Reciprocating impingement jet heat transfer with surface ribs

This article presents the experimental heat transfer results of an impinging jet onto a flat surface with discrete ribs in a reciprocating confinement. The test flows were systemically varied from static to reciprocating conditions with oscillating frequencies of 0.83, 1.25, and 1.67 Hz. Parametric ranges of tests in terms of Reynolds, pulsating, and buoyancy numbers were 10, 000-25, 000, 0-0.15, and 0-4.12 x 10 ^-7 , respectively. It was found that the nonreciprocating heat transfer close to and away from the stagnation point was respectively reduced and improved from the smooth-walled values, which led to the more spatially uniform heat transfer distribution. An empirical correlation was developed to permit the evaluation of nonreciprocating local Nusselt numbers. Under reciprocating environment with relatively weak pulsating force effects, a tendency of heat transfer deterioration from static reference developed, which trend could lead to about 20% of heat transfer reduction. Further increase of pulsating force ratio caused the subsequent heat transfer recovery, and the local reciprocating Nusselt number could be enhanced to a level about 240% of the equivalent static value at a pulsating number of 0.014. Considerable influence of reciprocating buoyancy interaction on heat transfer was detected to impede local heat transfer. As the present flow system in a reciprocating confinement could result in higher and more spatially uniform heat transfer rates in general, it could be an applicable cooling method for pistons.