivity coefficient of cooper-stainless steel weldment higher than that of stainless steel. The width of intermediate layer between stainless steel and commercially pure copper was 41-53 μm, microhardness was 128-170 HV0.01.

Thermal, spectroscopic and laser properties of Nd3+ in gadolinium scandium gallium garnet crystal produced by optical floating zone method

NASA Astrophysics Data System (ADS)

Tian, Li; Wang, Shuxian; Wu, Kui; Wang, Baolin; Yu, Haohai; Zhang, Huaijin; Cai, Huaqiang; Huang, Hui

2013-12-01

A neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG) single crystal with dimensions of Φ 5 × 20 mm2 has been grown by means of optical floating zone (OFZ). X-ray powder diffraction (XRPD) result shows that the as-grown Nd:GSGG crystal possesses a cubic structure with space group Ia3d and a cell parameter of a = 1.2561 nm. Effective elemental segregation coefficients of the Nd:GSGG as-grown crystal were calculated by using X-ray fluorescence (XRF). The thermal properties of the Nd:GSGG crystal were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficient, and the thermal conductivity of this crystal was calculated. The absorption and luminescence spectra of Nd:GSGG were measured at room temperature (RT). By using the Judd-Ofelt (J-O) theory, the theoretical radiative lifetime was calculated and compared with the experimental result. Continuous wave (CW) laser performance was achieved with the Nd:GSGG at the wavelength of 1062 nm when it was pumped by a laser diode (LD). A maximum output power of 0.792 W at 1062 nm was obtained with a slope efficiency of 11.89% under a pump power of 7.36 W, and an optical-optical conversion efficiency of 11.72%.

Thermal performance analysis of a flat heat pipe working with carbon nanotube-water nanofluid for cooling of a high heat flux heater

NASA Astrophysics Data System (ADS)

Arya, A.; Sarafraz, M. M.; Shahmiri, S.; Madani, S. A. H.; Nikkhah, V.; Nakhjavani, S. M.

2018-04-01

Experimental investigation on the thermal performance of a flat heat pipe working with carbon nanotube nanofluid is conducted. It is used for cooling a heater working at high heat flux conditions up to 190 kW/m2. The heat pipe is fabricated from aluminium and is equipped with rectangular fin for efficient cooling of condenser section. Inside the heat pipe, a screen mesh was inserted as a wick structure to facilitate the capillary action of working fluid. Influence of different operating parameters such as heat flux, mass concentration of carbon nanotubes and filling ratio of working fluid on thermal performance of heat pipe and its thermal resistance are investigated. Results showed that with an increase in heat flux, the heat transfer coefficient in evaporator section of the heat pipe increases. For filling ratio, however, there is an optimum value, which was 0.8 for the test heat pipe. In addition, CNT/water enhanced the heat transfer coefficient up to 40% over the deionized water. Carbon nanotubes intensified the thermal performance of wick structure by creating a fouling layer on screen mesh structure, which changes the contact angle of liquid with the surface, intensifying the capillary forces.

Development of Multi-physics (Multiphase CFD + MCNP) simulation for generic solution vessel power calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Seung Jun; Buechler, Cynthia Eileen

The current study aims to predict the steady state power of a generic solution vessel and to develop a corresponding heat transfer coefficient correlation for a Moly99 production facility by conducting a fully coupled multi-physics simulation. A prediction of steady state power for the current application is inherently interconnected between thermal hydraulic characteristics (i.e. Multiphase computational fluid dynamics solved by ANSYS-Fluent 17.2) and the corresponding neutronic behavior (i.e. particle transport solved by MCNP6.2) in the solution vessel. Thus, the development of a coupling methodology is vital to understand the system behavior at a variety of system design and postulated operatingmore » scenarios. In this study, we report on the k-effective (keff) calculation for the baseline solution vessel configuration with a selected solution concentration using MCNP K-code modeling. The associated correlation of thermal properties (e.g. density, viscosity, thermal conductivity, specific heat) at the selected solution concentration are developed based on existing experimental measurements in the open literature. The numerical coupling methodology between multiphase CFD and MCNP is successfully demonstrated, and the detailed coupling procedure is documented. In addition, improved coupling methods capturing realistic physics in the solution vessel thermal-neutronic dynamics are proposed and tested further (i.e. dynamic height adjustment, mull-cell approach). As a key outcome of the current study, a multi-physics coupling methodology between MCFD and MCNP is demonstrated and tested for four different operating conditions. Those different operating conditions are determined based on the neutron source strength at a fixed geometry condition. The steady state powers for the generic solution vessel at various operating conditions are reported, and a generalized correlation of the heat transfer coefficient for the current application is discussed. The assessment of multi-physics methodology and preliminary results from various coupled calculations (power prediction and heat transfer coefficient) can be further utilized for the system code validation and generic solution vessel design improvement.« less

Record figure of merit values of highly stoichiometric Sb 2Te 3 porous bulk synthesized from tailor-made molecular precursors in ionic liquids

DOE PAGES

Heimann, Stefan; Schulz, Stephan; Schaumann, Julian; ...

2015-08-06

We report on the synthesis of Sb 2Te 3 nanoparticles with record-high figure of merit values of up to 1.5. The central thermoelectric parameters, electrical conductivity, thermal conductivity and Seebeck coefficient, were independently optimized. Critical influence of porosity for the fabrication of highly efficient thermoelectric materials is firstly demonstrated, giving a strong guidance for the optimization of other thermoelectric materials.

Control of internal and external short circuits in lithium batteries using a composite thermal switch

NASA Technical Reports Server (NTRS)

Mcdonald, Robert C.; Pickett, Jerome; Goebel, Franz

1991-01-01

A composite material has been developed, consisting of a blend of metal and fluorocarbon particles, which behaves as an electronic conductor at room temperature and which abruptly becomes an insulator at a predetermined temperature. This switching behavior results from the difference in thermal expansion coefficients between the conductive and non-conductive portions of the composite. This material was applied as a thin film between the carbon cathode in Li/SOCl2 cells, and the metallic cathode current collector. Using test articles incorporating this feature it was shown that lithium cells externally heated or internally heated during a short circuit lost rate capability and the ability to overheat well below the melting point of lithium (180 C). Thus, during an internal or external cell short circuit, the potential for thermal runaway involving reactions of molten lithium is avoided.

Prediction and Characterization of NaGaS2, A High Thermal Conductivity Mid-Infrared Nonlinear Optical Material for High-Power Laser Frequency Conversion.

PubMed

Hou, Dianwei; Nissimagoudar, Arun S; Bian, Qiang; Wu, Kui; Pan, Shilie; Li, Wu; Yang, Zhihua

2018-06-15

Infrared nonlinear optical (IR NLO) crystals are the major materials to widen the output range of solid-state lasers to mid- or far-infrared regions. The IR NLO crystals used in the middle IR region are still inadequate for high-power laser applications because of deleterious thermal effects (lensing and expansion), low laser-induced damage threshold, and two-photon absorption. Herein, the unbiased global minimum search method was used for the first time to search for IR NLO optical materials and ultimately found a new IR NLO material NaGaS 2 . It meets the stringent demands for IR NLO materials pumped by high-power laser with the highest thermal conductivity among common IR NLO materials able to avoid two-photon absorption, a classic nonlinear coefficient, and wide infrared transparency.

Numerical analysis of phase change materials for thermal control of power battery of high power dissipations

NASA Astrophysics Data System (ADS)

Xia, X.; Zhang, H. Y.; Deng, Y. C.

2016-08-01

Solid-fluid phase change materials have been of increasing interest in various applications due to their high latent heat with minimum volume change. In this work, numerical analysis of phase change materials is carried out for the purpose of thermal control of the cylindrical power battery cells for applications in electric vehicles. Uniform heat density is applied at the battery cell, which is surrounded by phase change material (PCM) of paraffin wax type and contained in a metal housing. A two-dimensional geometry model is considered due to the model symmetry. The effects of power densities, heat transfer coefficients and onset melting temperatures are examined for the battery temperature evolution. Temperature plateaus can be observed from the present numerical analysis for the pure PCM cases, with the temperature level depending on the power densities, heat transfer coefficients, and melting temperatures. In addition, the copper foam of high thermal conductivity is inserted into the copper foam to enhance the heat transfer. In the modeling, the local thermal non-equilibrium between the metal foam and the PCM is taken into account and the temperatures for the metal foam and PCM are obtained respectively.

Shock initiated thermal and chemical responses of HMX crystal from ReaxFF molecular dynamics simulation.

PubMed

Zhou, Tingting; Song, Huajie; Liu, Yi; Huang, Fenglei

2014-07-21

To gain an atomistic-level understanding of the thermal and chemical responses of condensed energetic materials under thermal shock, we developed a thermal shock reactive dynamics (TS-RD) computational protocol using molecular dynamics simulation coupled with ReaxFF force field. β-Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) was selected as a a target explosive due to its wide usage in the military and industry. The results show that a thermal shock initiated by a large temperature gradient between the "hot" region and the "cold" region results in thermal expansion of the particles and induces a thermal-mechanical wave propagating back and forth in the system with an averaged velocity of 3.32 km s(-1). Heat propagating along the direction of thermal shock leads to a temperature increment of the system and thus chemical reaction initiation. Applying a continuum reactive heat conduction model combined with the temperature distribution obtained from the RD simulation, a heat conduction coefficient is derived as 0.80 W m(-1) K(-1). The chemical reaction mechanisms during thermal shock were analyzed, showing that the reaction is triggered by N-NO2 bond breaking followed by HONO elimination and ring fission. The propagation rates of the reaction front and reaction center are obtained to be 0.069 and 0.038 km s(-1), based on the time and spatial distribution of NO2. The pressure effect on the thermal shock was also investigated by employing uniaxial compression before the thermal shock. We find that compression significantly accelerates thermal-mechanical wave propagation and heat conduction, resulting in higher temperature and more excited molecules and thus earlier initiation and faster propagation of chemical reactions.

Modeling of steady-state convective cooling of cylindrical Li-ion cells

NASA Astrophysics Data System (ADS)

Shah, K.; Drake, S. J.; Wetz, D. A.; Ostanek, J. K.; Miller, S. P.; Heinzel, J. M.; Jain, A.

2014-07-01

While Lithium-ion batteries have the potential to serve as an excellent means of energy storage, they suffer from several operational safety concerns. Temperature excursion beyond a specified limit for a Lithium-ion battery triggers a sequence of decomposition and release, which can preclude thermal runaway events and catastrophic failure. To optimize liquid or air-based convective cooling approaches, it is important to accurately model the thermal response of Lithium-ion cells to convective cooling, particularly in high-rate discharge applications where significant heat generation is expected. This paper presents closed-form analytical solutions for the steady-state temperature profile in a convectively cooled cylindrical Lithium-ion cell. These models account for the strongly anisotropic thermal conductivity of cylindrical Lithium-ion batteries due to the spirally wound electrode assembly. Model results are in excellent agreement with experimentally measured temperature rise in a thermal test cell. Results indicate that improvements in radial thermal conductivity and axial convective heat transfer coefficient may result in significant peak temperature reduction. Battery sizing optimization using the analytical model is discussed, indicating the dependence of thermal performance of the cell on its size and aspect ratio. Results presented in this paper may aid in accurate thermal design and thermal management of Lithium-ion batteries.

Discrete component bonding and thick film materials study. [of capacitor chips bonded with solders and conductive epoxies

NASA Technical Reports Server (NTRS)

Kinser, D. L.

1976-01-01

The bonding reliability of discrete capacitor chips bonded with solders and conductive epoxies was examined along with the thick film resistor materials consisting of iron oxide phosphate and vanadium oxide phosphates. It was concluded from the bonding reliability studies that none of the wide range of types of solders examined is capable of resisting failure during thermal cycling while the conductive epoxy gives substantially lower failure rates. The thick film resistor studies proved the feasibility of iron oxide phosphate resistor systems although some environmental sensitivity problems remain. One of these resistor compositions has inadvertently proven to be a candidate for thermistor applications because of the excellent control achieved upon the temperature coefficient of resistance. One new and potentially damaging phenomenon observed was the degradation of thick film conductors during the course of thermal cycling.

Thermoelectric properties of pressure-sintered Si(0.8)Ge(0.2) thermoelectric alloys

NASA Technical Reports Server (NTRS)

Vining, Cronin B.; Laskow, William; Hanson, Jack O.; Van Der Beck, Roland R.; Gorsuch, Paul D.

1991-01-01

The thermoelectric properties of 28 sintered Si(0.8)Ge(0.2) alloys, heavily doped with either B or P and prepared from powders with median particle sizes ranging from about 1 to over 100 microns, have been determined from 300 to 1300 K. The thermal conductivity decreases with decreasing particle size; however, the figure of merit is not significantly increased due to a compensating reduction in the electrical conductivity. The thermoelectric figure of merit is in good agreement with results of Dismukes et al. (1964) on similarly doped alloys prepared by zone-leveling techniques. The electrical and thermal conductivity are found to be sensitive to preparation procedure while the Seebeck coefficient and figure of merit are much less sensitive. The high-temperature electrical properties are consistent with charge carrier scattering by acoustic or optical phonons.

Dispersion of Sound in Dilute Suspensions with Nonlinear Particle Relaxation

NASA Technical Reports Server (NTRS)

Kandula, Max

2010-01-01

The theory accounting for nonlinear particle relaxation (viscous and thermal) has been applied to the prediction of dispersion of sound in dilute suspensions. The results suggest that significant deviations exist for sound dispersion between the linear and nonlinear theories at large values of Omega(Tau)(sub d), where Omega is the circular frequency, and Tau(sub d) is the Stokesian particle relaxation time. It is revealed that the nonlinear effect on the dispersion coefficient due to viscous contribution is larger relative to that of thermal conduction

Present state of boron-carbon thermoelectric materials

NASA Technical Reports Server (NTRS)

Elsner, N. B.; Reynolds, G. H.

1983-01-01

Boron-carbon p-type thermoelectric materials show promise for use in advanced thermal-to-electric space power conversion systems. Here, recent data on the thermoelectric properties of boron-carbon materials, such as B9C, B13C2, B15C2, and B4C, are reviewed. In particular, attention is given to the effect of the compositional homogeneity and residual impurity content on the Seeback coefficient, electrical resistivity, and thermal conductivity of these materials. The effect of carbon content for a given level of impurity and degree of homogeneity is also discussed.

Thermally induced fracture for core-veneered dental ceramic structures.

PubMed

Zhang, Zhongpu; Guazzato, Massimiliano; Sornsuwan, Tanapon; Scherrer, Susanne S; Rungsiyakull, Chaiy; Li, Wei; Swain, Michael V; Li, Qing

2013-09-01

Effective and reliable clinical uses of dental ceramics necessitate an insightful analysis of the fracture behaviour under critical conditions. To better understand failure characteristics of porcelain veneered to zirconia core ceramic structures, thermally induced cracking during the cooling phase of fabrication is studied here by using the extended finite element method (XFEM). In this study, a transient thermal analysis of cooling is conducted first to determine the temperature distributions. The time-dependent temperature field is then imported to the XFEM model for viscoelastic thermomechanical analysis, which predicts thermally induced damage and cracking at different time steps. Temperature-dependent material properties are used in both transient thermal and thermomechanical analyses. Three typical ceramic structures are considered in this paper, namely bi-layered spheres, squat cylinders and dental crowns with thickness ratios of either 1:2 or 1:1. The XFEM fracture patterns exhibit good agreement with clinical observation and the in vitro experimental results obtained from scanning electron microscopy characterization. The study reveals that fast cooling can lead to thermal fracture of these different bi-layered ceramic structures, and cooling rate (in terms of heat transfer coefficient) plays a critical role in crack initiation and propagation. By exploring different cooling rates, the heat transfer coefficient thresholds of fracture are determined for different structures, which are of clear clinical implication. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Study of the thermoelectric properties of lead selenide doped with boron, gallium, indium, or thallium.

PubMed

Zhang, Qian; Cao, Feng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Parker, David; Singh, David J; Chen, Gang; Ren, Zhifeng

2012-10-24

Group IIIA elements (B, Ga, In, and Tl) have been doped into PbSe for enhancement of thermoelectric properties. The electrical conductivity, Seebeck coefficient, and thermal conductivity were systematically studied. Room-temperature Hall measurements showed an effective increase in the electron concentration upon both Ga and In doping and the hole concentration upon Tl doping to ~7 × 10(19) cm(-3). No resonant doping phenomenon was observed when PbSe was doped with B, Ga, or In. The highest room-temperature power factor ~2.5 × 10(-3) W m(-1) K(-2) was obtained for PbSe doped with 2 atom % B. However, the power factor in B-doped samples decreased with increasing temperature, opposite to the trend for the other dopants. A figure of merit (ZT) of ~1.2 at ~873 K was achieved in PbSe doped with 0.5 atom % Ga or In. With Tl doping, modification of the band structure around the Fermi level helped to increase the Seebeck coefficient, and the lattice thermal conductivity decreased, probably as a result of effective phonon scattering by both the heavy Tl(3+) ions and the increased grain boundary density after ball milling. The highest p-type ZT value was ~1.0 at ~723 K.

Composite films of highly ordered Si nanowires embedded in SiGe0.3 for thermoelectric applications

NASA Astrophysics Data System (ADS)

Kikuchi, Akiou; Yao, Akifumi; Mori, Isamu; Ono, Takahito; Samukawa, Seiji

2017-10-01

We fabricated a high-density array of silicon nanowires (SiNWs) with a diameter of 10 nm embedded in silicon germanium (SiGe0.3) to give a composite thin film for thermoelectric device applications. The SiNW array was first fabricated by bio-template mask and neutral beam etching techniques. The SiNW array was then embedded in SiGe0.3 by thermal chemical vapor deposition. The cross-plane thermal conductivity of the SiNW-SiGe0.3 composite film with a thickness of 100 nm was 3.5 ± 0.3 W/mK in the temperature range of 300-350 K. Moreover, the temperature dependences of the in-plane electrical conductivity and in-plane Seebeck coefficient of the SiNW-SiGe0.3 composite were evaluated. The fabricated SiNW-SiGe0.3 composite film displayed a maximum power factor of 1 × 103 W/m K2 (a Seebeck coefficient of 4.8 × 103 μV/K and an electrical conductivity of 4.4 × 103 S/m) at 873 K. The present high-density SiNW array structure represents a new route to realize practical thermoelectric devices using mature Si processes without any rare metals.

