Normal heat diffusion in many-body system via thermal photons

A normal-diffusion theory for heat transfer in many-body systems via carriers of thermal photons is developed. The thermal conductivity tensor is rigorously derived from fluctuational electrodynamics as a coefficient of diffusion term for the first time. In addition, a convection-like heat transfer behavior is revealed in systems of asymmetric distribution of particles, indicating violation of Fourier's law for such system. Considering the central role of thermal conductivity in heat transfer, this work paves a way for understanding, analysis and manipulation of heat transfer in nanoparticle system via thermal photons with many-body interactions.Comment: 4 figure

Radiative heat transfer and radiative thermal energy for 2D nanoparticle ensembles

Radiative heat transfer (RHT) and radiative thermal energy (RTE) for 2D nanoparticle ensembles are investigated in the framework of many-body radiative heat transfer theory. We consider nanoparticles made of different materials: metals (Ag), polar dielectrics (SiC) or insulator-metallic phase-change materials (VO$_2$). We start by investigating the RHT between two parallel 2D finite-size square-lattice nanoparticle ensembles, with particular attention to many-body interactions (MBI) effects. We systematically analyze the different physical regimes characterizing the RHT. When $p\ll \lambda_T$, a multiple scattering of the electromagnetic field inside the systems gives rise to a MBI regime. MBI effects manifest themselves in different ways, depending on $d$: (a) if $d > \lambda_T$, due to the pure intra-ensemble MBI inside each 2D ensemble, the total heat conductance is less affected, and the thermal conductance spectrum manifests a single peak which is nonetheless shifted with respect to the one typical of two isolated nanoparticles. (b) if $d < \lambda_T$, there is a strong simultaneous intra- and inter-ensemble MBI. In this regime there is a direct quantitative effect on the heat conductance, in addition to a qualitative effect on the thermal conductance spectrum which now manifests a new second peak. As for the RTE, to correctly describe the radiation emitted by metallic nanoparticles, we derive an expression of the Poynting vector including also magnetic contribution, in addition to the electric one. By analyzing both periodic and non-periodic ensembles, we show that the RTE emitted by a single 2D nanoparticle ensemble is sensitive to the particle distribution. As instance, we see that the RTE emitted by 2D concentric ring-configuration ensemble has an inhibition feature near the center of the ensemble.Comment: 20 pages, 21 figure

Radiative heat transfer between metallic nanoparticle clusters in both near field and far field

Micro-nanoparticle systems have wide applications in thermal science and technology. In dense particulate system, the particle separation distance may be less than the characteristic thermal wavelength and near field effect will be significant and become a key factor to influence thermal radiation transfer in the system. In this study, radiative heat transfer (RHT) between two metallic nanoparticles clusters are explored using many-body radiative heat transfer theory implemented with the coupled electric and magnetic dipole (CEMD) approach, which effectively takes into account the contribution of magnetic polarization of metallic nanoparticles on heat exchange. As the focus, the effects of magnetic polarization and many-body interaction (MBI) on RHT were analyzed. The effects of fractal dimension and relative orientation of the clusters were also analyzed. Results show that the contribution of magnetically polarized eddy-current Joule dissipation dominates the RHT between Ag nanoparticle clusters. If only electric polarization (EP approach) is considered, the heat conductance will be underestimated as compared with the CEMD approach in both near field and far field regime. The effect of MBI on the RHT between Ag nanoparticle clusters is unobvious at room temperature, which is quite different from the SiC nanoparticle clusters. For the latter, MBI tends to suppress RHT significantly. The relative orientation has remarkable effect on radiative heat flux for clusters with lacy structure when the separation distance is in the near field. While for the separation distance in far field, both the relative orientation and the fractal dimension has a weak influence on radiative heat flux. This work will help the understanding of thermal transport in dense particulate system.Comment: 7 figure