Augmented heat and mass transfer effect on performance of a solar still using porous absorber: Experimental investigation and exergetic analysis

In this paper, an experimental study is performed to investigate the influence of heat and mass transfer enhancement on the solar still thermodynamic performance by using porous absorber. This study used two identical solar stills with the basin area of 1 m(2): one is conventional and the other has a layer of fine basalt stones in the base of the still as a porous absorber with different particle size (1 cm, 1.5 cm and 2 cm). The experimental results showed that the average Nusselt and Sherwood numbers inside the solar still cavity by using porous bed with different porosity based on stone particle size were enhanced by about 115% and 51.95% respectively. Also, The exergy efficiency of the solar still with the 1 cm, 1.5 cm and 2 cm fine stone particle size was enhanced by about 65%, 104.4% and 123% respectively compared to solar still without stones. In addition, the empirical correlations to estimate the Nusselt and Sherwood numbers inside the solar still cavity were obtained. The agreement between these correlations and experimental results was fairly good.