In physics, thermal conductivity is the property of a material to conduct heat. It is evaluated primarily in terms of Fouriers Law for heat conduction. Heat transfer occurs at a higher rate across materials of high thermal conductivity than across materials of low thermal conductivity. Correspondingly materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation. Thermal conductivity of materials is temperature dependent. The reciprocal of thermal conductivity is called thermal resistivity. The SI unit of thermal conductivity is watts per meter Kelvin (W•m⁻¹•K⁻¹).. ...
The thermal conductivity of undoped, Sn-doped, and Fe-doped beta-Ga2O3 bulk crystals was measured by the 3 omega technique in the temperature range of 295-410 K. A unique approach for extracting the thermal conductivity along the lateral and transverse heat flow directions was used in order to determine the thermal conductivity along different crystallographic directions. The data analysis at room temperature confirmed the expected anisotropy of the thermal conductivity of beta-Ga2O3, revealing the highest value of similar to 29 W/m K in the [010] direction. The thermal conductivity of the Sn-doped and Fe-doped beta-Ga2O3 samples was found to be lower than that of the undoped samples due to the enhanced phonon-impurity scattering contribution, which reduces the thermal conductivity. This tendency was maintained for the thermal conductivity at elevated temperatures. The thermal conductivity in all samples decreased with increasing temperature, but the slope of the temperature dependence was found ...
In this paper we present the results of calculations of the lattice thermal conductivity of layered complex metal oxide NaxCoO2 within the Green-Kubo theory. Using NaxCoO2 we identify the two competing mechanisms responsible for the favorable scaling properties of the Green-Kubo method for calculating the lattice thermal conductivity. The artificial correlations of the heat flux fluctuations due to the finite size of the supercells are partially cancelled by the missing long wavelength acoustic phonon modes. We compute the lattice thermoelectric properties of bulk NaxCoO2 with varying stoichiometry, structural defects, and temperature. We also calculate the thermal conductivity of NaxCoO2 in the nanosheet geometry. While the dependence of thermal conductivity on Na fractions x in the middle range (0.5 | x | 0.8) is relatively weak, introducing Co vacancies results in significant lattice thermal conductivity reduction. The material exhibits strong anisotropy of lattice thermal conductivity due to a
MCM-41 consists of a hexagonal array of long, unconnected cylindrical pores with diameters that can be tailored within the range 1.6-10nm. As a porous silica nano-material, MCM-41 is thought to have a special thermal conductivity and is a promising porous substrate for mesoporous composites with high or low thermal conductivity. The Equilibrium Molecular Dynamics numerical simulations of thermal conductivity of MCM-41 are performed in this paper. FB potential equation and procedure of annealing are employed to get the structure of MCM-41. The Green-Kubo method is used to calculate the thermal conductivity of MCM-41. At the same time, the kinetic method is used to predict the thermal conductivity of MCM-41 for comparison. It turns out that the shell thermal conductivities of MCM-41 distribute within a reasonable range and increases linearly as porosity decreases, approaching the thermal conductivity of aerogels.. Copyright © 2010 by ASME ...
The bulk thermal conductivity of Stillinger-Weber (SW) wurtzite GaN in the [0001] direction at a temperature of 300 K is calculated using equilibrium molecular dynamics (EMD), non-equilibrium MD (NEMD), and lattice dynamics (LD) methods. While the NEMD method predicts a thermal conductivity of 166 ± 11 W/m·K, both the EMD and LD methods predict thermal conductivities that are an order of magnitude greater. We attribute the discrepancy to significant contributions to thermal conductivity from long-mean free path phonons. We propose that the Grüneisen parameter for low-frequency phonons is a good predictor of the severity of the size effects in NEMD thermal conductivity prediction. For weakly anharmonic crystals characterized by small Grüneisen parameters, accurate determination of thermal conductivity by NEMD is computationally impractical. The simulation results also indicate the GaN SW potential, which was originally developed for studying the atomic-level structure of dislocations, is not ...
TY - JOUR. T1 - Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation. AU - Zhu, Gaohua. AU - Liu, Jun. AU - Zheng, Qiye. AU - Zhang, Ruigang. AU - Li, Dongyao. AU - Banerjee, Debasish. AU - Cahill, David G.. N1 - Publisher Copyright: © 2016 The Author(s). Copyright: Copyright 2017 Elsevier B.V., All rights reserved.. PY - 2016/10/21. Y1 - 2016/10/21. N2 - Thermal conductivity of two-dimensional (2D) materials is of interest for energy storage, nanoelectronics and optoelectronics. Here, we report that the thermal conductivity of molybdenum disulfide can be modified by electrochemical intercalation. We observe distinct behaviour for thin films with vertically aligned basal planes and natural bulk crystals with basal planes aligned parallel to the surface. The thermal conductivity is measured as a function of the degree of lithiation, using time-domain thermoreflectance. The change of thermal conductivity correlates with the lithiation-induced structural and ...
The present work investigates heat conduction from lattice vibrations in a class of materials called half-Heuslers. The composition under investigation was XNiSn half-Heusler alloys where X=Ti, Zr or Hf. These materials have received a lot of attention for their favorable properties for hermoelectric applications. However, their lattice thermal conductivity is too high to be applicable as a thermoelectric material. Previous studies have shown that lattice thermal conductivity can be reduced by isoelectronic substitutions on the X-site or by reducing the grain size. The lattice thermal conductivity is calculated by using density functional theory and the phonon Boltzmann transport equation with the frozen phonon approach. Anharmonic three-phonon scattering was used to assess lattice thermal conductivity of pure TiNiSn, ZrNiSn and HfNiSn, the results had good accordance to experimental values. However, a slight overestimation was observed due to the fact that experimental samples exhibit ...
TY - JOUR. T1 - Thermal conductivity dependence of MgO thermal insulation on porosity in temperature range 500-2000 K. AU - Litovsky, E.. AU - Litovsky, T.. AU - Shapiro, M.. AU - Shavit, A.. N1 - Copyright: Copyright 2020 Elsevier B.V., All rights reserved.. PY - 1997. Y1 - 1997. N2 - Thermal conductivity of MgO (magnesia) foam thermal insulation with porosity 0.49-0.81 have been measured by the non-steady plane flow method in the temperature range of 500-2000 K at atmospheric pressure. We have demonstrated a significant influence of porosity on the apparent thermal conductivity of MgO insulating materials in the temperature range 500-1500 K. Materials with porosities exceeding 0.75, have relatively low radiation attenuation coefficients. This results in a relatively large contribution to the radiative component of the apparent thermal conductivity. For such materials this property measured at temperatures above 1700 K weakly depends on porosity. The measured apparent thermal conductivities are ...
TY - JOUR. T1 - Nanoparticles for convective heat transfer enhancement. T2 - heat transfer coefficient and the effects of particle size and zeta potential. AU - Liu, Lande. AU - Stetsyuk, Viacheslav. AU - Kubiak, Krzysztof. AU - Fatt, Yap Yit. AU - Goharzadeh, Afshin. AU - Chai, John. PY - 2019/6/3. Y1 - 2019/6/3. N2 - This work presents a study of using the Wilson Plot method to determine the convective heat transfer coefficient (CHTC) of the following nanoparticles in water as the base fluid: SiO2, TiO2, and Al2O3. The experiments were carried out in a double layer concentric glass tube in which the hot fluid and nanofluids exchange heat in a counter current fashion without direct contact. Attention was also given to the volumetric concentration, flow rate, and the size of nanoparticles to investigate their effects on CHTC. From the experiments, it was found that by adding nanoparticles, the CHTC of water can generally be enhanced and a 45% increase has been achieved with a 0.5 vol% ...
Thermal Conductivity. Thermal conductivity of a polymer composite is a function of resin type, fiber type and architecture, fiber volume fraction, direction of heat flow, and service temperature. In physics, thermal conductivity is the property of the material to conduct heat and its evaluated primarily in terms of Fouriers Law for heat conduction. As a rule of thumb, materials of low thermal conductivity are used in thermal insulation applications.. Thermal Insulation. Composites are both thermal and electrical insulators. Composites are good insulators-they do not easily conduct heat or cold (low thermal conductivity). They are used in buildings for doors, panels, and windows where extra protection is needed from severe weather.. As a specific example, silicone resin glass reinforced thermoset composites offer excellent thermal, mechanical, and electrical insulation properties. Their high temperature performance and insulation properties make them equal or superior to many high priced ...
