The effects of nozzle diameter on impinging jet heat transfer and fluid flow

The effects of nozzle diameter on heat transfer and fluid flow are investigated for a round turbulent jet impinging on a flat plate surface. The flow at the nozzle exit has a fully developed velocity profile. A uniform heat flux boundary is created at the plate surface by using gold film Intrex, and liquid crystals are used to measure the plate surface temperature. The experiments are performed for the jet Reynolds number (Re) of 23, 000, with a dimensionless distance between the nozzle and plate surface (L/d) ranging from 2 to 14 and a nozzle diameter (d.) ranging from 1.36 to 3.40 cm. The results show that the local Nusselt numbers increase with the increasing nozzle diameter in the stagnation point region corresponding to 0 less than or equal to r/d less than or equal to 0.5. This may be attributed to an increase in the jet momentum and turbulence intensity level with the larger nozzle diameter which results in the heat transfer augmentation. In the mean time, the effect of the nozzle diameter on the local Nusselt numbers is negligibly small at the wall jet region corresponding to r/d >0.5.