Experimental study on the combined effects of inclination angle and insert devices on the performance of a flat-plate solar collector

We report an experimental study investigating the thermal performance of a flat-plate solar collector using insert devices, over a Reynolds number range 200-8000 and a Prandtl number range 5-8, using water as the working fluid. A variety of conventional and novel insert configurations were considered which include, twisted-tape inserts, wire coil inserts and wire mesh insert. The results clearly indicate the enhancement of the Nusselt number by all insert devices. Comparison of the best inserts from different insert families show that in the laminar flow regime, the mesh insert performed the best whereas, the concentric coils achieved the highest Nusselt number augmentation in the turbulent regime, relative to the smooth pipe with no inserts. From the practical aspects, concentric coils were recommended as the best insert among those tested, which shows an overall Nusselt number enhancement of 110% in the low Reynolds number range and 460% in the high Reynolds number range. The impact of collector inclination of the performance of these insert devices was also investigated. The results show that the channel inclination does not have a significant impact on the Nusselt number enhancement. (C) 2013 Elsevier Ltd. All rights reserved.