This thesis presents the evaluation of thermal conductivity of thin films of silicon dioxide on silicon substrate. The method used for measuring the thermal conductivity is named as 3 omega method which can operate within a temperature range of 20K to 320K. This method, first proposed by David G. Cahill [7] is a method where a metallic strip remained in close contact with the specimen surface. The details of 3 omega method will be described in the later chapter of this thesis.In this thesis, a mathematical modeling of 3 omega method is presented. The thermal conductivity of thin film was measured by 3 omega method. The data were taken from 20K to 120K. At temperatures of 20K, 30K, 50K and 80K the values of thermal conductivities of 0.14, 0.24, 0.35 and 0.55 W/m-K were obtained, respectively. At 90K, 100K, 110K, 120K the values of thermal conductivities of 0.62, 0.69, 0.77 and 0.84 W/m-K were obtained, respectively. The results show that the values obtained by 3 omega method match closely with ...
Bulk polymers are generally regarded as thermal insulators, and typically have thermal conductivities on the order of 0.1 W m−1 K−1 (ref. 1). However, recent work2,3,4 suggests that individual chains of polyethylene-the simplest and most widely used polymer-can have extremely high thermal conductivity. Practical applications of these polymers may also require that the individual chains form fibres or films. Here, we report the fabrication of high-quality ultra-drawn polyethylene nanofibres with diameters of 50-500 nm and lengths up to tens of millimetres. The thermal conductivity of the nanofibres was found to be as high as ∼104 W m−1 K−1, which is larger than the conductivities of about half of the pure metals. The high thermal conductivity is attributed to the restructuring of the polymer chains by stretching, which improves the fibre quality toward an ideal single crystalline fibre. Such thermally conductive polymers are potentially useful as heat spreaders and could supplement
The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223 m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.
Effect of formalin fixation on thermal conductivity of the biological tissues is presented. A self-heated thermistor probe was used to measure the tissue thermal conductivity. The thermal conductivity of porcine aorta, fat, heart, and liver was measured before the formalin fixation and then 1 day, 4 days, and 11 days after formalin fixation. The results indicate that the formalin fixation does not cause a significant change in the tissue thermal conductivity of the tissues studied. In the clinical setting, tissues removed surgically are often fixed in formalin for subsequent pathological analysis. These results suggest that, in terms of thermal properties, it is equally appropriate to perform in vitro studies in either fresh tissue or formalin-fixed tissue.. ...
This study aimed to improve the thermal conductivity of the Aluminium 6063 for heat sinks applications used in Central Processing Unit (CPU) of computers. Several studies had used different additional elements for this goal. In this paper, we studied the influence of Titanium and Boron addition on the thermal conductivity of Aluminium 6063. Several casting alloys samples were prepared with different percentage of addition elements and then heat-treated by homogenization and aging treatments. The results showed an important modification in thermal conductivity value per rapport to the reference metal, depending on the element of addition and its percentage. The bigger evolution was by using Boron in small percentage. More than 13% of the improvement was realized in the thermal conductivity with the addition of only 0.05% of Boron.
No. of Report Pages: 106. Price of Report (single User Licence): $2900. Purchase the Report at: http://www.absolutereports.com/purchase/10503023. The report covers the market projection and analysis of Oxygen-free High Thermal Conductivity (OFHC) Copper Market Research Report 2016 on a global as well as regional level.. The Global Oxygen-free High Thermal Conductivity (OFHC) Copper Market Research Report 2016 highlights key dynamics of Oxygen-free High Thermal Conductivity (OFHC) Copper sector. The current market scenario and future prospects of the sector has also been studied. Additionally, prime strategical activities in the market which includes product developments, mergers and acquisitions, partnerships, etc., are discussed.. Get Discount on Purchase of this Report at: http://www.absolutereports.com/enquiry/request-discount/10503023. The research report has offered answers to several important questions related to the growth of the Oxygen-free High Thermal Conductivity (OFHC) Copper ...
Thermal conductivity of frost is not only related to density, but also affected by its microstructure and environmental conditions, and it will continuously change with the formation and growth of frost. Images of frost formation and growth on the cryogenic surface in various shapes at different stages were obtained by experimental measurements, and a numerical simulation of frost formation and growth was carried out based on Diffusion Limited Aggregation (DLA) model of fractal theory in this paper. Based on the frost structure obtained by experiment, the fractal dimension of pore area distribution and porosity of frost layer on the cryogenic finned-tube vaporizer were calculated by using fractal method, and combined with heat conduction model of frost layer obtained by thermal resistance method, the thermal conductivity of frost on the cryogenic surface was calculated. The result shows that the thermal conductivity calculated by the fractal model coincides with the range of the experimental data.
Thermal diffusivity is an important parameter in unsteady-state heat transfer processes. Compared to other physical properties, there appears to be very few predictive models for thermal diffusivity in the literature. Most experimental studies have focussed on the influence of moisture content and temperature on thermal diffusivity and there is very little about the influence of porosity. In this study, the effects of porosity on thermal diffusivity are examined for selected foods and thermal diffusivity models from the literature are compared against measured data. The thermal diffusivity model proposed by Choi and Okos based on a weighted arithmetic mean of the components thermal diffusivities is not suitable for porous foods, resulting in large prediction errors. Applying a similar approach based on the harmonic mean rather than the arithmetic mean provided closer estimates of thermal diffusivity for both types of porous foods considered, but still produced unacceptable prediction errors ...
Thermal Conductivity Measurement of Zr-ZrO2 Simulated Inert Matrix Nuclear Fuel Pellet. . Biblioteca virtual para leer y descargar libros, documentos, trabajos y tesis universitarias en PDF. Material universiario, documentación y tareas realizadas por universitarios en nuestra biblioteca. Para descargar gratis y para leer online.
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This work discusses measurement of thermal conductivity (k) of films using a scanning hot probe method in the 3ω mode and investigates the calibration of thermal contact parameters, specifically the thermal contact resistance (RthC) and thermal exchange radius (b) using reference samples with different therm
Accurate information on the temperature field and associated heat transfer rates are particularly important in devising appropriate heat and water management strategies in proton exchange membrane (PEM) fuel cells. An important parameter in fuel cell performance analysis is the effective thermal conductivity of the gas diffusion layer (GDL). Estimation of the effective thermal conductivity is complicated because of the random nature of the GDL micro structure. In the present study, a compact analytical model for evaluating the effective thermal conductivity of fibrous GDLs is developed. The model accounts for the salient geometric features, effects of bipolar pressure variation, gas rarefaction effects, and spreading resistance. The model predictions are in good agreement with existing experimental data over a wide range of porosities. Parametric studies are performed using the proposed model to investigate the effect of bipolar plate pressure, aspect ratio, fiber diameter, fiber angle, and ...
Knowledge of the size and distribution of nanoparticles in solution is critical to understanding the observed enhancements in thermal conductivity and heat transfer of nanofluids. We have applied smallangle X-ray scattering (SAXS) to the characterization of SiO2 nanoparticles (10-30 nm) uniformly dispersed in a water-based fluid using the Advanced Photon Source at Argonne National Laboratory. Size distributions for the suspended nanoparticles were derived by fitting experimental data to an established model. Thermal conductivity of the SiO2 nanofluids was also measured, and the relation between the average particle size and the thermal conductivity enhancement was established. The experimental data contradict models based on fluid interfacial layers or Brownian motion but support the concept of thermal resistance at the liquid-particle interface. © 2008, Springer ...
Data for the viscosity and thermal conductivity coeffients of dense gaseous and liquid methane have been evaluated. Selected data were fitted to a function derived in our previous work and tables of values were generated for temperatures from 95 to 500 K and for pressures up to 50 MPa (approximately to 500 atm). The uncertainties of the tabular values are estimated to be approximately 3% and 5% for the viscosity and thermal conductivity coefficients, respectively. The contribution for the thermal conductivity enhancement in the critical region is included in the tables. Care has been taken to ensure that the calculated values are consistent with reliable equation-of-state data and also with dilute gas transport coefficients determined previously.*METHANE
Investigating thermal conductivity quiz questions | Footprints-Science - GCSE science animations and quizzes - Metals have a high thermal conductivity - Method for investigating which metal is has the highest thermal conductivity - Independent and dependent variables - Control variables - Conclusion
In this study, experimental and simulation studies of the evaporation heat transfer coefficient and pressure drop of R-134a flowing through corrugated tubes are conducted. The test section is a horizontal counter-flow concentric tube-in-tube heat exchanger 2.0 m in length. A smooth tube and corrugated tubes with inner diameters of 8.7 mm are used as the inner tube. The outer tube is made from a smooth copper tube with an inner diameter of 21.2 mm. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm, respectively. The results show that the maximum heat transfer coefficient and pressure drop obtained from the corrugated tube are up to 22 and 19 % higher than those obtained from the smooth tube, respectively. In addition, the average difference of the heat transfer coefficient and pressure drop between the simulation model and experimental data are about 10 and 15 %, respectively. ...
