Comparison between energy and exergy efficiencies in a weir type cascade solar still

In this paper, a theoretical and experimental study of the energy and exergy efficiencies of cascade solar still is presented. By writing energy and exergy conservation equations for glass cover, brine, and absorber plate; correlations among climatic parameters, energy efficiency, exergy efficiency, and irreversibilities were provided. A computer simulation package was developed to analyze the energy and exergy effects. Effects of various parameters such as inlet brine flow rate, water thickness over the absorber plate, solar radiation intensity, ambient temperature, and inlet brine temperature on the energy and exergy efficiencies were investigated. The simulation results are in good agreement with the experimental data. Data analysis revealed that the maximum energy and exergy efficiencies which are 83.3% and 10.5% respectively are met when inlet brine flow rate reaches its minimum at 0.065 kg/min. Moreover, a comparison between exergy and energy efficiencies in terms of computational and experimental data for minimum and maximum input brine flow rates yielded RMSD of 7.34% and 3.8% for exergy efficiency and 6.11% and 4.25% for energy efficiency. Also, the analysis of irreversibility for different parts of the still in a specific day revealed that 84.17% of the entire system irreversibility was produced by the absorber plate.