Heat transfer enhancement of an impinging synthetic air jet using diffusion-shaped orifice

Abstract

Impingement heat transfer from a synthetic air jet through a diffusion-shaped orifice was investigated in this study. The effect of the opening angle (60 degrees and 90 degrees), orifice thickness (1-3 mm), and driven frequencies (400-800 Hz) were examined. Hot-wire anemometry was used to measure the instantaneous and average flow velocities ejected from the jet holes. At a small jet-to-surface spacing, synthetic jets from a diffusion-shaped orifice produced higher heat transfer than that from a round orifice. The highest heat transfer enhancement from using a diffusion-shaped orifice was approximately 30% compared with the round orifice at an opening angle of 60 degrees. The diffusion-shaped orifice achieved the highest area averaged heat transfer coefficient and Nusslet number of 80 W/m(2).K and 8.9, respectively. When the opening angle increased to 90 degrees, heat transfer enhancement was degraded because of increased flow circulation and reduced ejection flow velocity. The effect of orifice configuration on the heat transfer diminished as the jet-to-surface spacing increased. (C) 2015 Elsevier Ltd. All rights reserved.