الفهرس 
Chapter 1 : Introduction and Literature reviewOnly 14 pages are availabe for public view
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Abstract
The present study aims at augmentation of tubular solar still performance by additional improvements on designing and manufacturing of the tubular solar stills and by utilizing energy storage materials. The present study aims at obtaining the highest performance of tubular solar still. To achieve this goal, the present study has with five proposed modifications, they are as follows:
In the first proposed modified design of tubular solar stills, the trough was proposed in the form of two concentric semi-cylinders to increases the absorbing surface area of the solar radiation. Also, the cylindrical parabolic concentrator, CPC, was used to increase the intensity of the incident solar radiation on the absorbing surface. Also, the effect of saltwater layer thickness between the two concentric semi-cylinders on the performance of modified tubular still was studied to obtain the optimal saltwater-layer thickness. Four different designs of the modified tubular solar still with several saltwater-layer thicknesses (1, 2, 3, and 4 cm) were studied and compared to the conventional tubular still with a rectangular trough to obtain the optimal design of the modified tubular solar still. Experimental results showed that the improvement in accumulated productivity of the modified tubular still reached to 87.9%, 90.8%, 81.9%, and 68.1% for the saltwater layer thickness 1, 2, 3, and 4 cm, respectively compared to conventional tubular still with a rectangular trough. Also, the daily efficiency of modified design reached 60.4%, 61.4%, 58.5%, and 54.1% for saltwater-layer thicknesses 1, 2, 3, and 4 cm, respectively. But for the conventional case, the daily efficiency reached 32.2%. It is clear from the results of the experimental study, the modified design of tubular solar still is more effective, and the optimal thickness of the saltwater layer between two concentric semi-cylinders is 2 cm.
In the second proposed modified design of a tubular solar still, effects of using hybrid storage materials and using cylindrical parabolic concentrator, CPC, on a performance of the modified tubular solar still with two concentric semi-cylinders were investigated. The inner semi-cylinder was filled with paraffin wax and a graphite sheet was placed on the top surface of the inner semi-cylinder in order to improve thermal properties. The paraffin wax and graphite are the hybrid storage materials utilized in this study. To achieve experimentally this goal, conventional tubular solar still and the proposed modified tubular solar still with hybrid storage materials and with CPC have been tested in the city of Tanta under Egyptian climatic conditions. The experimental results show that the accumulated productivity ranges between (5.79-5.94) and (9.56-9.81 l/m2) for conventional and developed tubular stills, respectively. Also, the daily efficiency ranges between (37.2-38.1) and (44.2-45.3%) for the conventional and developed tubular stills, respectively. Improvements in the daily productivity and daily efficiency of developed tubular still ranges between 65.1-65.4% and 18.9-19.1% respectively compared to a conventional tubular still.
In the third proposed modified design of tubular solar stills, the closed copper tubes filled with, phase change material, PCM, also, to extend the distilled water production time after the sunset. To investigate the influences of using the proposed modified design on the performance, both the conventional unit and the modified the tubular still were tested at the same Egyptian climate conditions. During the period June-August 2019, the results show that accumulated productivity of the conventional tubular still varies between 4.1-4.31 l/m2/day, while the productivity of the modified still varies between 8.82-9.05 l/m2/day with 110-115.1% enhancement. Also, during this period the daily efficiency of conventional tubular still ranges between 32.9-33.8%, while the design modification increases the daily efficiency to 70.9-72.7% with 114.4-115.5% enhancement. These results presented that the copper tubes filled with PCM represent good options to obtain a higher performance of tubular solar still.
In the fourth proposed modified design of tubular solar stills, the modification was done by using the v-corrugated absorbers and including wick materials to maximize the rate of evaporation, by maximizing utilization of the large condensing surface area that characterizes the tubular solar stills to increase the distilled water productivity. This goal was achieved by forming the absorbing surface in a v-corrugated form and using black jute cloths that are attached to the v-corrugated surface so that they take the same corrugated form and the lower half of the corrugated black jute cloths was immersed in water and the rest of the cloths are saturated with water by the capillary property. The performance of modified tubular still with v-corrugated wick materials and conventional tubular still with flat absorber surface was compared under the weather Egyptian conditions to characterize the performance enhancement of the modified design. The results show that the conventional tubular still gives the accumulated distillate production of 4150 ml/m2 while the v-corrugated wick materials utilization improves the distillate production to 6010 ml/m2, with 44.82% improvement in the productivity. Also, the average efficiency along the test days for the conventional tubular still reached 35%, while the v-corrugated wick materials utilization improves the average efficiency to 51.4%, with 46.86% improvement in average efficiency.
In the fifth proposed modified design of tubular solar stills, the influences of a floating sponge on the tubular solar still performance were investigated. Several thicknesses (20 - 40 mm) and densities (16 - 30 kg/m3) of the floating sponge layers were tested at the same saltwater depth of 10 mm in basin to obtain the optimal feature (density and thickness) of a floating sponge layer. The results report that the utilization of a floating sponge improves the tubular still performance. The utilization of a sponge with a density of 16 kg/m3 gives the distillate production and efficiency higher than conventional units, this improvement decreases with increasing the density of sponge. Moreover, the efficiency and pure water production increases with increasing the sponge thickness from 20 - 30 mm and then decreasing at 40 mm thickness. Finally, the maximum recorded accumulated distilled water productivity and thermal efficiency reached 5.92 l/m2/day and 48.37%, respectively, when utilizing a sponge layer with a 30 mm thickness and 16 kg/m3 density, with the corresponding improvement of 59.8% and 58.5%, respectively, compared to the conventional unit.
The six proposed modified design of tubular solar stills utilizes pin fins and an external condenser is coupled with the tubular solar distiller.
The tubular distillers characterized by having a large receiving and condensing surface area compared to a conventional single-slope distiller, therefore, the utilization of pin fins is very effective to increase the evaporation rate, as well as, the external condenser was utilized to increase the condensation rate. In order to achieve this vision, the experimental study mainly included two axes, namely: in the first axis, the effect of utilizing the pin fins on the cumulative yield of tubular solar distillers was studied, as well as, obtain the optimal orientation of the pin fins to reduce the shadow effect generated inside the basin. In the second axis, the effect of utilizing an external condenser and the inclined pin fins on an accumulative yield of the tubular solar distiller was studied
A conventional tubular solar still, modified tubular solar still with vertical pin fins, and modified tubular solar still with inclined pin fins were constructed and tested simultaneously. In the second study axis, a conventional tubular solar still and a modified tubular solar still with inclined pin fins and condenser were constructed and tested. The results indicate that the enhancement in accumulative yield reached 18% and 27.6% for utilizing the vertical and inclined pin fins, respectively as compared to the conventional tubular solar still. These results show that the utilization of inclined pin fins represents a good option to improve the accumulative yield of tubular distillers. Also, the accumulative yield and the daily efficiency achieved by utilization of the external condenser and the inclined pin fins reached to 5.94 L/m2/day and 54.9% with an improvement of 70.2% and 71.6%, respectively as compared to the conventional tubular solar still.