A comparative investigation of thermo-hydraulic performance in a solar air heater roughened with quarter petal shaped ribs

Through a numerical study, the thermo-hydraulic behavior of a solar air heater with quarter petal shaped ribs on its absorber plate is examined including a comparative evaluation of three unique rib configurations. The continuity, momentum (Reynolds-Averaged Navier-Stokes) and energy equations of steady, incompressible, turbulent flow are solved. Renormalization Group (RNG) k -ε turbulence model was chosen to solve the turbulent flow phenomena. The thermal performance has been studied under varying design parameters: relative roughness pitch (7.14 ≤ P/e ≤ 17.86), Reynolds number (4000 ≤ Re ≤ 20,000), while the relative roughness height was kept constant at e/D h = 0.042. The key performance indicators of the SAH performance are measured against the Nusselt number (Nu), the friction factor ( f ), the thermal-hydraulic performance factor (TPF) and observation of critical flow features. Results indicated that the configuration of the quarter petal shaped ribs has a decisive impact on the heat transfer and the friction factor features, and its performance becomes very sensitive to the variation in P/e and Re. With the artificially rough SAH, the optimal configuration achieved a TPF of 2.155, which corresponded to a 115.5 % thermal performance enhancement. Correlations for Nu and f as functions of the Reynolds number and relative roughness pitch were obtained by non-linear regression analysis.