Thermal Conductivity and Specific Heat Measurements of Single Nanowires

2005 ◽  
Author(s):  
Chris Dames ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Bulk Material ◽  
Si Nanowires ◽  
Quantum Confinement Effects ◽  
Single Nanowires ◽  
Effective Use ◽  
20 Nm ◽  
Theory And Experiments ◽  
Good Agreement

For the effective use of nanowires and nanotubes in their many possible applications in sensing, computation and memory, optoelectronics, and energy conversion, it is important to understand their thermal properties, which may differ considerably from bulk [1]. For example, there is good agreement between theory and experiments on Si nanowires showing that the classical size effect of phonon boundary scattering may reduce the thermal conductivity by up to several orders of magnitude for diameters of 40 nm and up [2, 3, 12, 13]. However, more experiments are needed at 20 nm and smaller diameters. There is also a need for experiments on the specific heat of single nanowires, which is intimately related to thermal conductivity by kinetic theory, and may be altered by quantum confinement effects. We have previously measured the specific heat of a pellet of TiO2 nanotubes of ∼3 nm wall thickness and found it similar to the bulk material at temperatures above ∼80 K [4]; however, questions remain about the possible interactions between adjacent tubes, which single-tube studies would resolve.

Theory of Thermal Conductivity of Micro- and Nano-structured Materials

2009 ◽  
Vol 1172 ◽  
Author(s):  
Gyaneshwar P. Srivastava
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Polycrystalline Diamond ◽  
Comprehensive Treatment ◽  
Si Nanowires ◽  
Quantitative Investigation ◽  
Debye Relaxation ◽  
Structured Materials ◽  
20 Nm

AbstractWe provide a brief discussion of the Boltzmann equation derived Callaway-Debye relaxation time theory of lattice thermal conductivity of micro- and nano-structured materials (of size greater than 20 nm. Incorporated in the theory is a comprehensive treatment of three-phonon scattering events. Using numerical results from this theory, we present a quantitative investigation of the magnitude and temperature variation of the conductivity of CVD polycrystalline diamond films, suspended GaAs nanostructures, Si nanowires, and AlN micro- and nano-ceramics.

Theoretical Phonon Thermal Conductivity of Si/Ge Superlattice Nanowires

2003 ◽  
Author(s):  
Chris Dames ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Radiative Heat ◽  
Interface Condition ◽  
Segment Length ◽  
Phonon Thermal Conductivity ◽  
Quantum Confinement Effects ◽  
Frequency Independent ◽  
Side Walls ◽  
The Common ◽  
20 Nm

The net-radiation method of radiative heat transfer has been combined with the diffuse mismatch interface condition to develop a model for the phonon thermal conductivity of superlattice nanowires. The important size effect is increased classical scattering at interfaces and side walls, which is treated as diffuse and gray (frequency independent). Coherence and quantum confinement effects are neglected, which should be appropriate for typical nanowires at room temperature. An isotropic, sine-type dispersion relation is used which is a significant improvement over the common Debye dispersion. Without any adjustable parameters, the model captures the effects of diameter, segment length, and transmissivity. A simpler picture is offered in terms of Matthiessen’s rule and effective mean free paths. The limitations of the model are also discussed. For a model Si/Ge superlattice nanowire at 300 K, the thermal conductivity is reduced below the alloy limit (7.0 W/m-K) when the diameter is less than 15 nm and/or the segment length is less than 20 nm.

PHONON HEAT CONDUCTIVITY OF InSb AND CdS

2011 ◽  
Vol 25 (10) ◽  
pp. 1409-1418 ◽  
Author(s):  
M. ATAULLAH ANSARI ◽  
VINOD ASHOKAN ◽  
B. D. INDU
Keyword(s):  
Thermal Conductivity ◽  
Heat Conductivity ◽  
Lattice Thermal Conductivity ◽  
Relaxation Times ◽  
Temperature Range ◽  
Callaway Model ◽  
Theory And Experiments ◽  
Good Agreement

The lattice thermal conductivity of InSb and CdS has been analyzed on the basis of the most acquiescent Callaway model in the temperature range 2–300.779 K and 2.296–283.565 K. To reinvigorate the effects of phonon anharmonicities, more rigorous expressions for the phonon–phonon interactions, resonance, impurity and interference scattering relaxation times have been introduced to theoretically justify the experimentally observed results. A fairly good agreement between theory and experiments has been presented.

