The Effect Mechanisms Of The Microstructured Surfaces On The Near-field Thermal Radiation

The theoretical and experimental investigations during the recent decades indicate that the radiative heat transfer between two closely placed objects(near-field thermal radiation)can exceed the black body limit by several orders of magnitude.Numerous researches on the radiative heat transfer between two slabs have been conducted based on the assumptions that the objects are infinite and the surfaces of the objects are smooth.With the development of the research,the importance of the surface microstructures on the near-field thermal radiation attracts the attentions of the researchers.With the development of the research,the importance of the surface microstructures on the near-field thermal radiation attracts the attentions of the researchers.This work aims to further explore the underlying physical mechanism of the surface structures on the near-field radiative heat transfer,which is rare in the existing researches.Based on the fluctuation-dissipation theorem and the Maxwell equations,this work theoretically investigates the following intriguing issues:1.The near-field radiative heat flux between the two-dimensional gratingsThe radiative heat transfer between two gratings can be enhanced by the SPPs and the HPs.The one-dimensional rectangle gratings have been widely investigated during the past decades.In this work,the radiative heat transfer between two two-dimensional gratings is investigated by using the finite difference time domain(FDTD)method.The structure feature is characterized by the parameter Λ,which is defined as the ratio of the amplitude to the period of the two-dimensional sinusoidal grating surface.When the parameter Λ is changed,the radiative heat fluxes between the two-dimensional gratings have been computed.Moreover,the effect of the relative position of the two gratings is also studied.The results of this work demstrate the underlying physical mechanisims of the two-dimensional grating on the near-field radiative heat transfer.2.The influence of the surface roughness on the near-field radiative heat fluxThe surface roughness on the surface can be regarded as the special microstructure.In this work,the Gaussian type rough surface is established and characterized by the parameters root mean square height and correlation length.The surface roughness effects on the near-field radiation are investigated by employing the Wiener Chaos Expansion(WCE)based finite difference time domain(FDTD)method.The roughness factor is defined to represent the effects of the surface roughness on the near-field radiative heat flux between two slabs,which is a function of the geometrical parameters.Results of this work indicate that the effect of roughness on near-field thermal radiation in high frequency is remarkable.This interesting feature can be applied for adjusting the spectral radiative heat transfer without contact.3.The near-field radiative heat transfer between two finite objectsNumerous researches have investigated the radiative heat transfer between two semi-infinite structures or periodic structures.This work has studied the near-field radiative heat flux between the finite objects.In this work,the dimensionless distance between the slabs is defined to characterize the geometrical feature of the cavity.Based on the BEM,the edge effects on the near-field radiative heat flux are illustrated by comparing the results of the finite doped silicon slabs with the semi-infinite doped silicon slabs.Furthermore,the effects of the boundary material on the near-field radiation between the finite slabs are demenstrated.The inner physical mechanisms are also demonstrated by calculating the radiative heat flux distributions between the finite slabs.This work can be applied to the thermal management in the nano-scale.4.The application of the lattice Boltzmann method on near-field radiative heat transferThe contribution of the evanescent waves on the radiative heat flux between two closely placed objects can exceed the black body limit.Numerical methods can deal with the problem of complicated structures.The lattice Boltzmann method has been used to deal with the radiative heat transfer problems.However,this method has not been applied to predict the enhancement of the radiative heat transfer induced by the evanescent waves.Based on the Maxwell equations,the lattice Boltzmann method for the evanescent waves is derived.Results indicate that the radiative heat flux induced by the evanescent waves coincide with the classical Boltzmann equation.The expression on the interface between different media is illustrated.Furthermore,the discrete equations and numerical examples for this method are given.5.The effective near-field radiative thermal switch based on the multilayer structuresThe multilayer films have heen demonstrated to be used to control the near-field radiative heat transfer by appropriatly choosing the film thicknesses.In this work,the multilayer based electrochromic devices are presented as the gates of the thermal switch.The radiative heat flux tunneling the thermal switch is varied when the optical state of the gates is changed by the applied voltage.The switching factor is defined to characterize the capability of the radiative thermal switch.The geometry effects of the thermal switch on the switching factor are investigated to understand the inner mechanism of the thermal switch.The results indicate that the switching factor can be as high as 98% when the vacuum gap is small.This work can pave the way for the nano-scale thermal management and has potential applications for thermal based recording technology.