Specific features of heat transfer at the stagnation point of an impact axisymmetric jet at low Reynolds numbers

Resumo

The average and pulsating thermal characteristics at the stagnation point of a plate at inflow of an impact axisymmetric air jet have been studied. The influence of the Reynolds number (100 < Re < 12000) on heat transfer has been investigated for a jet flowing from a long tube (diameter d = 5 mm, relative length h/d = 200) with the output located at a distance h/d = 20 from the obstacle. The measurements have been carried out using a heat-flow sensor with high spatial and temporal resolutions. A nonmonotonic change in heat transfer having a maximum is found in the range Re < 4000 (in contrast to the known monotonic increase in heat transfer). A significant increase (200–600%) in the Nusselt number is observed for outflow from a tube in comparison with jet outflow from a nozzle. At Re > 4000, the difference in heat transfers for two cases of jet formation (from a tube and a nozzle) decreases asymptotically.