Isaac Garawayand Gershon Grossman
Faculty Of Mechanical Engineering
Technion — Israel Institute of Technology
Haifa, Israel, 32000
e-mail: grace@tx. technion. ac. il
Tel.: +972-4-829-2946 (2074)

Two factors have made solar driven distillation attractive. The first is economical: Desalination, in general, and distillation specifically are energy intensive processes, with the highest single aspect of operating costs being the required energy. With this in mind it would be ideal if one could drive a desalination distillation process with the high amounts of energy provided by the sun. The other aspect that makes this type of desalination desirable is geographical: Most arid and desert regions that are in highest need of desalination are the same areas that have high amounts of solar irradiation. This combination of lacking fresh water and having solar irradiation makes the use of solar energy as the driving force for a desalination process very inviting. At this point however, it is important to mention that even though solar irradiation releases large amounts of energy, it is of low concentration and thus effective collection is generally at low temperatures. An ideal solution to harnessing this energy for desalination would be a device that would operate efficiently at these low temperatures.

As the use of solar irradiation to desalinate water (at temperatures below boiling) became more widespread and accepted, there has begun a more serious development stage focused on trying to improve the operating efficiency over the “simple distiller’s” single effect. In the latter half of the 20th century research has begun on regeneration of the heat provided by the sun for multiple use. Since then, the regenerative process has slowly developed and gained recognition as a form of distillation. Presently this type of distillation is referred to as the MEH cycle — Multi Effect Humidification. To date there are several installations functioning worldwide that employ regeneration [1]. These projects and others reveal an increase in interest and renewed ambition to improve the capabilities of low temperature distillation.

The main objective of this research project has been to improve the design of a solar regenerative distiller. Computational Fluid Dynamics (CfD) was employed to determine the optimum geometry for which such a regenerative distiller operates most efficiently. A laboratory apparatus was constructed and the optimized design tested.