CFD Analysis of SAH System Employing Different Rib Shapes

The purpose of this work is to conduct a computational analysis of a roughened solar air heater (SAH) using artificial roughness in the form of several types of ribs. A solar air heater is a kind of heat exchanger that uses sun radiation to produce heat energy. Smooth solar air heaters are considered inefficient because of the poor convective heat transfer coefficient from the absorber plate to the air. To improve the heat transfer rate, artificial roughness is used in the form of double concave ribs. The geometric variables that will be selected are relative roughness height (e/D), relative roughness pitch (P/e), and relative arc radius (r/e). These variables will be analyzed at five different values of Reynolds number (Re), and their impact on heat transfer, friction factor, and thermohydraulic performance parameter (THPP) will be examined using commercial computational fluid dynamics (CFD) software, Ansys Fluent. After examining past studies, it has been concluded that the Nusselt number grows as the Reynolds number increases, and the opposite is true for the friction factor. However, when it comes to the relative arc radius (r/e), both the Nusselt number and the friction factor decrease as r/e increases. When a/H is increased from 0.2 to 0.5, the Nusselt number rises from 65.64 to 242.72, and the friction factor rises from 0.0806 to 0.2155 for the range of Re. The Nusselt number rises from 68.88 to 274.29, and the friction factor rises from 0.0876 to 0.6290 over the range of Re considered when e/H increases from 0.4 to 0.8 with a constant value of a/H of 0.3 and β of 30%. When β is increased from 13% to 30% while keeping e/H at a constant value of 0.4 and a/H at a constant value of 0.3, the Nusselt number reduces from 207.92 to 70.26, and the friction factor decreases from 0.1707 to 0.0877 across the range of Re. For a/H, the maximum Nusselt number enhancement and friction factor increment are determined to be 5.86 and 22.15, respectively. These values correspond to a/H of 0.5, e/H of 0.4, and an open area ratio of 30% for the Reynolds number range examined across the smooth duct.