Structural, electronic, mechanical, and thermoelectric properties of a novel half Heusler compound HfPtPb

NASA Astrophysics Data System (ADS)

Kaur, Kulwinder; Rai, D. P.; Thapa, R. K.; Srivastava, Sunita

2017-07-01

We explore the structural, electronic, mechanical, and thermoelectric properties of a new half Heusler compound HfPtPb, an all metallic heavy element, recently proposed to be stable [Gautier et al., Nat. Chem. 7, 308 (2015)]. In this work, we employ density functional theory and semi-classical Boltzmann transport equations with constant relaxation time approximation. The mechanical properties, such as shear modulus, Young's modulus, elastic constants, Poisson's ratio, and shear anisotropy factor, have been investigated. The elastic and phonon properties reveal that this compound is mechanically and dynamically stable. Pugh's ratio and Frantsevich's ratio demonstrate its ductile behavior, and the shear anisotropic factor reveals the anisotropic nature of HfPtPb. The band structure predicts this compound to be a semiconductor with a band gap of 0.86 eV. The thermoelectric transport parameters, such as Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and lattice thermal conductivity, have been calculated as a function of temperature. The highest value of Seebeck coefficient is obtained for n-type doping at an optimal carrier concentration of 1.0 × 1020 e/cm3. We predict the maximum value of figure of merit (0.25) at 1000 K. Our investigation suggests that this material is an n-type semiconductor.

Enhancement of thermoelectric performance in strontium titanate by praseodymium substitution

NASA Astrophysics Data System (ADS)

Kovalevsky, A. V.; Yaremchenko, A. A.; Populoh, S.; Weidenkaff, A.; Frade, J. R.

2013-02-01

In order to identify the effects of Pr additions on thermoelectric properties of strontium titanate, crystal structure, electrical and thermal conductivity, and Seebeck coefficient of Sr1-xPrxTiO3 (x = 0.02-0.30) materials were studied at 400 < T < 1180 K under highly reducing atmosphere. The mechanism of electronic transport was found to be similar up to 10% of praseodymium content, where generation of the charge carriers upon substitution resulted in significant increase of the electrical conductivity, moderate decrease in Seebeck coefficient, and general improvement of the power factor. Formation of point defects in the course of substitution led to suppression of the lattice thermal conductivity, whilst the contribution from electronic component was increasing with carrier concentration. Possible formation of layered structures and growing distortion of the perovskite lattice resulted in relatively low thermoelectric performance for Sr0.80Pr0.20TiO3 and Sr0.70Pr0.30TiO3. The maximum dimensionless figure of merit was observed for Sr0.90Pr0.10TiO3 and amounted to ˜0.23 at 670 K and ˜0.34 at 1170 K, close to the values, obtained in similar conditions for the best bulk thermoelectrics, based on rare-earth substituted SrTiO3.

Preparation and Some Properties of N-Type IrxCo1-xSB3 Solid Solutions

NASA Technical Reports Server (NTRS)

Caillat, Thierry

1995-01-01

A number of studies have been recently devoted to the preparation and characterization of binary skutterudite materials to investigate their potential as advanced thermoelectric materials. These studies show that the potential of these binary skutterudite compounds is limited because of their relatively large thermal conductivity. In order to achieve high thermoelectric figure of merits for these materials, efforts should focus on thermal conductivity reduction. Recent results obtained on n-type CoSb3 and IrSb3 compounds have shown that n-type skutterudite materials might have a better potential for thermoelectric applications than p-type materials. The thermoelectric properties of p-type IrxCo1-xSb3 solid solutions have been recently investigated and it was shown that a substantial reduction in thermal conductivity was achieved. We prepared and measured some properties of n-type IrxCo1-xSb3 solid solutions. The samples are characterized by large Seebeck coefficient values and significantly lower thermal conductivity values than those measured on the binary compounds CoSb3 and IrSb3. A maximum ZT value of about 0.4 was obtained at a temperature of about 300(deg)C. Improvements in the figure of merit are possible in this system by optimization of the doping level.

Thermal and thermoelectric transport measurements of an individual boron arsenide microstructure

NASA Astrophysics Data System (ADS)

Kim, Jaehyun; Evans, Daniel A.; Sellan, Daniel P.; Williams, Owen M.; Ou, Eric; Cowley, Alan H.; Shi, Li

2016-05-01

Recent first principles calculations have predicted that boron arsenide (BAs) can possess an unexpectedly high thermal conductivity that depends sensitively on the crystal size and defect concentration. However, few experimental results have been obtained to verify these predictions. In the present work, we report four-probe thermal and thermoelectric transport measurements of an individual BAs microstructure that was synthesized via a vapor transport method. The measured thermal conductivity was found to decrease slightly with temperature in the range between 250 K and 350 K. The temperature dependence suggests that the extrinsic phonon scattering processes play an important role in addition to intrinsic phonon-phonon scattering. The room temperature value of (186 ± 46) W m-1 K-1 is higher than that of bulk silicon but still a factor of four lower than the calculated result for a defect-free, non-degenerate BAs rod with a similar diameter of 1.15 μm. The measured p-type Seebeck coefficient and thermoelectric power factor are comparable to those of bismuth telluride, which is a commonly used thermoelectric material. The foregoing results also suggest that it is necessary to not only reduce defect and boundary scatterings but also to better understand and control the electron scattering of phonons in order to achieve the predicted ultrahigh intrinsic lattice thermal conductivity of BAs.

Investigations on the Impact of Material-Integrated Sensors with the Help of FEM-Based Modeling

PubMed Central

Dumstorff, Gerrit; Lang, Walter

2015-01-01

We present investigations on the impact of material-integrated sensors with the help of finite element-based modeling. A sensor (inlay) integrated with a material (matrix) is always a foreign body in the material, which can lead to a “wound effect”, that is degradation of the macroscopic behavior of a material. By analyzing the inlay's impact on the material in terms of mechanical load, heat conduction, stress during integration and other impacts of integration, this wound effect is analyzed. For the mechanical load, we found out that the inlay has to be at least as stretchable and bendable as the matrix. If there is a high thermal load during integration, the coefficients of the thermal expansion of the inlay have to be matched to the matrix. In the case of a high thermal load during operation, the inlay has to be as thin as possible or its thermal conductivity has to be adapted to the thermal conductivity of the matrix. To have a general view of things, the results are dimensionless and independent of the geometry. In each section, the results are illustrated by examples. Based on all of the results, we present our idea for the fabrication of future material-integrated sensors. PMID:25621607

Determining in-situ thermal conductivity of coarse textured materials through numerical analysis of thermal

NASA Astrophysics Data System (ADS)

Saito, H.; Hamamoto, S.; Moldrup, P.; Komatsu, T.

2013-12-01

Ground source heat pump (GSHP) systems use ground or groundwater as a heat/cooling source, typically by circulating anti-freezing solution inside a vertically installed closed-loop tube known as a U-tube to transfer heat to/from the ground. Since GSHP systems are based on renewable energy and can achieve much higher coefficient of performance (COP) than conventional air source heat pump systems, use of GSHP systems has been rapidly increasing worldwide. However, environmental impacts by GSHP systems including thermal effects on subsurface physical-chemical and microbiological properties have not been fully investigated. To rigorously assess GSHP impact on the subsurface environment, ground thermal properties including thermal conductivity and heat capacity need to be accurately characterized. Ground thermal properties were investigated at two experimental sites at Tokyo University of Agriculture and Technology (TAT) and Saitama University (SA), both located in the Kanto area of Japan. Thermal properties were evaluated both by thermal probe measurements on boring core samples and by performing in-situ Thermal Response Tests (TRT) in 50-80 m deep U-tubes. At both TAT and SU sites, heat-pulse probe measurements gave unrealistic low thermal conductivities for coarse textured materials (dominated by particles > 75 micrometers). Such underestimation can be partly due to poor contact between probe and porous material and partly to markedly decreasing sample water content during drilling, carrying, and storing sandy/gravelly samples. A more reliable approach for estimating in-situ thermal conductivity of coarse textured materials is therefore needed, and may be based on the commonly used TRT test. However, analyses of TRT data is typically based on Kelvin's line source model and provides an average (effective) thermal property for the whole soil profile around the U-tube but not for each geological layer. The main objective of this study was therefore to develop a method for estimating thermal conductivity values of coarse textured layers by numerically analyzing TRT data. A numerical technique combining three-dimensional conductive heat transport and one-dimensional convective heat transport to simulate heat exchange processes between the U-tube and the ground was used. In the numerical simulations, the thermal conductivities for the fine textured layers were kept at the probe-measured values, while the thermal conductivity for the coarse textured layers (constituting around half of the profile depth at both sites) was calibrated. The numerically-based method yielded more reasonable thermal conductivity values for the coarse-textured materials at both TAT and SU sites as compared to the heat pulse probe measurements, while the temperature changes of the heat carry fluid inside the U-tubes were also well simulated.

Mixed convection flow of viscoelastic fluid by a stretching cylinder with heat transfer.

PubMed

Hayat, Tasawar; Anwar, Muhammad Shoaib; Farooq, Muhammad; Alsaedi, Ahmad

2015-01-01

Flow of viscoelastic fluid due to an impermeable stretching cylinder is discussed. Effects of mixed convection and variable thermal conductivity are present. Thermal conductivity is taken temperature dependent. Nonlinear partial differential system is reduced into the nonlinear ordinary differential system. Resulting nonlinear system is computed for the convergent series solutions. Numerical values of skin friction coefficient and Nusselt number are computed and discussed. The results obtained with the current method are in agreement with previous studies using other methods as well as theoretical ideas. Physical interpretation reflecting the contribution of influential parameters in the present flow is presented. It is hoped that present study serves as a stimulus for modeling further stretching flows especially in polymeric and paper production processes.

Exact solution of conductive heat transfer in cylindrical composite laminate

NASA Astrophysics Data System (ADS)

Kayhani, M. H.; Shariati, M.; Nourozi, M.; Karimi Demneh, M.

2009-11-01

This paper presents an exact solution for steady-state conduction heat transfer in cylindrical composite laminates. This laminate is cylindrical shape and in each lamina, fibers have been wound around the cylinder. In this article heat transfer in composite laminates is being investigated, by using separation of variables method and an analytical relation for temperature distribution in these laminates has been obtained under specific boundary conditions. Also Fourier coefficients in each layer obtain by solving set of equations that related to thermal boundary layer conditions at inside and outside of the cylinder also thermal continuity and heat flux continuity between each layer is considered. In this research LU factorization method has been used to solve the set of equations.

Mixed Convection Flow of Viscoelastic Fluid by a Stretching Cylinder with Heat Transfer

PubMed Central

Hayat, Tasawar; Anwar, Muhammad Shoaib; Farooq, Muhammad; Alsaedi, Ahmad

2015-01-01

Flow of viscoelastic fluid due to an impermeable stretching cylinder is discussed. Effects of mixed convection and variable thermal conductivity are present. Thermal conductivity is taken temperature dependent. Nonlinear partial differential system is reduced into the nonlinear ordinary differential system. Resulting nonlinear system is computed for the convergent series solutions. Numerical values of skin friction coefficient and Nusselt number are computed and discussed. The results obtained with the current method are in agreement with previous studies using other methods as well as theoretical ideas. Physical interpretation reflecting the contribution of influential parameters in the present flow is presented. It is hoped that present study serves as a stimulus for modeling further stretching flows especially in polymeric and paper production processes. PMID:25775032

Thermoelectric converter for SP-100 space reactor power system

NASA Technical Reports Server (NTRS)

Terrill, W. R.; Haley, V. F.

1986-01-01

Conductively coupling the thermoelectric converter to the heat source and the radiator maximizes the utilization of the reactor and radiator temperatures and thereby minimizes the power system weight. This paper presents the design for the converter and the individual thermoelectric cells that are the building block modules for the converter. It also summarizes progress on the fabrication of initial cells and the results obtained from the preparation of a manufacturing plan. The design developed for the SP-100 system utilizes thermally conductive compliant pads that can absorb the displacement and distortion caused by the combinations of temperatures and thermal expansion coefficients. The converter and cell designs provided a 100 kWe system which met the system requirements. Initial cells were fabricated and tested.

Ceramic thermal barrier coating for rapid thermal cycling applications

DOEpatents

Scharman, Alan J.; Yonushonis, Thomas M.

1994-01-01

A thermal barrier coating for metal articles subjected to rapid thermal cycling includes a metallic bond coat deposited on the metal article, at least one MCrAlY/ceramic layer deposited on the bond coat, and a ceramic top layer deposited on the MCrAlY/ceramic layer. The M in the MCrAlY material is Fe, Ni, Co, or a mixture of Ni and Co. The ceramic in the MCrAlY/ceramic layer is mullite or Al.sub.2 O.sub.3. The ceramic top layer includes a ceramic with a coefficient of thermal expansion less than about 5.4.times.10.sup.-6 .degree.C.sup.-1 and a thermal conductivity between about 1 J sec.sup.-1 m.sup.-1 .degree.C.sup.-1 and about 1.7 J sec.sup.-1 m.sup.-1 .degree.C.sup.-1.

The Role of Radial Clearance on the Performance of Foil Air Bearings

NASA Technical Reports Server (NTRS)

Radil, Kevin; Howard, Samuel; Dykas, Brian

2002-01-01

Load capacity tests were conducted to determine how radial clearance variations affect the load capacity coefficient of foil air bearings. Two Generation III foil air bearings with the same design but possessing different initial radial clearances were tested at room temperature against an as-ground PS304 coated journal operating at 30,000 rpm. Increases in radial clearance were accomplished by reducing the journal's outside diameter via an in-place grinding system. From each load capacity test the bearing load capacity coefficient was calculated from the rule-of-thumb (ROT) model developed for foil air bearings. The test results indicate that, in terms of the load capacity coefficient, radial clearance has a direct impact on the performance of the foil air bearing. Each test bearing exhibited an optimum radial clearance that resulted in a maximum load capacity coefficient. Relative to this optimum value are two separate operating regimes that are governed by different modes of failure. Bearings operating with radial clearances less than the optimum exhibit load capacity coefficients that are a strong function of radial clearance and are prone to a thermal runaway failure mechanism and bearing seizure. Conversely, a bearing operating with a radial clearance twice the optimum suffered only a 20 percent decline in its maximum load capacity coefficient and did not experience any thermal management problems. However, it is unknown to what degree these changes in radial clearance had on other performance parameters, such as the stiffness and damping properties of the bearings.

A MEMS Infrared Thermopile Fabricated from Silicon-On-Insulator with Phononic Crystal Structures and Carbon Nanotube Absorption Layer

NASA Astrophysics Data System (ADS)

Gray, Kory Forrest

The goal of this project was to examine the possibility of creating a novel thermal infrared detector based on silicon CMOS technology that has been enhanced by the latest nano-engineering discoveries. Silicon typically is not thought as an efficient thermoelectric material. However recent advancements in nanotechnology have improved the potential for a highly sensitive infrared detector based on nano-structured silicon. The thermal conductivity of silicon has been shown to be reduced from 150 W/mK down to 60 W/mK just by decreasing the scale of the silicon from bulk down to the sub-micron scale. Further reduction of the thermal conductivity has been shown by patterning silicon with a phonon crystal structure which has been reported to have thermal conductivities down to 10 W/mK. The phonon crystal structure consists of a 2D array of holes that are etched into the silicon. The size and pitch of the holes are on the order of the mean free path of the phonons in silicon which is approximately 200-500nm. This particular device had 200nm holes on a 400nm pitch. The Seebeck coefficient of silicon can also be enhanced by the reduction of the material from the bulk to sub-micron scale and with degenerate level doping. The combination of decreased thermal conductivity and increased Seebeck coefficient allow silicon to be a promising material for thermoelectric infrared detectors. The highly doped silicon is desired to reduce the electrical resistance of the device. The low electrical resistance is required to reduce the Johnson noise of the device which is the dominant noise source for most thermal detectors. This project designed a MEMS thermopile using a silicon-on-insulator substrate, and a CMOS compatible process. The basic thermopile consists of a silicon dioxide membrane with phononic crystal patterned silicon thermocouples around the edges of the membrane. Vertical aligned, multi-walled, carbon nanotubes were used as the infrared absorption layer. A MEMS thermoelectric detector with a D* of 3 * 107 cm Hz 0.5/W was demonstrated with a time response of 3-10 milliseconds. With this initial research, it is possible to improve the D* to the high 108 cm Hz 0.5/W range by slightly changing the design of the thermopile and patterning the absorption layer.

Measurements of LGS, LGN, and LGT thermal coefficients of expansion and density.

PubMed

Malocha, Donald C; François-Saint-Cyr, Hugues; Richardson, Kathleen; Helmbold, Robert

2002-03-01

This paper will report on the measurements of the thermal coefficients of expansion and density of langasite (LGS), langanite (LGN), and langatate (LGT). The data were obtained by fabricating cubes with X, Y, and Z faces with nominal dimensions of 1 cm on a side for each material under test. The techniques used for measurement of density and thermal coefficients of expansion (TCE) of the materials are discussed. The data sets obtained and the extracted coefficients are presented.

