The paucity of freshwater is very dangerous in the coming years. Many coastal countries suffer from a scarcity of freshwater. Solar desalination is the cheapest way to produce freshwater from any type of non-drinkable water (brackish water and seawater). In this work, single-slope single-basin solar still for seawater desalination was examined under Upper Egyptian weather conditions of Qena City (latitude 26.16°, longitude 32.71°). The main goal of the work is to compare the performance of conventional solar still, solar still supported with PCM, and solar still supported with local clay material to augment the solar still yield during both daytime and nighttime periods of operation. The results demonstrated that the total production of desalinated water from the simple conventional solar still, the solar still with PCM, and the solar still with local clay reached about 3885, 4704, and 5388.6 ml/m², respectively. Moreover, compared to the conventional solar still, the yield was increased by about 21% when using the PCM, and about 38.7% when using the local clay material. Furthermore, it can be observed that the daytime productivity in the case of solar still supported with local clay was higher than that for the solar still supported with PCM, while the nighttime productivity was higher in the case of solar still supported with PCM compared with solar still supported with local clay. Moreover, the average daily efficiency of conventional solar still, solar still with PCM, and solar still with local clay reached about 34, 41.2, and 47%, respectively. Therefore, it is recommended to use the solar still with local clay for seawater desalination in such arid and hot climate of Qena City.

Clean water is quickly decreasing as the necessity for it rises year after year. Desalination of seawater is the only means to remedy this problem. The scientific community has focused on solar powered salty water desalination devices as a clean alternative throughout the last few decades. Solar stills convert solar energy into the heat required to generate clean water through the evaporation and condensation processes. The two very popular varieties of solar stills are active, and passive based on the heat source to evaporate the basin water, which can be either directly through the sun or indirectly using external heat sources such as concentrating collectors which are coupled with desalination units. This article provides an exhaustive analysis of active solar stills’ advancement with solar concentrating systems and techniques for improving performance, desalinated water production, efficiency, and maximum output. This work intends to keep researchers and the scientific community informed about developments in active solar stills equipped with solar concentrators.

The concentric impact on a sessile drop is relevant in many applications, including spray coating and icing phenomena. Herein, the spreading and retraction phases yielded during the impact of a coaxial drop with a sessile drop on a solid substrate were empirically and analytically examined. We analyzed the effects of surface wettability on the impact outcomes utilizing five distinctive surfaces (i.e., smooth glass, aluminum, copper, Teflon, and coated glass). The results showed that the merged drop takes longer to attain its maximum spreading diameter at a relatively higher contact angle of the sessile drop with the solid surface. Furthermore, based on energy balance, a model for predicting the maximum spreading diameter of the drop with varying surface wettability was presented. This model considers the assumption of viscous energy loss during the merging of falling and sessile drops and at the maximum spreading diameter. Additionally, the maximum retraction height during the impact on the coated glass surface was investigated. Our model results matched well with the experimental data.

Water scarcity poses a major challenge for the next generation. Additionally, increasing agricultural and industrial activities are creating an unprecedented demand for freshwater supplies throughout Egypt. The Nile River serves as Egypt’s primary water source, accounting for 69.4% of the total water resources. Moreover, Egypt's annual share of water has decreased to approximately 500 m ³ per person because of the completion of the Renaissance dam in Ethiopia and the rapid increase in population growth. Solar distillation has been presented as a long-term and promising method for producing edible drinkable water. The present research goal is to increase the daily freshwater output from a stepped pyramid solar still (SPSS) by coupling with a solar parabolic dish (SPD). The proposed system consists of a conventional pyramid solar still (CPSS) and a modified pyramid solar still (MPSS). The main components of an MPSS include an SPSS, a PV panel, an SPD with a spiral coil, a circulating pump, and an Arduino Mega Unit. The developed system was designed, fabricated, and verified from July to August 2023 at the Faculty Engineering, South Valley University. The results of the experiments indicated that the daily productivity of freshwater from MPSS was greater than that from CPSS and reached 6038 and 2612 mL/day, respectively, with an increase in the daily yield of 131%. The peak energy efficiency is 56% for the MPSS and 24% for the CPSS. The peak exergy efficiency is 4.26% for the MPSS and 3.79% for the CPSS. Additionally, the cost analysis of the suggested system revealed that the estimated cost per liter of the proposed system is 0.01635 USD/L.

In this work, an experimental study on new series connection of two Ranque-Hilsch vortex tubes with new vortex generator materials, potential in seawater desalination was implemented, this combined modification has not been studied in open literature. Polycarbonate and Polyamide-Nylon 6 were tested and compared as new vortex generator materials that enhance the heat transfer between the two air streams inside the vortex tube. Moreover, using new seawater preheater by utilizing the waste heat in the exit air stream from the last vortex tube in the arrangement. The results revealed that the hot fraction of both arrangements should be kept at 0.5 for optimum vortex tubes series connection performance. Moreover, the modified series arrangement with Polycarbonate generator had higher evaporator main hot temperature and lower condenser main cold temperature than that of the modified series arrangement with Polyamide-Nylon 6 generator. Furthermore, the desalinated water percentage of Polycarbonate generator connection and Polyamide-Nylon 6 generator connection were reached about 94% and 89%, respectively. Therefore, the modified series hot connection of Ranque-Hilsch vortex tubes with Polycarbonate based vortex generator is recommended for use in seawater desalination applications.