Thermo-hydraulic performance of solar air heater having discrete D-shaped ribs as artificial roughness

In this paper, the thermo-hydraulic performance of a solar air heater (SAH) duct roughened with discrete D-shaped ribs is numerically investigated using ANSYS Fluent 2020 R . The numerical investigation is carried out at rib radius to transverse pitch ratio (r/P ) from 0.1 to 0.35 and longitudinal pitch to rib radius ratio (P /r) from 4 to 10 under various operating conditions with Reynolds number (Re) varied from 10,200 to 20,200. The numerical results are validated with previous experimental results for the Nusselt number (Nu) values, and good agreement is found with mean absolute percentage error (MAPE) of 3.6%. Based on the results of the numerical investigation, it was found that the value of Nu and the friction factor (f) decreases with the increase of the value of P /r, while the ratio r/P is kept constant. From the overall analysis, it is concluded that the optimum results are obtained for r/P of 0.25 and P /r = 4, and the maximum thermo-hydraulic performance parameter is 1.12. Further correlations are developed for the value of Nu and f for the whole range of r/P as 0.10-0.35 and P /r as 4-10. According to the developed correlations, the values of Nu are within ± 2% of the results of CFD, while the values of f are within ± 2.7% of the results of CFD.