Experimental study on convective heat transfer of hybrid impingement configuration by square-array continuous jets and a center-positioned synthetic jet

Abstract

An experimental investigation is performed to illustrate the heat transfer characteristics for a specific hybrid-jet impingement configuration that is comprised of a square-layout continuous-jet array and a center-positioned loudspeaker-driven synthetic-jet actuator. Herein four continuous-jet Reynolds numbers (ranging from Re=3000 to Re=10,000), 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 central synthetic jet is operated at f = 250 Hz with a characteristic Reynolds number of about Re0=4500. It is identified that the integration of central synthetic jet in the array-jet unit is indeed an effective means to enhance the overall heat transfer performance, which is more suitable for the practical applications wherein the synthetic jet Reynolds number is greater than or equivalent to the array-jet Reynolds number. By the integration of central synthetic jet, a significant localized heat transfer augment is achieved at the central zone of array-jet unit, especially under small and moderate array-jet Reynolds numbers. In terms of the spatially-averaged Nusselt number, an increase of more than 100% could be achieved by the central synthetic jet integration at H/d ≥ 6 under Re=3000. The benefit of the central synthetic jet integration is also clearly demonstrated under Re=5000, wherein the spatially-averaged Nusselt number could be increased by 30%-60%, taking a monotonous increasing trend along with the impinging distance generally. Under Re=7000, a relative increase among 10%-30% still remains. When the array-jet Reynolds number is increased up to 10,000, only in the sparse continuous-jet array (X/d = Y/d = 6) the benefit of the central synthetic jet integration could behave, with a limited relative increase of less than 20%.