Experimental investigation for improving of stepped solar still efficiency by using paraffin / graphene oxide

The aim of this study is to use graphene oxide (GO) with a volumetric concentration of 0.2, 0.4 and 0.6 in paraffin as phase change material (PCM) to improve the efficiency of solar desalinization for concentrated water desalination programs. The results show that by adding graphene oxide to paraffin, the melting temperature decreases. The solar desalination, which uses paraffin and graphene oxide, has a 25% improvement in sub cooling factor compare to solar desalination, which only works with phase change materials. The Nusselt number obtain during melting also suggests that the free heat transfer in the melting zone of the solar still by adding graphene oxide with a suitable weight percentage in the phase change material compare with that in which paraffin alone is used as a phase change material has been increased. Also, increasing the temperature of the upper hot wall (Th) increases the Nusselt number. Finally, an empirical equation for the relationship between the average Nusselt number as a function of Rayleigh number (Ra), Stefan number (Ste), cooling factor (Sb) and Fourier number (Fo) is presented. The obtain formula shows that increasing the Nusselt number has an inverse relationship with the Fourier number.