Improving performance of an inverted absorber multi-effect solar still by applying exergy analysis

Abstract

In this paper, the energetic and exergetic analyses of an inverted absorber multi-effect solar still has been studied. A new criterion was defined to determine the efficiency of the first law of thermodynamics for multi-effect solar stills. Energy and exergy balance equations have been developed for water basins, condensing surfaces and absorber plate to evaluate the irreversibility through the various components. Heat and modified mass transfer coefficients along with accurate properties of humid air were used to solve the governing system of differential equations. Results affirmed that the exergy loss through the absorber plate, water basins and condensing covers in a certain basin decrease as the number of effects increase. However, the increase in basins number from one to ten leads to increase in total irreversibility through the water basins by 337%. Calculations on energy balance equations showed that with increase in effect from one to ten, heat transfer to ambient decreased by 74.8%, which in turn increased the first law efficiency by 174.6%. It is found that with increase in effect from one to ten, the total yield, irreversibility and overall second efficiency increased by 407.3%, 10.4% and 471%, respectively, but global second efficiency decreased by 20.6%.