A comprehensive hydrothermal-economy-environmental analysis of flat solar heaters featuring a novel helically canaliculated absorber tube and windowed design turbulator

Flat plate solar collectors provide a cost-effective solution for residential water heating due to their simple design and low production cost. However, their inherently low thermal efficiency limits wider adoption. To address this, the present study proposes a passive enhancement method combining a helically canaliculated flat absorber tube (HCFT) with a novel windowed ramp-shaped turbulator (WRST) to improve heat transfer performance. The design aims to disrupt the thermal boundary layer and promote turbulence, significantly enhancing thermal efficiency. A parametric analysis investigated the effects of channel depth (1–3 mm) and window area (0–56 mm2) on thermal-hydraulic behavior, economic characteristics, and CO₂ emission reduction. Results demonstrated a maximum Nusselt number enhancement of 4.53 times compared to a conventional circular tube, achieved at a 2 mm channel depth and zero window area. This configuration also delivered the lowest levelized cost of energy (0.122 $/kWh), shortest payback period (0.81 years), and highest CO₂ emission reduction (122.3 tons/lifetime), marking it as the optimal economic and environmental choice. From a hydrothermal perspective, the highest performance evaluation criterion (PEC = 1.82) was observed with a 2 mm channel depth and a 56 mm2 windowed WRST, illustrating the trade-off between heat transfer improvement and pressure drop.