Study Of Radiative Properties And Near- Field Radiative Heat Transfer Of Particles Using Coupled Dipole Method

Thermal radiation problems of particles is a research focus in thermal radiation heat transfer,which find applications in energy utilization,biomedical science,atmosphere science and so forth.According to the relation between the particle separation gaps and the thermal wavelength,particle systems can be classified into dilute particle system and dense particle system.In dilute particle systems,the independent scattering condition of particles is satisfied,and the challenge of the radiative heat transfer in dilute particle systems is to obtain the radiative properties of non-spherical and inhomogeneous particles.In dense particle systems,however,near-field effects like wave interference and evanescent wave tunneling should be accounted for,whereas the definition of particle radiative properties in the classical electromagnetic theory and the classic radiative transfer equation cannot consider the near-field effects.The newly proposed many-body radiative heat transfer theory,on the other hand,accounts for the near-field effects in the calculation of the radiative heat transfer between particles,which provides a new tool for the study of radiative heat transfer in dense particle system.Yet the theory is incomplete and the disciplines of near-field radiative heat transfer still need to be revealed.This work uses the coupled dipole method to study the above mentioned problems of particle in both the far-and near-field.The coupled dipole method builds coupled equations via Green's function,which is convenient to calculate the electromagnetic field in the near-and farfield.This work first studies the radiative properties of black carbon aerosols and microalgae,then this work studies the radiative heat transfer between dense particle clusters,and develops the many-body radiative heat transfer theory.The detais of this study are:Black carbon aerosols distributed in the atmosphere and microalgae suspended in water are two typical dilute particle systems.Black carbon aerosol exhibits fractal structure,which frequently gets internally mixed with other aerosols.Black carbon aerosol absorbs visible light strongly and exerts an important impact on the global climate.The radiative properties of microalgae is fundamental for the solution of radiative transfer in photobioreactors.Microalgae usually pocess spine-like surface structures which is not considered in frequently used model particles.Accounting for the real morphologies of the two types of particles,this work builds model particles and applies the discrete dipole approximation(DDA)to investigate their radiative properties.It is found that the absorption and scattering cross sections,the single scattering albedo of black carbon are enhanced after internal mixing.For totally coated black carbon,the absorption is enhanced by 1.5 to 2.0 times,the enhancement being larger for black caron with higher fractal dimension.Both the equivalent volume sphere based on effective medium theory(EMT)and the core-shell sphere can produce large errors,but the former simplified model is better than the latter.Surface spines can increase the scattering,absorption cross sections and the asymmetry parameter of microalgae.The equivalent volume sphere overestimates the scattering cross section but underestimates the asymmetry parameter.The core shell model based on the EMT introduced in this work predicts well the absorption,scattering cross sections and the asymmetry parameter of the microalgae with surface spines.For dense particle system,the radiative properties of particles and the radiative transfer equation is no longer valid.To investigate the near-field effects in dense particle system,this work builds particle clusters through fractal theory and studies the radiative heat transfer between two Si C nanoparticle clusters using the many-body radiative heat transfer theory that is based on the coupled electric dipole method.It is found that the near-field radiative heat transfer is orders of magnitude larger than that of the far-field.The radiative heat transfer is larger for larger fractal dimension and the equivalent volume sphere overestimates the heat flux.The many-body interaction in the clusters inhibits the overall heat flux between clusters.For metal nanoparticles,the magnetic dipole moment induced by eddy currents can not be ignored.The many-body radiative heat transfer theory cannot consider the magnetic dipole moment and the crossed interactions between electric and magnetic dipole moment.To solve this problem,this work developed the coupled electric and magnetic dipole method for the many-body radiative heat transfer,which can be used to calculate the radiative heat transfer in systems containing both metal and dielectric nanoparticles.It is found that the electric and the magnetic dipole moments and their crossed interactions can all dominate the heat transfer depending on the position and composition of the particles.For nanoparticle systems containing metal nanoparticles,it will introduce very large errors if only the electric dipole moment is considered.The nearfield radiative heat transfer and the local energy density can be greatly increased for particles in coupled resonances,in which the surface plasmon polariton and the surface phonon polariton can be coupled.The enhancement of the near-field radiative heat transfer is due to the evanescent wave tunneling.The evanescent wave,however,decays exponentially in the vertical direction from the surface,which makes the near-field radiative heat transfer confined to sub-wavelength gaps.In real applications,it is expected that the near-field energy can be transported to larger distances.This work theoretically proves that the propagating surface waves can be used for the long-distance transport of near-field energy.This work first develop the many-body radiative heat transfer theory near a surface by the coupled dipole method.Based on this theory,it is found that the radiative heat flux between two Si C nanoparticles near a Si C surface is enhanced by 1 to 2 orders of magnitude for separation distances larger than the dominate thermal wavelength,which is attributed to the strong coupling between the localized phonon polariton of the particles and the propagating phonon polariton of the surface.The propagating surface wave can propagate a much longer distance,which provides new channel for the radiative heat transfer.The new channel can also enhance the radiative heat transfer through closely space nanoparticle chains.The many-body radiative heat transfer theory treats the nanoparticle as dipoles in the quasi-static approximation.To consider particles that might be arbitrary in the shape,the composition and the size,and the effect of external incident field and anisotropic electric permittivity,this work develops the many-body thermal discrete dipole approximation(T-DDA),which provides a feasible method for the analysis of the radiative heat transfer in complex many-body systems.By the many-body T-DDA,it is found that the radiative heat transfer between two Si O2 cubic particles can exceed that of black bodies by 2 orders of magnitude.The coupled surface phonon polariton can enhance the radiative heat transfer and the absorption of the background radiation in cubic particle systems.The transfer coeffiecient in the Si O2 array decays quickly with increasing distance to outside directions,and the decaying is more rapid for more closely spaced array,which indicates that the radiative heat transfer is a local phenomenon in dense particle system.