Thermal Rectification in Bulk Material Through Unusual Behavior of Electron Thermal Conductivity of Al-Cu-Fe Icosahedral Quasicrystal

2014 ◽  
Vol 44 (1) ◽  
pp. 356-361 ◽  
Author(s):  
Ryu-suke Nakayama ◽  
Tsunehiro Takeuchi
Keyword(s):  
Thermal Conductivity ◽  
Bulk Material ◽  
Icosahedral Quasicrystal ◽  
Unusual Behavior ◽  
Thermal Rectification ◽  
Electron Thermal Conductivity

Thermal Rectification Under Transient Conditions: The Role of Thermal Capacitance and Thermal Conductivity

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Francisco A. Herrera ◽  
Tengfei Luo ◽  
David B. Go
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Temperature Dependent ◽  
Unusual Behavior ◽  
Transient Conditions ◽  
Thermal Rectification ◽  
Practical Applications ◽  
Thermal Capacitance ◽  
Temperature Dependent Thermal Conductivity

A thermal rectifier transmits heat asymmetrically, transmitting heat in one direction and acting as an insulator in the opposite direction. For conduction at steady-state, thermal rectification can occur naturally in systems where the thermal conductivity of the material(s) varies in space and with temperature. However, in practical applications, rectification may often need to be controlled or understood under transient conditions. Using a bulk composite, specifically a two-slab composite, as a model system, we analyze transient rectifying behavior. We find that under some conditions transient rectification can be several times larger than steady-state rectification. Further, both the thermal diffusivity of the system and the temperature-dependent thermal conductivity or thermal capacitance play an important role in affecting the transient rectifying behavior of the system, with the nonlinearity of the system leading to unusual behavior where rectification is maximized.

Thermal Design of Highly-Efficient Thermoelectric Materials With Atomic-Scale Three-Dimensional Phononic Crystals

2007 ◽  
Author(s):  
Jean-Numa Gillet ◽  
Yann Chalopin ◽  
Sebastian Volz
Keyword(s):  
Thermal Conductivity ◽  
Bulk Material ◽  
Phononic Crystal ◽  
Three Dimensional ◽  
Mean Free Path ◽  
Dispersion Curves ◽  
Phononic Crystals ◽  
Thermal Design ◽  
Atomic Scale ◽  
Thermal Insulating

Owing to their thermal insulating properties, superlattices have been extensively studied. A breakthrough in the performance of thermoelectric devices was achieved by using superlattice materials. The problem of those nanostructured materials is that they mainly affect heat transfer in only one direction. In this paper, the concept of canceling heat conduction in the three spatial directions by using atomic-scale three-dimensional (3D) phononic crystals is explored. A period of our atomic-scale 3D phononic crystal is made up of a large number of diamond-like cells of silicon atoms, which form a square supercell. At the center of each supercell, we substitute a smaller number of Si diamond-like cells by other diamond-like cells, which are composed of germanium atoms. This elementary heterostructure is periodically repeated to form a Si/Ge 3D nanostructure. To obtain different atomic configurations of the phononic crystal, the number of Ge diamond-like cells at the center of each supercell can be varied by substitution of Si diamond-like cells. The dispersion curves of those atomic configurations can be computed by lattice dynamics. With a general equation, the thermal conductivity of our atomic-scale 3D phononic crystal can be derived from the dispersion curves. The thermal conductivity can be reduced by at least one order of magnitude in an atomic-scale 3D phononic crystal compared to a bulk material. This reduction is due to the decrease of the phonon group velocities without taking into account that of the phonon average mean free path.

Guided Acoustic Phonon Modes in Layered Anisotropic Nanowires

2003 ◽  
Author(s):  
Osama M. Mukdadi ◽  
Subhendu K. Datta ◽  
Martin L. Dunn
Keyword(s):  
Thermal Conductivity ◽  
Acoustic Phonon ◽  
Energy Transport ◽  
Bulk Material ◽  
Rectangular Cross Section ◽  
Critical Role ◽  
Acoustic Phonons ◽  
Phonon Modes ◽  
Low Velocity ◽  
Analysis Technique

Acoustic phonons play a critical role in energy transport in nanostructures. The dispersion of acoustic phonons strongly influences thermal conductivity. Recent observations show lower values of thermal conductivity in finite dimensional nanostructures than in the bulk material. In this work, we will present results for guided acoustic phonon modes in (a) a bilayered GaAs-Nb nanowire of rectangular cross section and (b) a trapezoidal Si nanowire. The former has been used for phonon counting in a nanocalorimeter for measuring thermal conductivity and the latter is commonly used in MEMS applications. A semi-analytical finite element (SAFE) analysis technique has been used to investigate the effects of layering, anisotropy, and boundaries on the dispersion of modes of propagation. Many interesting features of group velocities are found that show confinements around the corners, in the low velocity layer, and coupling of the longitudinal and flexural modes. These would strongly influence thermal conductivity and might provide means of nondestrutive evaluation of mechanical properties.

