Investigation into sky temperature estimation, its variation, and significance in heat transfer calculations of solar cookers

Abstract

The determination of sky temperature assumes great importance in engineering applications such as radiative cooling of buildings. Many studies that involve a radiative exchange with the sky employ different reported models of sky temperature interchangeably. However, until now, hardly any systematic study has been done to quantify the errors/variations that might be encountered in calculating this radiative exchange employing these different correlations. In the current paper, first, a thorough analysis has been presented on the sky temperature correlations and a possible range of variation in sky temperature based on the estimation of sky emissivity is computed. Both diurnal-nocturnal variation in sky temperature and seasonal disparities in sky temperature have been reported. Next, the case of a box-type solar cooker has been taken up for investigation with respect to the possible influence of the sky temperature estimation in predicting its performance parameter, first-figure-of-merit on a daily, seasonal, and climatic basis. Our observations show an enormous difference in sky temperature depending upon the expressions of emissivity from which it is derived. The variability of sky temperature has a nominal influence on the prediction of first-figure-of-merit, although a marked discrepancy is observed across the seasons at the same location.