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Heat transfer systems have been employed in numerous industrial and residential settings to convert and recover heat. One effective approach for enhancing heat transfer rates involves incorporating artificial roughness in the form of regularly spaced ribs on the heated surface. In this particular study, the researchers conducted numerical simulations to analyze the turbulent heat and flow properties within a rectangular duct of a solar air heater (SAH). The duct featured three different types of transverse rib shapes: equilateral‐triangular, trapezoidal, and square sectional ribs. The governing equations have been solved numerically using a finite‐volume technique via ANSYS FLUENT. For solving the transport equations of turbulent kinetic energy and its dissipation rate, the RNG k–ε $\varepsilon $ turbulence model was utilized. At a broad range of Reynolds numbers (6000 ≤ Re ≤ 18,000), relative roughness height (0.021≤e/Dh≤0.043 $0.021\le e/{D}_{h}\le 0.043$), and a fixed relative roughness pitch (P/e=10 $P/e=10$), the Nusselt number (Nu ${Nu}$), friction factor (f $f$), and thermal performance factor (TPF) have been examined. The maximal Nu was obtained for equilateral‐triangular ribs, while the minimum friction factor was seen for square sectional ribs. The highest TPF of 1.591 was achieved with equilateral‐triangular ribs at Re=6000 ${Re}\,=\,6000$ and e/Dh = 0.032. Contours of kinetic energy, turbulent intensity, velocity, and pressure produced significant findings for comprehending the SAH's physical phenomena. [ABSTRACT FROM AUTHOR]

The convective heat transfer coefficient in solar air heaters suffers from a reduction due to the formation of a laminar sub-layer between the absorber plate and the air in motion. A viable and efficient strategy to augment the heat transfer coefficient involves introducing artificial roughness in the form of ribs. This study employs numerical simulations to examine the turbulent heat and flow characteristics within a rectangular duct of a solar air heater (SAH) featuring trapezoidal ribs as roughness elements. The governing equations were numerically solved using the finite-volume method and ANSYS FLUENT. The transport equations of turbulent kinetic energy and its dissipation rate were addressed by the RNG k-ε turbulence model. The Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF) were computed across a broad range of conditions, including Reynolds number (6,000≤Re≤18,000), relative roughness height (0.021≤e/Dnd relative roughness pitch (5≤P/e≤20) under constant heat flux conditions. It was determined that the maximum enhancement ratio of Nu was 2.124 times that of a smooth duct when e/Dh=0.043, P/e=20, and Re=6,000. Additionally, the TPF for the SAH featuring trapezoidal ribs attained a peak value of 1.64. [ABSTRACT FROM AUTHOR]