Browsing by Author "Ngiliule, Wilfred"

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    Radiative cooling with pigmented films
    (University of Dar es Salaam, 1991) Ngiliule, Wilfred
    Master exchange energy with its surrounding continuously. The exchange can be dominated by radiation, conduction, or convection. In this dissertation a proper design for optimization of spectrally selective surface is considered for radiative cooling with pigment films. These selective surfaces can be capable of reaching low temperature. Radiative cooling occurs under clear and dry sky conditions because the atmospheric emittance is low in the wavelength region of 8-13 um. Efficient radiative cooling is possible with materials which radiate mainly in the atmospheric window and non- absorbing elsewhere. Polyethylene foils containing a non- absorbing pigment can be suitable for radiative cooling. Optical properties in the wavelength range 0.3-100um of extruded polyethylene foil containing several dimension of radius of magnesium oxide, lithium floured and titanium dioxide particles pigmented in to polyethylene foil with varying thickness and fill factors have been studied. They have shown that some pigmented foil and white paint can prevent heating of the underlying material, even when directly exposed to sunlight. LorenZ-Mie theory is used to model the scattering and absorption of single particles. The single scattering parameters are introduced into the four flux theory, by which the totsl transmittance and reflectance are computed and compared to those of Tio2 by Niklasson et al (1998). A satisfactory agreement between then have been observed in most cases.