Lattice-structures and constructs with designed thermal expansion coefficients

DOEpatents

Spadaccini, Christopher; Hopkins, Jonathan

2014-10-28

A thermal expansion-managed lattice structure having a plurality of unit cells each having flexure bearing-mounted tabs supported on a base and actuated by thermal expansion of an actuator having a thermal expansion coefficient greater than the base and arranged so that the tab is inwardly displaced into a base cavity. The flexure bearing-mounted tabs are connected to other flexure-bearing-mounted tabs of adjacent unit cells so that the adjacent unit cells are spaced from each other to accommodate thermal expansion of individual unit cells while maintaining a desired bulk thermal expansion coefficient of the lattice structure as a whole.

Analysis of Advanced Thermoelectric Materials and Their Functional Limits

NASA Technical Reports Server (NTRS)

Kim, Hyun Jung

2015-01-01

The world's demand for energy is increasing dramatically, but the best energy conversion systems operate at approximately 30% efficiency. One way to decrease energy loss is in the recovery of waste heat using thermoelectric (TE) generators. A TE generator is device that generates electricity by exploiting heat flow across a thermal gradient. The efficiency of a TE material for power generation and cooling is determined by the dimensionless Figure of Merit (ZT): ZT = S(exp. 2)sigmaT/?: where S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature, and ? is the thermal conductivity. The parameters are not physically independent, but intrinsically coupled since they are a function of the transport properties of electrons. Traditional research on TE materials has focused on synthesizing bulk semiconductor-type materials that have low thermal conductivity and high electrical conductivity affording ZT values of 1. The optimization of the s/? ratio is difficult to achieve using current material formats, as these material constants are complementary. Recent areas of research are focusing on using nanostructural artifacts that introduce specific dislocations and boundary conditions that scatter the phonons. This disrupts the physical link between thermal (phonon) and electrical (electron) transport. The result is that ? is decreased without decreasing s. These material formats give ZT values of up to 2 which represent approximately 18% energy gain from waste heat recovery. The next challenge in developing the next generation of TE materials with superior performance is to tailor the interconnected thermoelectric physical parameters of the material system. In order to approach this problem, the fundamental physics of each parameter S, sigma, and ? need to be physically understood in their context of electron/phonon interaction for the construction of new high ZT thermoelectric devices. Is it possible to overcome the physical limit imposed by of the effect of phonon lattice oscillation and energetic electrons towards thermal conductivity? Is the Seebeck coefficient, based on the difference in voltage over temperature gradient ( deltaV/deltaT), an intrinsic parameter of each material? All these parameters were manipulated using nano-bridge and twin-lattice structural concepts at the NASA Langley Research Center. This talk will review the current trend of TE research to optimize the ZT and discuss about new approaches on increasing ZT within functional limits of each parameter.

Synthesis and Characterization of Rare-Earth Tellurides and Their Composites For High-Temperature Thermoelectric Applications

NASA Astrophysics Data System (ADS)

Cheikh, Dean

Radioisotope thermoelectric generators (RTGs) are solid-state energy conversion devices and have been a vital power generation technology for deep space missions conducted by the National Aeronautics and Space Administration (NASA). At the heart of these generators are thermoelectric materials that convert heat given off by a radioisotope decay into electricity through the Seebeck effect. While these systems have demonstrated long-term reliability, the current state-of-practice materials have thermoelectric figures of merit, ZT, near 1, leading to low system level efficiencies of 6.5%. The figure of merit is defined as ZT = sigmaS 2/kappa T where sigma, S, kappa, and T are electrical conductivity, Seebeck coefficient, thermal conductivity, and temperature, respectively. Development of higher ZT materials would enable future NASA missions to perform a greater number of scientific experiments and extend mission lifetimes. Lanthanum telluride (La3-xTe4) is a state-of-the-art n-type high-temperature thermoelectric material, with a ZT of 1.1 at 1275 K. It has been demonstrated that the electrical resistivity and Seebeck coefficient of this material can be decoupled when nickel inclusions are added to form a composite. This new phenomenon, known as composite assisted funneling of electrons (CAFE), allows for the resistivity of the composite to decrease while leaving the Seebeck coefficient unaffected when 12-15 vol% nickel was incorporated. The initial work presented in this dissertation focused on microstructural modifications to La3-xTe4-Ni composites to attain a better understanding of the CAFE mechanism. This investigation was conducted by varying the size of the nickel particles compared to what were used in the previous composite study. A 60% increase in ZT to a value of 1.9 at 1200 K for the composites with the smallest Ni particle size was obtained due to an increased Seebeck coefficient and decreased thermal conductivity. The next study focused on the extension of the CAFE effect in La 3-xTe4 to use inclusions other than nickel. Cobalt of a similar size to the nickel in the initial La3-xTe4-Ni composite work was used. A series of La3-xTe4-Co composites were synthesized and their thermoelectric properties characterized. A gradual decrease in resistivity was observed above 8 vol% cobalt, suggesting the CAFE mechanism was occurring. An 18% increase to the Seebeck coefficient was observed between 5-8 vol% cobalt, likely due to contamination on the cobalt powder, altering the carrier concentration of the matrix. The increase to the Seebeck coefficient allowed for a ZT of 1.5 at 1225 K to be achieved at 5 vol% cobalt. The final investigation in this dissertation focused on the synthesis and thermoelectric characterization of praseodymium telluride (Pr3-x Te4). Density functional theory (DFT) calculations predicted a large peak in the density of states (DOS) of Pr3-xTe4 at its Fermi level compared to La3-xTe4, due to the 4ƒ electrons of praseodymium. This change in the band structure was predicted to increase the Seebeck coefficient of Pr3-xTe4 over La3-xTe4. A series of Pr3-xTe4 with varying vacancy concentrations were mechanochemically synthesized and characterized. A 25% improvement in the Seebeck coefficient and 25% decrease in the thermal conductivity compared to La3-xTe4 was observed. The thermoelectric properties were found to optimize at a composition of Pr2.74Te4, reaching a ZT of 1.7 at 1200 K.

Hydromagnetic Rarefied Fluid Flow over a Wedge in the Presence of Surface Slip and Thermal Radiation

NASA Astrophysics Data System (ADS)

Das, K.; Sharma, R. P.; Duari, P. R.

2017-12-01

An analysis is presented to investigate the effects of thermal radiation on a convective slip flow of an electrically conducting slightly rarefied fluid, having temperature dependent fluid properties, over a wedge with a thermal jump at the surface of the boundary in the presence of a transverse magnetic field. The reduced equations are solved numerically using the finite difference code that implements the 3-stage Lobatto IIIa formula for the partitioned Runge-Kutta method. Numerical results for the dimensionless velocity and temperature as well as for the skin friction coefficient and the Nusselt number are presented through graphs and tables for pertinent parameters to show interesting aspects of the solution.

Structural and optical properties of axial silicon-germanium nanowire heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, X.; Tsybeskov, L., E-mail: tsybesko@njit.edu; Kamins, T. I.

2015-12-21

Detailed studies of the structural and optical properties of axial silicon-germanium nanowire heterojunctions show that despite the 4.2% lattice mismatch between Si and Ge they can be grown without a significant density of structural defects. The lattice mismatch induced strain is partially relieved due to spontaneous SiGe intermixing at the heterointerface during growth and lateral expansion of the Ge segment of the nanowire. The mismatch in Ge and Si coefficients of thermal expansion and low thermal conductivity of Si/Ge nanowire heterojunctions are proposed to be responsible for the thermally induced stress detected under intense laser radiation in photoluminescence and Ramanmore » scattering measurements.« less

Evaluation of a method for heat transfer measurements and thermal visualization using a composite of a heater element and liquid crystals. [thermal performance of turbine blade cooling configurations

NASA Technical Reports Server (NTRS)

Hippensteele, S. A.; Russell, L. M.; Stepka, F. S.

1981-01-01

Commercially available elements of a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research. The particular feature of the composite is its ability to obtain local heat transfer coefficients and isotherm patterns that provide visual evaluation of the thermal performances of turbine blade cooling configurations. Examples of the use of the composite are presented.

Thermal response of a Fermi-Pasta-Ulam chain with Andersen thermostats

NASA Astrophysics Data System (ADS)

D'Ambrosio, Federico; Baiesi, Marco

2017-11-01

The linear response to temperature variations is well characterised for equilibrium systems but a similar theory is not available, for example, for inertial heat conducting systems, whose paradigm is the Fermi-Pasta-Ulam (FPU) model driven by two different boundary temperatures. For models of inertial systems out of equilibrium, including relaxing systems, we show that Andersen thermostats are a natural tool for studying the thermal response. We derive a fluctuation-response relation that allows to predict thermal expansion coefficients or the heat capacitance in nonequilibrium regimes. Simulations of the FPU chain of oscillators suggest that estimates of susceptibilities obtained with our relation are better than those obtained via a small perturbation.

Design and development of high efficiency 140W space TWT with graphite collector

NASA Astrophysics Data System (ADS)

Srivastava, V.; Purohit, G.; Sharma, R. K.; Sharma, S. M.; Bera, A.; Bhaskar, P. V.; Singh, R. R.; Prasad, K.; Kiran, V.

2008-05-01

4-stage graphite collector assembly has been designed and developed for a 140W Ku-band space TWT to achieve the collector efficiency more than 80%. The UHV compatible, high density, copper impregnated POCO graphite (DFP-1C) was used to fabricate the four collector electrodes of the 4-stage depressed collector. Copper impregnated graphite material is used for the collector electrodes because of its low secondary electron emission coefficient, high thermal and electrical conductivities, easy machining and brazing, low thermal expansion coefficient and low weight. The graphite material was characterized for the UHV compatibility. The collector electrodes were precisely fabricated by careful machining, and technology was developed for brazing of graphite electrodes with high voltage alumina insulators. Complete TWT with four-stage graphite collector was developed and 140W output power at gain more than 55 dB was achieved. The TWT was pumped from both the gun and the collector ends.

ProbeZT: Simulation of transport coefficients of molecular electronic junctions under environmental effects using Büttiker's probes

NASA Astrophysics Data System (ADS)

Korol, Roman; Kilgour, Michael; Segal, Dvira

2018-03-01

We present our in-house quantum transport package, ProbeZT. This program provides linear response coefficients: electrical and electronic thermal conductances, as well as the thermopower of molecular junctions in which electrons interact with the surrounding thermal environment. Calculations are performed based on the Büttiker probe method, which introduces decoherence, energy exchange and dissipation effects phenomenologically using virtual electrode terminals called probes. The program can realize different types of probes, each introducing various environmental effects, including elastic and inelastic scattering of electrons. The molecular system is described by an arbitrary tight-binding Hamiltonian, allowing the study of different geometries beyond simple one-dimensional wires. Applications of the program to study the thermoelectric performance of molecular junctions are illustrated. The program also has a built-in functionality to simulate electron transport in double-stranded DNA molecules based on a tight-binding (ladder) description of the junction.

Evolution of Edge Pedestal Profiles Over the L-H Transition

NASA Astrophysics Data System (ADS)

Sayer, M. S.; Stacey, W. M.; Floyd, J. P.; Groebner, R. J.

2012-10-01

The detailed time evolution of thermal diffusivities, electromagnetic forces, pressure gradients, particle pinch and momentum transport frequencies (which determine the diffusion coefficient) have been analyzed during the L-H transition in a DIII-D discharge. Density, temperature, rotation velocity and electric field profiles at times just before and after the L-H transition are analyzed in terms of these quantities. The analysis is based on the fluid particle balance, energy balance, force balance and heat conduction equations, as in Ref. [1], but with much greater time resolution and with account for thermal ion orbit loss. The variation of diffusive and non-diffusive transport over the L-H transition is determined from the variation in the radial force balance (radial electric field, VxB force, and pressure gradient) and the variation in the interpreted diffusive transport coefficients. 6pt [1] W.M. Stacey and R.J. Groebner, Phys. Plasmas 17, 112512 (2010).

Thermoelectric properties of non-stoichiometric lanthanum sulfides

NASA Technical Reports Server (NTRS)

Shapiro, E.; Danielson, L. R.

1983-01-01

The lanthanum sulfides are promising candidate materials for high-efficiency thermoelectric applications at temperatures up to 1300 C. The non-stoichiometric lanthanum sulfides (LaS(x), where x is in the range 1.33-1.50) appear to possess the most favorable thermoelectric properties. The Seebeck coefficient and resistivity vary significantly with composition, so that an optimum value of alpha sq/rho (where alpha is the Seebeck coefficient and rho is the resistivity) can be chosen. The thermal conductivity remains approximately constant with stoichiometry, so a material with an optimum value of alpha sq/rho should possess the optimum figure-of-merit. Data for the Seebeck coefficient and electrical resistivity of non-stoichiometric lanthanum sulfides will be pressed, together with structural properties of these materials.

Effective Heat and Mass Transport Properties of Anisotropic Porous Ceria for Solar Thermochemical Fuel Generation

PubMed Central

Haussener, Sophia; Steinfeld, Aldo

2012-01-01

High-resolution X-ray computed tomography is employed to obtain the exact 3D geometrical configuration of porous anisotropic ceria applied in solar-driven thermochemical cycles for splitting H2O and CO2. The tomography data are, in turn, used in direct pore-level numerical simulations for determining the morphological and effective heat/mass transport properties of porous ceria, namely: porosity, specific surface area, pore size distribution, extinction coefficient, thermal conductivity, convective heat transfer coefficient, permeability, Dupuit-Forchheimer coefficient, and tortuosity and residence time distributions. Tailored foam designs for enhanced transport properties are examined by means of adjusting morphologies of artificial ceria samples composed of bimodal distributed overlapping transparent spheres in an opaque medium. PMID:28817039

Thermoelectric materials with filled skutterudite structure for thermoelectric devices

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Borshchevsky, Alex (Inventor); Caillat, Thierry (Inventor); Morelli, Donald T. (Inventor); Meisner, Gregory P. (Inventor)

2002-01-01

A class of thermoelectric compounds based on the skutterudite structure with heavy filling atoms in the empty octants and substituting transition metals and main-group atoms. High Seebeck coefficients and low thermal conductivities are achieved in combination with large electrical conductivities in these filled skutterudites for large ZT values. Substituting and filling methods are disclosed to synthesize skutterudite compositions with desired thermoelectric properties. A melting and/or sintering process in combination with powder metallurgy techniques is used to fabricate these new materials.

Thermoelectric devices based on materials with filled skutterudite structures

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Borshchevsky, Alex (Inventor); Caillat, Thierry (Inventor); Morelli, Donald T. (Inventor); Meisner, Gregory P. (Inventor)

2003-01-01

A class of thermoelectric compounds based on the skutterudite structure with heavy filling atoms in the empty octants and substituting transition metals and main-group atoms. High Seebeck coefficients and low thermal conductivities are achieved in combination with large electrical conductivities in these filled skutterudites for large ZT values. Substituting and filling methods are disclosed to synthesize skutterudite compositions with desired thermoelectric properties. A melting and/or sintering process in combination with powder metallurgy techniques is used to fabricate these new materials.

Thermoelectric Behavior of PbSe Single Crystals

DOE PAGES

Kogo, Gilbert; Pradhan, Aswini K.; Roy, Utpal N.

2016-12-05

The electrical conductivity and Seebeck coefficient of PbSe single crystals grown by the Bridgman technique display metallic behavior. The Seebeck coefficient increases linearly with increasing temperature and showed positive Seebeck values, typically valid for a p-type PbSe crystal. The electronic thermal conductivity decreases with increase in temperature. The power factor increases gradually with temperature until the maximum value of 6.51 × 10 -3 W/mK2 at 260 K, other values are 5.95 × 10 -3 W/mK 2 at 300 K, and 5.40 × 10 -3 W/mK 2 at 320 K. Our results demonstrate that as-grown PbSe crystal is generically p-type duemore » to excess in Pb and can be a potential candidate for thermoelectric power generation.« less

Hybrid local piezoelectric and conductive functions for high performance airborne sound absorption

NASA Astrophysics Data System (ADS)

Rahimabady, Mojtaba; Statharas, Eleftherios Christos; Yao, Kui; Sharifzadeh Mirshekarloo, Meysam; Chen, Shuting; Tay, Francis Eng Hock

2017-12-01

A concept of hybrid local piezoelectric and electrical conductive functions for improving airborne sound absorption is proposed and demonstrated in composite foam made of porous polar polyvinylidene fluoride (PVDF) mixed with conductive single-walled carbon nanotube (SWCNT). According to our hybrid material function design, the local piezoelectric effect in the PVDF matrix with the polar structure and the electrical resistive loss of SWCNT enhanced sound energy conversion to electrical energy and subsequently to thermal energy, respectively, in addition to the other known sound absorption mechanisms in a porous material. It is found that the overall energy conversion and hence the sound absorption performance are maximized when the concentration of the SWCNT is around the conductivity percolation threshold. For the optimal composition of PVDF/5 wt. % SWCNT, a sound reduction coefficient of larger than 0.58 has been obtained, with a high sound absorption coefficient higher than 50% at 600 Hz, showing their great values for passive noise mitigation even at a low frequency.

Analysis of heat conduction in a drum brake system of the wheeled armored personnel carriers

NASA Astrophysics Data System (ADS)

Puncioiu, A. M.; Truta, M.; Vedinas, I.; Marinescu, M.; Vinturis, V.

