Exergy analysis of solar desalination still combined with heat storage system using phase change material (PCM)

The exergy analysis of a passive solar still combined with heat storage system is presented in meteorological conditions taken on 15th of June 2011 at Errachidia city (Latitude: 31°58'N, Longitude: 4°20'W, Morocco), to determine the magnitude of exergy losses during the heat storage/retrieve period. Paraffin wax is used as phase change material (PCM) to store/retrieve energy in the process of changing the aggregate state from solid to liquid. The exergy balance equation for each element of the desalination unit as well as for the PCM is formulated and numerically solved. The variations versus time of temperature within PCM, the exergy destruction of solar still and that of PCM medium, the pure water productivity and exergy efficiency are shown in the obtained results. Effects of the influencing parameters (the thickness of the PCM medium, the ambient air velocity and the brackish water depth) on the exergy destruction (entropy generation) are highlighted. Moreover, the latent heat storage increases the water productivity and reduces the exergy efficiency.