EFFECT OF MODIFIED RECTANGULAR RIB ON THERMAL PERFORMANCE OF SOLAR AIR HEATER

Rib geometry has significant impact on the thermal performance of solar air heaters, and every geometry has its own limitations. However, a suitable modification of a given rib geometry can make further enhancement in thermal performance possible. This work presents the effect of geometry modification of a rectangular rib on the Nusselt number and friction factor characteristics of a rectangular duct solar air heater system under constant heat flux conditions using computational fluid dynamics (CFD) methodology. The rectangular rib geometry is modified to obtain four new rib configurations, such as T-rib, inverted T-rib, modified T-rib1, and modified T-rib2. The relative pitch is set as 15, and the rib height is fixed as 2 mm for all the rib configurations. The analysis shows that the use of the inverted T-rib is not recommended for heat transfer improvement in an air heater duct as it is characterized by the presence of large, entrapped eddies, which lowers the heat transfer capability. On the other hand, the modified T-rib2 shows considerable improvement in heat transfer due to the suppression of entrapped flow zones. The best heat transfer performance is exhibited by the modified T-rib2 configuration, which shows about a 2.02 times higher Nusselt number than that of the smooth duct at Re = 6 × 10³. The rise in friction factor is maximum for modified T-rib1 which is about 1.92