2015-11-01

This paper is an integrated study performed over the Braking System of the Wheeled Armored Personnel Carriers. It mainly aims to analyze the heat transfer process which is present in almost any industrial and natural process. The vehicle drum brake systems can generate extremely high temperatures under high but short duration braking loads or under relatively light but continuous braking. For the proper conduct of the special vehicles mission in rough terrain, we are talking about, on one hand, the importance of the possibility of immobilization and retaining position and, on the other hand, during the braking process, the importance movement stability and reversibility or reversibility, to an encounter with an obstacle. Heat transfer processes influence the performance of the braking system. In the braking phase, kinetic energy transforms into thermal energy resulting in intense heating and high temperature states of analyzed vehicle wheels. In the present work a finite element model for the temperature distribution in a brake drum is developed, by employing commercial finite element software, ANSYS. These structural and thermal FEA models will simulate entire braking event. The heat generated during braking causes distortion which modifies thermoelastic contact pressure distribution drum-shoe interface. In order to capture the effect of heat, a transient thermal analysis is performed in order to predict the temperature distribution transitional brake components. Drum brakes are checked both mechanical and thermal. These tests aim to establish their sustainability in terms of wear and the variation coefficient of friction between the friction surfaces with increasing temperature. Modeling using simulation programs led eventually to the establishment of actual thermal load of the mechanism of brake components. It was drawn the efficiency characteristic by plotting the coefficient of effectiveness relative to the coefficient of friction shoe-drum. Thus induced thermal loads determine thermo mechanical behavior of the structure of wheels. Study the transfer of heat generated during braking is useful because results can improve and validate existing theory or may lead to the development of a mathematical model to simulate the behavior of the brake system for various tactical and operational situations. Conclusions of this paper are relevant because theoretical data analysis results are validated by experimental research.

Investigating physical field effects on the size-dependent dynamic behavior of inhomogeneous nanoscale plates

NASA Astrophysics Data System (ADS)

Ebrahimi, Farzad; Reza Barati, Mohammad

2017-02-01

This article investigates the thermo-mechanical vibration frequencies of magneto-electro-thermo-elastic functionally graded (METE-FG) nanoplates in the framework of refined four-unknown shear deformation plate theory. The present nanoplate is subjected to various kinds of thermal loads with uniform, linear and nonlinear distributions. The nonlinear distribution is considered as heat conduction and sinusoidal temperature rise. The present refined theory captures the influences of shear deformations without the need for shear correction factors. Thermo-magneto-electro-elastic coefficients of the FG nanoplate vary gradually along the thickness according to the power-law form. The scale coefficient is taken into consideration implementing the nonlocal elasticity of Eringen. The governing equations are derived through Hamilton's principle and are solved analytically. The frequency response is compared with those of previously published data. The obtained results are presented for the thermo-mechanical vibrations of the FG nanobeams to investigate the effects of material graduation, nonlocal parameter, mode number, slenderness ratio and thermal loading in detail. The present study is associated to aerospace, mechanical and nuclear engineering structures which are under thermal loads.

Thermal expansion coefficients of obliquely deposited MgF2 thin films and their intrinsic stress.

PubMed

Jaing, Cheng-Chung

2011-03-20

This study elucidates the effects of columnar angles and deposition angles on the thermal expansion coefficients and intrinsic stress behaviors of MgF2 films with columnar microstructures. The behaviors associated with temperature-dependent stresses in the MgF2 films are measured using a phase-shifting Twyman-Green interferometer with a heating stage and the application of a phase reduction algorithm. The thermal expansion coefficients of MgF2 films at various columnar angles were larger than those of glass substrates. The intrinsic stress in the MgF2 films with columnar microstructures was compressive, while the thermal stress was tensile. The thermal expansion coefficients of MgF2 films with columnar microstructures and their intrinsic stress evidently depended on the deposition angle and the columnar angle.

Compositions, thermodynamic properties, and transport coefficients of high-temperature C5F10O mixed with CO2 and O2 as substitutes for SF6 to reduce global warming potential

NASA Astrophysics Data System (ADS)

Zhong, Linlin; Rong, Mingzhe; Wang, Xiaohua; Wu, Junhui; Han, Guiquan; Han, Guohui; Lu, Yanhui; Yang, Aijun; Wu, Yi

2017-07-01

C5F10O has recently been found to be a very promising alternative to SF6. This paper is devoted to the investigation of compositions, thermodynamic properties, and transport coefficients of high-temperature C5F10O mixed with CO2 and O2. Firstly, the partition functions and enthalpies of formation for a few molecules (CxFy and CxFyO) which are likely to exist in the mixtures, are calculated based on the G4(MP2) theory. The isomers of the above molecules are selected according to their Gibbs energy. The compositions of C5F10O-CO2-O2 mixtures are then determined using the minimization of the Gibbs free energy. Next, the thermodynamic properties (mass density, specific enthalpy, and specific heat) are derived from the previously calculated compositions. Lastly, the transport coefficients (electrical conductivity, viscosity, and thermal conductivity) are calculated based on Chapman-Enskog method. It is found that, as an arc quenching gas, C5F10O could not recombine into itself with the temperature decreasing down to room temperature after the arc extinction. Besides, the key species at room temperature are always CF4, CO2, and C4F6 if graphite is not considered. When taken into account, graphite will replace C4F6 as one of the dominate particles. The mixing of CO2 with C5F10O plasma significantly affects the thermodynamic properties (e.g. vanishing and/or shifting of the peaks in specific heat) and transport coefficients (e.g. reducing viscosity and changing the number of peaks in thermal conductivity), while the addition of O2 with C5F10O-CO2 mixtures has no remarkable influence on both thermodynamic and transport properties.

Effects of cooling system parameters on heat transfer in PAFC stack. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali A.

1985-01-01

Analytical and experimental study for the effects of cooling system parameters on the heat transfer and temperature distribution in the electrode plates of a phosphoric acid fuel-cell has been conducted. An experimental set-up that simulates the operating conditions prevailing in a phosphoric-acid fuel-cell stack was designed and constructed. The set-up was then used to measure the overall heat transfer coefficient, the thermal contact resistance, and the electrode temperature distribution for two different cooling plate configurations. Two types of cooling plate configurations, serpentine and straight, were tested. Air, water, and oil were used as coolants. Measurements for the heat transfer coefficient and the thermal contact resistance were made for various flow rates ranging from 16 to 88 Kg/hr, and stack clamping pressure ranging from O to 3448 Kpa. The experimental results for the overall heat transfer coefficient were utilized to derive mathematical relations for the overall heat transfer coefficient as a function of stack clamping pressure and Reynolds number for the three coolants. The empirically derived formulas were incorporated in a previously developed computer program to predict electrodes temperature distribution and the performance of the stack cooling system. The results obtained were then compared with those available in the literature. The comparison showed maximum deviation of +/- 11%.

High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

NASA Astrophysics Data System (ADS)

Chen, Long; Liu, Yamei; He, Jian; Tritt, Terry M.; Poon, S. Joseph

2017-06-01

Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta) as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase the Seebeck coefficient in the temperature range 300-1000 K, consistent with a resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as evident by the systematic decrease in electrical resistivity and Seebeck coefficient. The combination of enhanced Seebeck coefficient due to the presence of V resonant states and the reduced thermal conductivity has led to a state-of-the-art ZT of 1.3 near 850 K in n-type (Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.

With respect to coefficient of linear thermal expansion, bacterial vegetative cells and spores resemble plastics and metals, respectively.

PubMed

Nakanishi, Koichi; Kogure, Akinori; Fujii, Takenao; Kokawa, Ryohei; Deuchi, Keiji; Kuwana, Ritsuko; Takamatsu, Hiromu

2013-10-09

If a fixed stress is applied to the three-dimensional z-axis of a solid material, followed by heating, the amount of thermal expansion increases according to a fixed coefficient of thermal expansion. When expansion is plotted against temperature, the transition temperature at which the physical properties of the material change is at the apex of the curve. The composition of a microbial cell depends on the species and condition of the cell; consequently, the rate of thermal expansion and the transition temperature also depend on the species and condition of the cell. We have developed a method for measuring the coefficient of thermal expansion and the transition temperature of cells using a nano thermal analysis system in order to study the physical nature of the cells. The tendency was seen that among vegetative cells, the Gram-negative Escherichia coli and Pseudomonas aeruginosa have higher coefficients of linear expansion and lower transition temperatures than the Gram-positive Staphylococcus aureus and Bacillus subtilis. On the other hand, spores, which have low water content, overall showed lower coefficients of linear expansion and higher transition temperatures than vegetative cells. Comparing these trends to non-microbial materials, vegetative cells showed phenomenon similar to plastics and spores showed behaviour similar to metals with regards to the coefficient of liner thermal expansion. We show that vegetative cells occur phenomenon of similar to plastics and spores to metals with regard to the coefficient of liner thermal expansion. Cells may be characterized by the coefficient of linear expansion as a physical index; the coefficient of linear expansion may also characterize cells structurally since it relates to volumetric changes, surface area changes, the degree of expansion of water contained within the cell, and the intensity of the internal stress on the cellular membrane. The coefficient of linear expansion holds promise as a new index for furthering the understanding of the characteristics of cells. It is likely to be a powerful tool for investigating changes in the rate of expansion and also in understanding the physical properties of cells.

With respect to coefficient of linear thermal expansion, bacterial vegetative cells and spores resemble plastics and metals, respectively

PubMed Central

2013-01-01

Background If a fixed stress is applied to the three-dimensional z-axis of a solid material, followed by heating, the amount of thermal expansion increases according to a fixed coefficient of thermal expansion. When expansion is plotted against temperature, the transition temperature at which the physical properties of the material change is at the apex of the curve. The composition of a microbial cell depends on the species and condition of the cell; consequently, the rate of thermal expansion and the transition temperature also depend on the species and condition of the cell. We have developed a method for measuring the coefficient of thermal expansion and the transition temperature of cells using a nano thermal analysis system in order to study the physical nature of the cells. Results The tendency was seen that among vegetative cells, the Gram-negative Escherichia coli and Pseudomonas aeruginosa have higher coefficients of linear expansion and lower transition temperatures than the Gram-positive Staphylococcus aureus and Bacillus subtilis. On the other hand, spores, which have low water content, overall showed lower coefficients of linear expansion and higher transition temperatures than vegetative cells. Comparing these trends to non-microbial materials, vegetative cells showed phenomenon similar to plastics and spores showed behaviour similar to metals with regards to the coefficient of liner thermal expansion. Conclusions We show that vegetative cells occur phenomenon of similar to plastics and spores to metals with regard to the coefficient of liner thermal expansion. Cells may be characterized by the coefficient of linear expansion as a physical index; the coefficient of linear expansion may also characterize cells structurally since it relates to volumetric changes, surface area changes, the degree of expansion of water contained within the cell, and the intensity of the internal stress on the cellular membrane. The coefficient of linear expansion holds promise as a new index for furthering the understanding of the characteristics of cells. It is likely to be a powerful tool for investigating changes in the rate of expansion and also in understanding the physical properties of cells. PMID:24107328

Measurements of the thermal coefficient of optical attenuation at different depth regions of in vivo human skins using optical coherence tomography: a pilot study

PubMed Central

Su, Ya; Yao, X. Steve; Li, Zhihong; Meng, Zhuo; Liu, Tiegen; Wang, Longzhi

2015-01-01

We present detailed measurement results of optical attenuation’s thermal coefficients (referenced to the temperature of the skin surface) in different depth regions of in vivo human forearm skins using optical coherence tomography (OCT). We first design a temperature control module with an integrated optical probe to precisely control the surface temperature of a section of human skin. We propose a method of using the correlation map to identify regions in the skin having strong correlations with the surface temperature of the skin and find that the attenuation coefficient in these regions closely follows the variation of the surface temperature without any hysteresis. We observe a negative thermal coefficient of attenuation in the epidermis. While in dermis, the slope signs of the thermal coefficient of attenuation are different at different depth regions for a particular subject, however, the depth regions with a positive (or negative) slope are different in different subjects. We further find that the magnitude of the thermal coefficient of attenuation coefficient is greater in epidermis than in dermis. We believe the knowledge of such thermal properties of skins is important for several noninvasive diagnostic applications, such as OCT glucose monitoring, and the method demonstrated in this paper is effective in studying the optical and biological properties in different regions of skin. PMID:25780740

Towards High-Throughput, Simultaneous Characterization of Thermal and Thermoelectric Properties

NASA Astrophysics Data System (ADS)

Miers, Collier Stephen

The extension of thermoelectric generators to more general markets requires that the devices be affordable and practical (low $/Watt) to implement. A key challenge in this pursuit is the quick and accurate characterization of thermoelectric materials, which will allow researchers to tune and modify the material properties quickly. The goal of this thesis is to design and fabricate a high-throughput characterization system for the simultaneous characterization of thermal, electrical, and thermoelectric properties for device scale material samples. The measurement methodology presented in this thesis combines a custom designed measurement system created specifically for high-throughput testing with a novel device structure that permits simultaneous characterization of the material properties. The measurement system is based upon the 3o method for thermal conductivity measurements, with the addition of electrodes and voltage probes to measure the electrical conductivity and Seebeck coefficient. A device designed and optimized to permit the rapid characterization of thermoelectric materials is also presented. This structure is optimized to ensure 1D heat transfer within the sample, thus permitting rapid data analysis and fitting using a MATLAB script. Verification of the thermal portion of the system is presented using fused silica and sapphire materials for benchmarking. The fused silica samples yielded a thermal conductivity of 1.21 W/(m K), while a thermal conductivity of 31.2 W/(m K) was measured for the sapphire samples. The device and measurement system designed and developed in this thesis provide insight and serve as a foundation for the development of high throughput, simultaneous measurement platforms.

Thermoelectric properties and figure of merit of perovskite-type Ba1-xLaxSnO3 with x=0.002-0.008

NASA Astrophysics Data System (ADS)

Yasukawa, Masahiro; Kono, Toshio; Ueda, Kazushige; Yanagi, Hiroshi; Wng Kim, Sung; Hosono, Hideo

2013-10-01

Thermoelectric properties and figure of merit were evaluated from the Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ measured at high temperatures for perovskite-type ceramics of Ba1-xLaxSnO3 with x=0.002, 0.005, and 0.008, which were prepared by a polymerized complex method and a subsequent spark plasma sintering technique. All the polycrystalline dense ceramics showed n-type degenerate semiconducting behavior in the temperature range of 373-1073 K. The La content dependence of the S values revealed successful increase in the electron carriers with the La doping in this x range. The κ values remained almost unchanged with x showing ~9.6 Wm-1 K-1 at room temperature and decreased with increasing temperature. The electronic thermal conductivities calculated by the Wiedemann-Franz law as well as the T-1 dependence of the κ values indicate that the phonon thermal conductivity was dominant. The dimensionless figure of merit ZT increased with increasing temperature for all the ceramics and showed ~0.1 at 1073 K for the ceramics with x=0.002 and 0.005.

Soliton microdynamics and thermal conductivity of uranium nitride at high temperatures

NASA Astrophysics Data System (ADS)

Dubovsky, O. A.; Orlov, A. V.; Semenov, V. A.

2011-09-01

The microdynamics of soliton waves and localized modes of nonlinear vibrations of the acoustic and optical types in uranium nitride has been investigated. It has been shown that, with an increase in the excitation energy in the spectral gap between the bands of optical and acoustic phonons, the energies of solitons increase, whereas the energies of local modes decrease. The previously experimentally observed unidentified quasi-resonant features, which shift in the gap with variations in the temperature, can represent the revealed soliton waves and local modes. The microdynamics of heat conduction of uranium nitride has been studied for the stochastic generation of soliton waves and local modes in the case of spatially distant energy absorption. The thermal conductivity coefficient determined from the temperature gradient and the absorbed energy flux insignificantly exceeds the experimentally observed values, which are decreased because of the presence of structural defects of different types in the material.

First principles search for n-type oxide, nitride, and sulfide thermoelectrics

PubMed Central

Garrity, Kevin F.

2016-01-01

Oxides have many potentially desirable characteristics for thermoelectric applications, including low cost and stability at high temperatures, but thus far there are few known high zT n-type oxide thermoelectrics. In this work, we use high-throughput first principles calculations to screen transition metal oxides, nitrides, and sulfides for candidate materials with high power factors and low thermal conductivity. We find a variety of promising materials, and we investigate these materials in detail in order to understand the mechanisms that cause them to have high power factors. These materials all combine a high density of states near the Fermi level with dispersive bands, reducing the trade-off between the Seebeck coefficient and the electrical conductivity, but they do so for several different reasons. In addition, our calculations indicate that many of our candidate materials have low thermal conductivity. PMID:27885361

Annealing of Heavily Boron-Doped Silicon: Effect on Electrical and Thermoelectric Properties.

PubMed

Zulian, Laura; Segrado, Francesco; Narducci, Dario

2017-03-01

In previous studies it was shown that heavily boron-doped nanocrystalline silicon submitted to thermal treatments at temperatures ≥800 °C is characterized by an anomalously high thermoelectric power factor. Its enhanced performances were ascribed to the formation of SiBx precipitates at grain boundary, leading to the formation of potential barriers that filter out low-energy carriers, then causing a simultaneous enhancement of the Seebeck coefficient and of the electrical conductivity. To further investigate the effect of thermal treatment on boron-doped nanocrystalline silicon, samples were submitted to a host of annealing processes or of sequences of them at temperatures between 900 and 1000 °C and for various amounts of time. Electrical conductivity and Hall effect measurements were carried out after each thermal treatment over the temperature range 20–300 K. They provided evidence of the formation of an impurity band, and of hopping conduction at very low temperatures. Hall resistivity data versus temperature provided therefore important insights in the electronic structure of the system, which will enable a more complete understanding of the factors ruling energy filtering in this class of materials.

Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system

NASA Astrophysics Data System (ADS)

Liu, Minsheng; Lin, Mark Chingcheng; Wang, Chichuan

2011-12-01

In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system

PubMed Central

2011-01-01

In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid. PMID:21711787

Enhancements of thermal conductivities with Cu, CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system.

PubMed

Liu, Minsheng; Lin, Mark Chingcheng; Wang, Chichuan

2011-04-05

In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.

The electrical conductivity of in vivo human uterine fibroids.

