Thermal Conductivity and Thermal Transport Relaxation Time of CNT Packed Beds

2012 ◽  
Author(s):  
K. Liu ◽  
S. Cui ◽  
X. Qi ◽  
C. Chen ◽  
X. Hu
Keyword(s):  
Relaxation Time ◽  
Thermal Transport ◽  
Room Temperature ◽  
Experimental Measurements ◽  
Phase Lag ◽  
Heat Transfer Characteristics ◽  
Thermal Energy Conversion ◽  
Order Of Magnitude ◽  
Transient Thermal ◽  
Transport Relaxation

We report on experimental measurements of transient heat transfer characteristics of carbon nanotube (CNT) aggregates for the temperature range from 120K to 370K. Giant thermal transport relaxation time (τ) is observed: about 100s at room temperature and increased up to 260s at lower temperatures, one order of magnitude bigger than the biggest value reported so far in literatures. These unusual big τ values may imply significant thermal transport phase lag across CNT contacts. A relaxation time based model is proposed to characterize the transient thermal transport behavior between contacting CNTs. This finding may stimulate new ways to improve the efficiency of thermal energy conversion by using nanoscale materials.

scholarly journals Observation of second sound in a rapidly varying temperature field in Ge

2021 ◽  
Vol 7 (27) ◽  
pp. eabg4677
Author(s):  
Albert Beardo ◽  
Miquel López-Suárez ◽  
Luis Alberto Pérez ◽  
Lluc Sendra ◽  
Maria Isabel Alonso ◽  
...  
Keyword(s):  
Temperature Field ◽  
Relaxation Time ◽  
High Frequency ◽  
Room Temperature ◽  
Heat Waves ◽  
Thermal Response ◽  
Thermal Excitation ◽  
Phase Lag ◽  
Second Sound ◽  
Temperature Waves

Second sound is known as the thermal transport regime where heat is carried by temperature waves. Its experimental observation was previously restricted to a small number of materials, usually in rather narrow temperature windows. We show that it is possible to overcome these limitations by driving the system with a rapidly varying temperature field. High-frequency second sound is demonstrated in bulk natural Ge between 7 K and room temperature by studying the phase lag of the thermal response under a harmonic high-frequency external thermal excitation and addressing the relaxation time and the propagation velocity of the heat waves. These results provide a route to investigate the potential of wave-like heat transport in almost any material, opening opportunities to control heat through its oscillatory nature.

Influence of Superhydrophobic Walls on the Thermal Transport to Liquid Droplets

2011 ◽  
Author(s):  
D. Maynes ◽  
N. Tullett ◽  
R. Nielson ◽  
J. Vanderhoff ◽  
B. W. Webb
Keyword(s):  
Thermal Transport ◽  
Saturation Temperature ◽  
Thermal Response ◽  
Superhydrophobic Surfaces ◽  
Hydrophilic Surface ◽  
Liquid Droplets ◽  
Transfer Coefficients ◽  
Surface Temperatures ◽  
Order Of Magnitude ◽  
Transient Thermal

This paper presents an experimental investigation of the thermal transport to liquid droplets resting on heated horizontal superhydrophobic surfaces. The superhydrophobic surfaces considered here exhibit alternating micro-ribs and cavities. Specifically, we consider the transient thermal response to water droplets as they are placed on heated superhydrophobic surfaces. For comparative purpose we also consider the same scenario with smooth hydrophobic and smooth hydrophilic surfaces. Experiments were conducted over a range of surface temperatures varying from 60 to 165 °C. The results show radically different behavior in the transient thermal transport for the three surface types considered. At all temperatures the total droplet evaporation time on the superhydrophobic surfaces was nearly an order of magnitude greater than on the smooth hydrophilic surface. At temperatures elevated above the saturation temperature, where vigorous boiling was evident on the hydrophilic surface, the droplets on the superhydrophobic surfaces remained at bulk temperatures significantly lower than the saturation temperature. Further, the droplets on the superhydrophobic surfaces exhibited Leidenfrost-like behavior at surface temperatures far below the typical Leidenfrost point. Analysis of the data reveals overall heat transfer coefficients that are much lower on the superhydrophobic surfaces than on the other surfaces, over the entire range of temperatures explored.

Luminescence Properties of Europium-Doped Yttrium Oxides Derived from Their Dodecylsulfate-Templated Mesostructure and Nanotube Forms

2003 ◽  
Vol 775 ◽  
Author(s):  
Tsuyoshi Kijima ◽  
Kenichi Iwanaga ◽  
Tomomi Hamasuna ◽  
Shinji Mohri ◽  
Mitsunori Yada ◽  
...  
Keyword(s):  
Room Temperature ◽  
Broad Band ◽  
Concentration Quenching ◽  
Precipitation Method ◽  
Homogeneous Precipitation ◽  
Bulk Materials ◽  
Main Band ◽  
Homogeneous Precipitation Method ◽  
Order Of Magnitude ◽  
Weak Luminescence

AbstractEuropium-doped hexagonal-mesostructured and nanotubular yttrium oxides templated by dodecylsulfate species as well as surfactant free bulk oxides were synthesized by the homogeneous precipitation method. All the as grown nanostructured or bulk materials with amorphous or poorly crystalline frameworks showed weak luminescence bands at room temperature. On calcination at 1000°C these materials were converted into highly crystalline yttrium oxides, resulting in a total increase in intensity of all the bands by one order of magnitude. In the hexagonal-mesostructured system, the main band due to the 5D0-7F2 transition for the calcined phases showed a sharp but asymmetrical multiplet splitting indicating multiple Eu sites. Concentration quenching was found at a Eu content of 3 mol% or above for these phases. In contrast, the main emission for the calcined solids in the nanotubular system occurred as poorly resolved broad band and the intensity of the main band at higher Eu content was significantly enhanced compared with those for the other two systems.

