Steady-State Exergy Analysis of a Simple Solar Still

Abstract

THIS PAPER PRESENTS A STEADY-STATE, THEORETICAL EXERGY ANALYSIS OF A SOLAR STILL, FOCUSED ON THE EXERGY FLOWS IN THE COMPONENTS OF THE STILL: COLLECTOR PLATE, BRINE AND GLASS COVER. THE ANALYTICAL APPROACH STATES AN ENERGY BALANCE FOR EACH COMPONENT RESULTING IN THREE COUPLED EQUATIONS WHERE THREE PARAMETERS SOLAR IRRADIANCE, AMBIENT TEMPERATURE AND INSULATION THICKNESS ARE STUDIED. THE ENERGY BALANCES ARE SOLVED TO FIND TEMPERATURES OF EACH COMPONENT; THESE TEMPERATURES ARE USED TO COMPUTE ENERGY AND EXERGY FLOWS. RESULTS IN THE STEADY-STATE REGIME SHOW THAT THE COLLECTOR TRANSPORTS 13% OF INCIDENT RADIATION EXERGY TO THE HEAT THE BRINE, WHILE IN THE BRINE THE EVAPORATION EXERGY ACCOUNTS FOR THE 6% OF TOTAL EXERGY. EXERGY/ENERGY RATIO SHOWS THAT THE MOST EFFICIENT COMPONENT IS THE BRINE REACHING MORE THAN 90% FOR ALMOST ANY VALUE OF THE PARAMETERS UNDER STUDY, WHILE THE COLLECTOR HAS A 23% EXERGY/ENERGY RATIO FOR A 1,000 W/M² SOLAR ENERGY INPUT. THE SOLAR STILL IS A DEVICE THAT USES EFFICIENTLY THE HEATING OF A COLLECTOR AND THE GENERAL DISCUSSION ABOUT ITS PROMOTION SHOULD NOT, AS IT MUST BE WITH ALMOST EVERY OTHER SOLAR DEVICE, BE ABOUT THERMODYNAMIC LIMITATIONS.