A Comparison of Transverse Section with Arc Shaped Turbulators as an Artificial Roughness on the Absorber Plate of a Solar Air Heater

Solar energy is most important renewable energy resource due to its quantitative abundance. The simplest and most efficient way to utilize solar energy is to convert it into thermal energy for heating applications. A solar collector is a device designed to absorb the incoming solar radiant energy converting into thermal energy at the absorbing surface and transforming this energy to a fluid flowing through the collector. Solar air heaters, because of their inherent simplicity, are cheap and most widely used collection devices. The primary disadvantage of solar air heaters is the need for handling relatively large volumes of air because of its low thermal capacity as working fluid. The thermal performance of a conventional solar air heater is poor because of relatively low heat transfer coefficient between absorber plate and the carrier fluid (air). Use of artificial roughness on the absorber plate has been found to be an effective method of enhancing heat transfer coefficient. In this present work an attempt is made to study the performance of solar air heater using wire geometry of arc shaped thin circular wires as a turbulators on the absorber plate. The investigation has covered a Reynolds number (Re) range of 3000-8000, relative roughness height (e/Dh) of 0.034, duct aspect ratio (W/B) is kept 5, the relative roughness pitch (p/e) used is 10, 20, 30 and 40. The heat transfer and friction factor values obtained are compared with those of smooth duct and Transverse wire geometry under similar flow conditions. Investigation shows the maximum enhancement of average Nusselt number is found to be 1.12 times for transverse wire geometry and 1.17 times for single arc wire geometry compared to that of smooth plate. The maximum enhancement of average friction factor is found to be 5.61 times for transvers wires geometry, 5.89 times for single arc wire geometry. The comparison of transverse and single arc shows that the Nusselt number, friction factor and efficiency index is highest for arc shaped roughness followed by transverse and least for smooth absorber plate.