Heat and mass transfer analysis in a solar water recovery device: Experimental and theoretical distillate output study

In this paper, an experimental study is presented to investigate the effect of improved heat and mass transfer by using lenses and reflector on the solar still's thermodynamic processes. This study used two identical solar stills with the basin area of 1 m(2): one is conventional solar still (SS) and the other one is a new solar still (NSS) equipped with lenses and mirror. The experimental results showed that the average Nusselt and Grashof numbers inside NSS cavity were enhanced by about 50% and 125% respectively, compared to SS. The maximum output per hour of NSS was 0.437 L/(m(2).hr), and a new thermal model for convective mass transfer in solar still was proposed and established, and the modified values of C and n for Nu = C(GrPr)(n) were proposed as C = 0.9, n = 0.175 for 4.65 x 10(7) < Gr < 3.07 x 10(8). The agreement between the correlations and experimental results was fairly good with an error of about 10%. However, there were deviations between theoretical values and experimental values for Dunkle Model (base on C = 0.075, n = 1/3), and Kumar & Tiwari Model (base on C = 0.0322, n = 0.4114). The maximum value of evaporative heat transfer coefficient predicted by Kumar & Tiwari Model was 218.51% higher than that of the new thermal model in this research. The maximum value of evaporative heat transfer coefficient predicted by Dunkle Model was 137.33% higher than that of the new thermal model. After the performance assessment, it was found that NSS is more effective than the conventional type, and the price of 1 L of fresh water equals 0.305 RMB for this kind solar water recovery device.