An experimental study of radiation heat transfer from opposing parallel plates is described. Surfaces composed of many small grooves were used to fabricate plates having direction-dependent radiation properties. These plates possessed a collimated emission pattern which was found to influence significantly the heat transfer rate, the largest observed effects being approximately 40 percent. It appears that somewhat larger alterations could be achieved with further effort. The measurements obtained in this study establish the potential value of specially prepared surfaces for certain applications requiring improved thermal performance.

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