Effects of microstructural evolution on the thermal conductivity of α–Al2O3 prepared from nano-size γ–Al2O3 powder

2000 ◽  
Vol 15 (3) ◽  
pp. 744-750 ◽  
Author(s):  
Eduardo J. Gonzalez ◽  
Grady White ◽  
Lanhua Wei
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Microstructural Evolution ◽  
Vickers Hardness ◽  
Room Temperature ◽  
Volume Fraction ◽  
Al2o3 Powder ◽  
Α Al2o3 ◽  
Thermal Diffusivities ◽  
Nano Size

The thermal diffusivities (D) of porous α–Al2O3 specimens prepared from nano-size γ–Al2O3 powder and from conventional submicrometer-size alumina powders were measured at room temperature, and the thermal conductivity (κ) was calculated from D. Plots of κ versus the volume fraction of porosity (P) showed that the data from both sets of samples followed similar linear curves. Similarly, data of Vickers hardness versus P obtained from the same specimens also followed a single linear curve. The good correlation of thermal diffusivity with P suggests that grain boundaries have a lesser effect on thermal transport than porosity.

Simultaneous Measurement of the Effective Thermal Conductivity and Effective Thermal Diffusivity of Nanofluids

2008 ◽  
Author(s):  
S. M. Sohel Murshed ◽  
Kai Choong Leong ◽  
Chun Yang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Effective Thermal Conductivity ◽  
Simultaneous Measurement ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Maximum Increase ◽  
Effective Thermal Diffusivity ◽  
Thermal Diffusivities ◽  
Volumetric Loading

A transient double hot-wire technique was developed for precise and simultaneous measurement of the effective thermal conductivity and effective thermal diffusivity of nanofluids. The measured effective thermal conductivities and effective thermal diffusivities of nanofluids were found to be higher than those of base fluids and they increase significantly with increasing volume fraction of nanoparticles. The increments of the thermal diffusivities were found to be slightly larger compared to the thermal conductivity values. For example, at 5% volumetric loading of TiO2 nanoparticles of 15 nm and 10 × 40 nm in ethylene glycol, the maximum increase in effective thermal conductivity was found to be 17% and 20%, whereas the maximum increase in effective thermal diffusivity was 25% and 29%, respectively. Besides particle volume fraction, particle material, particle size and the nature of the base fluid were found to have influence on the effective thermal conductivity and diffusivity of nanofluids. Based on the calibration results obtained for the base fluids the measurement error was estimated to be within 1.2 to 2%.

Thermal Diffusivity of Dispersed Materials

1978 ◽  
Vol 100 (4) ◽  
pp. 720-724 ◽  
Author(s):  
T. Y. R. Lee ◽  
R. E. Taylor
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Room Temperature ◽  
Volume Fraction ◽  
Transient State ◽  
Second Phase ◽  
Effective Thermal Diffusivity ◽  
Variable Dispersion ◽  
Flash Technique ◽  
Effective Diffusivities

Measurements have been made of the effective thermal diffusivity at room temperature of composites consisting of one phase randomly dispersed in a second phase. The method is based on the flash technique. Data are presented for four types of composites ranging in particle-to-matrix diffusivity ratios from 0.48 to 1137, in volume specific heat ratios 0.04 to 1.16, and in volume fraction of dispersed particle from zero up to 34 percent. The results show that the limitations of the concept of an effective thermal diffusivity are far beyond the situations to which it is currently applied in the transient state heat conduction problems. Values of effective diffusivities derived from values of the effective thermal conductivity calculated from the Bruggeman variable-dispersion equation are found to agree well with the measured diffusivity values.

Thermo-Physical Properties of Copper Matrix Composites Reinforced with 3D-SiC Network

2010 ◽  
Vol 150-151 ◽  
pp. 144-149
Author(s):  
Hong Wei Xing ◽  
Jin Song Zhang ◽  
Xiao Ming Cao
Keyword(s):  
Thermal Conductivity ◽  
Physical Properties ◽  
Room Temperature ◽  
Volume Fraction ◽  
Copper Matrix ◽  
High Thermal Stability ◽  
Matrix Composites ◽  
Copper Matrix Composites ◽  
Specific Heat Capacities ◽  
Thermo Physical Properties

Copper matrix composites reinforced with 3D-SiC network (15v% and 20v% SiC) were fabricated by squeezing copper alloy into 3D-SiC network preforms. The thermo-physical properties of the copper matrix composites were investigated. The specific heat capacities of the composites were about 0.39~0.50 J•g-1•K-1. The coefficients of thermal expansion (CTEs) of the composites were found to be lower than 6.9×10-6 -1 at Room Temperature. The composites exhibited high thermal stability for 3D-SiC network advent. The thermal conductivity of the composites was in the range of 50~80W•m−1•K−1. The thermo-physical properties of Cu matrix composites had a great relationship with the structures of 3D-SiC network preforms. The thermal conductivity of the composites decreased with an increase in the volume fraction of SiC or the structures of the limbs changing compacted, but the CTEs were not completely according this rule.