Modeling of Effective Stagnant Thermal Conductivity of Porous Media

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Yasuyuki Takatsu ◽  
Takashi Masuoka ◽  
Takahiro Nomura ◽  
Yuji Yamada
Keyword(s):  
Thermal Conductivity ◽  
Porous Media ◽  
Heat Conduction ◽  
Local Thermal Equilibrium ◽  
Two Phase ◽  
Spatially Periodic ◽  
Phase Systems ◽  
Multi Phase ◽  
Theory And Experiments ◽  
Good Agreement

Based on one-dimensional analysis of heat conduction, a general formula for the effective stagnant thermal conductivity of spatially periodic porous media is derived without assuming local thermal equilibrium. Furthermore, we discuss the contribution of the contact area between particles to the effective stagnant thermal conductivity in detail, and the modification of the formula is proposed to predict the actual effective stagnant thermal conductivity for the porous media. The present results are in good agreement with experimental results of Nozad et al. (1985, “Heat Conduction in Multi-Phase Systems I: Theory and Experiments for Two-Phase Systems,” Chem. Eng. Sci., 40(5), pp. 843–855) for a packed-sphere bed.

Теплофизические характеристики теплозащитного материала корпуса ракетного двигателя при температурах до 1000 оС

2021 ◽  
pp. 11-18
Author(s):  
Геннадий Александрович Фролов ◽  
Юрий Игоревич Евдокименко ◽  
Вячеслав Михайлович Кисель ◽  
Ирина Александровна Гусарова
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Temperature Fields ◽  
Thermophysical Characteristics ◽  
Furnace Heating ◽  
Temperature Dependences ◽  
Good Agreement

An experimental determination of the temperature dependences of the specific heat capacity and the thermal conductivity coefficient of the multifunctional coating MFP-92 at temperatures up to 1000 °C has been carried out. At temperatures up to 450 °C, an IT-c-400 device was used to determine the specific heat capacity. IT-l-400 device was used for the determination of thermal conductivity. At higher temperatures, the determination of the thermophysical characteristics (TPC) was carried out by solving the inverse problem of thermal conductivity (IPT) in a flat plate under conditions of one-sided heating in a muffle furnace. Composite material MFP-92 is a multilayer structure with upper layers based on silica fabric and chromophosphate binder and lower layers based on mullite-silica fabric and aluminosilicate binder. The TPC of the layers also differ from each other, and, accordingly, the properties of this material as a whole can be determined only in the form of their effective values, averaged in one way or another over the thickness of the coating. In addition, during heating, the material undergoes significant physicochemical transformations associated with the thermal destruction of its components, manifested in the form of abundant gas release, and a decrease in the density of the material, which significantly changes its TPC and determines its dependence on the heating rate. Therefore, studies of the thermophysical characteristics of the MFP-92 material were carried out with several (2-5) consecutive heating cycles. It was found that in four heating cycles of the MFP-92 material up to 450 °C for 75 minutes when measuring the specific heat on the IT-c-400 device, its temperature dependence significantly changes qualitatively and quantitatively. With furnace heating to 1000 °C, the temperature dependences of the TPC of the material, determined in the first and second heating cycles, have a different form, but change insignificantly in subsequent heating cycles. This makes it possible to ascribe to the MFP-92 material a set of two sets of TPC related to its initial (phase A) and annealed after heating to 1000 °C (phase B) states. Using the obtained TPС of phase A (including the magnitude of the thermal effect of irreversible endothermic phase transition at 100 °C) and phase B, good agreement was obtained between the calculated and experimental temperature fields in the samples under furnace heating conditions.

Thermal conductivity and specific heat of oil sand samples

1981 ◽  
Vol 18 (5) ◽  
pp. 926-931 ◽  
Author(s):  
M. R. Cervenan ◽  
F. E. Vermeulen ◽  
F. S. Chute
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Oil Sands ◽  
Water Saturation ◽  
Fluid Model ◽  
Electrical Power ◽  
Mining Operation ◽  
Electrical Heating ◽  
Oil Sand ◽  
Good Agreement

The thermal conductivity and specific heat of reconstituted samples of Athabasca oil sands were measured at room temperature. The samples originated from the SUNCOR mining operation and varied in bitumen and moisture contents. Thermal conductivity was deduced from the dependence of the thermal resistance of samples on sample thickness, with the samples being held in a hot plate configuration.The values obtained for thermal conductivity are correlated with pore-water saturation and are compared to values of thermal conductivity calculated from a single-fluid model involving only water saturation. Good agreement with the single-fluid model was observed for bitumen-free samples; however, samples containing bitumen at low water saturation show higher thermal conductivities than those predicted by the single-fluid model, suggesting a significant contribution by the bitumen to the thermal conductivity of these oil sand samples.Values of specific heat were obtained by conductive electrical heating of oil sand samples and by relating the increase in temperature to the electrical power supplied.