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Thermal conductivity plays an important role in dominating a functional materials behavior in heat conduction processes and its applicability. Thus it is important to develop a prediction method for thermal conductivity to improve the thermal design and manufacturing processes of functional materials. According to the microscopy theories of heat conduction and the Koop-Neumann Law, a new method of predicting the thermal conductivity in close relationship to the average relative atomic mass and density of semiconducting compound functional crystals materials is developed in this paper. A new formula for calculating thermal conductivity that results in a simple but accurate approach is proposed. The thermal conductivities calculated using the formula are compared with the values obtained by experimental measurement and found to be in agreement for many semiconducting compound functional crystals and ceramic materials. It is discovered in further analysis that the larger the average relative ...
In recent years the thermal conductivity of materials has become an important area of research. High thermal conductivity is useful for heat removal in electronic devices, and low thermal conductivity results in a larger thermoelectric figure of merit. The question is how to control the thermal conductivity. Many physical properties of semiconductors are successfully controlled by adding impurity atoms. The electrical conductivity can be substantially increased using dopants, the mechanical strength of Si can be improved by introducing O and N, optical properties are tailored using rare-earth elements such as Er. But is it possible to control the thermal conductivity with impurities as well? The impact of impurity scattering (whatever this really means) on the thermal conductivity of materials is well known, but only qualitatively. However, it is never described at the atomic level. A better understanding of the physics behind the impact of impurities on the thermal conductivity could lead to ...
In recent years the thermal conductivity of materials has become an important area of research. High thermal conductivity is useful for heat removal in electronic devices, and low thermal conductivity results in a larger thermoelectric figure of merit. The question is how to control the thermal conductivity. Many physical properties of semiconductors are successfully controlled by adding impurity atoms. The electrical conductivity can be substantially increased using dopants, the mechanical strength of Si can be improved by introducing O and N, optical properties are tailored using rare-earth elements such as Er. But is it possible to control the thermal conductivity with impurities as well? The impact of impurity scattering (whatever this really means) on the thermal conductivity of materials is well known, but only qualitatively. However, it is never described at the atomic level. A better understanding of the physics behind the impact of impurities on the thermal conductivity could lead to ...
This research focused on the synthesis and phase formation of zirconium carbide with different carbon contents, and lattice thermal conductivity of zirconium carbide with different carbon vacancy, hafnium, and oxygen contents.. Nominally pure phase ZrCx was synthesized by solid-state reaction of zirconium hydride (ZrHs) and carbon black at a temperature as low as 1300°C. The powder synthesized at 1300C was carbon deficient ZrCx . Carbon stoichiometry of the as- synthesized powders increased as the synthesis temperature increased. As the synthesis temperature increase, the oxygen content of ZrCx decreased due to the increasing C site occupancy. Low stoichiometry ZrC0.6 powders were synthesized at 1300C and 2000C, and the formed phases were investigated. Carbon vacancy ordered phases were detected by neutron diffraction and selected area electron diffraction.. Lattice thermal conductivities of ZrCx with different carbon contents (x = 1.0, 0.75, 0.5) and different hafnium contents (3.125 at% and ...
The need for maximizing the performance of micro-mechanical systems and electronic components has resulted in a trend of minimization. Minimized sizes and dimensions have come along with a complex heat transfer and fluid problem within these devices and components. For a variety of fields in which these devices are used, such as; biomedicine, micro fabrication, and optics, fluid flow and heat transfer at the microscale needs to be understood and modeled with an acceptable reliability. In general, models are prepared by making some extensions to the conventional theories by including the scaling effects that become important for microscale. Studies performed in the last decade have shown that, some of the effects that are thought to become significant for a microscale gas flow are; axial conduction, viscous dissipation, and rarefaction. In addition to these effects, the temperature variable thermal conductivity and viscosity may become important in microscale gas flow due to the high temperature ...
China High Thermal Conductivity Al2O3 Alumina Ceramic Thermocouple Tube, Find details about China Alumina Tube, Ceramic Tube from High Thermal Conductivity Al2O3 Alumina Ceramic Thermocouple Tube - Hunan Rui Yue Industrial and Trade Co., Ltd.
Graphene nanoplatelets (GNPs) have excellent thermal conductivity. It can significantly improve the heat-conducting property of epoxy resin (EP) matrix. In this paper, the GNPs/EP composites were successfully prepared by using ultrasonication and the cast molding method. The prepared GNPs/EP composites were systematically characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermal conductivity analyzer. Some factors affecting the thermal transfer performance of the composites were discussed. The defoamation has great influence on the thermal conductivity of composite. There is a nearly linear relationship between the mass fraction and the thermal conductivity of composite when the mass fraction of GNPs is below 4.3%. The results show that when the mass fraction of GNPs is 4.3% with crushing time of 2 s, the thermal conductivity of GNPs/EP composite is up to 0.99 W/m K. The thermal conductivity is increased by 9.0% compared with that without pulverization treatment ...
China Wholesale High Thermal Conductivity Pyrolytic Graphite Coated Crucible, Find details about China Pbn Coating, Pyrolytic Boron Nitride Crucible from Wholesale High Thermal Conductivity Pyrolytic Graphite Coated Crucible - Hunan Rui Yue Industrial and Trade Co., Ltd.
On the other hand, high thermal conductivity resins are researched now, but it has just begun.. PBI Advanced Materials can offer high filler content materials because PBI Advanced Materials can make materials by compression molding. The compression molding method makes it easier to mix polymers with high content fillers than other molding method. PBI Advanced Materials also focuses the electrical insulative property of plastics and aims to development of the materials with high thermal conductivity and electrical insulation. ...
TY - JOUR. T1 - Thermal Conductivity Comparison of Indium Gallium Zinc Oxide Thin Films. T2 - Dependence on Temperature, Crystallinity, and Porosity. AU - Cui, Boya. AU - Zeng, Li. AU - Keane, Denis. AU - Bedzyk, Michael J.. AU - Buchholz, D. Bruce. AU - Chang, Robert P. H.. AU - Yu, Xinge. AU - Smith, Jeremy. AU - Marks, Tobin J. AU - Xia, Yu. AU - Facchetti, Antonio F.. AU - Medvedeva, Julia E.. AU - Grayson, M.. PY - 2016/4/21. Y1 - 2016/4/21. N2 - The cross-plane thermal conductivity of InGaZnO (IGZO) thin films was measured using the 3ω technique from 18 to 300 K. The studied morphologies include amorphous (a-IGZO), semicrystalline (semi-c-IGZO), and c-axis-aligned single-crystal-like IGZO (c-IGZO) grown by pulsed laser deposition (PLD) as well as a-IGZO deposited by sputtering and by solution combustion processing. The atomic structures of the amorphous and crystalline films were simulated with ab initio molecular dynamics. The film quality and texturing information was assessed by X-ray ...
The units of thermal conductivity are watts per meter-kelvin. Watts are a measure of power, meters are a measure of length, and kelvins are a measure of temperature. From the units, we can see that thermal conductivity is a measure of how much power moves through a distance due to a temperature difference. Some great thermal insulators are: Vacuum, Aerogel, Polyurethane Some great thermal conductors are: Silver, Copper, Diamond Silver is one of the most thermally conductive materials (and is relatively common), and because of this there are some cool experiments you can do with silver that show extremely well how thermal conduction works. One example is when you put 2 spoons in boiling water, one spoon is steel and the other is silver. When you take the spoons out of the boiling water, the silver spoon is hotter than the steel spoon. The reason for this is that silver conducts heat better than steel. The silver spoon will also cool off faster because of this, as it is better at releasing heat. ...
