Radiative Heat Transfer Between Two Closely-Space Plates

Abstract

*Enhanced radiative heat transfer by proximity effect has been confirmed both theoretically and experimentally since the early 1970’s. The proximity effect indicates that heat transfer increases rapidly with spacing much smaller than dominated wavelength. This topic was recently investigated on dielectric materials for a thermophotovoltaic application, in which photovoltaic efficiency may be enhanced through proximity effect. We report a numerical result on the radiative heat transfer between a pair of parallel electrodes in a new thermotunneling application, in which the spacing between the electrodes is in the nanometers range. Two electron models along with optical data were used for the calculation. Although the calculation is mainly for absorptive materials, review for homogeneous media is also included. The motivation of our work is to compute the heat loss through thermal radiation as part of energy budget in a thermotunneling, direct thermal to electric conversion (DTEC) device. This device may offer a much higher theoretical efficiency than thermoelectric devices since it has a vacuum gap so thermal backflow and Joule loss are minimal in the gap. We have found that the radiative heat loss is greater than Planck blackbody radiation by one to two orders of magnitude.