Performance Analysis and Enhancement of Solar Water Heaters Using Passive Augmentation Techniques

With conventional fossil fuels depleting rapidly and process heating consuming over 42% of refined crude oil, solar water heating systems (SWHS) have emerged as a paramount renewable technology. Solar thermal systems achieve conversion efficiencies exceeding 70%, greatly surpassing photovoltaic systems (~20%). However, flat-plate and evacuated-tube solar collectors (ETSC) suffer from severe internal thermohydraulic bottlenecks, including laminar flow regimes, boundary-layer conductive resistance, and bi-filamental counter- current flow with stagnant bottom dead-zones. This review synthesizes key experimental, numerical, and thermodynamic findings across three foundational review documents, covering continuous twisted tapes, pitch variation, strip orientation, cutouts, circular perforations, wavy tapes, and phase change materials (PCMs). Passive inserts induce secondary swirl flow, generate Dean vortices, disrupt thermal boundary layers, and reduce hydraulic diameter, enhancing convective heat transfer coefficients by 18% to 70%. In evacuated tubes, drilled twisted tapes elevate water temperature to 82.4°C (+28.8°C over plain) and daily thermal efficiency to 87.9% (+28.4%). Perforated wavy tapes eliminate bottom dead-zones, achieving 49.36% energy efficiency and 5.20% exergy efficiency (+70.2%). Combining wavy tapes with eutectic PCM (stearic-palmitic acid) yields peak temperatures of 74.4°C and a 75.5% surge in daily exergy efficiency while mitigating up to 42.81 tons of CO2 annually. Authentically reproduced diagrams from all three uploaded papers are integrated to visually elucidate the underlying hydrodynamics, test facilities, and thermal performance characteristics.