Energy and exergy analyses of a solar desalination plant for Karachi Pakistan

This paper focuses on the energy and exergy analyses of a passive vacuum solar flash desalination plant for Karachi Pakistan in order to carryout optimum performance analyses and suggest necessary changes by identifying the major losses occurring during the process. Three different novel designs have been analyzed during the course of research. Real time data of solar flux for the region of Karachi has been utilized. To check the performance of all designs throughout the year, average hourly data of solar irradiance for the month of April, June, September and December was taken depicting four major weather conditions at Karachi. Analyses showed that design-1 has higher thermal and exergy efficiency than design-2. However, design-2 promises the longer life of solar collectors by introducing a separate fresh water circuit with inclusion of heat exchanger allowing fresh water to pass through collectors. However, huge amount of exergy destroyed with the brine overboard. Design-3 utilizes economizer heat exchanger aimed to extract heat from high temperature brine overboard. Design-3 yields highest energy and exergy efficiency. Fresh water produced, energy efficiency and exergy efficiency of three designs have been compared for optimum performance. It is concluded that proposed design-3 has highest production rate.