PubMed

DeLonzor, Russ; Spero, Richard K; Williams, Joseph J

2011-01-01

The purpose of this study was to determine the value of electrical conductivity that can be used for numerical modelling in vivo radiofrequency ablation (RFA) treatments of human uterine fibroids. No experimental electrical conductivity data have previously been reported for human uterine fibroids. In this study electrical data (voltage) from selected in vivo clinical procedures on human uterine fibroids were used to numerically model the treatments. Measured versus calculated power dissipation profiles were compared to determine uterine fibroid electrical conductivity. Numerical simulations were conducted utilising a wide range of values for tissue thermal conductivity, heat capacity and blood perfusion coefficient. The simulations demonstrated that power dissipation was insensitive to the exact values of these parameters for the simulated geometry, treatment duration, and power level. Consequently, it was possible to determine tissue electrical conductivity without precise knowledge of the values for these parameters. Results of this study showed that an electrical conductivity for uterine fibroids of 0.305 S/m at 37°C and a temperature coefficient of 0.2%/°C can be used for modelling Radio Frequency Ablation of human uterine fibroids at a frequency of 460 kHz for temperatures from 37°C to 100°C.

Thermal expansion coefficient determination of polylactic acid using digital image correlation

NASA Astrophysics Data System (ADS)

Botean, Adrian-Ioan

2018-02-01

This paper aims determining the linear thermal expansion coefficient (CTE) of polylactic acid (PLA) using an optical method for measuring deformations called digital image correlation method (DIC). Because PLA is often used in making many pieces with 3D printing technology, it is opportune to know this coefficient to obtain a higher degree of precision in the construction of parts and to monitor deformations when these parts are subjected to a thermal gradient. Are used two PLA discs with 20 and 40% degree of filling. In parallel with this approach was determined the linear thermal expansion coefficient (CTE) for the copper cylinder on the surface of which are placed the two discs of PLA.

EFFECT OF CORRELATIONS ON THE TRANSPORT COEFFICIENTS OF A PLASMA (in French)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balescu, R.; de Gottal, Ph.

1961-01-01

A closed formula is obtained for the long-lived corre1ations in an inhomogeneous plasma; it is expressed in terms of the one particle distribution function. This forms an appropriate starting point for a rigorous theory of transport phenomena in plasmas, including the effect of molecular corrclations. An expressson is obtained for the thermal conductivity. (auth)

Development of advanced thermoelectric materials, phase A

NASA Technical Reports Server (NTRS)

1980-01-01

Work performed on the chemical system characterized by chrome sulfide, chrome selenide, lanthanum selenide, and lanthanum sulfide is described. Most materials within the chemical systems possess the requisites for attractive thermoelectric materials. The preparation of the alloys is discussed. Graphs show the Seebeck coefficient, electrical resistivity, and thermal conductivity of various materials within the chemical systems. The results of selected doping are included.

The super-hydrophobic IR-reflectivity TiO2 coated hollow glass microspheres synthesized by soft-chemistry method

NASA Astrophysics Data System (ADS)

Hu, Yan; Wang, Yuanhao; An, Zhenguo; Zhang, Jingjie; Yang, Hongxing

2016-11-01

The super-hydrophobic and IR-reflectivity hollow glass microspheres (HGM) was synthesized by being coated with anatase TiO2 and a super-hydrophobic material. The super-hydrophobic self-cleaning property prolong the life time of the IR reflectivity. TBT and PFOTES were firstly applied and hydrolyzed on HGM and then underwent hydrothermal reaction to synthesis anatase TiO2 film. For comparison, the PFOTES/TiO2 mutual-coated HGM (MCHGM), PFOTES single-coated HGM (F-SCHGM) and TiO2 single-coated HGM (Ti-SCHGM) were synthesized as well. The MCHGM had bigger contact angle (153°) but smaller sliding angle (16°) than F-SCHGM (contact angle: 141.2°; sliding angle: 67°). Ti-SCHGM and MCHGM both showed similar IR reflectivity with ca. 5.8% increase compared with original HGM and F-SCHGM. For the thermal conductivity, coefficients of F-SCHGM (0.0479 W/(m K)) was basically equal to that of the original HGM (0.0475 W/(m K)). Negligible difference was found between the thermal conductivity coefficients of MCHGM-coated HGM (0.0543 W/(m K)) and Ti-SCHGM (0.0546 W/(m K)).

Numerical study of the enhancement of heat transfer for hybrid CuO-Cu Nanofluids flowing in a circular pipe.

PubMed

Balla, Hyder H; Abdullah, Shahrir; Mohdfaizal, Wan; Zulkifli, Rozli; Sopian, Kamaruzaman

2013-01-01

A numerical simulation model for laminar flow of nanofluids in a pipe with constant heat flux on the wall was built to study the effect of the Reynolds number on convective heat transfer and pressure loss. The investigation was performed for hybrid nanofluids consisting of CuO-Cu nanoparticles and compared with CuO and Cu in which the nanoparticles have a spherical shape with size 50, 50, 50nm respectively. The nanofluids were prepared, following which the thermal conductivity and dynamic viscosity were measured for a range of temperatures (10 -60°C). The numerical results obtained were compared with the existing well-established correlation. The prediction of the Nusselt number for nanofluids agrees well with the Shah correlation. The comparison of heat transfer coefficients for CuO, Cu and CuO-Cu presented an increase in thermal conductivity of the nanofluid as the convective heat transfer coefficient increased. It was found that the pressure loss increases with an increase in the Reynolds number, nanoparticle density and particle volume fraction. However, the flow demonstrates enhancement in heat transfer which becomes greater with an increase in the Reynolds number for the nanofluid flow.

Pulsational stabilities of a star in thermal imbalance - Comparison between the methods

NASA Technical Reports Server (NTRS)

Vemury, S. K.

1978-01-01

The stability coefficients for quasi-adiabatic pulsations for a model in thermal imbalance are evaluated using the dynamical energy (DE) approach, the total (kinetic plus potential) energy (TE) approach, and the small amplitude (SA) approaches. From a comparison among the methods, it is found that there can exist two distinct stability coefficients under conditions of thermal imbalance as pointed out by Demaret. It is shown that both the TE approaches lead to one stability coefficient, while both the SA approaches lead to another coefficient. The coefficient obtained through the energy approaches is identified as the one which determines the stability of the velocity amplitudes. For a prenova model with a thin hydrogen-burning shell in thermal imbalance, several radial modes are found to be unstable both for radial displacements and for velocity amplitudes. However, a new kind of pulsational instability also appears, viz., while the radial displacements are unstable, the velocity amplitudes may be stabilized through the thermal imbalance terms.

Progressive Failure Analysis of Advanced Composites

DTIC Science & Technology

2008-07-25

Fracture angle. αii Coefficients of thermal expansion . βii Coefficients of hygroscopic expansion . β Shear response factor. ηL Coefficient of... thermal expansion in the longitudinal and transverse direc- tions. To enable the calculation of the thermal stresses, the user should define in the...development of this second VUMAT subroutine was planned for the second year of this project). 4.2 Input into Abaqus explicit 4.2.1 Shell elements

The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics.

PubMed

Zhang, Ping; Zhao, Yonggui; Wang, Xiuyu

2015-06-28

The crystalline structure refinement, chemical bond ionicity, lattice energy and coefficient of thermal expansion were carried out for Nd(Nb(1-x)Sb(x))O4 ceramics with a monoclinic fergusonite structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, lattice energy, coefficient of thermal expansion, and microwave dielectric properties. The bond ionicity, lattice energy, and coefficient of thermal expansion of Nd(Nb(1-x)Sb(x))O4 ceramics were calculated using a semiempirical method based on the complex bond theory. The phase structure stability varied with the lattice energy which was resulted by the substitution constant of Sb(5+). With the increasing of the Sb(5+) contents, the decrease of Nb/Sb-O bond ionicity was observed, which could be contributed to the electric polarization. The ε(r) had a close relationship with the Nb/Sb-O bond ionicity. The increase of the Q×f and |τ(f)| values could be attributed to the lattice energy and the coefficient of thermal expansion. The microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics with the monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion.

Elastic and transport properties of topological semimetal ZrTe

NASA Astrophysics Data System (ADS)

Guo, San-Dong; Wang, Yue-Hua; Lu, Wan-Li

2017-11-01

Topological semimetals may have substantial applications in electronics, spintronics, and quantum computation. Recently, ZrTe was predicted as a new type of topological semimetal due to the coexistence of Weyl fermions and massless triply degenerate nodal points. In this work, the elastic and transport properties of ZrTe are investigated by combining the first-principles calculations and semiclassical Boltzmann transport theory. Calculated elastic constants prove the mechanical stability of ZrTe, and the bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio also are calculated. It is found that spin-orbit coupling (SOC) has slightly enhanced effects on the Seebeck coefficient, which along the a(b) and c directions for pristine ZrTe at 300 K is 46.26 μVK-1 and 80.20 μVK-1, respectively. By comparing the experimental electrical conductivity of ZrTe (300 K) with the calculated value, the scattering time is determined as 1.59 × 10-14 s. The predicted room-temperature electronic thermal conductivity along the a(b) and c directions is 2.37 {{Wm}}-1{{{K}}}-1 and 2.90 {{Wm}}-1{{{K}}}-1, respectively. The room-temperature lattice thermal conductivity is predicted as 17.56 {{Wm}}-1{{{K}}}-1 and 43.08 {{Wm}}-1{{{K}}}-1 along the a(b) and c directions, showing very strong anisotropy. Calculated results show that isotope scattering produces an observable effect on lattice thermal conductivity. To observably reduce lattice thermal conductivity by nanostructures, the characteristic length should be smaller than 70 nm, based on cumulative lattice thermal conductivity with respect to the phonon mean free path (MFP) at 300 K. It is noted that the average room-temperature lattice thermal conductivity of ZrTe is slightly higher than that of isostructural MoP, which is due to larger phonon lifetimes and smaller Grüneisen parameters. Finally, the total thermal conductivity as a function of temperature is predicted for pristine ZrTe. Our works provide valuable information for ZrTe-based nano-electronics devices, and motivate further experimental works to study elastic and transport properties of ZrTe.

High-Temperature Thermoelectric Properties of Perovskite-Type Pr0.9Sr0.1Mn1- x Fe x O3 (0 ≤ x ≤ 1)

NASA Astrophysics Data System (ADS)

Nakatsugawa, H.; Saito, M.; Okamoto, Y.

2017-05-01

Polycrystalline samples of Pr0.9Sr0.1Mn1- x Fe x O3 (0 ≤ x ≤ 1) have been synthesized using a conventional solid-state reaction method, and the crystal structure studied at room temperature. The magnetic susceptibility was measured from 5 K to 350 K. The electrical resistivity, Seebeck coefficient, and thermal conductivity were investigated as functions of temperature below 850 K. For all samples, the perovskite structure at room temperature exhibited orthorhombic Pbnm phase. While the Pr0.9Sr0.1MnO3 ( x = 0) sample exhibited ferromagnetic-like ground state below T C = 145 K (Curie temperature), the ferromagnetic transition temperature T C decreased with increasing x. The Seebeck coefficient of the samples with 0 ≤ x ≤ 0.8 decreased with increasing temperature because of double-exchange interaction of Mn ions. In fact, the carrier type for x = 0 changed from hole-like to electron-like behavior above 800 K. On the other hand, the samples with x ≥ 0.9 showed large positive Seebeck coefficient over the entire temperature range, indicating that the low-spin state of Fe ions dominated the electronic structure for this x range. In particular, the sample with x = 1 exhibited p-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical resistivity, and low thermal conductivity. Thus, the sample with x = 1 showed power factor of 20 μW m-1 K-2 at 850 K leading to ZT of 0.024 at this temperature, indicating that hole-doped perovskite-type iron oxide is a good candidate high-temperature thermoelectric p-type oxide.

Residual Tensile Property of Plain Woven Jute Fiber/Poly(Lactic Acid) Green Composites during Thermal Cycling

PubMed Central

Katogi, Hideaki; Takemura, Kenichi; Akiyama, Motoki

2016-01-01

This study investigated the residual tensile properties of plain woven jute fiber reinforced poly(lactic acid) (PLA) during thermal cycling. Temperature ranges of thermal cycling tests were 35–45 °C and 35–55 °C. The maximum number of cycles was 103 cycles. The quasi-static tensile tests of jute fiber, PLA, and composite were conducted after thermal cycling tests. Thermal mechanical analyses of jute fiber and PLA were conducted after thermal cycling tests. Results led to the following conclusions. For temperatures of 35–45 °C, tensile strength of composite at 103 cycles decreased 10% compared to that of composite at 0 cycles. For temperatures of 35–55 °C, tensile strength and Young’s modulus of composite at 103 cycles decreased 15% and 10%, respectively, compared to that of composite at 0 cycles. Tensile properties and the coefficient of linear expansion of PLA and jute fiber remained almost unchanged after thermal cycling tests. From observation of a fracture surface, the length of fiber pull out in the fracture surface of composite at 103 cycles was longer than that of composite at 0 cycles. Therefore, tensile properties of the composite during thermal cycling were decreased, probably because of the decrease of interfacial adhesion between the fiber and resin. PMID:28773694

The Shubnikov-de Haas effect and thermoelectric properties of Tl-doped Sb{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulbachinskii, V. A., E-mail: kulb@mig.phys.msu.ru; Kudryashov, A. A.; Kytin, V. G.

2015-06-15

The influence of doping with Tl on the Shubnikov-de Haas effect at T = 4.2 K in magnetic fields up to 38 T in p-Sb{sub 2−x}Tl{sub x}Te{sub 3} (x = 0, 0.005, 0.015, and 0.05) and n-Bi{sub 2−x}Tl{sub x}Se{sub 3} (x = 0, 0.01, 0.02, 0.04, and 0.06) single crystals is investigated. Extreme cross-sections of the Fermi surface in both materials decrease upon doping with Tl: the hole concentration decreases in Sb{sub 2−x}Tl{sub x}Te{sub 3} due to the donor effect of Tl and the electron concentration in n-Bi{sub 2−x}Tl{sub x}Se{sub 3} decreases due to the acceptor effect of Tl. Themore » temperature dependences of the Seebeck coefficient, electrical conductivity, thermal conductivity, and dimensionless thermoelectric figure of merit in a temperature range of 77–300 K are measured. The thermal conductivity and electrical conductivity decrease upon doping with Tl both in p-Sb{sub 2−x}Tl{sub x}Te{sub 3} and in n-Bi{sub 2−x}Tl{sub x}Se{sub 3}. The Seebeck coefficient increases in all compositions upon an increase in doping over the entire measured temperature range. The thermoelectric figure of merit increases upon doping with Tl.« less

Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

NASA Astrophysics Data System (ADS)

Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Okuhata, Ryo; Ishibe, Takafumi; Watanabe, Kentaro; Suzuki, Takeyuki; Fujita, Takeshi; Sawano, Kentarou; Nakamura, Yoshiaki

2017-05-01

We have investigated the intrinsic thermoelectric properties of epitaxial β-FeSi2 thin films and the impact of phosphorus (P) doping. Epitaxial β-FeSi2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β-FeSi2 thin films on Si(111) substrates, and MBE of β-FeSi2 thin films on epitaxial β-FeSi2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β-FeSi2/Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β-FeSi2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β-FeSi2. We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β-FeSi2. A route to enhance the thermoelectric performance of β-FeSi2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.

Use of unbalanced laminates as a screening method for microcracking

NASA Technical Reports Server (NTRS)

Papadopoulos, Demetrios S.; Bowles, Kenneth J.

1990-01-01

State-of-the-art, high temperature polyimide matrix composites, reinforced with continuous graphite fibers are known to be susceptible to intraply cracking when thermally cycled over their useful service temperature range. It is believed that the transply cracking, in part, results from residual stresses caused by differences in coefficients of thermal expansion (CTE) between the polymer matrix and the reinforcement. Thermal cycling tests to investigate this phenomenon involve expensive time and energy consuming programs which are not economically feasible for use as a part of a materials screening process. As an alternative to thermal cycling studies, a study of unbalanced crossply graphite fiber reinforcement composites was conducted to assess the effect of the composite ply layup and surface condition on the residual stresses that remain after the processing of these materials. The residual stresses were assessed by measuring the radii of curvature of the types of laminates that were studied. The temperature at which stress-free conditions existed were determined and a dye penetrant method was used to observe surface damage resulting from excessive residual stress buildup. These results are compared with some published results of thermal cycling tests that were previously conducted on balanced polyimide composites.

Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

PubMed Central

Roshni, Satheesh Babu; Sebastian, Mailadil Thomas; Surendran, Kuzhichalil Peethambharan

2017-01-01

Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (−60 ppmK−1). The present paper explores the potentiality of a ceramic composite 0.83ZnAl2O4-0.17TiO2 (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK−1 and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm−1K−1 (thermal conductivity of alumina is about 24.5 Wm−1K−1), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates. PMID:28084459

Thermal Expansion Coefficient of Cold-Pressed Silicon Carbide

NASA Astrophysics Data System (ADS)

Olivieri, E.; Pasca, E.; Ventura, G.; Barucci, M.; Risegari, L.

2004-07-01

The measurement of the thermal linear expansion coefficient of a cold sintered SiC has been carried out in the 4.2 - 293 K temperature range. The properties of silicon carbide are specially suitable to realise high quality mirrors and complete optomechanical structures for space astronomy. The thermal contraction of the material used for the realization of the mirror is, of course, of primary interest. We present here both a plot and smoothed data of SiC thermal contraction coefficient. Details of the dilatometric interferometer used to carry out the measurements are also reported together with a control test of the measuring bench on a material (brass) of known thermal contraction.

