A solar driven sea water desalination system operating under natural vacuum has been developed,
constructed and tested. The system utilizes the natural forces of gravity and atmospheric pressure to create
vacuum under which water can be evaporated at temperatures lower than those in conventional techniques
and allowing the use of low -grade heat sources. The proposed desalination system consists of a condenser
and a solar flat plate collector acting as an evaporator. An extensive experimental study has been carried
out to investigate the effect of condenser cooling mode on the system performance. The external surface of
the condenser has been cooled by using three cooling modes; namely, free convection air cooling, forced
convection air cooling, and forced convection water cooling. The effect of cooling modes on the system
performance has been studied under actual weather conditions. The system performance has been
characterized by its fresh water productivity and the performance ratio. The results showed that forced
cooling mode causes a lower pressure inside the system than free cooling mode, and water cooling is more
effective than air cooling. The average pressure inside the system is about 0.122, 0.106, and 0.09 bars
absolute respectively for free air cooling, forced air cooling and water cooling. The cumulative productivity
is maximum in the case of external water cooled reaching a value of 6.6 l/m2
.day. In case of forced and free
air convection, the daily system productivity 5.3 and 2.7 l/m2
.day respectively. The average performance
ratio was about 70 % which is twice the value for a conventional solar still reported in the literature.