Non-gray radiative and conductive heat transfer in single and double glazing solar collector glass covers

A rigorous model for the radiative heat transfer combined with the conduction and the convection has been applied for a solar collector glazing. The glass cover is analysed as a non-gray plane-parallel medium subjected to solar and thermal irradiation in one-dimensional case, using the radiation element method by ray emission model. The model allows the calculation of the steady-state heat flux and the temperature distribution within the glass cover. The spectral dependence of the relevant radiation properties of glass (i.e. specular reflectivity, refraction angle and absorption coefficient) is taken into account. Both collimated and diffuse incident irradiations are applied at the boundary surfaces using the spectral solar model proposed by Bird and Riordan. Single and double glasses commonly used for the glass cover are considered. The optical constant of a commercial clear glass material have been used. These optical constants of real and imaginary parts of the complex refractive index of the glass, determined by the author from 0.19 to 5 μm combined by those reported by Rubin from 6 to 300 μm have been used. The calculation has been performed for both single and double glazing cover at low and high temperature of the absorber. The effect of the thickness of the single glass cover has been also discussed. The result shows that increasing the thickness of the single glass cover, the steady heat flux decreases at both low and high temperature of the absorber. It has been also shown that the double-glazing cover assembly is more suitable than the single one at high temperature of the absorber.