Radiative Thermal Rectification between SiC and SiO2

By means of fluctuationnal electrodynamics, we calculate radiative heat flux between two pla-nar materials respectively made of SiC and SiO2. More specifically, we focus on a first (direct) situation where one of the two materials (for example SiC) is at ambient temperature whereas the second material is at a higher one, then we study a second (reverse) situation where the material temperatures are inverted. When the two fluxes corresponding to the two situations are different, the materials are said to exhibit a thermal rectification, a property with potential applications in thermal regulation. Rectification variations with temperature and separation distance are here reported. Calculations are performed using material optical data experimentally determined by Fourier transform emission spectrometry of heated materials between ambient temperature (around 300 K) and 1480 K. It is shown that rectification is much more important in the near-field domain, i.e. at separation distances smaller than the thermal wavelength. In addition, we see that the larger is the temperature difference, the larger is rectification. Large rectification is finally interpreted due to a weakening of the SiC surface polariton when temperature increases, a weakening which affects much less SiO2 resonances

Quantum Thermal Rectification to design thermal diodes and transistors

We study in this article how heat can be exchanged between two level systems (TLS) each of them being coupled to a thermal reservoir. Calculation are performed solving a master equation for the density matrix using the Born markov-approximation. We analyse the conditions for which a thermal diode and a thermal transistor can be obtained as well as their optimization

VO2-based radiative thermal transistor with a semi-transparent base

International audienc

Simultaneous determination of thermal diffusivity and thermal conductivity of a thin layer using double modulated thermal excitations

International audienceA theoretical model is developed to determine simultaneously and in different ways thermal diffusivity and thermal conductivity of thin layers. This is done by using the accurate expression of the temperature distribution derived from the parabolic heat equation when the front surface of the thin layer is excited by a periodic heat flux, while the rear surface is maintained at one of three different types of boundary conditions: modulated periodic heat flux, modulated temperature, or constant temperature. Our approach exploits the modulation frequencies at which the normalized front surface temperature reaches its first maximum and first minimum. It is shown that (i) these characteristic frequencies can be used to obtain the thermal diffusivity of the finite layer under three different types of boundary conditions. (ii) The ratio between the values of the maxima and minima of the temperature can be utilized to determine the thermal conductivity of the finite layer. These two thermal properties are sensitive to the nature of the boundary conditions as well as the modulation frequency of the heat excitation. This paper provides a theoretical basis for the determination of the thermal diffusivity and thermal conductivity of the finite layer using laser-based heating photothermal techniques

Modulated heat conduction in a two-layer dielectric system with dynamical interface thermal resistance

International audienceHeat conduction in a two-layer dielectric system excited with a laser beam of modulated intensity is studied in terms of a dynamical interface thermal resistance predicted by the phonon Boltzmann transport equation under the gray relaxation time approximation. This is done by using accurate expressions for both the modulated temperature and heat flux profiles, which describe both the diffusive and ballistic regimes of heat transport. It is shown that (i) for modulation frequencies much smaller than the phonon collision frequency f1 of the finite layer, the values of this dynamical resistance in the pure ballistic regime agree well with those of the diffuse mismatch model, while they differ by about 10% in the diffusive one. (ii) In the diffusive regime, the thermal resistance reaches a maximum at the characteristic modulation frequency fc≃(10⎯⎯⎯⎯√/2π)(l1/L)2f1, where l1 and L are the phonon mean free path and thickness of the finite layer, respectively. This maximum thermal resistance is associated with the minimum of the modulated heat flux at the interface. The theoretical basis is used to establish a methodology to determine the dominant thermal relaxation time and phonon mean free path of the finite layer. The obtained results can thus be applied for describing the modulated heat conduction in dielectric thin films through the comparison of our theoretical model with experimental data measured by thermoreflectance or other relevant photothermal techniques