Effect of Absorption of Solar Radiation in Glass Cover(s) on Heat Transfer Coefficients in Flat Plate Solar Collectors with Single and Double Glazing

摘要

The governing heat transfer equations for the case of single as well as double glazed flat plate solar collectors including the effect of absorption of solar radiation have been solved for inner and outer surface temperatures of glass cover(s) with appropriate boundary conditions. The effects of absorption of solar radiation on inner and outer surface temperatures and consequently on convective and radiative heat transfer coefficients have been studied. The increase in glass cover temperature due to absorption of solar radiation of a single glazed collector could be as high as 6 degrees. For a double glazed collector the increase in temperatures of first and second glass covers could be as high as 14 degrees and 11 degrees, respectively. The increase in glass cover temperature due to absorption of solar radiation affects the values of heat transfer coefficients, specifically the convective heat transfer coefficient between the absorber plate and the glass cover. The difference in the values of the convective heat transfer coefficients between the absorber plate and the first glass cover (h_(cp1)) of a double glazed collector for the two cases: (i) including the effect of absorption and (ii) neglecting the effect of absorption in glass cover, could be as high as 49 percent. Correlations for computing the temperatures of inner and outer surfaces of the glass cover(s) of single and double glazed flat plate collectors including the effect of absorption of solar radiation in glass cover(s) are developed. By making use of the relations developed for inner and outer surface temperatures of glass cover(s) the convective and radiative heat transfer coefficients can be calculated so close to those obtained by making use of surface temperatures of glass cover(s) obtained by numerical solutions of heat balance equations that numerical solutions of heat balance equations are not required.