Long-term weathering effects on the thermal performance of the Libbey-Owens-Ford (liquid) solar collector

NASA Technical Reports Server (NTRS)

1979-01-01

Thermal performance tests were conducted on the Libbey-Owens-Ford liquid collector, following long term exposure to natural weathering conditions. Visual inspection of the collector, prior to the retest, indicated noticeable clouding of the inner cover glass, probably resulting from outgassing of the insulation. The absorber plate also showed some discoloration. The test results indicated that performance degradation had occurred at inlet temperatures significantly above ambient. The change in the slope of the efficiency curve, from the original data, is a direct indicator of an increase in the collector heat loss coefficient.

Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badruddin, Irfan Anjum; Quadir, G. A.

2016-06-08

Heat transfer in a porous medium embedded with vertical flat plate is investigated by using thermal non-equilibrium model. Darcy model is employed to simulate the flow inside porous medium. It is assumed that the heat transfer takes place by natural convection and radiation. The vertical plate is maintained at isothermal temperature. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method. Results are presented in terms of isotherms and streamlines for various parameters such as heat transfer coefficient parameter, thermal conductivity ratio, and radiation parameter.

Active Control of Interface Shape During the Crystal Growth of Lead Bromide

NASA Technical Reports Server (NTRS)

Duval, W. M. B.; Batur, C.; Singh, N. B.

2003-01-01

A thermal model for predicting and designing the furnace temperature profile was developed and used for the crystal growth of lead bromide. The model gives the ampoule temperature as a function of the furnace temperature, thermal conductivity, heat transfer coefficients, and ampoule dimensions as variable parameters. Crystal interface curvature was derived from the model and it was compared with the predicted curvature for a particular furnace temperature and growth parameters. Large crystals of lead bromide were grown and it was observed that interface shape was in agreement with the shape predicted by this model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hubaud, Aude A.; Schroeder, David J.; Ingram, Brian J.

The thermal expansion (TE) coefficients of the lithium-stable lithium-ion conducting garnet lithium lanthanum zirconium oxide (LLZ) and the effect of aluminum substitution were measured from room temperature up to 700 °C by a synchrotron-based X-ray diffraction. The typical TE value measured for the most reported composition (LLZ doped with 0.3 wt.% or 0.093 mol% aluminum) was 15.498 × 10-6 K-1, which is approximately twice the value reported for other garnet-type structures. As the Al(III) concentration has been observed to strongly affect the structure observed and the ionic conductivity, we also assessed its role on thermal expansion and noted only amore » small variation with increasing dopant concentration. The materials implications for using LLZ in a solid state battery are discussed.« less

Thrust chamber life prediction. Volume 1: Mechanical and physical properties of high performance rocket nozzle materials

NASA Technical Reports Server (NTRS)

Esposito, J. J.; Zabora, R. F.

1975-01-01

Pertinent mechanical and physical properties of six high conductivity metals were determined. The metals included Amzirc, NARloy Z, oxygen free pure copper, electroformed copper, fine silver, and electroformed nickel. Selection of these materials was based on their possible use in high performance reusable rocket nozzles. The typical room temperature properties determined for each material included tensile ultimate strength, tensile yield strength, elongation, reduction of area, modulus of elasticity, Poisson's ratio, density, specific heat, thermal conductivity, and coefficient of thermal expansion. Typical static tensile stress-strain curves, cyclic stress-strain curves, and low-cycle fatigue life curves are shown. Properties versus temperature are presented in graphical form for temperatures from 27.6K (-410 F) to 810.9K (1000 F).

K1.33Mn8O16 as an electrocatalyst and a cathode

NASA Astrophysics Data System (ADS)

Jalili, Seifollah; Moharramzadeh Goliaei, Elham; Schofield, Jeremy

2017-02-01

Density functional theory (DFT) calculations are carried out to investigate the electronic, magnetic and thermoelectric properties of bulk and nanosheet K1.33Mn8O16 materials. The catalytic activity and cathodic performance of bulk and nanosheet structures are examined using the Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential. Electronic structure calculations reveal an anti-ferromagnetic ground state, with a TB-mMBJ band gap in bulk K1.33Mn8O16 that is in agreement with experimental results. Density of state plots indicate a partial reduction of Mn4+ ions to Mn3+, without any obvious sign of Jahn-Teller distortion. Moreover, use of the O p-band center as a descriptor of catalytic activity suggests that the nanosheet has enhanced catalytic activity compared to the bulk structure. Thermoelectric parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity are also calculated, and it is found that the Seebeck coefficients decrease with increasing temperature. High Seebeck coefficients for both spin-up and spin-down states are found in the nanosheet relative to their value in the bulk K1.33Mn8O16 structure, whereas the electrical and thermal conductivity are reduced relative to the bulk. In addition, figures of merit values are calculated as a function of the chemical potential and it is found that the nanosheet has a figure of merit of 1 at room temperature, compared to 0.5 for the bulk material. All results suggest that K1.33Mn8O16 nanosheets can be used both as a material in waste heat recovery and as an electrocatalyst in fuel cells and batteries.

Thermoelectric properties of an ultra-thin topological insulator.

PubMed

Islam, S K Firoz; Ghosh, T K

2014-04-23

Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In the absence of a magnetic field, the thermopower increases and thermal conductivity decreases with an increase in the hybridization energy. In the presence of a magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and whose phase factor is governed by the product of the Landé g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results for the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, at a frequency that depends on the Landé g-factor.

Transport coefficients in nonequilibrium gas-mixture flows with electronic excitation.

PubMed

Kustova, E V; Puzyreva, L A

2009-10-01

In the present paper, a one-temperature model of transport properties in chemically nonequilibrium neutral gas-mixture flows with electronic excitation is developed. The closed set of governing equations for the macroscopic parameters taking into account electronic degrees of freedom of both molecules and atoms is derived using the generalized Chapman-Enskog method. The transport algorithms for the calculation of the thermal-conductivity, diffusion, and viscosity coefficients are proposed. The developed theoretical model is applied for the calculation of the transport coefficients in the electronically excited N/N(2) mixture. The specific heats and transport coefficients are calculated in the temperature range 50-50,000 K. Two sets of data for the collision integrals are applied for the calculations. An important contribution of the excited electronic states to the heat transfer is shown. The Prandtl number of atomic species is found to be substantially nonconstant.

Shockwave Consolidation of Nanostructured Thermoelectric Materials

NASA Technical Reports Server (NTRS)

Prasad, Narasimha S.; Taylor, Patrick; Nemir, David

2014-01-01

Nanotechnology based thermoelectric materials are considered attractive for developing highly efficient thermoelectric devices. Nano-structured thermoelectric materials are predicted to offer higher ZT over bulk materials by reducing thermal conductivity and increasing electrical conductivity. Consolidation of nano-structured powders into dense materials without losing nanostructure is essential towards practical device development. Using the gas atomization process, amorphous nano-structured powders were produced. Shockwave consolidation is accomplished by surrounding the nanopowder-containing tube with explosives and then detonating. The resulting shock wave causes rapid fusing of the powders without the melt and subsequent grain growth. We have been successful in generating consolidated nano-structured bismuth telluride alloy powders by using the shockwave technique. Using these consolidated materials, several types of thermoelectric power generating devices have been developed. Shockwave consolidation is anticipated to generate large quantities of nanostructred materials expeditiously and cost effectively. In this paper, the technique of shockwave consolidation will be presented followed by Seebeck Coefficient and thermal conductivity measurements of consolidated materials. Preliminary results indicate a substantial increase in electrical conductivity due to shockwave consolidation technique.

Synthesis and thermoelectric properties of tantalum-doped ZrNiSn half-Heusler alloys

NASA Astrophysics Data System (ADS)

Zhao, Degang; Zuo, Min; Wang, Zhenqing; Teng, Xinying; Geng, Haoran

2014-04-01

The Ta-doped ZrNiSn half-Heusler alloys, Zr1-xTaxNiSn, were synthesized by arc melting and hot-press sintering. Microstructure of Zr1-xTaxNiSn compounds were analyzed and the thermoelectric (TE) properties of Zr1-xTaxNiSn compounds were measured from room temperature to 823 K. The electrical conductivity increased with increasing Ta content. The Seebeck coefficient of Zr1-xTaxNiSn compounds was sharply decreased with increasing Ta content. The Hall mobility was proportional to T-1.5 above 673 K, indicating that the acoustic phonon scattering was predominant in the temperature range. The thermal conductivity was effectively depressed by introducing Ta substitution. The figure of merit of ZrNiSn compounds was improved due to the decreased thermal conductivity and increased electrical conductivity. The maximum ZT value of 0.60 was achieved for Zr0.97Ta0.03NiSn sample at 823 K.

Multiscale calculations of thermoelectric properties of n-type Mg2Si1-xSnx solid solutions

NASA Astrophysics Data System (ADS)

Tan, X. J.; Liu, W.; Liu, H. J.; Shi, J.; Tang, X. F.; Uher, C.

2012-05-01

The band structure of Mg2Si1-xSnx solid solutions with 0.250 ⩽ x ⩽ 0.875 is calculated using the first-principles pseudopotential method. It is found that the low-lying light and heavy conduction bands converge and the effective mass reaches a maximum value near x = 0.625. Using the semiclassical Boltzmann transport theory and relaxation-time approximation, we find that the system with x = 0.625 exhibits both higher Seebeck coefficient and higher electrical conductivity than other solid solutions at intermediate temperatures. By fitting first-principles total energy calculations, a modified Morse potential is constructed, which is used to predicate the lattice thermal conductivity via equilibrium molecular dynamics simulations. Due to relatively higher power factor and lower thermal conductivity, the Mg2Si0.375Sn0.625 is found to exhibit enhanced thermoelectric performance at 800 K, and additional Sb doping is considered in order to make a better comparison with experiment results.

Thermal and thermoelectric transport measurements of an individual boron arsenide microstructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jaehyun; Sellan, Daniel P.; Ou, Eric

2016-05-16

Recent first principles calculations have predicted that boron arsenide (BAs) can possess an unexpectedly high thermal conductivity that depends sensitively on the crystal size and defect concentration. However, few experimental results have been obtained to verify these predictions. In the present work, we report four-probe thermal and thermoelectric transport measurements of an individual BAs microstructure that was synthesized via a vapor transport method. The measured thermal conductivity was found to decrease slightly with temperature in the range between 250 K and 350 K. The temperature dependence suggests that the extrinsic phonon scattering processes play an important role in addition to intrinsic phonon-phononmore » scattering. The room temperature value of (186 ± 46) W m{sup −1 }K{sup −1} is higher than that of bulk silicon but still a factor of four lower than the calculated result for a defect-free, non-degenerate BAs rod with a similar diameter of 1.15 μm. The measured p-type Seebeck coefficient and thermoelectric power factor are comparable to those of bismuth telluride, which is a commonly used thermoelectric material. The foregoing results also suggest that it is necessary to not only reduce defect and boundary scatterings but also to better understand and control the electron scattering of phonons in order to achieve the predicted ultrahigh intrinsic lattice thermal conductivity of BAs.« less

Investigation on an ammonia supply system for flue gas denitrification of low-speed marine diesel

PubMed Central

Yuan, Han; Zhao, Jian; Mei, Ning

2017-01-01

Low-speed marine diesel flue gas denitrification is in great demand in the ship transport industry. This research proposes an ammonia supply system which can be used for flue gas denitrification of low-speed marine diesel. In this proposed ammonia supply system, ammonium bicarbonate is selected as the ammonia carrier to produce ammonia and carbon dioxide by thermal decomposition. The diesel engine exhaust heat is used as the heating source for ammonium bicarbonate decomposition and ammonia gas desorption. As the ammonium bicarbonate decomposition is critical to the proper operation of this system, effects have been observed to reveal the performance of the thermal decomposition chamber in this paper. A visualization experiment for determination of the single-tube heat transfer coefficient and simulation of flow and heat transfer in two structures is conducted; the decomposition of ammonium bicarbonate is simulated by ASPEN PLUS. The results show that the single-tube heat transfer coefficient is 1052 W m2 °C−1; the thermal decomposition chamber fork-type structure gets a higher heat transfer compared with the row-type. With regard to the simulation of ammonium bicarbonate thermal decomposition, the ammonia production is significantly affected by the reaction temperature and the mass flow rate of the ammonium bicarbonate input. PMID:29308269

NT-SiC (new-technology silicon carbide) : Φ 650mm optical space mirror substrate of high-strength reaction-sintered silicon carbide

NASA Astrophysics Data System (ADS)

Suyama, Shoko; Itoh, Yoshiyasu; Tsuno, Katsuhiko; Ohno, Kazuhiko

2005-08-01

Silicon carbide (SiC) is the most advantageous as the material of various telescope mirrors, because of high stiffness, low density, low coefficient of thermal expansion, high thermal conductivity and thermal stability. Newly developed high-strength reaction-sintered silicon carbide (NTSIC), which has two times higher strength than sintered SiC, is one of the most promising candidates for lightweight optical mirror substrate, because of fully dense, lightweight, small sintering shrinkage (+/-1 %), good shape capability and low processing temperature. In this study, 650mm in diameter mirror substrate of NTSIC was developed for space telescope applications. Three developed points describe below. The first point was to realize the lightweight to thin the thickness of green bodies. Ribs down to 3mm thickness can be obtained by strengthen the green body. The second point was to enlarge the mirror size. 650mm in diameter of mirror substrate can be fabricated with enlarging the diameter in order. The final point was to realize the homogeneity of mirror substrate. Some properties, such as density, bending strength, coefficient of thermal expansion, Young's modulus, Poisson's ratio, fracture toughness, were measured by the test pieces cutting from the fabricated mirror substrates.

Investigation on an ammonia supply system for flue gas denitrification of low-speed marine diesel

NASA Astrophysics Data System (ADS)

Huang, Xiankun; Yuan, Han; Zhao, Jian; Mei, Ning

2017-12-01

Low-speed marine diesel flue gas denitrification is in great demand in the ship transport industry. This research proposes an ammonia supply system which can be used for flue gas denitrification of low-speed marine diesel. In this proposed ammonia supply system, ammonium bicarbonate is selected as the ammonia carrier to produce ammonia and carbon dioxide by thermal decomposition. The diesel engine exhaust heat is used as the heating source for ammonium bicarbonate decomposition and ammonia gas desorption. As the ammonium bicarbonate decomposition is critical to the proper operation of this system, effects have been observed to reveal the performance of the thermal decomposition chamber in this paper. A visualization experiment for determination of the single-tube heat transfer coefficient and simulation of flow and heat transfer in two structures is conducted; the decomposition of ammonium bicarbonate is simulated by ASPEN PLUS. The results show that the single-tube heat transfer coefficient is 1052 W m2 °C-1; the thermal decomposition chamber fork-type structure gets a higher heat transfer compared with the row-type. With regard to the simulation of ammonium bicarbonate thermal decomposition, the ammonia production is significantly affected by the reaction temperature and the mass flow rate of the ammonium bicarbonate input.

Thermoelectric Properties of Cu-doped Bi0.4Sb1.6Te3 Prepared by Hot Extrusion

NASA Astrophysics Data System (ADS)

Jung, Woo-Jin; Kim, Il-Ho

2018-06-01

Cu0.003Bi0.4Sb1.6Te3 alloys were prepared by using encapsulated melting and hot extrusion (HE). The hot-extruded specimens had the relative average density of 98%. The ( 00l) planes were preferentially oriented parallel to the extrusion direction, but the specimens showed low crystallographic anisotropy with low orientation factors. The specimens were hot-extruded at 698 K, and they showed excellent mechanical properties with a Vickers hardness of 76 Hv and a bending strength of 59 MPa. However, as the HE temperature increased, the mechanical properties degraded due to grain growth. The hot-extruded specimens showed positive Seebeck coefficients, indicating that the specimens have p-type conduction. These specimens exhibited negative temperature dependences of electrical conductivity, and thus behaved as degenerate semiconductors. The Seebeck coefficient reached the maximum value at 373 K and then decreased with increasing temperature due to intrinsic conduction. Cu-doped specimens exhibited high power factors due to relatively higher electrical conductivities and Seebeck coefficients than those of undoped specimens. A thermal conductivity of 1.00 Wm-1 K-1 was obtained at 373 K for Cu0.003Bi0.4Sb1.6Te3 hot-extruded at 723 K. A maximum dimensionless figure of merit, ZT max = 1.05, and an average dimensionless figure of merit, ZT ave = 0.98, were achieved at 373 K.

Numerical Analysis of a Paraffin/Metal Foam Composite for Thermal Storage

NASA Astrophysics Data System (ADS)

Di Giorgio, P.; Iasiello, M.; Viglione, A.; Mameli, M.; Filippeschi, S.; Di Marco, P.; Andreozzi, A.; Bianco, N.

2017-01-01

In the last decade, the use of Phase Change Materials (PCMs) as passive thermal energy storage has been widely studied both analytically and experimentally. Among the PCMs, paraffins show many advantages, such as having a high latent heat, a low vapour pressure, being chemically inert, stable and non-toxic. But, their thermal conductivity is very low with a high volume change during the melting process. An efficient way to increase their poor thermal conductivity is to couple them with open cells metallic foams. This paper deals with a theoretical analysis of paraffin melting process inside an aluminum foam. A mathematical model is developed by using the volume-averaged governing equations for the porous domain, made up by the PCM embedded into the metal foam. Non-Darcian and buoyancy effects are considered in the momentum equation, while the energy equations are modelled with the Local Thermal Non-Equilibrium (LTNE) approach. The PCM liquefaction is treated with the apparent heat capacity method and the governing equations are solved with a finite-element scheme by COMSOL Multiphysics®. A new method to calculate the coupling coefficients needed for the thermal model has been developed and the results obtained have been validated comparing them to experimental data in literature.

