الفهرس 
CHAPTER (1): INTRODUTIONOnly 14 pages are availabe for public view
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Abstract
The world demand of potable water is a major problem in under-developed and in some developing countries. Water is evaporated on the earth’s surface with absorption of evaporation heat from solar energy. The basin-type solar still duplicates this natural process on a small-scale. The saline water and abundant solar energy are available in Egypt. The basin-type solar still may be an important source of fresh water in remote areas or arid zones. In this work, three solar still models were designed, fabricated and tested at Faculty of Engineering, Shebin El-Kom (latitude of 30.5° N - Longitude of 31° E) Menoufia University, Egypt. These models are constructed with materials that are readily available in the local area. The models are: 1- Double Slope Solar Still [DSSS]. 2- Modified Double Slope Solar Still with Internal Parabolic Reflector [MDSSS]. 3- Modified Double Slope Solar Still with External Flat and Internal Parabolic Reflectors [MDSSSER]. The model 1 was used to compare the performance of the models 2 and 3. The experiments were carried out during the months of June and July 2013 and continued at July 2015. All solar still models were operated under the same hour in each tested day to compare their performance and to determine the best productivity. All solar still models were constructed using the same basin area of 1000 mm x 500 mm. The solar still models condensing glass covers are inclined at 21° on both sides with respect to horizontal. The temperatures of the condensing glass cover surface, vapour, water and basin surface as well as the ambient and wet bulb temperatures are measured every hour. In addition, the both solar radiation and distilled fresh water are recorded continuously. In this study, the effect of the external flat reflector tilt angle on the performance of the modified double slope solar still [MDSSSER] and the best tilt angle are investigated. The external flat reflector is tilted at 30°, 45°, 60° and 75° on the horizontal plane directed to south facing when the water depth inside the basin is 1 cm. The best external reflector tilt angle is found to be 60° with a maximum experimental daily productivity of 9.89 lit/m2 for the modified double slope solar still [MDSSSER].
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The effect of water depth on the performance as well as the productivity of solar still models was studied. In addition, the analogy between heat and mass transfer was taking into consideration. The depth of water in the basin was maintained at 1 cm, 2 cm and 3 cm after fixing the orientation of tested solar stills towards the south to receive the largest possible amount of solar radiation. The combined effect of evaporative and convective internal heat transfer can be predicted by Nu = C(Gr.Pr)n and the convective mass transfer coefficient can be determined by Sh = C’(Gr.Sc)n’. The constants C, n, C’ and n’ for the dimensionless convective heat and mass transfer correlations were determined using linear regression analysis. It was observed that the proposed models give closed results with the experimental observation for all tested solar stills.
The solar still [MDSSSER] with external reflector tilt angle of 60° on horizontal plane and water depth of 1 cm has the highest accumulated productivity compared to the other tested solar still models and water depths, while the solar still [DSSS] has the smallest values. The maximum amount of accumulated productivity reaches to 9.89 lit/m2, 8.7 lit/m2 and 8.118 lit/m2 at water depths of 1 cm, 2 cm and 3 cm respectively with respect of [MDSSSER], while the minimum values of 3.26 lit/m2,
2.95 lit/m2 and 2.676 lit/m2 are recorded at the same water depths, respectively with respect of [DSSS]. The use of the solar still [MDSSSER] with external reflector tilt angle of 60° increases the fresh water accumulated productivity compared to solar still [DSSS] and solar still [MDSSS] at constant water depth of 1 cm by 203.37 % and 30.61 %, respectively. These values reached to 194.92 % and 18.17 % as well as 203.36 % and 18.10 % at water depths of 2 cm and 3 cm for the previous tested solar stills, respectively. Finally, the performance of the fixed and moveable solar still [MDSSS] with changing solar radiation direction was studied. The results showed that, the amount of accumulated fresh distillate water for the fixed solar still [MDSSS] is higher than that of the moveable one by 72.5 % at water depth of 1 cm.