The addition of appropriately shaped macroscale structures to a surface results in a directionally selective surface capable of high absorption of direct solar radiation and low hemispherical emission. This work investigates the effect of adding sub-macroscale structures to a smooth surface on net radiative heat transfer. The Monte Carlo method was used to characterize the net radiative heat transfer of rectangular micro- and mini-channels. The effects of varying the aspect ratio, surface absorptivity, and incident angle were determined. The effect of diffuse and specular reflections was also examined. For a diffuse surface, as the absorptivity increases so does the net heat transfer however, higher incident angles result in lower net heat transfer. For a specular surface, net heat transfer increases with both incidence angle and aspect ratio. In general, deeper channels increase net heat transfer. The effect of channel periodicity was also examined. In general, shorter periods increase net heat transfer when normalized by system length.

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