Thermal conductivity curves for polycrystalline uranium are presented for the temperature range below 373$sup 0$K. The curves are for specimens prepared by different fabrication procedures from material of known purity and hardness. Included is a curve for U/2wt percent Mo alloy. Different mechanisms appear to be influencing the thermal conductivity behavior of uranium in well- defined temperature regions: below 37 to 43$sup 0$K, approximately 40 to approximately 80$sup 0$K, 80 to approximately 280$sup 0$K, and from 280$sup 0$K to the $alpha$ $Yields$ $beta$ transformation temperature. Mechanisms responsible for results in one temperature region continue to exert a strong influence in the next higher temperature region. Impurities and initial microstructure seem to influence results at any starting temperature. Evidence is presented for the possibility of imperfection ordering in uranium between approximately 40 and approximately 280$sup 0$K. It is postulated that the type of ordering is capable with a
Using an optical pyrometer method, the thermal conductivity of tungsten has been found to vary linearly from 1.170 watts/(cm2 K°/cm) at 1100°K to 1.026 watts/(cm2 K°/cm) at 2000°K. Similarly, the thermal conductivity of molybdenum has been found to vary linearly from 1.083 watts/(cm2 K°/cm) at 1200°K to 0.666 watt/(cm2 K°/cm) at 1900°K. Spectrographic analysis indicated only traces of impurities in samples of the two metals used in the investigation.. © 1941 Optical Society of America. Full Article , PDF Article ...
A model for the prediction of the density, viscosity and thermal conductivity of non-polar fluid mixtures over the entire range of PVT states is presented. The model is based on the extended corresponding states model and covers molecular weight ranges including C20. Only pure component equilibrium data such as the critical constants are required as input to the calculation procedure--no transport data are required. Extensive comparisons with experimental data for pure fluids and binary mixtures are presented. The average percentage deviation for both the viscosity and thermal conductivity was observed to be less than 8 percent. A computer program (TRAPP) which performs the calculations reported in this manuscript is described and listed in the Appendices. (Author)*COMPUTER PROGRAMS
The effective thermal conductivity (ETC) of particle beds has been shown to be anisotropic under uniaxial compression. The objective of this study is to validate the assumption that vertical and horizontal effective thermal conductivities of particle beds under uniaxial (vertical) compression can be correlated to compressive stresses in each direction. The horizontal compressive pressure, which is perpendicular to the applied compressive pressure, can be calculated with the use of the at-rest pressure coefficient and subsequently used in a modified macro-contact thermal resistance model to predict the horizontal ETC. The vertical ETC is obtained using the same model by substituting the vertical compressive pressure into the macro-contact thermal resistance. The modified model prediction is shown to match well with experimental data of both vertical and horizontal ETCs of particle beds under uniaxial compression in air and vacuum.
I am working on the calculation of thermal conductivity using green-kubo method. At first steps the magnitude of thermal conductivity is approximately close to the experimental magnitude. But there is a problem. As I increase the simulation time, the final result decreases continuously. For example the exact result is 0.5 and the MD result is 0.4 at first iterates. But by increasing the time it changes to 0.39 0.38 0.36 0.35 and so on. I have attached the MD input code and the log file to this email. I dont know why this happens. Any one can help me with this ...
To date, there is no experimental characterization of thermal conductivity of semiconductor polymeric individual nanowires embedded in a matrix. This work reports on scanning thermal microscopy measurements in a 3ω configuration to determine how the thermal conductivity of individual nanowires made of a mode
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Most (79.9±2.7%) heat transfer from starlings during flight occurs by convection, so our calculation of Pmet,heat is most sensitive to any error in convective heat transfer. An increase of 10% in convective heat transfer would raise Pmet,heat by 8.0±0.3%. Accordingly, we paid most attention to computation of convective heat transfer, especially how we expected convection from the wings to vary during the wing beat cycle. Comparison between the heat transfer coefficient that we calculated for the wings and those determined empirically from a heated model of a starling suggested that the assumptions that we used were realistic (Ward et al., 1999). A possible source of error is our assumption of laminar flow over the surface of the wings and body. Turbulent flow would increase convective heat transfer, especially towards the trailing edge of the wings and towards the tail, because turbulence prevents the build-up of a thermal boundary layer (Holman, 1986). Maybury and Rayner (2001) have shown ...
Chemical vapor deposited (CVD) diamond, due to its high thermal conductivity, is an attractive candidate for thermal management of GaN-based high-electron mobility transistors (HEMTs). However, because of its heterogeneous grain structure, CVD diamond has a spatially inhomogeneous thermal conductivity at the microscale. To understand this inhomogeneity and the effect of structural imperfections on thermal conduction, time-domain thermoreflectance (TDTR) is used to study the local thermal conductivity of two samples: a heavily boron-doped ~534 μm-thick diamond sample with an average surface grain size of ~23 μm, and an undoped diamond sample that was cut from a bulk piece of CVD diamond. For the doped diamond, large thermal conductivity variations (of nearly 50 %) are observed across the surface of the sample. For the undoped sample, the large average grain size (several hundred ?m) results in a high local thermal conductivity (,2000 W/m-K, close to the conductivity of bulk diamond). The ...
With the aim of preparing stable nanofluids for heat exchange applications and to study the effect of surfactant on the aggregation of nanoparticles and thermal diffusivity, stable silver colloids were synthesized in water by a green method, reducing AgNO3 with fructose in the presence of poly-vinylpyrollidone (PVP) of various molecular weights. A silver nanopowder was precipitated from the colloids and redispersed at 4 vol% in deionized water. The Ag colloids were characterized by UV-Visible spectroscopy, combined Dynamic Light Scattering and ζ-potential measurements, Laser Flash Thermal Diffusivity. The Ag nanopowders were characterized by Scanning Electron Microscopy and Thermal Gravimetric Analysis. It has been found that the molecular weight of PVP strongly affects the ζ-potential and the aggregation of nanoparticles, and thereby affecting the thermal diffusivity of the obtained colloids. A maximum improvement of thermal diffusivity by about 10 % was found for nanofluids prepared with PVP having
TY - JOUR. T1 - Metallic-like thermal conductivity in a lightweight insulator: Solid-state processed Ultra High Molecular Weight Polyethylene tapes and films. AU - Ronca, Sara. AU - Igarashi, Tamito. AU - Forte, Giuseppe. AU - Rastogi, Sanjay. N1 - Generated from Scopus record by KAUST IRTS on 2021-02-16. PY - 2017/8/11. Y1 - 2017/8/11. N2 - Ultra High Molecular Weight Polyethylene with a reduced number of entanglements can be stretched in the solid state both uni- or biaxially to produce highly oriented tapes and films. The chain orientation, in combination with the reduced number of chain ends, is responsible for the high tensile modulus and tensile strength of the drawn materials, and, as we report here, also for the high thermal conductivity achieved through lattice movements. A property such as thermal conductivity in an electrical insulator makes UHMWPE tapes and films of great applicative interest. In-plane laser-flash thermal analysis has been applied to measure the thermal diffusivity ...
We investigate the harmonic and anharmonic contributions to the phonon spectrum of lead telluride and perform a complete characterization of how thermal properties of PbTe evolve as temperature increases. We analyze the thermal resistivitys variationwith temperature and clarify misconceptions about existing experimental literature. The resistivity initially increases sublinearly because of phase space effects and ultra strong anharmonic renormalizations of specific bands. This effect is the strongest factor in the favorable thermoelectric properties of PbTe, and it explains its limitations at higher T. This quantitative prediction opens the prospect of phonon phase space engineering to tailor the lifetimes of crucial heat carrying phonons by considering different structure or nanostructure geometries. We analyze the available scattering volume between TO and LA phonons as a function of temperature and correlate its changes to features in the thermal conductivity.. ...
This thesis studies the general heat conduction law, irreversible thermodynamics and the size effect of thermal conductivity exhibited in nanosystems from the perspective of recently developed thermomass theory. The derivation bridges the microscopic phonon Boltzmann equation and macroscopic
Parallel to the developments in micro/nano manufacturing techniques, component sizes in micro/nano electro mechanical systems have been decreasing to nanometer scales. Decrease in lengths in heat transfer direction below the heat carrier phonon length scales reduces thermal conduction in semiconductors. This study shows that such altered phonon spectrums with the decrease of size also reduce the heat transfer at the solid/liquid interfaces and can be correlated with the thermal conductivity of the slab. Using Molecular Dynamics (MD), we measured heat transfer between water and silicon of different thickness between 5 nm and 60 nm. Silicon slabs exhibit a linear temperature profile through the bulk where thermal conductivities measured based on Fourier law decreased by the decreasing slab thickness. We applied a semi-theoretical formulism on variation of conductivity by slab thickness. At the interface of these slabs and water, heat passage is disturbed due to the phonon mismatch of dissimilar ...
