2011 Volume 6 Issue 4 Pages 453-464
The centerline velocity of an orifice jet increases in the downstream direction from the nozzle exit and reaches a maximum of 1.2uce (where uce is the nozzle exit maximum velocity) at x/do≈2 (where do is the nozzle exit diameter) due to the vena contracta effect; this may be effective for enhancing the heat transfer performance of an impinging jet. However, the sudden contraction at the nozzle exit creates a large flow resistance. In this study, we considered the use of notches to reduce the flow resistance and increase turbulence for the sake of good heat transfer performance from the vena contracta effect. Specifically, the effects of using a notched-orifice nozzle with taper angle α on heat transfer characteristics were examined experimentally. Hot-wire measurements were also conducted to demonstrate the spreading or mixing performance of the notched-orifice nozzle. The small notches reduced the nozzle resistance or operating power as well as increased the turbulence at the nozzle exit. The heat transfer characteristics of the notched orifice jets with tapering increased significantly because of the high turbulence intensity introduced by the notches.
