scholarly journals Ballistic-Diffusive Model for Heat Transport in Superlattices and the Minimum Effective Heat Conductivity

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 167 ◽  
Author(s):  
Federico Vázquez ◽  
Péter Ván ◽  
Róbert Kovács
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Heat Conductivity ◽  
Room Temperature ◽  
Heat Fluxes ◽  
Multilayer Systems ◽  
Effective Heat Conductivity ◽  
Effective Heat ◽  
Kinetic Calculations

There has been much interest in semiconductor superlattices because of their low thermal conductivities. This makes them especially suitable for applications in a variety of devices for the thermoelectric generation of energy, heat control at the nanometric length scale, etc. Recent experiments have confirmed that the effective thermal conductivity of superlattices at room temperature have a minimum for very short periods (in the order of nanometers) as some kinetic calculations had anticipated previously. This work will show advances on a thermodynamic theory of heat transport in nanometric 1D multilayer systems by considering the separation of ballistic and diffusive heat fluxes, which are both described by Guyer-Krumhansl constitutive equations. The dispersion relations, as derived from the ballistic and diffusive heat transport equations, are used to derive an effective heat conductivity of the superlattice and to explain the minimum of the effective thermal conductivity.

Anisotropic Thermal Conductivity of Superconducting Lanthanum Cuprate

1989 ◽  
Vol 169 ◽  
Author(s):  
D.T. Morelli ◽  
G.L. Doll ◽  
J.P. Heremans ◽  
H.P. Jenssen ◽  
A. Cassanho ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Copper Oxide ◽  
Heat Transport ◽  
Electron Scattering ◽  
Heat Conductivity ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Lanthanum Copper Oxide ◽  
Anisotropic Thermal Conductivity

AbstractThe thermal conductivities of superconducting, Sr-doped lanthanum copper oxide single crystals have been measured from room temperature to below 100 mK parallel and perpendicular to the copper oxide planes. While the results indicate that the heat conduction is strongly anisotropic, the data have been analyzed in terms of a modified Bardeen-Rickhayzen-Tewordt theory of lattice thermal conductivity. It is shown that while electron scattering plays an important role in limiting the in-plane heat conductivity, this scattering channel is masked by other mechanisms for heat transport across the planes.

Design Formulas for Oscillatory Heat Transport in Open-Ended Tubes

2003 ◽  
Vol 125 (6) ◽  
pp. 1183-1186 ◽  
Author(s):  
Masao Furukawa
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Pipe Flow ◽  
Tube Bundle ◽  
Womersley Number ◽  
Algebraic Expressions ◽  
Conductivity Increase ◽  
Bundle Size ◽  
Relative Conductivity

Modified Watson’s functions dependent on the Womersley Number, concerning a forced oscillatory pipe flow, are introduced to mathematically simply express the effective thermal conductivity, the tidal displacement, and the tidal work of fluid. Those three are developed into algebraic expressions giving the required electrical oscillating power and the necessary number of capillary tubes. The relative conductivity increase, the specific shaker driving power, and the specific tube bundle size are graphically shown in the figures for several fluids of interest to contribute to designing a heaterless liquid warmer.

An Experimental Study of a Bubble-Driven Heat-Transport Device

2007 ◽  
Author(s):  
Osamu Suzuki
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Tube Bundle ◽  
Temperature Fluctuations ◽  
Temperature Gradients ◽  
Heating And Cooling ◽  
Tube Bundles ◽  
Steady State Time ◽  
Transport Device

We experimentally measured the heat-transport characteristics of a bubble-driven heat-transport device. The device consisted of a non-looped copper tube containing water. The tube was either meandered or spiraled to form tube bundles. The inner surface of the tube was smooth and its diameter small enough to enable the formation of vapor and liquid plugs in it. Two copper blocks were attached to the tube bundles, one as a heating block and the other as a cooling block. In the experiment, most of the wall temperatures measured on the tube fluctuated periodically at a quasi-steady state. Time-averaged temperature gradients between the heating and cooling sections of the device were constant. By increasing heater input from 300W to 350W, the amplitude of the temperature fluctuations decreased and the temperature gradients increased significantly. This behavior was regarded as a transition to critical heat transport condition. The effective thermal conductivity of the device was proportional to the heat-transport rate but did not depend on the formation of the tube bundle and the gravity effect. The temperature fluctuations had specific peak frequencies and a positive correlation was found between the frequency and effective thermal conductivity. These experimental results strongly suggest that the main heat-transport mechanism of the investigated device is based on the oscillation-induced transport of sensible heat.

Effective Thermal Conductvity of Three-Phase Soils

2012 ◽  
Author(s):  
Fabio Gori ◽  
Sandra Corasaniti
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Fluxes ◽  
Water Volume ◽  
Two Phase ◽  
Empirical Constant ◽  
Three Phase ◽  
Theoretical Predictions ◽  
Porosity Ratio ◽  
Good Agreement

The aim of the present paper is to determine the effective thermal conductivity of three-phase soils, made of a quasi-spherical solid grain, and surrounded by two phase, which can be water and air or water and ice. The effective thermal conductivity is obtained theoretically by integrating the conduction equation under the thermal distribution of parallel heat fluxes in steady-state. The effective thermal conductivity is evaluated at a given degree of porosity (ratio between the void volume and the total one) and different degrees of saturation (ratio between the water volume and the void one) from dryness up to saturation. Comparisons between experimental data and theoretical predictions confirm that the present model can predict the effective thermal conductivity with a fairly good agreement without using any empirical constant.

scholarly journals Роль взаимодействия частиц в кластерной модели теплопроводности наножидкостей

2018 ◽  
Vol 44 (3) ◽  
pp. 17
Author(s):  
Б.В. Бошенятов
Keyword(s):  
Experimental Data ◽  
Continuum Mechanics ◽  
Heat Conductivity ◽  
Temperature Fields ◽  
Spherical Particles ◽  
Heat Conductivity Coefficient ◽  
Effective Heat Conductivity ◽  
Effective Heat ◽  
Individual Cluster

AbstractAnalytical dependences of the effective heat conductivity coefficient of an individual cluster and cluster nanofluid are obtained on the basis of classical equations of continuum mechanics with allowance for the interaction of temperature fields of spherical particles inside a cluster. The calculated dependences of the heat-conductivity coefficient of the cluster nanofluid agree with the corresponding experimental data.

Experimental Investigation of a Three-Layer Oscillating Heat Pipe

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
C. D. Smoot ◽  
H. B. Ma
Keyword(s):  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Total Power ◽  
Oscillating Heat Pipe ◽  
Layer Effect ◽  
Layering Effect ◽  
Heat Transport Capability

An experimental investigation of a compact, triple-layer oscillating heat pipe (OHP) has been conducted to determine the channel layer effect on the heat transport capability in an OHP. The OHP has dimensions 13 mm thick, 229 mm long, and 76 mm wide embedded with two-independent closed loops forming three layers of channels. The unique design of the investigated OHP can be readily used to explore the channel layering effect on the heat transport capability in the OHP. The experimental results show that the addition of channel layers can increase the total power and at the same time, it can increase the effective thermal conductivity of the OHP. When the OHP switches from one layer of channels to two layers of channels, the highest effective thermal conductivity can be increased from 5760 W/mK to 26,560 W/mK. At the same time, the dryout limit can be increased. With three layers of channels, the OHP investigated herein can transport a power up to 8 kW with a heat flux level of 103 W/cm2 achieving an effective thermal conductivity of 33,170 W/mK.

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