Al/ oil nanofluids inside annular tube: an experimental study on convective heat transfer and pressure drop

NASA Astrophysics Data System (ADS)

Jafarimoghaddam, Amin; Aberoumand, Sadegh; Javaherdeh, Kourosh; Arani, Ali Akbar Abbasian; Jafarimoghaddam, Reza

2018-04-01

In this work, an experimental study on nanofluid preparation stability, thermo-physical properties, heat transfer performance and friction factor of Al/ Oil nanofluids has been carried out. Electrical Explosion Wire ( E.E.W) which is one of the most reliable one-step techniques for nanofluids preparation has been used. An annular tube has been considered as the test section in which the outer tube was subject to a uniform heat flux boundary condition of about 204 W. The utilized nanofluids were prepared in three different volume concentrations of 0.011%, 0.044% and 0.171%. A wide range of parameters such as Reynolds number Prandtl number, viscosity, thermal conductivity, density, specific heat, convective heat transfer coefficient, Nusselt number and the friction factor have been studied. The experiment was conducted in relatively low Reynolds numbers of less than 160 and within a hydrodynamically fully-developed regime. According to the results, thermal conductivity, density and viscosity increased depending on the volume concentrations and working temperatures while the specific heat declined. More importantly, it was observed that convective heat transfer coefficient and Nusselt number enhanced by 28.6% and 16.4%, respectively, for the highest volume concentration. Finally, the friction factor (which plays an important role in the pumping power) was found to be increased around 18% in the volume fraction of 0.171%.

Nano- and Microstructure Engineering: An Effective Method for Creating High Efficiency Magnesium Silicide Based Thermoelectrics.

PubMed

Farahi, Nader; Prabhudev, Sagar; Botton, Gianluigi A; Salvador, James R; Kleinke, Holger

2016-12-21

Considering the effect of CO 2 emission together with the depletion of fossil fuel resources on future generations, industries in particular the transportation sector are in deep need of a viable solution to follow the environmental regulation to limit the CO 2 emission. Thermoelectrics may be a practical choice for recovering the waste heat, provided their conversion energy can be improved. Here, the high temperature thermoelectric properties of high purity Bi doped Mg 2 (Si,Sn) are presented. The samples Mg 2 Si 1-x-y Sn x Bi y with x(Sn) ≥ 0.6 and y(Bi) ≥ 0.03 exhibited electrical conductivities and Seebeck coefficients of approximately 1000 Ω -1 cm -1 and -200 μV K -1 at 773 K, respectively, attributable to a combination of band convergence and microstructure engineering through ball mill processing. In addition to the high electrical conductivity and Seebeck coefficient, the thermal conductivity of the solid solutions reached values below 2.5 W m -1 K -1 due to highly efficient phonon scattering from mass fluctuation and grain boundary effects. These properties combined for zT values of 1.4 at 773 K with an average zT of 0.9 between 400 and 773 K. The transport properties were both highly reproducible across several measurement systems and were stable with thermal cycling.

Intermetallic Al-, Fe-, Co- and Ni-Based Thermal Barrier Coatings Prepared by Cold Spray for Applications on Low Heat Rejection Diesel Engines

NASA Astrophysics Data System (ADS)

Leshchinsky, E.; Sobiesiak, A.; Maev, R.

2018-02-01

Conventional thermal barrier coating (TBC) systems consist of a duplex structure with a metallic bond coat and a ceramic heat insulating topcoat. They possess the desired low thermal conductivity, but at the same time they are very brittle and sensitive to thermal shock and thermal cycling due to the inherently low coefficient of thermal expansion. Recent research activities are focused on the developing of multilayer TBC structures obtained using cold spraying and following annealing. Aluminum intermetallics have demonstrated thermal and mechanical properties that allow them to be used as the alternative TBC materials, while the intermetallic layers can be additionally optimized to achieve superior thermal physical properties. One example is the six layer TBC structure in which cold sprayed Al-based intermetallics are synthesized by annealing in nitrogen atmosphere. These multilayer coating systems demonstrated an improved thermal fatigue capability as compared to conventional ceramic TBC. The microstructures and properties of the coatings were characterized by SEM, EDS and mechanical tests to define the TBC material properties and intermetallic formation mechanisms.

A Numerical Study of Coupled Non-Linear Equations of Thermo-Viscous Fluid Flow in Cylindrical Geometry

NASA Astrophysics Data System (ADS)

Pothanna, N.; Aparna, P.; Gorla, R. S. R.

2017-12-01

In this paper we present numerical solutions to coupled non-linear governing equations of thermo-viscous fluid flow in cylindrical geometry using MATHEMATICA software solver. The numerical results are presented in terms of velocity, temperature and pressure distribution for various values of the material parameters such as the thermo-mechanical stress coefficient, thermal conductivity coefficient, Reiner Rivlin cross viscosity coefficient and the Prandtl number in the form of tables and graphs. Also, the solutions to governing equations for slow steady motion of a fluid have been obtained numerically and compared with the existing analytical results and are found to be in excellent agreement. The results of the present study will hopefully enable a better understanding applications of the flow under consideration.

Joining Carbon-Carbon Composites and High-Temperature Materials with High Energy Electron Beams

NASA Technical Reports Server (NTRS)

Goodman, Daniel; Singler, Robert

1998-01-01

1. Program goals addressed during this period. Experimental work was directed at formation of a low-stress bond between carbon- carbon and aluminum, with the objective of minimizing the heating of the aluminum substrate, thereby minimizing stresses resulting from the coefficient of thermal expansion (CTE) difference between the aluminum and carbon-carbon. A second objective was to form a bond between carbon-carbon and aluminum with good thermal conductivity for electronic thermal management (SEM-E) application. 2. Substrates and joining materials selected during this period. Carbon-Carbon Composite (CCC) to Aluminum. CCC (Cu coated) to Aluminum. Soldering compounds based on Sn/Pb and Sn/Ag/Cu/Bi compositions. 3. Soldering experiments performed. Conventional techniques. High Energy Electron Beam (HEEB) process.

Indoor thermal performance evaluation of Daystar solar collector

NASA Technical Reports Server (NTRS)

Shih, K., Sr.

1977-01-01

The test procedures used and results obtained from a test program to obtain thermal performance data on a Daystar Model 21B, S/N 02210, Unit 2, liquid solar collector under simulated conditions are described. The test article is a flat plate solar collector using liquid as a heat transfer medium. The absorber plate is copper and coated with black paint. Between the tempered low iron glass and absorber plate is a polycarbonate trap used to suppress convective heat loss. The collector incorporates a convector heat dump panel to limit temperature excursions during stagnation. The following tests were conducted: (1) collector thermal efficiency; (2) collector time constant; (3) collector incident angle modifier; (4) collector heat loss coefficient; and (5) collector stagnation.

Thermal and Fluid Modeling of the CRYogenic Orbital TEstbed (CRYOTE) Ground Test Article (GTA)

NASA Technical Reports Server (NTRS)

Piryk, David; Schallhorn, Paul; Walls, Laurie; Stopnitzky, Benny; Rhys, Noah; Wollen, Mark

2012-01-01

The purpose of this study was to anchor thermal and fluid system models to data acquired from a ground test article (GTA) for the CRYogenic Orbital TEstbed - CRYOTE. To accomplish this analysis, it was broken into four primary tasks. These included model development, pre-test predictions, testing support at Marshall Space Flight Center (MSFC} and post-test correlations. Information from MSFC facilitated the task of refining and correlating the initial models. The primary goal of the modeling/testing/correlating efforts was to characterize heat loads throughout the ground test article. Significant factors impacting the heat loads included radiative environments, multi-layer insulation (MLI) performance, tank fill levels, tank pressures, and even contact conductance coefficients. This paper demonstrates how analytical thermal/fluid networks were established, and it includes supporting rationale for specific thermal responses seen during testing.

Controllable rectification of the axial expansion in the thermally driven artificial muscle

NASA Astrophysics Data System (ADS)

Yue, Donghua; Zhang, Xingyi; Yong, Huadong; Zhou, Jun; Zhou, You-He

2015-09-01

At present, the concept of artificial muscle twisted by polymers or fibers has become a hot issue in the field of intelligent material research according to its distinguishing advantages, e.g., high energy density, large-stroke, non-hysteresis, and inexpensive. The axial thermal expansion coefficient is an important parameter which can affect its demanding applications. In this letter, a device with high accuracy capacitive sensor is constructed to measure the axial thermal expansion coefficient of the twisted carbon fibers and yarns of Kevlar, and a theoretical model based on the thermal elasticity and the geometrical features of the twisted structure are also presented to predict the axial expansion coefficient. It is found that the calculated results take good agreements with the experimental data. According to the present experiment and analyses, a method to control the axial thermal expansion coefficient of artificial muscle is proposed. Moreover, the mechanism of this kind of thermally driven artificial muscle is discussed.

Thermal requirements of Dermanyssus gallinae (De Geer, 1778) (Acari: Dermanyssidae).

PubMed

Tucci, Edna Clara; do Prado, Angelo P; de Araújo, Raquel Pires

2008-01-01

The thermal requirements for development of Dermanyssus gallinae were studied under laboratory conditions at 15, 20, 25, 30 and 35 degrees C, a 12h photoperiod and 60-85% RH. The thermal requirements for D. gallinae were as follows. Preoviposition: base temperature 3.4 degrees C, thermal constant (k) 562.85 degree-hours, determination coefficient (R(2)) 0.59, regression equation: Y= -0.006035 + 0.001777x. Egg: base temperature 10.60 degrees C, thermal constant (k) 689.65 degree-hours, determination coefficient (R(2)) 0.94, regression equation: Y= -0.015367 + 0.001450x. Larva: base temperature 9.82 degrees C, thermal constant (k) 464.91 degree-hours, determination coefficient (R(2)) 0.87, regression equation: Y= -0.021123 + 0.002151x. Protonymph: base temperature 10.17 degrees C, thermal constant (k) 504.49 degree-hours, determination coefficient (R(2)) 0.90, regression equation: Y= -0.020152 + 0.001982x. Deutonymph: base temperature 11.80 degrees C, thermal constant (k) 501.11 degree-hours, determination coefficient (R(2)) 0.99, regression equation: Y= -0.023555 + 0.001996x. The results obtained showed that 15 to 42 generations of Dermanyssus gallinae may occur during the year in the State of São Paulo, as estimated based on isotherm charts. Dermanyssus gallinae may develop continually in the State of São Paulo, with a population decrease in the winter. There were differences between the developmental stages of D. gallinae in relation to thermal requirements.

Measurement and modelling of forced convective heat transfer coefficient and pressure drop of Al2O3- and SiO2-water nanofluids

NASA Astrophysics Data System (ADS)

Julia, J. E.; Hernández, L.; Martínez-Cuenca, R.; Hibiki, T.; Mondragón, R.; Segarra, C.; Jarque, J. C.

2012-11-01

Forced convective heat transfer coefficient and pressure drop of SiO2- and Al2O3-water nanofluids were characterized. The experimental facility was composed of thermal-hydraulic loop with a tank with an immersed heater, a centrifugal pump, a bypass with a globe valve, an electromagnetic flow-meter, a 18 kW in-line pre-heater, a test section with band heaters, a differential pressure transducer and a heat exchanger. The test section consists of a 1000 mm long aluminium pipe with an inner diameter of 31.2 mm. Eighteen band heaters were placed all along the test section in order to provide a uniform heat flux. Heat transfer coefficient was calculated measuring fluid temperature using immersed thermocouples (Pt100) placed at both ends of the test section and surface thermocouples in 10 axial locations along the test section (Pt1000). The measurements have been performed for different nanoparticles (Al2O3 and SiO2 with primary size of 11 nm and 12 nm, respectively), volume concentrations (1% v., 5% v.), and flow rates (3 103Re<105). Maximum heat transfer coefficient enhancement (300%) and pressure drop penalty (1000%) is obtained with 5% v. SiO2 nanofluid. Existing correlations can predict, at least in a first approximation, the heat transfer coefficient and pressure drop of nanofluids if thermal conductivity, viscosity and specific heat were properly modelled.

Experimental and theoretical analysis of nanofluids based on high temperature-heat transfer fluid with enhanced thermal properties

NASA Astrophysics Data System (ADS)

Navas, Javier; Sánchez-Coronilla, Antonio; Martín, Elisa I.; Gómez-Villarejo, Roberto; Teruel, Miriam; Gallardo, Juan Jesús; Aguilar, Teresa; Alcántara, Rodrigo; Fernández-Lorenzo, Concha; Martín-Calleja, Joaquín

2017-04-01

In this work, nanofluids were prepared using commercial Cu nanoparticles and a commercial high temperature-heat transfer Fluid (eutectic mixture of diphenyl oxide and biphenyl) as the base fluid, which is used in concentrating solar power (CSP) plants. Different properties such as density, viscosity, heat capacity and thermal conductivity were characterized. Nanofluids showed enhanced heat transfer efficiency. In detail, the incorporation of Cu nanoparticles led to an increase of the heat capacity up to 14%. Also, thermal conductivity was increased up to 13%. Finally, the performance of the nanofluids prepared increased up to 11% according to the Dittus-Boelter correlation. On the other hand, equilibrium molecular dynamics simulation was used to model the experimental nanofluid system studied. Thermodynamic properties such as heat capacity and thermal conductivity were calculated and the results were compared with experimental data. The analysis of the radial function distributions (RDFs) and the inspection of the spatial distribution functions (SDFs) indicate the important role that plays the metal-oxygen interaction in the system. Dynamic properties such as the diffusion coefficients of base fluid and nanofluid were computed according to Einstein relation by computing the mean square displacement (MSD). Supplementary online material is available in electronic form at http://www.epjap.org

Mechanisms of double stratification and magnetic field in flow of third grade fluid over a slendering stretching surface with variable thermal conductivity

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Qayyum, Sajid; Alsaedi, Ahmed; Ahmad, Bashir

2018-03-01

This article addresses the magnetohydrodynamic (MHD) stagnation point flow of third grade fluid towards a nonlinear stretching sheet. Energy expression is based through involvement of variable thermal conductivity. Heat and mass transfer aspects are described within the frame of double stratification effects. Boundary layer partial differential systems are deduced. Governing systems are then converted into ordinary differential systems by invoking appropriate variables. The transformed expressions are solved through homotopic technique. Impact of embedded variables on velocity, thermal and concentration fields are displayed and argued. Numerical computations are presented to obtain the results of skin friction coefficient and local Nusselt and Sherwood numbers. It is revealed that larger values of magnetic parameter reduces the velocity field while reverse situation is noticed due to wall thickness variable. Temperature field and local Nusselt number are quite reverse for heat generation/absorption parameter. Moreover qualitative behaviors of concentration field and local Sherwood number are similar for solutal stratification parameter.

High Temperature Electronic and Thermal Transport Properties of EuGa2- x In x Sb2

NASA Astrophysics Data System (ADS)

Chanakian, Sevan; Weber, Rochelle; Aydemir, Umut; Ormeci, Alim; Fleurial, Jean-Pierre; Bux, Sabah; Snyder, G. Jeffrey

2017-08-01

The Zintl phase EuGa2Sb2 was synthesized via ball milling followed by hot pressing. The crystal structure of EuGa2Sb2 is comprised of a 3-D network of polyanionic [Ga2Sb2]2- tunnels filled with Eu cations that provide charge balance (Eu2+[Ga2Sb2]2-). Here we report the temperature-dependent resistivity, Hall Effect, Seebeck coefficient and thermal conductivity for EuGa2- x In x Sb2 ( x = 0, 0.05, 0.1) from 300 K to 775 K. Experimental results demonstrate that the material is a p-type semiconductor. However, a small band gap (˜0.1 eV) prevents EuGa2Sb2 from having high zT at higher temperatures. Isoelectronic substitution of In on the Ga site leads to point defect scattering of holes and phonons, thus reducing thermal conductivity and resulting in a slight improvement in zT.

Development of improved lithium tantalate pyroelectric detectors

NASA Technical Reports Server (NTRS)

Byer, N. E.; Vanderjagt, A.; Holton, W.

1978-01-01

A program was undertaken to increase the detectivity of LiTaO3 pyroelectric detectors to meet a performance requirement of D star (500 K, 15 Hz)=4x10 to the 9th power cm Hz1/2W-1. Emphasis was placed on reduction of the thermal conductance of the detector element to its surroundings, thinning the detector wafer to a thickness less than 3 micrometers, and increasing the absorptivity of the standard metallic film coatings. During the program, thermal conductance was reduced 41 percent through the use of reticulated (slotted) structures. Self-supported detector wafers less than 2 micrometers thick were fabricated. Multiple layer coatings, including an AR coating, with 16 percent more absorptance, were designed and fabricated. Later refinements in the multilayer design program have absorptivities of 75-80 percent, but detectors with these coatings had to be more than 2 micrometers thick because of a mismatch in the thermal expansion coefficients with LiTaO3.

Porosimetric, Thermal and Strength Tests of Aerated and Nonaerated Concretes

NASA Astrophysics Data System (ADS)

Strzałkowski, Jarosław; Garbalińska, Halina

2017-10-01

The paper presents the results of porosimetry tests of lightweight concretes, obtained with three research methods. Impact of different porosity structures on the basic thermal and strength properties was also evaluated. Tests were performed, using the pressure gauge method on fresh concrete mixes, as well as using the mercury porosimetry test and optic RapidAir method on specimens prepared from mature composites. The study was conducted on lightweight concretes, based on expanded clay aggregate and fly ash aggregate, in two variants: with non-aerated and aerated cement matrix. In addition, two reference concretes, based on normal aggregate, were prepared, also in two variants of matrix aeration. Changes in thermal conductivity λ and volumetric specific heat cv throughout the first three months of curing of the concretes were examined. Additionally, tests for compressive strength on cubic samples were performed during the first three months of curing. It was found that the pressure gauge method, performed on a fresh mix, gave lowered values of porosity, compared to the other methods. The mercury porosity tests showed high sensitivity in evaluation of pores smaller than 30μm. Unfortunately, this technique is not suitable for analysing pores greater than 300μm. On the other hand, the optical method proves good in evaluation of large pores, greater than 300μm. The paper also presents results of correlation of individual methods of porosity testing. A consolidated graph of the pore structure, derived from both mercury and optical methods, was presented, too. For the all of six tested concretes, differential graphs of porosity, prepared with both methods, show a very broad convergence. The thermal test results indicate usefulness of aeration of the cement matrix of the composites based on lightweight aggregates for the further reduction of the thermal conductivity coefficient λ of the materials. The lowest values of the λ coefficient were obtained for the aerated concretes based of fly ash aggregate. A diminishing influence of aeration on the volumetric heat capacity cv is clearly seen. Simultaneous aeration of the matrix and use of lightweight aggregates brought about also a significant decrease in the average compressive strength fcm of the tested composites.