Graphene-based materials exhibit intriguing phononic and thermal properties. In this paper, we have investigated the heat conductance in graphene sheets under shear-strain-induced wrinkling deformation, using equilibrium molecular dynamics simulations. A significant orientation dependence of the thermal conductivity of graphene wrinkles (GWs) is observed. The directional dependence of the thermal conductivity of GWs stems from the anisotropy of phonon group velocities as revealed by the G-band broadening of the phonon density of states (DOS), the anisotropy of thermal resistance as evidenced by the G-band peak mismatch of the phonon DOS, and the anisotropy of phonon relaxation times as a direct result of the double-exponential-fitting of the heat current autocorrelation function ...
TY - JOUR. T1 - Enhanced figure of merit of a porous thin film of bismuth antimony telluride. AU - Kashiwagi, Makoto. AU - Hirata, Shuzo. AU - Harada, Kentaro. AU - Zheng, Yanqiong. AU - Miyazaki, Koji. AU - Yahiro, Masayuki. AU - Adachi, Chihaya. PY - 2011/1/10. Y1 - 2011/1/10. N2 - A porous thin film of Bi0.4Te3Sb1.6 with an enhanced figure of merit of 1.8 at room temperature was fabricated by flash evaporation on an alumina substrate containing hexagonally arranged nanopores with an average diameter of 20 nm, separated by an average distance of 50 nm. The thermal conductivity was significantly reduced compared with standard Bi0.4Te3Sb1.6 films to 0.25 W/(m·K) with no major decrease in either the electrical conductivity (398 S/cm) or the Seebeck coefficient (198 μV/K). The reduction in thermal conductivity was rationalized using a model for the full distribution of the phonon mean free path in the film.. AB - A porous thin film of Bi0.4Te3Sb1.6 with an enhanced figure of merit of 1.8 at room ...
In the present work, a three-dimensional, dynamic and non-linear finite element to simulate thermoelectric behavior under a hyperbolic heat conduction model is presented. The transport equations, which couple electric and thermal energies by the Seebeck, Peltier and Thomson effects, are analytically obtained through extended non-equilibrium thermodynamics, since the local equilibrium hypothesis is not valid under the hyperbolic model. In addition, unidimensional analytical solutions are obtained to validate the finite element formulation. Numerically, isoparametric eight-node elements with two degrees of freedom (voltage and temperature) per node are used. Non-linearities due to the temperature-dependence on the transport properties and the Joule effects are addressed with the Newton-Raphson algorithm. For the dynamic problem, HHT and Newmark-ß algorithms are compared to obtain accurate results, since numerical oscillations (Gibbs phenomena) are present when the initial boundary conditions are ...
The ultralow thermal conductivity $\kappa$ observed experimentally in intentionally roughened silicon nanowires (SiNWs) is reproduced in phonon Monte Carlo simulations with exponentially correlated real-space rough surfaces similar to measurement [J. Lim, K. Hippalgaonkar, S. C. Andrews, A. Majumdar, and P. Yang, Nano Lett. 12, 2475 (2012)]. Universal features of thermal transport are revealed by presenting $\kappa$ as a function of the normalized geometric mean free path $\bar\lambda$ ($0,\bar\lambda,1$); the diffusive (Casimir) limit corresponds to $\bar\lambda=1/2$. $\kappa$ vs $\bar\lambda$ is exponential at low-to-moderate roughness (high $\bar\lambda$), where internal scattering randomly interrupts phonon bouncing across the SiNW, and linear at high roughness (low $\bar\lambda$), where multiple scattering events at the same surface results in ultralow, amorphous-limit thermal conductivity ...
In simple kinetic theory [with well-define acoustic phonon quasi-particles] the thermal conductivity is proportional to the phonon velocity and the phonon mean-free path. In glasses there is so much structural disorder the concept of phonon quasi-particles and a mean-free path is ill defined. In the quasi-particle picture one could reduce the thermal conductivity either by decreasing the phonon mean-free path or by decreasing the phonon speed, or both. The former can happen via a large anharmonicity, which is what is responsible for phonon-phonon scattering. The latter can happen in a soft material or by strongly coupling the acoustic phonons to low frequency optical phonons ...
Despite the uniquely high thermal conductivity of graphene is well known, the exploitation of graphene into thermally conductive nanomaterials and devices is limited by the inefficiency of thermal contacts between the individual nanosheets. A fascinating yet experimentally challenging route to enhance thermal conductance at contacts between graphene nanosheets is through molecular junctions, allowing covalently connecting nanosheets, otherwise interacting only via weak Van der Waals forces. Beside the bare existence of covalent connections, the choice of molecular structures to be used as thermal junctions should be guided by their vibrational properties, in terms of phonon transfer through the molecular junction. In this paper, density functional tight-binding combined with Green functions formalism was applied for the calculation of thermal conductance and phonon spectra of several different aliphatic and aromatic molecular junctions between graphene nanosheets. Effects of molecular junction length,
This work reports temperature-dependent thermal conductivity, specific heat and thermal diffusivity measurements of multi-wall carbon nanotube strands. The
Secondly, while microwaves are extremely good at heating liquid water, ice is almost totally transparent to them, so it is actually quite difficult to get ice to melt in a domestic microwave oven. The defrost option on a microwave oven relies on intermittent heating of a small amount of liquid water present on the food, and heat conduction from these areas into frozen material. By putting frozen material into the microwave oven with continuous energy input, no time is given for thermal conductivity effects, and therefore a colossal heating effect occurs on a very localised surface area. These areas, typically at the extreme point of the carrot, will dry out rapidly and then char, essentially forming small carbon points ...
The very shallow geothermal potential (vSGP) is increasingly recognized as a viable resource for providing clean thermal energy in urban and rural areas. This is primarily due to its reliability, low-cost installation, easy maintenance, and little constraints regarding ground-related laws and policies. We propose a methodology to extract the theoretical vSGP (installed in the uppermost 10 m of the ground, and mostly at depths of 1-2 m) at the national scale for Switzerland, based on a combination of Geographic Information Systems, traditional modelling, and machine learning (ML). The theoretical vSGP is based on the estimation of three thermal characteristics of the ground that impact significantly the geothermal potential, namely the monthly temperature at various depths in the surface layer, the thermal conductivity, and the thermal diffusivity. Each of the three variables is estimated separately, to a depth of 1 m below the surface, using the following general strategy: (1) collect significant data
The present work deals with the study of heat transfer, fluid flow and solidification phenomena of rapidly solidifying amorphous ribbons in the melt spinning process. Finite volume based mathematical model using Navier-Strokes equation coupled with heat transfer equations has been developed for the melt spinning process. The model uses volume of fluid method to capture free surface interface. The surface tension force has been coupled with the goveminff equation in order to get capillary effects on shape and size of the metal pool. The SIMpLE algorithm is used to solve the goveminff equations. The model Predicts the effects of different process parameter such as wheel RPM, wheel geometry, superheat, crucible gap and cooling conditions on ribbon thickness, wheel temperature and melt pool, Transient development of heat transfer coefficient over wheel surface and wheel temperature have been studied. The simulation result have been verified with the experimental data. Reasonably good match between ...
Polyurethane foam insulation is a two component polyurethane system formulated to obtain closed-cell rigid foams to be sprayed-in-place for thermal insulation. The system contains approved ecological foaming agents that are not ozone depletion potential and are mainly used to obtain excellent thermal insulation. (Polyurethane Spray Foam Insulation protected with acrylic coating.) Polyurethane Spray Systems are applied by spraying with a high pressure equipment fitted with heating, with a mixing ratio 1:1 in volume. Their main applications are the thermal insulation of building closings, houses (partitioning), industrial buildings, tanks, cool stores etc. The application type (Roofs, flooring, buildings etc.) defines the applied Density of the System. Rigid polyurethane foams applied outdoors are darkened and brittle by the action of UV radiation.. ...
