Designing of low cost solar air heater equipped with roughness of streamlined cross-section

Abstract

In the current investigation an attempt is made to design a low cost solar air heater (SAH) using numerical simulation and exergy analysis approach. The thermo-hydraulic behaviour of SAH duct (aspect ratio = 10) with rib roughness of rectangular and symmetric half NACA 0020 (reverse orientation) cross-sections on one of its broad walls are analysed numerically. This novel design of the symmetric half NACA 0020 has been tailored to maximise heat transmission by capitalising on the benefits offered by secondary flows. For Reynolds numbers (Re) ranges from 6000 to 18000, fixed relative roughness pitch (P/e = 13), and relative roughness height (e/D = 0.06), the Nusselt number (Nu) and friction factor (f) are calculated. Ribs with NACA 0020 cross-section have higher heat transfer and lower flow friction. With NACA 0020 rib roughness, the maximum thermo-hydraulic performance parameter (THPP) is observed at Re = 6000. Contours of temperature, pressure, turbulence kinetic energy and velocity streamlines provides essential information for explanation of phenomenon in the SAH. Experimental results are used to validate the numerical outcomes. Exergy analysis is also carried out for the comparison of performance of SAH roughened with bluff (rectangular) and streamlined (reverse NACA 0020) roughness elements.