Flow and heat transfer characteristics under synthetic jets impingement driven by piezoelectric actuator

Synthetic jet is a novel flow technique which synthesizes stagnant air to form a jet, and is potentially useful for cooling applications. An experimental measurement utilizing particle image velocimetry (PIV), hot-wire anemometer and infrared camera on the synthetic jet impingement cooling driven by piezoelectric actuator was carried out in the present investigation. The flow and heat transfer characteristics of impinging synthetic jets formed from a single cavity but with different orifices, such as single-slot, single-hole, three-slots and three-holes, were explored. The synthetic jet output from the piezoelectric actuator reaches a peak value when it is excited at its optimum frequency. The synthetic jet output from the piezoelectric actuator reaches a peak value when it is excited at its optimum frequency. For single-hole synthetic jet, the optimum frequency is nearly the same as that of single-slot orifice given the same orifice exit area. But the optimum frequency for the multi-orifices is lower than that of single-orifice synthetic jet. In general, the synthetic jet originated from the single-slot orifice introduces a stronger entrainment and more vigorous penetration in relative to that from the single-hole orifice, performing better than the single-hole synthetic jet orifice. And the multiple synthetic jets exhibit complex influence on the heat transfer by comparison to single synthetic jet for a given actuator cavity and a single actuator. Only when the multi-slots or multi-holes are arranged in their optical mode, the multiple synthetic jets could achieve competitive heat transfer capacity with the single synthetic jet.

► Illustrate flow and heat transfer features of a synthetic jet impingement.
► Assess heat transfer enhancement of the synthetic jet impingement.
► Optimum frequency is the most important influence for the synthetic jet output from the piezoelectric actuator.
► Multiple synthetic jets exhibit complex influence on the heat transfer by comparison to single synthetic jet.