INTRODUCTION OF TWO SOLAR MSF DESALINATION SYSTEMS AND EXERGY ANALYSIS OF THEM BY ``STREAM WISE'' AND ``SINK AND SOURCE'' METHODS

According to the comparison of desalination systems and other energy consuming processes, it is observed that the energy consumption rate of desalination systems is high than that of others. Solar energy is one of the best forms of renewable energies in the world. Therefore, recently, the utilization of solar energy for setting up desalination systems has become quite widespread. Common exergy analysis method by ``Stream wise'' uses input and output exergy of streams assess the exergy efficiency and irreversibility. In the present study, an exergy analysis method namely ``Sink and Source'' is illustrated. The common exergy analysis method usually computes a system's efficiency by more than a rational value. For example, computed exergy efficiency of a high- capacity system through the Stream wise method is 91.84%, while exergy efficiency of a high-capacity system is assessed to be 7.43% through the Sink and Source method. The inefficiency of the traditional method is also shown in the analysis of a low-capacity system. For example, the computed exergy efficiency of a low- capacity desalination system through the Stream wise method is 96.77%, while exergy efficiency of a low- capacity desalination system is 19.57% through the Sink and Source method. There is a theory about the reverse relation of utility fluid temperature and exergy efficiency of systems. The validation of the mentioned theory is measured by Sink and Source exergy analysis method. In the following, in order to reduce energy consumption of the analyzed system, a solar field is suggested for a high- capacity system. Due impossibility of implementing of the mentioned solar field in Iran and the low efficiency of high-capacity desalination plants, a new low-capacity desalination plant is suggested by the imposition of little changes on operating parameters of the high-capacity system. The presented low- capacity desalination system has higher exergetic efficiency and is capable of working with non-concentrating solar collectors. Finally, the proposed argument is validated based on the obtained results, and it is shown that the Stream wise method loses its functionality in some conditions.