TY - JOUR. T1 - Comparison of Calculation Methods for Basic Clothing Insulation with a Thermal Manikin. AU - Tanabe, Shin ichi. AU - Hasebe, Yae. AU - Nishimura, Mika. PY - 1994/1/1. Y1 - 1994/1/1. N2 - A comparative analysis is presented on the three conventional methods and our new one for eval uating the basic thermal insulation of cloting. A thermal manikin regulated at constant temperature over all parts was seated on a chair and, in the steady state, the environmental temperature, the amount of heat which the manikin lost, and the local skin temperature at nineteen points were measured for various cloth ing ensembles covering the body. From the data obtained were estimated the thermal insulation only by the skin when the manikin was unclothed and that by the total when clothed ; based on these the basic ther mal insulation of each clothing was evaluated by the current methods as well as ours and the results were compared. An investigation also on the role of the insulation by the outer ...
In this research, the performance of single-walled carbon nanotube (SWCN) as a sensor and nanocarrier for procarbazine (PC) was investigated by infra-red (IR), natural bond orbital (NBO), frontier molecular orbital (FMO) computations. All of the computations were done using the density functional theory method in the B3LYP/6-31G (d) level of theory The calculated negative values of adsorption energy, enthalpy changes, Gibbs free energy changes showed the PC interaction with SWCN is exothermic, spontaneous and experimentally possible. The increasing of specific heat capacity (CV) of SWCN after adsorption of PC showed the thermal conductivity improved during the interaction process and this nanostructure is an excellent sensing material for the detection of PC. The NBO results demonstrate in all of the evaluated conformers a chemical bond with SP3 hybridization is formed between the medicine and SWCN. The great values of thermodynamic constants showed the adsorption process is irreversible and SWCN is not
ISO 11611:2015 specifies minimum basic safety requirements and test methods for protective clothing including hoods, aprons, sleeves, and gaiters that are designed to protect the wearers body including head (hoods) and feet (gaiters) and that are to be worn during welding and allied processes with comparable risks., Thermal ,protective clothing, design, One-dimensional ,heat conduction, model, Difference ,equation,, ,Heat, balance analysis, Dichotomy search Cite This Paper Zhaoqing Tian, Siming Wang, Optimal Design Model of Thermal ,Protective Clothing, Based on ,Heat Conduction, Difference ,Equation,.
After their discovery in 1991 by Iijima [1], carbon nanotubes (CNTs) have attracted considerable interest because of their unique as well as superior physical, electrical, magnetic, chemical stability, thermal conductivity and mechanical properties [2]. Due to their exceptionally high aspect ratio and mechanical properties, incorporation of small amounts of CNTs into a polymer matrix is expected to enhance the properties of the resulting nanocomposites more than any existing material. The most critical issue of CNTs/polymer nanocomposites is the adhesion/compatibility between the nanotubes and polymer which ultimately controls the interface between the CNTs and the polymer matrix. Unfortunately pure CNTs are insoluble in any organic solvents and they tend to form agglomerates because of strong Van der Wall forces which results in negative effects on the properties of the resulting nanocomposites. As such achieving a high degree of dispersion of CNTs in any polymer matrix is quite a challenging ...
Ambient temperature physical properties of stainless steels to BS EN 10088-1 Ambient temperature physical properties, including density, modulus of elasticity (Youngs modulus), coefficient of thermal expansion, thermal conductivity, specific heat (heat content or heat capacity) and electrical resistivity for a range of ferritic, martensitic, austenitic and duplex stainless steel types are tabulated. Some explanation of the units used for these properties is given.. ...
The lubricants of the future have to be more environmentally adapted, show a higher level of performance, and give a lower total life cycle cost (LCC) than the lubricants that are used today. One way to be able to produce, choose and formulate these lubricants is to have good knowledge about the properties of the base fluids and their additive response. The base fluid properties can be divided into four different groups, i.e. physical, chemical, film formation properties and additive response. This thesis is based on the results from the Swedish HiMeC research project Environmentally adapted lubricants for high performance components. A number of different environmentally adapted ester fluids, suitable for formulation of environmentally adapted lubricants were investigated according to properties, molecular structure and film formation capability. I t was found that both thermal conductivity and specific heat capacity are high for the esters compared to mineral fluids. There is a strong ...
The thermal conductivity of carbon nanotubes exceeds that of diamond or any other natural material but because carbon nanotubes are so chemically stable, their chemical interactions with most other materials are relatively weak, which makes for high thermal interface resistance, Ogletree says. Intel came to the Molecular Foundry wanting to improve the performance of carbon nanotubes in devices. Working with Nachiket Raravikar and Ravi Prasher, who were both Intel engineers when the project was initiated, we were able to increase and strengthen the contact between carbon nanotubes and the surfaces of other materials. This reduces thermal resistance and substantially improves heat transport efficiency.. Sumanjeet Kaur, lead author of the Nature Communications paper and an expert on carbon nanotubes, with assistance from co-author and Molecular Foundry chemist Brett Helms, used reactive molecules to bridge the carbon nanotube/metal interface - aminopropyl-trialkoxy-silane (APS) for oxide-forming ...
An absorbent article including a liquid-permeable top layer, an absorbent core layer, a breathable outer cover, and a creped inner nonwoven fibrous layer between the absorbent core and breathable outer cover. The creped inner nonwoven fibrous layer has a level of creping of about 5-75%, and is preferably permanently creped. The creped inner nonwoven fibrous layer serves as a dampness inhibitor which reduces or prevents perceived dampness on the external surface of the outer cover by lowering thermal conductivity between the absorbent core and the outer cover surface.
Ricolfi, T. and Barber, R. (1990) Radiation Thermometers, in Sensors: Thermal Sensors, Volume 4 (eds T. Ricolfi and J. Scholz), Wiley-VCH Verlag GmbH, Weinheim, Germany. doi: 10.1002/9783527620159.ch5 ...
Right from the initial report of the existence of carbon nanotubes by Iijima, studies have been performed to understand their properties. Carbon nanotubes are tube-shaped nanostructures of carbon with electrical, mechanical, and thermal properties that derive from the special features of carbon bonds, their quasi-one-dimensional nature, and their cylindrical symmetry. These properties include very high elastic modulus, tensile strength, thermal conductivity, and electrical conductivity.. Because of their unique properties, carbon nanotubes have been considered as potential candidates for a variety of electrical, mechanical, and chemical applications. However, in order to use them commercially, many issues need to be resolved. One of the major issues is the controlling of the chirality of carbon nanotubes during its synthesis. Chirality is a special property of nanotube which describes how much it is twisted, and is defined by two integer numbers n and m, which are called chiral indices. Most of ...
Broader applications of carbon nanotubes to real-world problems have largely gone unfulfilled because of difficult material synthesis and laborious processing. We report high-performance multifunctional carbon nanotube (CNT) fibers that combine the specific strength, stiffness, and thermal conductivity of carbon fibers with the specific electrical conductivity of metals. These fibers consist of bulk-grown CNTs and are produced by high-throughput wet spinning, the same process used to produce high-performance industrial fibers. These scalable CNT fibers are positioned for high-value applications, such as aerospace electronics and field emission, and can evolve into engineered materials with broad long-term impact, from consumer electronics to long-range power transmission. ...
Here we present the results of pilot polycrystalline study of PrNi_4Si. The X-ray study did not confirm the expected CaCu_5-type structure. Instead of this, the orthorhombic structure with the space group Cmmm was found. The zero-field specific heat was measured in the temperature range 2-300 K. The data were analyzed using the sum of the phonon, electronic, and magnetic contributions to specific heat, respectively. The magnetic part of the specific heat can be well described using the Schottky formula for the 9 crystal-field singlet levels of the pz3 H4 ground-state multiplet of the Pr^{3+} ion ...
The crucible is a utensil or melting tank vessels that is made of refractory material (such as clay, graphite, clay, quartz or difficult molten metal iron, etc.).. Honsin Industry is specialized in high performance Graphite Crucible, which is divided into general type of graphite crucible, special type of graphite crucible, high purity graphite crucible.. The main raw materials of Graphite crucible is natural crystalline graphite. Therefore, it maintains the original natural graphite various physical and chemical properties.. Graphite crucible has good thermal conductivity and high temperature resistance. Under the high temperature, our Graphite Crucibles demonstrate very low thermal expansion coefficient with rapid heating and quench with certain anti-strain properties. The Graphite Crucibles provide also excellent chemical stability and strong corrosion resistance of acid.. We provide different series of graphite crucible according to customers requirements.. ...