The maximal cooling power of magnetic and thermoelectric refrigerators with La(FeCoSi)13 alloys

NASA Astrophysics Data System (ADS)

Skokov, K. P.; Karpenkov, A. Yu.; Karpenkov, D. Yu.; Gutfleisch, O.

2013-05-01

Using our data on magnetic entropy change ΔSm, adiabatic temperature change ΔTad and heat capacity CH for La(FeCoSi)13 alloys, the upper limit of heat Qc transferred per cycle, and the lowest limit of consumed work Wc were established for magnetic refrigerators operating in Δμ0H =1.9 T. In order to estimate the cooling power, attributable to thermoelectric refrigerators with La(FeCoSi)13, thermal conductivity λ, resistivity ρ, and Seebeck coefficient α were measured and the maximal cooling power QL, the input power Pi, and coefficient of performance have been calculated.

A comparative entropy based analysis of Cu and Fe3O4/methanol Powell-Eyring nanofluid in solar thermal collectors subjected to thermal radiation, variable thermal conductivity and impact of different nanoparticles shape

NASA Astrophysics Data System (ADS)

Jamshed, Wasim; Aziz, Asim

2018-06-01

The efficiency of any nanofluid based thermal solar system depend on the thermophysical properties of the operating fluids, type and shape of nanoparticles, nanoparticles volumetric concentration in the base fluid and the geometry/length of the system in which fluid is flowing. The recent research in the field of thermal solar energy has been focused to increase the efficiency of solar thermal collector systems. In the present research a simplified mathematical model is studied for inclusion in the thermal solar systems with the aim to improve the overall efficiency of the system. The flow of Powell-Eyring nanofluid is induced by non-uniform stretching of porous horizontal surface with fluid occupying a space over the surface. The thermal conductivity of the nanofluid is to vary as a linear function of temperature and the thermal radiation is to travel a short distance in the optically thick nanofluid. Numerical scheme of Keller box is implemented on the system of nonlinear ordinary differential equations, which are resultant after application of similarity transformation to governing nonlinear partial differential equations. The impact of non dimensional physical parameters appearing in the system have been observed on velocity and temperature profiles along with the entropy of the system. The velocity gradient (skin friction coefficient) and the strength of convective heat exchange (Nusselt number) are also investigated.

Impact of Fe powder sintering and soldering in production of porous heating surface on flow boiling heat transfer in minichannels

NASA Astrophysics Data System (ADS)

Depczyński, Wojciech; Piasecki, Artur; Piasecka, Magdalena; Strąk, Kinga

2017-10-01

This paper focuses on identification of the impact of porous heated surface on flow boiling heat transfer in a rectangular minichannel. The heated element for Fluorinert FC-72 was a thin plate made of Haynes-230. Infrared thermography was used to determine changes in the temperature on its outer smooth side. The porous surface in contact with the fluid in the minichannel was produced in two processes: sintering or soldering of Fe powder to the plate. The results were presented as relationships between the heat transfer coefficient and the distance from the minichannel inlet and as boiling curves. Results obtained for using a smooth heated plate at the saturated boiling region were also presented to compare. In the subcooled boiling region, at a higher heat flux, the heat transfer coefficient was slightly higher for the surface prepared via soldering. In the saturated boiling region, the local heat transfer coefficients obtained for the smooth plate surface were slightly higher than those achieved from the sintered plate surface. The porous structures formed have low thermal conductivity. This may induce noticeable thermal resistance at the diffusion bridges of the sintered structures, in particular within the saturated boiling region.

Development and characterization of a tissue-mimicking material for high-intensity focused ultrasound.

PubMed

King, Randy L; Liu, Yunbo; Maruvada, Subha; Herman, Bruce A; Wear, Keith A; Harris, Gerald R

2011-07-01

A tissue-mimicking material (TMM) for the acoustic and thermal characterization of high-intensity focused ultrasound (HIFU) devices has been developed. The material is a high-temperature hydrogel matrix (gellan gum) combined with different sizes of aluminum oxide particles and other chemicals. The ultrasonic properties (attenuation coefficient, speed of sound, acoustical impedance, and the thermal conductivity and diffusivity) were characterized as a function of temperature from 20 to 70°C. The backscatter coefficient and nonlinearity parameter B/A were measured at room temperature. Importantly, the attenuation coefficient has essentially linear frequency dependence, as is the case for most mammalian tissues at 37°C. The mean value is 0.64f(0.95) dB·cm(-1) at 20°C, based on measurements from 2 to 8 MHz. Most of the other relevant physical parameters are also close to the reported values, although backscatter signals are low compared with typical human soft tissues. Repeatable and consistent temperature elevations of 40°C were produced under 20-s HIFU exposures in the TMM. This TMM is appropriate for developing standardized dosimetry techniques, validating numerical models, and determining the safety and efficacy of HIFU devices.

Transport properties in mixtures involving carbon dioxide at low and moderate density: test of several intermolecular potential energies and comparison with experiment

NASA Astrophysics Data System (ADS)

Moghadasi, Jalil; Yousefi, Fakhri; Papari, Mohammad Mehdi; Faghihi, Mohammad Ali; Mohsenipour, Ali Asghar

2009-09-01

It is the purpose of this paper to extract unlike intermolecular potential energies of five carbon dioxide-based binary gas mixtures including CO2-He, CO2-Ne, CO2-Ar, CO2-Kr, and CO2-Xe from viscosity data and compare the calculated potentials with other models potential energy reported in literature. Then, dilute transport properties consisting of viscosity, diffusion coefficient, thermal diffusion factor, and thermal conductivity of aforementioned mixtures are calculated from the calculated potential energies and compared with literature data. Rather accurate correlations for the viscosity coefficient of afore-cited mixtures embracing the temperature range 200 K < T < 3273.15 K is reproduced from the present unlike intermolecular potentials energy. Our estimated accuracies for the viscosity are to within ±2%. In addition, the calculated potential energies are used to present smooth correlations for other transport properties. The accuracies of the binary diffusion coefficients are of the order of ±3%. Finally, the unlike interaction energy and the calculated low density viscosity have been employed to calculate high density viscosities using Vesovic-Wakeham method.

VANADIUM ALLOYS

DOEpatents

Smith, K.F.; Van Thyne, R.J.

1959-05-12

This patent deals with vanadium based ternary alloys useful as fuel element jackets. According to the invention the ternary vanadium alloys, prepared in an arc furnace, contain from 2.5 to 15% by weight titanium and from 0.5 to 10% by weight niobium. Characteristics of these alloys are good thermal conductivity, low neutron capture cross section, good corrosion resistance, good welding and fabricating properties, low expansion coefficient, and high strength.

Thermoelectric Properties of Lanthanum Sulfide

NASA Technical Reports Server (NTRS)

Wood, C.; Lockwood, R.; Parker, J. B.; Zoltan, A.; Zoltan, L. D.; Danielson, L.; Raag, V.

1987-01-01

Report describes measurement of Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect in gamma-phase lanthanum sulfide with composition of La3-x S4. Results of study, part of search for high-temperature thermoelectric energy-conversion materials, indicate this sulfide behaves like extrinsic semiconductor over temperature range of 300 to 1,400 K, with degenerate carrier concentration controlled by stoichiometric ratio of La to S.

Electronic, thermoelectric and transport properties of cesium cadmium trifluoride: A DFT study

NASA Astrophysics Data System (ADS)

Abraham, Jisha Annie; Pagare, G.; Sanyal, Sankar P.

2018-04-01

The full potential linearized augmented plane wave method based on density functional theory is employed to investigate the electronic structure of CsCdF3. The electronic properties of this compound have been studied from the band structure plot and density of states. The presence of indirect energy gap reveals its insulating nature. Using constant relaxation time, the electrical conductivity, electronic thermal conductivity, Seebeck coefficient and figure of merit are calculated by using Boltzmann transport theory. We have also studied the temperature dependence of thermoelectric properties of this compound.

Determination of Optimal Heat-Storage Thickness of Layer for “Smart Wall” by Methods of Nonlinear Heat Conduction Equations for Phase-transition Materials

NASA Astrophysics Data System (ADS)

Pospelova, I.

2017-11-01

The article suggests an original way of keeping heat load and its compensation for a microclimate system by proposing the “Smart Wall”. The construction consists of specially combined composite materials including phase-transition materials. The method for determination of the layer thickness is proposed for a certain accumulation time. Varying the thickness and composition of the layer it is possible to achieve a low amount of the thermal conductivity coefficient and to obtain various functional characteristics of fences.

Reduction of thermal stresses in continuous fiber reinforced metal matrix composites with interface layers

NASA Technical Reports Server (NTRS)

Jansson, S.; Leckie, F. A.

1990-01-01

The potential of using an interface layer to reduce thermal stresses in the matrix of composites with a mismatch in coefficients of thermal expansion of fiber and matrix was investigated. It was found that compliant layers, with properties of readily available materials, do not have the potential to reduce thermal stresses significantly. However, interface layers with high coefficient of thermal expansion can compensate for the mismatch and reduce thermal stresses in the matrix significantly.

Thermal and electrical transport in metals and superconductors across antiferromagnetic and topological quantum transitions

NASA Astrophysics Data System (ADS)

Chatterjee, Shubhayu; Sachdev, Subir; Eberlein, Andreas

2017-08-01

We study thermal and electrical transport in metals and superconductors near a quantum phase transition where antiferromagnetic order disappears. The same theory can also be applied to quantum phase transitions involving the loss of certain classes of intrinsic topological order. For a clean superconductor, we recover and extend well-known universal results. The heat conductivity for commensurate and incommensurate antiferromagnetism coexisting with superconductivity shows a markedly different doping dependence near the quantum critical point, thus allowing us to distinguish between these states. In the dirty limit, the results for the conductivities are qualitatively similar for the metal and the superconductor. In this regime, the geometric properties of the Fermi surface allow for a very good phenomenological understanding of the numerical results on the conductivities. In the simplest model, we find that the conductivities do not track the doping evolution of the Hall coefficient, in contrast to recent experimental findings. We propose a doping dependent scattering rate, possibly due to quenched short-range charge fluctuations below optimal doping, to consistently describe both the Hall data and the longitudinal conductivities.

Autofrettage to Counteract Coefficient of Thermal Expansion Mismatch in Cryogenic Pressurized Pipes with Metallic Liners

NASA Technical Reports Server (NTRS)

Wen, Ed; Barbero, Ever; Tygielski, Phlip; Turner, James E. (Technical Monitor)

2001-01-01

Composite feedlines with metal liners have the potential to reduce weight/cost while providing the same level of permeation resistance and material compatibility of all-metal feedlines carrying cryogenic propellants in spacecraft. The major technical challenges are the large difference in Coefficient of Thermal Expansion between the liner and the composite, and the manufacturing method required to make a very thin liner with the required strength and dimensional tolerance. This study investigates the use of autofrettage (compressive preload) to counteract Coefficient of Thermal Expansion when pre-pressurization procedures cannot be used to solve this problem. Promising materials (aluminum 2219, Inconel 718, nickel, nickel alloy) and manufacturing techniques (chemical milling, electroplating) are evaluated to determine the best liner candidates. Robust, autofrettaged feedlines with a low Coefficient of Thermal Expansion liner (Inconel 718 or nickel alloy) are shown to successfully counteract mismatch at LOX temperature. A new concept, autofrettage by temperature, is introduced for high Coefficient of Thermal Expansion materials (aluminum and pure nickel) where pressure cannot be used to add compressive preload.

Molecular level assessment of thermal transport and thermoelectricity in materials: From bulk alloys to nanostructures

NASA Astrophysics Data System (ADS)

Kinaci, Alper

The ability to manipulate material response to dynamical processes depends on the extent of understanding of transport properties and their variation with chemical and structural features in materials. In this perspective, current work focuses on the thermal and electronic transport behavior of technologically important bulk and nanomaterials. Strontium titanate is a potential thermoelectric material due to its large Seebeck coefficient. Here, first principles electronic band structure and Boltzmann transport calculations are employed in studying the thermoelectric properties of this material in doped and deformed states. The calculations verified that excessive carrier concentrations are needed for this material to be used in thermoelectric applications. Carbon- and boron nitride-based nanomaterials also offer new opportunities in many applications from thermoelectrics to fast heat removers. For these materials, molecular dynamics calculations are used to evaluate lattice thermal transport. To do this, first, an energy moment term is reformulated for periodic boundary conditions and tested to calculate thermal conductivity from Einstein relation in various systems. The influences of the structural details (size, dimensionality) and defects (vacancies, Stone-Wales defects, edge roughness, isotopic disorder) on the thermal conductivity of C and BN nanostructures are explored. It is observed that single vacancies scatter phonons stronger than other type of defects due to unsatisfied bonds in their structure. In pristine states, BN nanostructures have 4-6 times lower thermal conductivity compared to C counterparts. The reason of this observation is investigated on the basis of phonon group velocities, life times and heat capacities. The calculations show that both phonon group velocities and life times are smaller in BN systems. Quantum corrections are also discussed for these classical simulations. The chemical and structural diversity that could be attained by mixing hexagonal boron nitride and graphene provide further avenues for tuning thermal and electronic properties. In this work, the thermal conductivity of hybrid graphene/hexagonal-BN structures: stripe superlattices and BN (graphene) dots embedded in graphene (BN) are studied. The largest reduction in thermal conductivity is observed at 50% chemical mixture in dot superlattices. The dot radius appears to have little effect on the magnitude of reduction around large concentrations while smaller dots are more influential at dilute systems.

The influence of surface functionalization on thermal transport and thermoelectric properties of MXene monolayers.

PubMed

Sarikurt, Sevil; Çakır, Deniz; Keçeli, Murat; Sevik, Cem

2018-05-10

The newest members of a two-dimensional material family, involving transition metal carbides and nitrides (called MXenes), have garnered increasing attention due to their tunable electronic and thermal properties depending on the chemical composition and functionalization. This flexibility can be exploited to fabricate efficient electrochemical energy storage (batteries) and energy conversion (thermoelectric) devices. In this study, we calculated the Seebeck coefficients and lattice thermal conductivity values of oxygen terminated M2CO2 (where M = Ti, Zr, Hf, Sc) monolayer MXene crystals in two different functionalization configurations (model-II (MD-II) and model-III (MD-III)), using density functional theory and Boltzmann transport theory. We estimated the thermoelectric figure-of-merit, zT, of these materials by two different approaches, as well. First of all, we found that the structural model (i.e. adsorption site of oxygen atom on the surface of MXene) has a paramount impact on the electronic and thermoelectric properties of MXene crystals, which can be exploited to engineer the thermoelectric properties of these materials. The lattice thermal conductivity κl, Seebeck coefficient and zT values may vary by 40% depending on the structural model. The MD-III configuration always has the larger band gap, Seebeck coefficient and zT, and smaller κl as compared to the MD-II structure due to a larger band gap, highly flat valence band and reduced crystal symmetry in the former. The MD-III configuration of Ti2CO2 and Zr2CO2 has the lowest κl as compared to the same configuration of Hf2CO2 and Sc2CO2. Among all the considered structures, the MD-II configuration of Hf2CO2 has the highest κl, and Ti2CO2 and Zr2CO2 in the MD-III configuration have the lowest κl. For instance, while the band gap of the MD-II configuration of Ti2CO2 is 0.26 eV, it becomes 0.69 eV in MD-III. The zTmax value may reach up to 1.1 depending on the structural model of MXene.

Thermoelectric Properties of Highly Conductive Poly(3,4-ethylenedioxythiophene) Polystyrene Sulfonate Printed Thin Films.

PubMed

Beretta, Davide; Barker, Alex J; Maqueira-Albo, Isis; Calloni, Alberto; Bussetti, Gianlorenzo; Dell'Erba, Giorgio; Luzio, Alessandro; Duò, Lamberto; Petrozza, Annamaria; Lanzani, Guglielmo; Caironi, Mario

2017-05-31

Organic conductors are being evaluated for potential use in waste heat recovery through lightweight and flexible thermoelectric generators manufactured using cost-effective printing processes. Assessment of the potentiality of organic materials in real devices still requires a deeper understanding of the physics behind their thermoelectric properties, which can pave the way toward further development of the field. This article reports a detailed thermoelectric study of a set of highly conducting inkjet-printed films of commercially available poly(3,4-ethylenedioxythiophene) polystyrene sulfonate formulations characterized by in-plane electrical conductivity, spanning the interval 10-500 S/cm. The power factor is maximized for the formulation showing an intermediate electrical conductivity. The Seebeck coefficient is studied in the framework of Mott's relation, assuming a (semi-)classical definition of the transport function. Ultraviolet photoelectron spectroscopy at the Fermi level clearly indicates that the shape of the density of states alone is not sufficient to explain the observed Seebeck coefficient, suggesting that carrier mobility is important in determining both the electrical conductivity and thermopower. Finally, the cross-plane thermal conductivity is reliably extracted thanks to a scaling approach that can be easily performed using typical pump-probe spectroscopy.