scholarly journals Calculations of the thermal conductivity of Si1-xGex films with nonuniform composition

2018 ◽  
Vol 19 (1) ◽  
pp. 48-52
Author(s):  
V. V. Kuryliuk ◽  
O. M. Krit
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Boltzmann Equation ◽  
Temperature Interval ◽  
Thermoelectric Properties ◽  
Bulk Material ◽  
Nonuniform Distribution ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
Available Information

SiGe films have attracted much attention recently due to experimental demonstrations of improved thermoelectric properties over those of the corresponding bulk material. However, despite this increasing attention, available information on the thermoelectric properties of Si1-xGex films is quite limited, especially for nonuniform composition in wide temperature interval. In this paper we have used the Boltzmann equation under the relaxation-time approximation to calculate the thermal conductivity of Si1-xGex films with nonuniform composition. It is confirmed that SiGe films with nonuniform composition has significantly lower thermal conductivity than its uniform counterpart. This suggests that an improvement in thermoelectric properties is possible by using the SiGe films with nonuniform distribution of germanium.

Ag9TlTe5: A high-performance thermoelectric bulk material with extremely low thermal conductivity

2005 ◽  
Vol 87 (6) ◽  
pp. 061919 ◽  
Author(s):  
Ken Kurosaki ◽  
Atsuko Kosuga ◽  
Hiroaki Muta ◽  
Masayoshi Uno ◽  
Shinsuke Yamanaka
Keyword(s):  
Thermal Conductivity ◽  
High Performance ◽  
Bulk Material ◽  
Low Thermal Conductivity

scholarly journals CuSO4/[Cu(NH3)4]SO4-Composite Thermochemical Energy Storage Materials

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2485
Author(s):  
Danny Müller ◽  
Christian Knoll ◽  
Georg Gravogl ◽  
Daniel Lager ◽  
Jan M. Welch ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Energy Storage ◽  
Bulk Material ◽  
Large Change ◽  
Solid Material ◽  
Energy Storage Materials ◽  
Energy Storage Density ◽  
Medium Temperature ◽  
Storage Density ◽  
Support Materials

The thermochemical energy-storage material couple CuSO4/[Cu(NH3)4]SO4 combines full reversibility, application in a medium temperature interval (<350 °C), and fast liberation of stored heat. During reaction with ammonia, a large change in the sulfate solid-state structure occurs, resulting in a 2.6-fold expansion of the bulk material due to NH3 uptake. In order to limit this volume work, as well as enhance the thermal conductivity of the solid material, several composites of anhydrous CuSO4 with inorganic inert support materials were prepared and characterized with regard to their energy storage density, reversibility of the storage reaction, thermal conductivity, and particle morphology. The best thermochemical energy storage properties were obtained for a 10:1 CuSO4-sepiolite composite, combining an attractive energy storage density with slightly improved thermal conductivity and decreased bulk volume work compared to the pure salt.

Characterization of Anisotropic and Irregularly-Shaped Materials by High-Sensitive Thermal Conductivity Measurements

2007 ◽  
Vol 124-126 ◽  
pp. 1641-1644 ◽  
Author(s):  
M. Gustavsson ◽  
Hideaki Nagai ◽  
Takeshi Okutani
Keyword(s):  
Thermal Conductivity ◽  
Structural Changes ◽  
Bulk Material ◽  
Thermal Contact ◽  
Measurement Techniques ◽  
High Sensitivity ◽  
Conductivity Measurements ◽  
Destructive Testing ◽  
Analysis And Design ◽  
Wide Range

In modern thermal analysis and design involving thermal transport in solid components it is necessary to apply different modeling of the thermal heat flow in bulk material and across solid surface interfaces either in shape of a layer or a solid-solid interface. Similar differences occur when applying different measurement techniques. Some techniques have been developed specifically for the purpose of performing measurements of bulk properties by removing the influence from thermal contact resistance between the measurement probe and the sample material. Thermal conductivity measurements on metal and ceramic objects of various geometries such as thin bars, thin sheets as well as coatings or layers are here described when using the Transient Plane Source technique. A summary overview of the recent developments of this technique, including its ability to be applied in measurement situations covering a wide range of length and time scales, is also presented. Structural changes in anisotropy can be recorded with high sensitivity by comparative measurements. The technique may be applied in situations requiring non-destructive testing, e.g. samples of particular geometry used for mechanical or tensile testing.

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