Small distance expansion for radiative heat transfer between curved objects

We develop a small distance expansion for the radiative heat transfer between gently curved objects, in terms of the ratio of distance to radius of curvature. A gradient expansion allows us to go beyond the lowest-order proximity transfer approximation. The range of validity of such expansion depends on temperature as well as material properties. Generally, the expansion converges faster for the derivative of the transfer than for the transfer itself, which we use by introducing a near-field adjusted plot. For the case of a sphere and a plate, the logarithmic correction to the leading term has a very small prefactor for all materials investigated.National Science Foundation (U.S.) (NSF Grant No. DMR-12-06323)United States. Dept. of Energy (DOE grant No. DE-FG02-02ER45977)Deutsche Forschungsgemeinschaft (DFG grant No.KR3844/1-1