A new fenestration material for heat protection

Abstract

This work applies the Mie scattering theory to the case of polydisperse spherical air bubbles embedded in a transparent medium. It calculates the attenuation through such medium of normally incident solar radiation. The attenuation depends on the size parameter, x; where x is 2 π times the ratio of bubble radius to the incident wavelength. By proper choice of the bubble size the attenuation can be made skew with respect to the wavelengths of incident solar radiation. A practical application of this theory has been made in the design of fenestration material. The bubble size can be so chosen as to attenuate the larger wavelengths considerably more than the shorter ones. This will suit the fenestration requirements of the tropical climate, insofar as the elimination of heat is desirable. A fenestration material (a Perspex sheet with air bubbles embedded in it) based on these considerations has been prepared and attenuation of normally incident radiation from an artificial source, simulating solar radiation, through it has been measured experimentally. The results are in good agreement with the theoretical calculations obtained for such case. The cut-off is about 14%.