1,721,012 research outputs found
A two-temperature model for thermoelectric effects and its consequences in practical applications
No full textIn recent papers, a two-temperature model for thermoelectric effects has been introduced. That model is able to account for the difference in phonon and electron temperature and may open new lines of research in thermoelectricity. Here, we perform a scrutiny of that model in order to check its physical standing. We further provide some useful characteristic numbers which may be used in practical applications in order to reduce to a simpler level the analysis. The consequences of that model on the usual Kelvin relations are pointed out, as well
Crossed nonlocal effects and breakdown of the Onsager symmetry relation in a thermodynamic description of thermoelectricity
No full textNonlocal nonlinear effects coupling the heat flux and the electric-current density in an enlarged thermodynamic description of thermoelectric systems are considered. The influence of such terms on the breakdown of the Onsager reciprocity relation between the effective transport coefficients, depending on the electric field and the temperature gradient, is analyzed up to second-order in the thermodynamic forces. The maximum value of the thermoelectric efficiency is derived as a function of the figure-of-merit and of the degree of the Onsager symmetry breaking. © 2014 Elsevier B.V. All rights reserved
Frequency dependent figure-of-merit in cylindrical thermoelectric nanodevices
No full textWe use a theoretical mesoscopic model accounting for memory and nonlocal effects in thermoelectricity in order to investigate how the figure-of-merit in cylindrical thermoelectric nanodevices is conditioned in frequency-dependent situations. Two different situations, regarding the relative values of the particles' mean-free path and the characteristic size of the system, are analyzed. It is shown that in both situations the performances of the thermoelectric devices are reduced. However, nonlocal effects may be used as an aiding tool to have less marked reductions in those performances
A phonon-hydrodynamic approach to thermal conductivity of Si-Ge quantum dot superlattices
No full textIn this paper we attempt to provide an analysis of the effective thermal conductivity of Si/Ge quantum dot superlattices based on a phonon-hydrodynamic approach. We consider the inner Ge quantum dots as minute ellipsoidal obstacles which exert a thermal resistance against the phonon flow in the Si hosting matrix. This yields an additional reduction term to the effective medium reduction of the thermal conductivity. The contribution considered here depends on the size, the shape, the spatial distribution of the obstacles and plays an important role when the characteristic size of the Ge obstacles is much smaller than the phonon mean-free path in the Si matrix. The originality of the paper is that the physics of rarefied fluids is used to study the problem of heat transport
Focusing of heat pulses along nonequilibrium nanowires
No full textAs a consequence of the temperature dependence of the speed of heat pulses, rectangular heat pulses will shrink (or extend) spatially, and will increase (or decrease) their temperature when propagating along a temperature gradient. Here, we consider heat pulse propagation along silicon nanowires, because of their interest in nanotechnology. The relative rates of variation per meter may be very high, and variations along relatively short lengths could be experimentally observable. © 2009 Elsevier B.V. All rights reserved
Non-Fourier heat removal from hot nanosystems through graphene layer
No full textNonlocal effects on heat transport beyond a simple Fourier description are analyzed in a thermodynamical model. In the particular case of hot nanosystems cooled through a graphene layer, it is shown that these effects may increase in a ten percent the amount of removed heat, as compared with classical predictions based on the Fourier law
Geometrical dependence of thermal conductivity in elliptical and rectangular nanowires
No full textThe aim of this work is to analyze the shape dependence of the effective thermal conductivity of nanowires, based on the model of phonon hydrodynamics. In particular, we consider elliptical and rectangular nanowires, and we compare their respective thermal conductivities with those of circular nanowires and of wide thin plates
Influence of nonlinear effects on the efficiency of a thermoelectric generator
Full text linkWe propose a nonlinear model for thermoelectric coupling which is based on the thermomass theory for heat conduction. We show that in this model, the second Kelvin relation and the classical Onsager relations are no longer satisfied simultaneously, namely, if one holds, then the other one breaks down, and viceversa. As a function of the different breaking, we evaluate the efficiency of a thermoelectric generator. The influence of the electric-charge gradient on the efficiency of thermoelectric coupling is investigated as well
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