Significant improvements in the fracture resistance, fracture toughness and thermal properties of silicon nitride ceramics are obtained by tailoring the microstructure. Combined use of seeding and tape casting techniques allowed the production of highly anisotropic microstructures. The seeded silicon nitrides exhibited a distinct bimodal microstructure, with large elongated β-Si3N4 grains, grown from seeds, dispersed within a fine-grained matrix. These large grains in the seeded silicon nitrides lie in the casting planes and self-align along the casting direction during tape forming process. It is here, when due to the high degree of alignment that special boundaries without the, otherwise, ubiquitous amorphous phase occurs. These special boundaries, hardly seen in three dimensionally random microstructures, are the object of the present study.. Silicon nitride with high thermal conductivity of up to 120 W/mK (ref. 3) is produced by hot-pressing at 1800 °C for 2 h. powders with the ...
Construction methods and materials in the hot, humid, wet region of northern Thailand are often rudimentary. Shelters are left susceptible to harsh weather conditions, and weather-worn materials revealing gaping holes into buildings are common sights. Therefore, better insulation and more durable wall materials are needed in such underdeveloped areas prone to extreme weather.; Phenolic foam warrants consideration as a building material because of several characteristic features. It is lightweight and has low thermal conductivity, allowing for applications as a building insulation material. Moreover, the material has low flammability, low smoke toxicity, and is cost-competitive with conventional foams, such as polyurethane and expanded polystyrene (EPS).; This paper evaluated the potential of using phenolic foam as a building material in northern Thailand. Phenolic foams mechanical and insulation properties, sustainable benefits, and costs were evaluated when used as an insulation material in ...
The simultaneous evaluation of heat/mass transference procures momentous significance in the polymer industry and engineering activities. Extensive utilization of such aspects includes propylene flares, heat exchangers, energy transfiguration in chilling towers, and amputation of post fortuitous heat in nuclear reactors. Owing to such prospective demands, we interpreted the Jeffrey liquid reactive flow under non-linear convection. We scrutinized the transference of heat/mass under generalized Fourier-Fick relations. Thermal conductivity depends on temperature while mass diffusivity is dependent on concentration. Besides, heat source along with first-order chemical reaction aspects are accounted for. Relevant transformations are exerted to achieve non-linear differential systems that are solved through the homotopy scheme. Influences of divers factors are exhibited via graphical benchmark.
Carbon nanotubes and graphene are both nano-scale structures consisting of carbon atoms. Graphene is a sheet-like hexagonal lattice of carbon atoms, while nanotubes can be described as graphene wrapped into a cylinder with a nano-scale diameter. Despite the fact that both are made from the same carbon atoms, each has very distinct characteristics. Of any material found in nature, carbon nanotubes feature the highest thermal conductivity and mechanical strength as well as the ability to withstand the highest current density, making them an attractive material for wiring, heat dissipation, field electron emitters(4), and other potential applications. Research and development is underway to find technologies to synthesize carbon nanotubes at temperatures as low as approximately 400°C, a temperature that would enable its use in electronic devices vulnerable to heat. Since the discovery of its high electron mobility in 2004, graphene has become attractive as a channel material for future ...
This study was devoted to the development of pulp Luffa Cclindrica and its characterization paper (annual plant fiber of the family Cucurbitaceae). Baking at soda helps to achieve a high level of delignification (Kappa ≤ 10) and high yield (≈ 67%).The beatability stack Valley is comparable to refined wood fibers, the fibers develop a normally time with good hydrophilic properties without excessive morphological variations. The Comparing to the same level of physical properties of refining pulp Luffa cylindrica with different pulps annual plants (straw, bagasse or kenaf), obtained by different processes, shows good mechanical properties of the fibers, in addition its behavior would tend to approach more the hardwood pulps. The measured thermal conductivity on the handsheets Luffa Cylindrica was found equal to 0.112 W / m K, value being also in the rather broad range of the data of the literature on different types of pulp, between 0.1 and 0.2 W / m K.
At the Wittenburg Group we have developed an interesting feature through the production of flame retardant compounds. It is possible to add this property to nearly all our compounds by using halogen-free, chlorinated or brominated additives. Industry shows a much greater interest in the halogen-free compounds, because of demanding environmental standards (REACH, RoHS and WEEE) as well as the requirements of higher impact strength and reduced mould corrosion.. We use the UL94 standard to determine the flame retardancy. Depending on the application this will be measured at 0,8, 1,6 or 3,0 mm wall thickness. The table below shows the requirements to obtain V-0, V-1 or V-2 classification.. ...
Diamonds are known of their special properties. They are physically robust and chemically inert, have a high thermal conductivity and can act as an insulators. Adding an impurity, such as Boron, into the diamond lattice causes an extra valency into the lattice because Boron has only three valence electrons. These valencies can facilitate the movement of electrons through the diamond lattice and make diamond an electric conductor.. Adding Boron into the lattice has its drawbacks. Because Boron is slightly smaller atom than Carbon each Boron distorts the lattice slightly thus weakening the bonds throughout the crystal lattice. Also since one covalent bond is effectively missing it is easy to see that higher the Boron concentration in the lattice, better the electric conductivity of the diamond (due to holes) but worse the other diamond properties. It is therefore important to determine the concentration of Boron that gives an optimal (metallic) conductivity to the material but still retains all of ...
sources]. The new carbon nanotube (CNT) fibers have a thermal conductivity approaching that of the best graphite fibers but with 10 times greater electrical conductivity, says study co-author Marcin Otto, business development manager at Teijin Aramid.. Graphite fibers are also brittle, while the new CNT fibers are as flexible and tough as a textile thread. We expect this combination of properties will lead to new products with unique capabilities for the aerospace, automotive, medical, and smart-clothing markets.. Hairball-like clumps. Carbon nanotubes, which are nearly as wide as a strand of DNA, are about 100 times stronger than steel at one-sixth the weight. Nanotubes conductive properties-for both electricity and heat-rival the best metal conductors. They also can serve as light-activated semiconductors, drug-delivery devices and even sponges to soak up oil.. Unfortunately, carbon nanotubes are also the prima donna of nanomaterials; they are difficult to work with, despite their ...
Most of the available commercial solid-state gas/vapor sensors are based on metal oxide semiconductors. Metal oxides (MOs) change their conductivity while exposed to gas or vapors ambient can be utilized as gas or vapor sensing materials. In recent days, graphene has attracted tremendous attention owing to its two-dimensional structure with an extremely high surface to volume ratio, electron mobility, and thermal conductivity. However, intrinsic graphene is relatively inefficient for the adsorption of gas/vapor molecules. In this regard, graphene oxide (GO) and reduced graphene oxide (rGO), which are graphene species functionalized with different oxygen groups that offer a higher amount of adsorption sites improving the sensitivity of the film. Up to now, many research groups across the globe have reported the promising performance towards gas detection using various GO/rGO-metal oxide nanocomposites. This chapter reviews the composites of graphene oxide or reduced graphene oxide and metal oxides in
Graphite electrode is a major conduction material used in the electric smelting industry, which has the properties of superior electric conductivity,thermal conductivity,high mechanical strength, oxidation and corrosion resistance in high temperature,graphite electrode is typically used in EAF.Has become an important part of industrial raw materials ...
Graphene has become one of the most widely studied 2D materials since its separation by Geim-Novoselov in 2004. It has been used in a wide range of applications due to its incredible carrier mobility, mechanical strength and thermal conductivity. The applications of graphene are ranging from electronics to energy storage and conversion. Chemical vapor deposition (CVD) is a common method for growing graphene on a metal surface as a catalyst, since it promotes growth of large area and high uniform graphene film. This requires an additional step to transfer graphene onto other target substrates toward fabrication of graphene-based devices. Graphene transfer process comprises many challenges such as presence of polymeric/metal residuals, generation of several extrinsic defects (tears, cracks and wrinkles) and weak adhesion between graphene and underlying target substrate. All these kinds of imperfections degrade graphene properties and hence affect the performance of the fabricated graphene-based ...
