Enhanced webbed-tubes thermal storage unit for solar heaters

• The webbed tube HE, and NEPCM are used to improve solar water heater efficiency. • The tubes configuration highly influences the velocity and heat transmission. • Tube placement at the bottom reduced melting time by 44%. • Nanoparticles at 4% concentration reduced melting time by 8%. Transitioning to low-energy buildings is crucial for environmental sustainability and aligns with sustainable development goals (SDGs) 7, 11, and 13. This study aims to enhance the energy efficiency of domestic solar water heaters by integrating a thermal energy storage (TES) unit with nano-enhanced phase change material (NePCM). A webbed tube heat exchanger, consisting of four inner tubes and one outer tube, is investigated to optimize heat transfer performance. Using the enthalpy-porosity approach, the study numerically analyzes the effects of different tube arrangements (nine cases: C1–C9) and nanoparticle concentrations (0, 2%, and 4%) on the phase change process. The results demonstrate that tube arrangement significantly influences heat transfer uniformity and PCM melting efficiency. Configurations C4 and C5 (tubes positioned near the bottom) reduce the melting time by 44% compared to the reference case (C1). Increasing nanoparticle concentration to 4 vol% further accelerates PCM melting by 8% compared to 2 vol%. These findings provide valuable insights for optimizing TES systems in solar water heaters, promoting efficient energy storage and utilization in sustainable building applications of nanoparticles.