Thermal Characterization of Carbon-Carbon Composites

2011 ◽  
Author(s):  
Messiha Saad ◽  
Darryl Baker ◽  
Rhys Reaves
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Critical Role ◽  
Carbon Composite ◽  
Flash Method ◽  
Carbon Composites ◽  
Energy Storage Devices ◽  
Graphitized Carbon

Thermal properties of materials such as specific heat, thermal diffusivity, and thermal conductivity are very important in the engineering design process and analysis of aerospace vehicles as well as space systems. These properties are also important in power generation, transportation, and energy storage devices including fuel cells and solar cells. Thermal conductivity plays a critical role in the performance of materials in high temperature applications. Thermal conductivity is the property that determines the working temperature levels of the material, and it is an important parameter in problems involving heat transfer and thermal structures. The objective of this research is to develop thermal properties data base for carbon-carbon and graphitized carbon-carbon composite materials. The carbon-carbon composites tested were produced by the Resin Transfer Molding (RTM) process using T300 2-D carbon fabric and Primaset PT-30 cyanate ester. The graphitized carbon-carbon composite was heat treated to 2500°C. The flash method was used to measure the thermal diffusivity of the materials; this method is based on America Society for Testing and Materials, ASTM E1461 standard. In addition, the differential scanning calorimeter was used in accordance with the ASTM E1269 standard to determine the specific heat. The thermal conductivity was determined using the measured values of their thermal diffusivity, specific heat, and the density of the materials.

scholarly journals Influence of alkaline modification on selected properties of banana fiber paperbricks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Abayomi A. Akinwande ◽  
Adeolu A. Adediran ◽  
Oluwatosin A. Balogun ◽  
Oluwaseyi S. Olusoju ◽  
Olanrewaju S. Adesina
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Moisture Absorption ◽  
Water Volume ◽  
Banana Fiber ◽  
Fiber Loading ◽  
Banana Fibers ◽  
Alkaline Modification

AbstractIn a bid to develop paper bricks as alternative masonry units, unmodified banana fibers (UMBF) and alkaline (1 Molar aqueous sodium hydroxide) modified banana fibers (AMBF), fine sand, and ordinary Portland cement were blended with waste paper pulp. The fibers were introduced in varying proportions of 0, 0.5, 1.0 1.5, 2.0, and 2.5 wt% (by weight of the pulp) and curing was done for 28 and 56 days. Properties such as water and moisture absorption, compressive, flexural, and splitting tensile strengths, thermal conductivity, and specific heat capacity were appraised. The outcome of the examinations carried out revealed that water absorption rose with fiber loading while AMBF reinforced samples absorbed lesser water volume than UMBF reinforced samples; a feat occasioned by alkaline treatment of banana fiber. Moisture absorption increased with paper bricks doped with UMBF, while in the case of AMBF-paper bricks, property value was noted to depreciate with increment in AMBF proportion. Fiber loading resulted in improvement of compressive, flexural, and splitting tensile strengths and it was noted that AMBF reinforced samples performed better. The result of the thermal test showed that incorporation of UMBF led to depreciation in thermal conductivity while AMBF infusion in the bricks initiated increment in value. Opposite behaviour was observed for specific heat capacity as UMBF enhanced heat capacity while AMBF led to depreciation. Experimental trend analysis carried out indicates that curing length and alkaline modification of fiber were effective in maximizing the properties of paperbricks for masonry construction.

scholarly journals Thermophysical Properties of Cement Mortar Containing Waste Glass Powder

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 488
Author(s):  
Oumaima Nasry ◽  
Abderrahim Samaouali ◽  
Sara Belarouf ◽  
Abdelkrim Moufakkir ◽  
Hanane Sghiouri El Idrissi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Thermophysical Properties ◽  
Glass Powder ◽  
Cement Mortar ◽  
Soda Lime ◽  
Waste Glass ◽  
Soda Lime Glass ◽  
Volumetric Specific Heat ◽  
Waste Glass Powder

This study aims to provide a thermophysical characterization of a new economical and green mortar. This material is characterized by partially replacing the cement with recycled soda lime glass. The cement was partially substituted (10, 20, 30, 40, 50 and 60% in weight) by glass powder with a water/cement ratio of 0.4. The glass powder and four of the seven samples were analyzed using a scanning electron microscope (SEM). The thermophysical properties, such as thermal conductivity and volumetric specific heat, were experimentally measured in both dry and wet (water saturated) states. These properties were determined as a function of the glass powder percentage by using a CT-Meter at different temperatures (20 °C, 30 °C, 40 °C and 50 °C) in a temperature-controlled box. The results show that the thermophysical parameters decreased linearly when 60% glass powder was added to cement mortar: 37% for thermal conductivity, 18% for volumetric specific heat and 22% for thermal diffusivity. The density of the mortar also decreased by about 11% in dry state and 5% in wet state. The use of waste glass powder as a cement replacement affects the thermophysical properties of cement mortar due to its porosity as compared with the control mortar. The results indicate that thermal conductivity and volumetric specific heat increases with temperature increase and/or the substitution rate decrease. Therefore, the addition of waste glass powder can significantly affect the thermophysical properties of ordinary cement mortar.

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