Thermo-fluid analysis of a spring fin turbulator placement on the absorber plate of the solar air heater

This study examines the thermal performance of a solar air heater integrated with spring-shaped fins beneath the absorber plate, considering variations in both longitudinal and transverse pitch. The simulations are performed in ANSYS Workbench using the RNG k-ε turbulence model with enhanced wall treatment, accounting for thermal effects and viscous heating. The assumptions considered include steady, turbulent, fully developed flow at the test section inlet, thermally developing conditions, homogeneous and isotropic walls, and no-slip boundary conditions on all fluid-contact surfaces. The fins promote turbulence within the duct, improving convective heat transfer without significantly obstructing the flow. Results show that the Nusselt number increases with a higher number of springs, achieved by reducing either longitudinal or transverse pitch. The effective thermo-hydraulic efficiency rises initially but decreases at higher flow resistance. For varying longitudinal pitch ratios, a pitch of 0.08 produces the highest Nusselt number, while a pitch of 0.16 delivers the maximum thermo-hydraulic enhancement factor (THEF) when two springs are arranged across the width, consistent across the studied flow conditions. Correlations between spring pitch ratios, Nusselt number, and friction factor are developed through regression analysis, exhibiting a maximum deviation of ±10 % from numerical results.