Temperature Dependence of the Self-Assembled Styrene Based Random Ionomers in Aqueous Solution

2003 ◽  
Vol 775 ◽  
Author(s):  
Sung-Hwa Oh ◽  
Ju-Myung Song ◽  
Joon-Seop Kim ◽  
Hyang-Rim Oh ◽  
Jeong-A Yu
Keyword(s):  
Partition Coefficients ◽  
Room Temperature ◽  
Aqueous Media ◽  
The Self ◽  
Spectroscopic Methods ◽  
Ion Content ◽  
Repeat Units ◽  
Notable Effect ◽  
Order Of Magnitude ◽  
Experimental Errors

AbstractSolution behaviors of poly(styrene-co-sodium methacrylate) were studied by fluorescence spectroscopic methods using pyrene as a probe. The mol% of methacrylate was in the range 3.6–9.4. Water and N,N-dimethylforamide(DMF) mixture was used as a solvent (DMF/water = 0.2 mol %). The critical micelle (or aggregation) concentrations of ionomers and the partition coefficients of pyrene were obtained the temperature range 10–80°C. At room temperature, the values of CMCs (or CACs) were in the range 4.7 ×10-6 5.3 ×10-6 g/mL and we could not find any notable effect of the content of ionic repeat units within the experimental errors. Unlike CMCs, as the ion content increased, partitioning of pyrene between the hydrophobic aggregates and an aqueous media decreased from 1.5 ×105 to 9.4 ×104. As the temperature increased from 10 to 80 °C, the values of CMCs increased less than one order of magnitude. While, the partition coefficients of pyrene decreased one order of magnitude and the effect of the ion content became negligible.

scholarly journals Thermal transport in nanoporous holey silicon membranes investigated with optically induced transient thermal gratings

2020 ◽  
Vol 128 (23) ◽  
pp. 235106
Author(s):  
Ryan A. Duncan ◽  
Giuseppe Romano ◽  
Marianna Sledzinska ◽  
Alexei A. Maznev ◽  
Jean-Philippe M. Péraud ◽  
...  
Keyword(s):  
Thermal Transport ◽  
Silicon Membranes ◽  
Transient Thermal ◽  
Optically Induced

Structure and Conductivity of Iodine-Doped C60 Thin Films

1994 ◽  
Vol 359 ◽  
Author(s):  
Jun Chen ◽  
Haiyan Zhang ◽  
Baoqiong Chen ◽  
Shaoqi Peng ◽  
Ning Ke ◽  
...  
Keyword(s):  
Thin Films ◽  
Electrical Conductivity ◽  
Room Temperature ◽  
Conductivity Measurements ◽  
X Ray Diffraction ◽  
Temperature Conductivity ◽  
Room Temperature Conductivity ◽  
X Ray ◽  
Thermally Activated ◽  
Order Of Magnitude

ABSTRACTWe report here the results of our study on the properties of iodine-doped C60 thin films by IR and optical absorption, X-ray diffraction, and electrical conductivity measurements. The results show that there is no apparent structural change in the iodine-doped samples at room temperature in comparison with that of the undoped films. However, in the electrical conductivity measurements, an increase of more that one order of magnitude in the room temperature conductivity has been observed in the iodine-doped samples. In addition, while the conductivity of the undoped films shows thermally activated temperature dependence, the conductivity of the iodine-doped films was found to be constant over a fairly wide temperature range (from 20°C to 70°C) exhibiting a metallic feature.

Measurements of Inter-and-Intra Device Transient Thermal Transport on SOI FETs

2007 ◽  
Author(s):  
P. M. Solomon ◽  
M. Shamsa ◽  
K. A. Jenkins ◽  
C. P. D'Emic ◽  
A. A. Balandin ◽  
...  
Keyword(s):  
Thermal Transport ◽  
Transient Thermal

Impurity and Stoichiometry Control in Atomic Layer Epitaxy

1992 ◽  
Vol 262 ◽  
Author(s):  
H. Yokoyama ◽  
K. Ikuta ◽  
N. Inoue
Keyword(s):  
Point Defects ◽  
Resonant Tunneling ◽  
Room Temperature ◽  
Defect Density ◽  
Atomic Layer ◽  
Negative Resistance ◽  
Atomic Layer Epitaxy ◽  
Tunneling Diode ◽  
Order Of Magnitude ◽  
Stoichiometry Control

ABSTRACTWe investigate the intrinsic point defects in epilayers grown by atomic layer epitaxy (ALE). Ga vacancies and antisite As atoms in the epilayers are detected by photoluminescence spectroscopy. This shows that the ALE epilayer was grown under As-rich conditions. We propose increasing the TMG flux to reduce the number of point defects. With this method, the number of point defects in ALE epilayers can be decreased to less than that in conventionally grown epilayers. Moreover, it is'found that these point defects are formed by the incomplete Ga coverage, not by the steric hindrance as previously suggested. The carbon concentration is decreased by one order of magnitude by using nitrogen instead of hydrogen as the carrier gas. As an application of this low defect density, we fabricated a GaAs/AlAs resonant tunneling diode and observed the negative resistance at room temperature.

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