Experimental performance, exergy, and economic analysis of an oval tubular solar still integrated with nano-enhanced phase change material

Abstract Freshwater scarcity remains a major challenge in arid and coastal regions, and conventional solar stills often suffer from low productivity, limited thermal efficiency, and high operational costs, highlighting the need for improved designs. This work examines a new form of the oval tubular solar stills, OTSS. This study focuses on enhancing the daily, nighttime, and overall (diurnal) productivity of freshwater by employing advanced materials. In the present investigation, paraffin wax (PW) was used as a phase change material (PCM), while nano-alumina-enhanced paraffin wax (NAPW) was applied to improve the thermal conductivity of PW. The OTSS is a simply distinguish design, lower cost, and high production rate of desalinated water. The OTSS is used with PW, without PW, and with NAPW. The experiments were conducted under Cairo, Egypt climatic conditions (Latitude 30.10 N longitude 31.29E) with varying basin water depths (0.5–2 cm) and Al 2 O 3 concentrations (0.1–0.3 wt%). Results show that OTSS with PW achieved a maximum productivity of 6.53 L/m 2 /day, while the addition of NAPW further increased productivity to 7.26 L/m 2 /day and thermal efficiency to 68.24%. Daily thermal exergy efficiency improved from 3.41% (without PW) to 4.52% (with NAPW), and the production cost decreased from $0.0208 to $0.0163 per liter. The study demonstrates the effectiveness of integrating PCM and nanoparticles in OTSS to improve freshwater yield, thermal performance, and economic feasibility.