Chemical and Biomolecular Engineering Faculty Research


Modeling of Emission Properties from a Spatially Distributed Selective Emitter

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Preliminary analyses are presented to examine how the geometric distribution of rare-earth material in a thin film selective emitter influences the net emission. The general one-dimensional equation of radiation transfer is considered under the assumption of negligible rescattering by eliminating the phase function term. Due to the large value of the absorption coefficient for the materials under discussion, the diffusion approximation to this equation is used. Homogenization techniques are applied to this diffusion approximation to define expressions for the effective absorption and scattering coefficients for a spatially distributed selective emitting film. The emitting film consists of alternating layers of emitting and nonemitting materials into a form we call stacked layers. The optical properties of the individual layers are determined experimentally. These properties are input into the effective expressions for the absorption and scattering coefficients. The effective expressions are input into the general one-dimensional equation of radiation transfer to model the net radiation obtained from these emitting structures in directions parallel and perpendicular to the stacked layers. Results show that the emissivity of the film along the parallel direction of the stacked layers exceeds that along the perpendicular direction. Further, a film consisting of stacked layers with half the volume fraction of emitting material emits radiation along the parallel direction that is quantitatively comparable to the emission from a film consisting of a single layer of only emitting material. Hence, the reduction in emitting material may lead to a drop in the weight of the device and to lower costs.

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Journal of Applied Physics



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