Empirical correlations for heat transfer in a silver nanofluid-based direct absorption solar collector

In this paper, the experimental results of the performance test of a direct absorption solar collector using PVP (polyvinylpyrrolidone) coated silver nanofluid as working fluid were obtained at different operating conditions such as different nanofluid volume fractions, different tilt angles, and different rate of flows. The dimensional analysis technique was utilized to develop an empirical correlation for collector efficiency. Also an empirical correlation is introduced for calculating Nusselt number in terms of Reynolds and Prandtl numbers to specify the amount of heat loss in direct absorption solar collector. Also, a comparison between experimental and correlated results was carried out. The results showed that the bias errors were 2.46% and 5.98% for Nusselt number and collector efficiency, respectively. Consequently, Average Standard Deviation (ASD) values reached 7.31% and 18.04% for both, respectively. The correlations presented can be used in calculating Nusselt number and collector efficiency for performance analysis of direct absorption solar collectors. It helps to enhance design calculations of this new type of solar collectors.