Effects Of Near-field Thermal Radiation On The Performance Of Energy Conversion

Thermal radiation is generated by electromagnetic waves that are emitted outward due to the thermal fluctuation of free ions.When the gap between two or more bodies at different temperatures is smaller than the characteristic wave of thermal radiation,the heat flux of near-field radiation may great exceed the blackbody radiation limit.In recent years,near-field radiation has received extensive attention,and it has been widely applied in various fields.In this paper,based on efficient energy conversion and transfer characteristics of near-field radiation,the effects of space charge effects and near-field photon tunneling loss on the performance of photon-enhances thermionic emission(PETE)were studied.PETE is a new concept of power generation model to harvest full-spectrum solar energy,and overcome the defects of low efficiency of PV cells and P-N junction even fails when the temperature is high.To relieve harmful space charge effects,the inter-electrode distance is usually suggested to be as small as possible.However,the near-field thermal radiation loss will be increased greatly.Based on the space charge effects and near-field thermal radiation loss,a theoretical model was established to evaluate the performance of PETE.It was found that when the distance is reduced to relieve the space charge effects,the near-field thermal radiation also increase,and there exist an optimal vacuum gap.Through the optimization design of the electron affinity and the thickness parameters of the anode film,it is found that when the electron affinity is 0.88 e V and the vacuum spacing is 0.55?m,the efficiency is 30.3%.When the thickness of the anode film is 0.7?m,the near-field thermal radiation loss is reduced.In addition,the gap distance is separated by micro/nano polystyrene particle,and the near-field thermal radiation heat flux between two pieces of optical glass was measured.In order to verify the accuracy of experimental device,the near-field thermal radiation heat flux between glass-based Si C flim and glass was also measured.The phenomenon of near-field thermal radiation was observed clearly.Experiments are performed in a highly vacuum environment to ensure that the main heat transfer mode is radiative heat flux.Measured the total heat transfer and subtracted the heat transfer of the sphere to get the near-field radiative flux.Under the conditions of micro/nano gap and room temperature,the experimental results clearly show that the near-field thermal radiative flux between two pieces of glass with a diameter of 1cm exceeds the limit value of blackbody radiation.In this paper,a theoretical model combining space charge effect and near-field thermal radiation was proposed to balance the optimal performance parameters of a PETE device.The existence of near-field thermal radiation was verified by experiments,and there has certain reference significance for the subsequent experiments.