DESIGN AND CONSTRUCTION OF A PYRAMID-SHAPED SOLAR
CHAPTER ONE
1.1 INTRODUCTION
Distilled water is needed for drinking, irrigation and for many other applications. A diversity of approaches are used for these portions of fresh water from saline water; namely multi stage flash (MSF), multiple effect (ME), reverse osmosis (RO), electro dialysis, ion exchange, phase change, and solvent extraction. These methods are expensive, however, for the production of small amount of fresh water. The development of solar distillation has demonstrated its suitability for the desalination process when the weather conditions are suitable and the demand is not too large, i.e. less than 200 m³/d. The problem of low daily productivity of the solar stills triggered scientists to investigate various means of improving the stills productivity and thermal efficiency.
Different aspects of triangular-shaped solar stills (CSS), also called double slope stills, have been studied. Production in this still is influenced by the orientation, as shown by (Singh et al., 1995) who found the maximum yield for a cover with east–west. Detailed studies of heat transfer coefficients can also be found, (Sharma and Mullick, 1991), in which energy transfer mechanisms, such as convection, evaporation and radiation are investigated, and new empirical relations to estimate cover temperatures are proposed. To model heat and mass transfer in solar stills ( Dunkle, 1961)  proposed the use of a correlation of the form where C is 0.075 and n is 1/3 for air enclosed between horizontal parallel plates. This correlation is expressed in terms of a modified temperature difference that includes molecular weight and buoyancy, and considers the cover as a single element. This has been the most widely accepted model for solar stills and describes the basic heat and mass transport mechanism between heated water mass and a condenser.
