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

• Synthetic air jet was produced using a diffusion-shaped orifice.
• The effect of the opening angle and driven frequencies were studied.
• The diffusion-shaped orifices produced higher heat transfer enhancement.

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° and 90°), 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°. The diffusion-shaped orifice achieved the highest area-averaged heat transfer coefficient and Nusslet number of 80 W/m2⋅K and 8.9, respectively. When the opening angle increased to 90°, 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.