The aim of this study was to enhance the thermal comfort properties of crude glycerol (CG) derived polyurethane foams (PUFs) using phase change materials (PCMs) (2.5-10.0% (wt/wt)) to contribute to the reduction of the use of non-renewable resources and increase energy savings. The main challenge when adding PCM to PUFs is to combine the low conductivity of PUFs whilst taking advantage of the heat released/absorbed by PCMs to achieve efficient thermal regulation. The solution considered to overcome this limitation was to use expandable graphite (EG) (0.50-1.50% (wt/wt)). The results obtained show that the use of PCMs increased the heterogeneity of the foams cellular structure and that the incorporation of PCMs and EG increased the stiffness of the ensuing composite PUFs acting as filler-reinforcing materials. However, these fillers also caused a substantial increase of the thermal conductivity and density of the ensuing foams which limited their thermal energy storage. Therefore, numerical simulations
In this paper, the preparation and casting of sample composite, machining parameters and Scanning electron microscopy (SEM) studies on multi-walled carbon nanotubes (MWCNT) reinforced epoxy composites were discussed. Structurally, MWCNTs consist of multiple layers of graphite superimposed and rolled in on themselves to form a tubular shape. Three properties of MWCNTs are specifically interesting for the industry which are the electrical conductivity (as conductive as copper), their mechanical properties such as strength (up to 15 to 20 times stronger than steel and 5 times lighter) and their thermal conductivity (same as that diamond and more than 5 times that of copper). Dispersion of MWCNTs with epoxy resin were achieved using magnetic stirrer. MWCNT/epoxy composite was cured at 50 0C for four hours to form a Rigid MWCNT/epoxy composite. The effect of machining parameters on MWCNT/epoxy composite displays different surface morphology under SEM with control of 3 major parameters of spindle speed, feed
Graphene has excellent mechanical, thermal, optical and electrical properties and this has made it a prime target for use as a filler material in the development of multifunctional polymeric composites. However, several challenges need to be overcome to take full advantage of the aforementioned properties of graphene. These include achieving good dispersion and interfacial properties between the graphene filler and the polymeric matrix. In the present work, we report the thermal and mechanical properties of reduced graphene oxide/epoxy composites prepared via a facile, scalable and commercially viable method. Electron micrographs of the composites demonstrate that the reduced graphene oxide (rGO) is well dispersed throughout the composite. Although no improvements in glass transition temperature, tensile strength and thermal stability in air of the composites were observed, good improvements in thermal conductivity (about 36 %), tensile and storage moduli (more than 13 %) were recorded with the ...
Researchers from North Carolina State University have developed new techniques for stretching carbon nanotubes (CNT) and using them to create carbon composites that can be used as stronger, lighter materials in everything from airplanes to bicycles.. By stretching the CNT material before incorporating it into a composite for use in finished products, the researchers straighten the CNTs in the material, which significantly improves its tensile strength - and enhances the stiffness of the composite material and its electrical and thermal conductivity.. State-of-the-art carbon fiber composites are currently used to build airplanes and other products where strong, lightweight materials are desirable. Lighter airplanes, for example, are more fuel efficient. However, researchers have long thought that if these composites could be made with CNTs they could be just as strong, but 10 times lighter. Or they could be the same weight, but 10 times stronger.. Creating a strong CNT composite requires four ...
The paper presents an application of the finite elements method for stress and strain analysis of the hot water boiler structure. The aim of the research was to investigate the influence of the boiler scale on the thermal stresses and strains of the structure of hot water boilers. Results show that maximum thermal stresses appear in the zone of the pipe carrying wall of the first reversing chamber. This indicates that the most critical part of the boiler are weld spots of the smoke pipes and pipe carrying plate, which in the case of significant scale deposits can lead to cracks in the welds and water leakage from the boiler. The non-linear effects were taken into account by defining the bilinear isotropic hardening model for all boiler elements. Temperature dependency was defined for all relevant material properties, i. e. isotropic coefficient of thermal expansion, Youngs modulus, and isotropic thermal conductivity. The verification of the FEA model was performed by comparing the measured ...
References. Kulikovskiy, A.G., Lyubimov, G.A., Magnetohydrodynamics (1965), Addison-Wesley Reading, Massachusetts; Laudau, L.D., Lifshitz, E.M., Electrodynamics of Continuous Media (1984), second ed. Pergamon New York; Pratt, J., Busse, A., Müller, W.C., Fluctuation dynamo amplified by intermittent shear bursts in convectively driven magnetohydrodynamic turbulence (2013) Astronom. Astrophys., 557, p. A76; Temem, R., Infinite-Dimensional Dynamical Systems in Mechanics and Physics (1997), second ed. Springer-Verlag, New York, Inc; Mulone, G., Rionero, S., Necessary and sufficient conditions for nonlinear stability in the magnetic Bènard problem (2003) Arch. Ration. Mech. Anal., 166, pp. 197-218; Yamazaki, K., Global regularity of generalized magnetic Bènard problem (2017) Math. Methods Appl. Sci., 40, pp. 2013-2033; Zhou, Y., Fan, J., Nakamura, G., Global Cauchy problem for a 2D magnetic Bènard problem with zero thermal conductivity (2013) Appl. Math. Lett., 26, pp. 627-630; Bian, D., Gui, G., ...
U-values of building elements are often determined using point measurements, where infrared imagery may be used to identify a suitable location for these measurements. Current methods identify that surface areas exhibiting a homogeneous temperature-away from regions of thermal bridging-can be used to obtain U-values. In doing so, however, the resulting U-value is assumed to represent that entire building element, contrary to the information given by the initial infrared inspection. This can be problematic when applying these measured U-values to models for predicting energy performance. Three techniques have been used to measure the U-values of external building elements of a full-scale replica of a pre-1920s U.K. home under controlled conditions: point measurements, using heat flux meters, and two variations of infrared thermography at high and low resolutions. U-values determined from each technique were used to calibrate a model of that building and predictions of the heat transfer coefficient,
Earths similar to 3.45 billion year old magnetic field is regenerated by dynamo action in its convecting liquid metal outer core. However, convection induces an isentropic thermal gradient which, coupled with a high core thermal conductivity, results in rapid conducted heat loss. In the absence of implausibly high radioactivity or alternate sources of motion to drive the geodynamo, the Earths early core had to be significantly hotter than the melting point of the lower mantle. While the existence of a dense convecting basal magma ocean (BMO) has been proposed to account for high early core temperatures, the requisite physical and chemical properties for a BMO remain controversial. Here we relax the assumption of a well mixed convecting BMO and instead consider a BMO that is initially gravitationally stratified owing to processes such as mixing between metals and silicates at high temperatures in the core-mantle boundary region during Earths accretion. Using coupled models of crystallization and heat
TY - JOUR. T1 - Study on suppression of decay of trapped magnetic field in HTS bulk subject to AC magnetic field. AU - Zushi, Y.. AU - Asaba, I.. AU - Ogawa, J.. AU - Yamagishi, K.. AU - Tsukamoto, O.. AU - Murakami, M.. AU - Tomita, M.. PY - 2004/10/1. Y1 - 2004/10/1. N2 - The trapped magnetic field in a bulk is decayed and even erased by the application of the AC external magnetic field whose amplitude is much smaller than the trapped magnetic field. In the previous work, an experimental result showed that the decay of the trapped magnetic field was due to temperature rise of the bulk caused by the AC losses. Based on this result, it is considered that the decay can be suppressed by (a) improvement of the cooling of the bulk and (b) reduction of the AC losses. We verified the effectiveness of these methods by conducting an experiment using a recently developed metal impregnated bulk which has high critical current density and improved thermal conductivity.. AB - The trapped magnetic field in a ...
Body temperature measurements are obtained by scanning a thermal radiation sensor across the side of the forehead over the temporal artery. A peak temperature measurement is processed to compute an internal temperature of the body as a function of ambient temperature and the sensed surface temperature. The function includes a weighted difference of surface temperature and ambient temperature, the weighting being varied with target temperature through a minimum in the range of 96 F. and 100 F. The radiation sensor views the target surface through an emissivity compensating cup which is spaced from the skin by a circular lip of low thermal conductivity.
Thermal Conductivity for Opal Quartz is 3 times as normal quartz.with this quartz insert you can get pure flavor of vapor.. This insert can only used on ICA chamber.. Package Includes:. 1 x Opaque quartz Insert. DISCLAIMER: This item is not a puffco official product or endorsed by Puffco in any way,. This is an aftermarket product engineered by JCVAP Co.,Ltd to function in the Puffco Peak Pro device based on average measurements of many different Peak Pro units. By using this product, you acknowledge and agree that JCVAP is in no way liable or responsible for Puffco products or their respective warranties, nor is JCVAP responsible for Puffco product malfunctions and / or variance. ...