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Near-field heat radiation and transfer are rich in various exciting effects, in particular, regarding the amplification due to the geometrical configuration of the system. In this paper, we study heat exchange in situations where the objects are confined by additional objects so that the dimensionality of heat flow is reduced. In particular, we compute the heat transfer for spherical point particles placed between two parallel plates. The presence of the plates can enhance or reduce the transfer compared to the free case and provides a slower power-law decay for large distance. We also compute the heat radiation of a sphere placed inside a spherical cavity, finding that it can be larger or smaller compared to the radiation of a free sphere. This radiation shows strong resonances as a function of the cavitys size. For example, the cooling rate of a nanosphere placed in a cavity varies by a factor of $10^5$ between cavity radii $ 2 mu {rm m} $ and $ 5 mu {rm m} $.
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We study heat radiation and heat transfer for pointlike particles in a system of other objects. Starting from exact many-body expressions found from scattering theory and fluctuational electrodynamics, we find that transfer and radiation for point particles are given in terms of the Greens function of the system in the absence of the point particles. These general expressions contain no approximation for the surrounding objects. As an application, we compute the heat transfer between two point particles in the presence of a sphere of arbitrary size and show that the transfer is enhanced by several orders of magnitude through the presence of the sphere, depending on the materials. Furthermore, we compute the heat emission of a point particle in front of a planar mirror. Finally, we show that a particle placed inside a spherical mirror cavity does not radiate energy.
We investigate the full counting statistics of extreme-near-field radiative heat transfer using nonequilibrium Greens function formalism. In the extreme near field, the electron-electron interactions between two metallic bodies dominate the heat transfer process. We start from a general tight-binding electron Hamiltonian and obtain a Levitov-Lesovik like scaled cumulant generating function (SCGF) using random phase approximation to deal with electron-electron interaction. The expressions of heat current and its fluctuation (second cumulant) are obtained from the SCGF. The fluctuation symmetry relation of the SCGF is verified. In the linear response limit (small temperature gradient), we express the heat current cumulant by a linear combination of lower order cumulants. The heat current fluctuation is $2k_B T^2$ times the thermal conductance with $T$ the average temperature in the linear response limit, and this provides an evaluation of heat current fluctuation by measuring the thermal conductance in extreme-near field-radiative heat transfer.
We explore whether localized surface plasmon polariton modes can transfer heat between molecules placed in the hot spot of a nanoplasmonic cavity through optomechanical interaction with the molecular vibrations. We demonstrate that external driving of the plasmon resonance indeed induces an effective molecule-molecule interaction corresponding to a new heat transfer mechanism, which can even be more effective in cooling the hotter molecule than its heating due to the vibrational pumping by the plasmon. This novel mechanism allows to actively control the rate of heat flow between molecules through the intensity and frequency of the driving laser.
The study of radiative heat transfer in particulate system is usually based on radiative transfer equation (RTE) with effective radiative properties. However, for non-random, densely and regularly packed particulate systems, the applicability of RTE is questionable due to dependent scattering and weak randomness of particle arrangement. In this paper, a new continuum approach that does not explicitly rely on the RTE is proposed for radiative heat transfer in the densely packed particulate system. The new approach is based on the generalization of the concept of radiation distribution factor (RD) at discrete scale (or particle scale) to radiation distribution function (RDF) at continuum scale. The derived governing equation is in integral form, with RDF as the continuum scale physical parameter that characterize the radiative transfer properties of the system. The characteristics of the RDF for different particulate system (randomly or regularly packed) are studied. The RDF in regularly distributed particulate system is shown to be anisotropic. The continuum approach is verified by using heat transfer simulation at the particle scale, and demonstrated to have excellent performance in predicting the temperature distribution in dense particulate system. This work provides an alternative continuum theory, which will help the analysis and understanding of radiative heat transfer in densely packed media.
The low-temperature asymptotic expressions for the Casimir interaction between two real metals described by Leontovich surface impedance are obtained in the framework of thermal quantum field theory. It is shown that the Casimir entropy computed using the impedance of infrared optics vanishes in the limit of zero temperature. By contrast, the Casimir entropy computed using the impedance of the Drude model attains at zero temperature a positive value which depends on the parameters of a system, i.e., the Nernst heat theorem is violated. Thus, the impedance of infrared optics withstands the thermodynamic test, whereas the impedance of the Drude model does not. We also perform a phenomenological analysis of the thermal Casimir force and of the radiative heat transfer through a vacuum gap between real metal plates. The characterization of a metal by means of the Leontovich impedance of the Drude model is shown to be inconsistent with experiment at separations of a few hundred nanometers. A modification of the impedance of infrared optics is suggested taking into account relaxation processes. The power of radiative heat transfer predicted from this impedance is several times less than previous predictions due to different contributions from the transverse electric evanescent waves. The physical meaning of low frequencies in the Lifshitz formula is discussed. It is concluded that new measurements of radiative heat transfer are required to find out the adequate description of a metal in the theory of electromagnetic fluctuations.
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