In this study, the thermal and electrical performance of a photovoltaic/thermal (PV/T) system equipped with spiral and serpentine cooling tubes was numerically compared. The system's thermodynamic behavior was analyzed based on the first and second laws of thermodynamics—using ANSYS Fluent 18.1 software and the finite volume method. Simulations were performed over a Reynolds number () range of 500–20,000 to include both laminar and turbulent flow regimes. The results show that increasing the enhances heat transfer and reduces the PV panel surface temperature; however, this improvement gradually saturates in the turbulent regime due to increased pressure losses. In the laminar regime, the serpentine geometry provides better thermal performance, lowering the panel surface temperature by approximately 0.6–0.9 K compared with the spiral configuration. Conversely, under turbulent flow conditions, the spiral geometry achieves higher overall and second-law efficiencies owing to its more uniform flow distribution, lower pressure drop, and reduced frictional entropy generation. Second-law analysis indicates that although the serpentine path yields slightly higher useful thermal power, the spiral design offers greater energy quality and process reversibility at high values. Therefore, serpentine tubes are preferable for low -applications, while spiral tubes are superior for turbulent flow regimes.