Thermal Diffusivity and Conductivity of La0.7Ca0.3-xSrxMnO3 (x=0 to 0.10)

2012 ◽  
Vol 501 ◽  
pp. 319-323
Author(s):  
Hasan A. Alwi ◽  
Lay S. Ewe ◽  
Zahari Ibrahim ◽  
Noor B. Ibrahim ◽  
Roslan Abd-Shukor
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Grain Size ◽  
Transition Temperature ◽  
Thermal Diffusivity ◽  
Electrical Properties ◽  
Room Temperature ◽  
Electronic Contribution ◽  
Insulator Metal Transition ◽  
Thermal And Electrical Properties

We report the room temperature thermal conductivity κ and thermal diffusivity α of polycrystalline La0.7Ca0.3-xSrxMnO3 for x = 0 to 0.1. The samples were prepared by heating at 1220 and 1320oC. The insulator-metal transition temperature, TIM and thermal diffusivity increased with Sr content. Phonon was the dominant contributor to thermal conductivity and the electronic contribution was less than 1%. Enhancement of electrical conductivity σ and thermal diffusivity for x ≥ 0.08 was observed in both series of samples. The grain size of the samples (28 to 46 µm) does not show any affect on the thermal and electrical properties.

Influence of Mesocarp Fibre Inclusion on Thermal Properties of Foamed Concrete

2021 ◽  
Vol 87 (1) ◽  
pp. 1-11
Author(s):  
Siti Shahirah Suhaili ◽  
Md Azree Othuman Mydin ◽  
Hanizam Awang
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Volume Fraction ◽  
Thermal Constant ◽  
Volume Fractions ◽  
Foamed Concrete

The addition of mesocarp fibre as a bio-composite material in foamed concrete can be well used in building components to provide energy efficiency in the buildings if the fibre could also offer excellent thermal properties to the foamed concrete. It has practical significance as making it a suitable material for building that can reduce heat gain through the envelope into the building thus improved the internal thermal comfort. Hence, the aim of the present study is to investigate the influence of different volume fractions of mesocarp fibre on thermal properties of foamed concrete. The mesocarp fibre was prepared with 10, 20, 30, 40, 50 and 60% by volume fraction and then incorporated into the 600, 1200 and 1800 kg/m3 density of foamed concrete with constant cement-sand ratio of 1:1.5 and water-cement ratio of 0.45. Hot disk thermal constant analyser was used to attain the thermal conductivity, thermal diffusivity and specific heat capacity of foamed concrete of various volume fractions and densities. From the experimental results, it had shown that addition of mesocarp fibre of 10-40% by volume fraction resulting in low thermal conductivity and specific heat capacity and high the thermal diffusivity of foamed concrete with 600 and 1800 kg/m3 density compared to the control mix while the optimum amount of mesocarp fibre only limit up to 30% by volume fraction for 1200 kg/m3 density compared to control mix. The results demonstrated a very high correlation between thermal conductivity, thermal diffusivity and specific heat capacity which R2 value more than 90%.

Thermal Diffusivity of Copper/Linear-low-density Polyethylene Composites

2017 ◽  
Vol 25 (6) ◽  
pp. 447-452
Author(s):  
James K. Carson ◽  
Mohamed Alsowailem
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
High Density Polyethylene ◽  
Relative Increase ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Linear Low Density Polyethylene ◽  
Capacity Data ◽  
Thermal Diffusivities ◽  
Polyethylene Composites

The thermal diffusivities of copper/linear-low-density polyethylene (Cu/LLDPE) composites were measured relative to the thermal diffusivity of pure LLDPE. The relative thermal diffusivities were similar to those obtained for copper/high-density polyethylene composites, but were noticeably different from estimated values derived from thermal conductivity, density and specific heat capacity data for Cu/LLDPE from the literature. The thermal diffusivity of the composite material initially decreased below that of the pure polymer with the addition of a small amount of copper, before increasing above it as more was added. There would appear to be marginal or no benefit from adding less than about 15 to 20% metal by volume to a polymer, since the relative increase in thermal diffusivity only becomes significant for greater volumes.

