Heat Transfer Enhancement of Array Continuous-Jet Impingement with an Integrated Central Synthetic Jet

A novel concept is proposed in the present study for improving the impingement heat transfer of array continuous jets by integrating a synthetic jet into the array unit. To illustrate the potential of this concept, an experimental and numerical investigation is performed for a specific hybrid-jet impingement configuration comprised of a square-layout continuous-jet array and a center-positioned synthetic-jet actuator. Two continuous-jet Reynolds numbers ( Re =3000 and 5000), three hole-to-hole pitches ( X / d = Y / d =4, 5 and 6), and a series of impinging distances ( H / d =2~10) are considered while the synthetic jet is operated at a fixed frequency of 180Hz with a characteristic Reynolds number ( Re 0 ) of about 2200. The results confirm that the integrity of a central synthetic jet in the continuous-jet array is indeed an effective means to enhance the overall heat transfer performance, attributed to the localized heat transfer augment at the central zone of array unit on the coordination mechanism of ‘active pulsating’ synthetic jet and ‘passive pulsated’ wall jet. Its potential is tightly dependent on the array layout, Reynolds number and impinging distance of continuous jets. In the present study, the most pronounced role of synthetic-jet integrity occurs in the situations, i.e., small continuous-jet Reynolds number, dense array or small jet-to-jet spacing and large impinging distance. Of particular interest, the local Nusselt number at the array unit center in the presence of a central synthetic jet could exceed the continuous-jet stagnation Nusselt number for the continuous-jet layout of X / d = Y / d =4 at Re =3000 and H / d >6. For the specific situation wherein Re =3000 and X / d = Y / d =4 in the presence of central synthetic jet, the spatially-averaged Nusselt number is increased along with the dimensionless impinging distance, which is significantly opposite to the other situations