Combined effects of evaporation and cavitation on the performance of a renewable energy powered natural vacuum desalination unit in Bahrain

Abstract

The renewable energy powered natural vacuum desalination unit (NVDU) presents a promising alternative technique for seawater desalination and wastewater treatment, with low energy consumption, simple technology, and resulting clean environment. The problem of the low daily productivity of the NVDU motivated researchers to investigate various means of improving its productivity and thermal efficiency in order to reduce the production cost of freshwater. This study investigates experimentally the performance of the NVDU under the combined effects of evaporation and cavitation on freshwater production rate. The NVDU consists of an inverse U-shaped pipe, with one side acting as the evaporator and the other side as the condenser. The experiments were conducted under three different sets of conditions. The first had ambient conditions on both sides, the second used a water-ring vacuum pump to create a buoyancy effect, and the third was similar to the second set of conditions, but with cooling of the condensation side. The results show that the last case increased the freshwater production rate by approximately 70 times compared to the first case, while in the second case, the production rate was roughly 13 times better than in the first. These results could be attributed to the combined effects of evaporation and cavitation. This attribution is supported by the visualization of bubble motions.

Keywords:

• Renewable
• Natural vacuum
• Desalination
• Cavitation

Acknowledgments

This work was supported by the University Bahrain Deanship of Research under Grant (2008-10).

Devices were fabricated in the Mechanical Engineering Workshop at the University of Bahrain.