scholarly journals Phonon hydrodynamics and ultrahigh–room-temperature thermal conductivity in thin graphite

Science ◽  
2020 ◽  
Vol 367 (6475) ◽  
pp. 309-312 ◽  
Author(s):  
Yo Machida ◽  
Nayuta Matsumoto ◽  
Takayuki Isono ◽  
Kamran Behnia
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Wide Temperature Range ◽  
Room Temperature ◽  
Phonon Dispersion ◽  
High Conductivity ◽  
Temperature Range ◽  
A Value ◽  
Out Of Plane ◽  
Intimate Link

Allotropes of carbon, such as diamond and graphene, are among the best conductors of heat. We monitored the evolution of thermal conductivity in thin graphite as a function of temperature and thickness and found an intimate link between high conductivity, thickness, and phonon hydrodynamics. The room-temperature in-plane thermal conductivity of 8.5-micrometer-thick graphite was 4300 watts per meter-kelvin—a value well above that for diamond and slightly larger than in isotopically purified graphene. Warming enhances thermal diffusivity across a wide temperature range, supporting partially hydrodynamic phonon flow. The enhancement of thermal conductivity that we observed with decreasing thickness points to a correlation between the out-of-plane momentum of phonons and the fraction of momentum-relaxing collisions. We argue that this is due to the extreme phonon dispersion anisotropy in graphite.

Effect of timeliness on the thermal properties of paraffin-based Al2O3 nanofluids

2019 ◽  
Vol 33 (05) ◽  
pp. 1950051
Author(s):  
Yangyang Wu ◽  
Baichao Wang ◽  
Dong Li ◽  
Changyu Liu
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Volume Concentration ◽  
Volume Fraction ◽  
Thermal Conversion ◽  
Volumetric Heat Capacity ◽  
Energy Storage Material ◽  
Over Time

Paraffin is an excellent photo-thermal conversion phase change energy storage material, and extensively used in the thermal storage field at the medium-low temperature. However, the low thermal conductivity of paraffin restricts its application in practice. Adding nanoparticles into paraffin is one of the effective methods to improve its thermal conductivity. Nevertheless, the thermal diffusivity, specific heat and volumetric heat capacity of paraffin as well as timeliness were affected after the addition of nanoparticles. In this paper, the influences of volume fraction of Al2O3 nanoparticle and timeliness on these thermal parameters of paraffin were investigated. The results show that the thermal conductivity of paraffin-based Al2O3 nanofluids increases first and then decreases with time, and the maximum thermal conductivity is 0.34 W/[Formula: see text] for volume fraction 1% on third day. The higher volume concentration, the lower specific heat and volumetric heat capacity, all present downtrend over time, until stable in the range of 0.3 MJ/[Formula: see text] and 0.4 MJ/[Formula: see text]. The average enhancement rate of specific heat and volumetric heat capacity are concentrates on −6% to 9%, −10% to 0%, respectively. While increasing the volume concentration, the thermal diffusivity has no obvious regularity, and presents undulatory property over time.

Measurement of Effective Thermal Conductivity of CNT-Nanofluids by Transient Short-Wire Method

2009 ◽  
Author(s):  
Masamichi Kohno ◽  
Koichi Kimura ◽  
Shogo Moroe ◽  
Yasuyuki Takata ◽  
Peter L. Woodfield ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Hot Wire ◽  
Wire Method ◽  
Different Shapes ◽  
Transient Short Hot Wire ◽  
Al2o3 Particles ◽  
Particle Shapes

Thermal conductivity and thermal diffusivity of CNT-nanofluids and Al2O3-nanofulids were measured by the transient short-hot-wire method. The uncertainty of their measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. Three different shapes of Al2O3 particles were prepared for Al2O3–water nanofluids. For the thermal conductivity of Al2O3-water nanofluids, there are differences in the enhancement of thermal conductivity for differences in particle shapes. Hardly any enhancement of thermal conductivity was observed for SWCNT-water nanofluids because the volume fraction of SWCNT was extremely low. However, we consider by increasing the volume fraction of SWCNTs, it will be possible to enhance the thermal conductivity.

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