Research On The Near-field Radiative Heat Transfer Between Arbitrary Objects Based On Boundary Element Method

In recent years,with the rapid development of researches on nanotechnology,nanotechnology,MEMS,nano manufacturing technology and other engineering applications,traditional radiative heat-transfer theories are no longer applicable in micro and nano scale.The properties and mechanisms of radiation heat transfer between objects at nanoscale are totally different from those of macro scale.Near-field radiation plays a major role when the size of objects or gap approaches the thermal radiation wavelength.Due to the effect of the photon tunneling and surface polaritons,the near-field radiation heat flux is 5-6 orders of magnitude larger than that of far-field radiation.Research on near-field radiation can improve devices and technologies in near-field microscopy,thermophotovoltaic,and power generation.Therefore,near-field thermal radiation,as a rising topic of radiation heat transfer,has attracted extensive attention.In this paper,we will introduce some research methods of near-field radiation from the point of view of physical mechanism.Based on Maxwell equations,electromagnetic theory,wave-electrodynamics,and fluctuation dissipation theory are used to establish a universal method of near-field radiative heat transfer.The evanescent wave and surface polaritons of the dielectric surface and their effects are also mentioned.A boundary element method(BEM)with high accuracy and low computational cost is used to reduce the dimension of 3D model,by discretizing models with unstructured mesh.This paper aims at simulating the near-field radiation problems of real materials and models through the BEM method which is explained in detail in Chapter 3.The local density of states over infinite plane surface of gold,silver,copper and aluminum are calculated respectively to discuss the impact of distance,material,model partition and other factors on the electric local density and Purcell coefficient.The paper will analyze the contribution of the surface plasma polaritons over metals to near-field radiation with the properties of near-field enhancement and short wave-length.The paper will give priority to several simple structures such as,the near-field radiative heat transfer between two infinite plate structures and spheres.The contribution of dielectric materials and surface electromagnetic waves supported by two surface polarizations to nearfield radiation is investigated.It is found that,the increase of near-field radiation is not obvious for perfect conductor due to the frequency of oscillation of plasma of perfect conductor is usually much higher than that of heat source.On the other hand,for the semiconductor and metalloid with lower surface conductivity coupling by surface phonon polarization,the radiative heat flux can be greatly enhanced at the nanoscale.The spectral near-field radiative heat transfer energy density is calculated by the boundary element method for self-defined sphere array model,a probe-plate structure,and three-dimensional objects in arbitrary shape.The results are compared with the analytical solutions and another new thermal dipole discrete approximation method(T-DDA).It is found that another compact object will enhance the radiative heat transfer between two objects which is called the multi-body phenomenon.The boundary element method(BEM)will play an important role in the near-field radiation of complex 3D objects because of its advantages in reduction of dimension and computational simplification.