Research On The Transmission Mechanism And Control Method Of Near-field Radiative Heat Transfer And Its Application

When the distance between objects involved in radiative heat transfer process is much lager than the corresponding characteristic wavelength of thermal radiation,investigation on the radiative heat transfer process could be performed under radiative transfer equation(wihch describes the energy consevation in the radiative heat transfer process and is derived from Planck's law),ray tracing method and geometric optics approximation.This is called"far-field radiative heat transfer problem" or "traditional radiative heat transfer problem".Near-field effects are ignored in these methods and the radiative heat flux is limited by balckbody radiation.When the distance between objects involved in radiative heat transfer process becomes comparable to or smaller than the corresponding characteristic wavelength of thermal radiation,near-field effects become significant and play a key role in or even determine the entire radiative heat transfer process.As a result,the radiative heat flux(i.e.,near-field radiative heat flux)may be several orders of magnitude beyond that between blackbodies in the same temperature conditions and its spectrum may exhibit controllable monotonic property.This is called "near-field radiative heat transfer problem".These features of near-field radiative heat transfer have significant applications in near-field effects based thermophotovoltaic system,near-field effects based thermal rectifier system,near-field effects based thermal memory,near-field scanning thermal microscopy,microfabrication and nanofabrication,local heating or cooling technology etc.,invoking increasing efforts of researchers.In this thesis,theoretical investigations on the near-field radiative heat transfer including effects of magnetic material on near-field radiative heat transfer,tailoring near-field radiative heat transfer by inserting a suspended thin film between two parallel smooth planes,tailoring near-field radiative heat transfer by periodic grating surface,and improving performance of near-field thermal rectifier are performed.This thesis mainly contains the following aspects:1.A general theoretical method to deal with near-field radiative heat transfer for layered isotropic magnetic media.A general model to deal with near-field radiative heat transfer for layered isotropic magnetic media is reported,wich is also applicable for layered isotropic nonmagnetic media.This model lays the foundation for following theoretical investigations.It should be emphasized that this model can deal with near-field radiative heat transfer containing metamaterials.Metamaterials may excite surface polaritons(SPs)for s polarization,increasing channels for near-field radiative heat transfer and bringing new challenges for theoretical research on near-field radiative heat transfer.2.Near-field radiative heat transfer between two parallel smooth planes made of metamaterials and that between two parallel smooth planes made of metamaterials and general materials.Near-field radiative heat transfer between two parallel smooth planes made of metamaterials and that between two parallel smooth planes made of metamaterials and general materials are investigated.The effects of optical parameters of metamaterials,different assemblies of metamaterials and general materials,vacuum gap on the near-field radiative heat transfer are calculated and analyzed,revealing the physical mechansim under the near-field radiative heat transfer between two parallel smooth planes made of identical metamaterials and that between two parallel smooth planes made of metamaterials and general materials.3.Tailoring the near-field radiative heat transfer between two parallel smooth planes by inserting a suspended thin film between them.It is well known that far-field radiative heat transfer between two surfaces can be diminished by inserting a radiation shield between them.Due to the near-field effects,near-field radiative heat transfer exhibits much different features from far-field radiative heat transfer.Therefore,this configuration system is introduced into near-field case.By investigating the effects of the inserted suspended thin film on the near-field radiative heat transfer between two parallel smooth planes(including materials of the inserted thin film,position of the inserted thin film,vacuum gap,etc.),the regulation rule of this configuration system on far-field and near-field radiative heat transfer is revealed,establishing a way to control the near-field radiative heat transfer between two closely spaced parallel smooth planes by inserting a suspended thin film between them.4.Tailoring the near-field radiative heat transfer by periodic grating surfacesTailoring the far-field thermal radiation properties by micro/nanostructures has been considerable development.However,tailoring the near-field radiative heat transfer by micro/nanostructures is still in the initial stage and relevant physical mechanism under this radiative heat transfer process is still quite scarce.Based on the scattering matrix method and rigorous coupled wave analysis(RCWA)method,the near-field radiative heat transfer between two parallel graphene-covered rectangular gratings is investigated,which are made of Si-20(which refers to n-type doped silicon at a concentration of 1020 cm-3).The effects of chemical potential of graphene,volume filling factor of grating,grating depth on the near-field radiative heat transfer are calculated and analyzed,establishing a way to enhance and tailor the near-field radiative heat transfer by tuning chemical potential of graphene and volume filling factor of grating.5.Application of near-field radiative heat transfer:graphene-assisted near-field radiative thermal rectifierSimilar to electric rectifier(or electric diode),thermal rectifier(or thermal diode)is a concept of unidirectional thermal transport,in which propagation of heat flux is allowed in a specific direction and inhibited in the opposite direction.Traditional thermal rectifier is resulted from asymmetry of heat conduction or convection system.With the developement of near-field thermal radiation,thermal rectifier based on near-field radiative heat transfer(i.e.,near-field radiative thermal rectifier)invokes increasing efforts.Graphene is applied into near-field radiative thermal rectifier to modify surface properties of near-field radiative thermal rectifier.The effects of chemical potential of graphene and vacuum gap on the performance of near-field radiative thermal rectifier are calculated and analyzed,revealing the change in the radiative heat transfer process and the corresponding physical mechanism under the radiative heat transfer process when graphene is introduced into the near-field radiative thermal rectifier.This work will pave a way to apply graphene into near-field radiative thermal rectifier.