Performance Enhancement of Double-Slope Solar Still Using Evacuated Tubes under Jordanian Climate Conditions

This study presents an experimental investigation of a double-slope solar still integrated with an evacuated tube collector under the real climatic conditions such as scarcity, particularly in arid and semi-arid regions in Jordan. The system was designed to enhance thermal performance and freshwater productivity while maintaining simplicity and low cost. A key novelty of this work lies in the combined assessment of water pH and water depth as operational parameters in an evacuated-tube-enhanced solar desalination system, introducing a chemical dimension that has received limited attention in previous studies. A double slope solar still with a 1 m² basin area and an evacuated tube solar collector to raise basin water temperature and evaporation rate made up the experimental setup. Both saltwater and greywater were used to evaluate the system at different pH levels (5.0, 6.5, and 9.0) and water depths (2, 4, and 6 cm). The findings show that basin temperature and hourly distillate yield are greatly improved by incorporating evacuated tubes. At a water level of 2 cm, maximum productivity was reached at 5.8 L/day for greywater and 5.0 L/day for saltwater, which is an improvement of 36–52% over deeper water layers. With peak outputs of 7.8 L/day for greywater and 6.5 L/day for saltwater, raising the pH to 9.0 further increased productivity. The energy efficiency and exergy efficiency ranged from 5.2% to 16.2% and 0.8% to 2.5%, respectively, demonstrating the significant impact of operational parameters on thermal performance. Under the same circumstances, the output of greywater was found to be 21.4% greater than that of saltwater. The findings also demonstrated that solar radiation is essential to the desalination process and that productivity is directly increased by higher irradiance. This work offers fresh insight into operational optimization techniques by combining evacuated tubes with a double-slope solar still and concurrently investigating the linked effects of water pH and depth under outdoor settings. The results provide useful recommendations for the development and implementation of effective, affordable, small-scale desalination systems appropriate for areas with limited water resources.