NUMERICAL INVESTIGATION OF THE PERFORMANCE OF SOLAR AIR HEATER WITH SURFACE MOUNTED OBSTACLES

Abstract

Performance improvement of Solar Air Heaters by improving the heat-transfer coefficient between the absorber plate and air include the use of an absorber with fms, corrugated absorber, matrix type absorber; absorber with packed bed, with baffles and other different configurations. In the present investigation the flow structure and heat transfer enhancement by using delta shaped obstacle of non-zero thickness has been studied. Eddies and Vortices produced by the obstacle are the main reason of enhancing heat transfer. Obstacle is mounted on the absorber plate and is placed in the hydrodynamically developed and thermally developing turbulent flow. The flow .pattern is complex and consists of main, comer and induced vortices. It is 'observed that as compared to the absorber plate without obstacle the heat transfer - enhancement is considerably less as compared to the absorber pate mounted, with obstacle. Augmentation of heat transfer between the flowing fluid and rectangular channel wall is seen. The predictions are made through the numerical solution of complete Navier-Stokes and energy equations. The k-epsilon turbulent model has been ,used for the study. The effect of obstacle on the, heat transfer-.coefficient, friction factor, temperature distribution, skin friction coefficient and turbulent intensity have been studied for the range of height of the obstacle (approx. 25%, 50% and 75%). The average Nusselt number 'increases which confirms the increase in overall heat- transfer coefficient and so the net heat transfer. Effect of varying Reynolds number and the blockage due to varying height of the obstacle on the heat transfer augmentation has also been presented.