Experimental and numerical simulation of a synthetic jet for cooling of electronics

Compared to traditional continuous jets, synthetic jets have specific advantages, such as lower power requirement, simpler structure, and the ability to produce an unsteady turbulent flow which is known to be effective in augmenting heat transfer. This study presents experimental and computational results that document heat transfer coefficients associated with impinging a round synthetic jet flow on the tip region of a longitudinal fin surface used in an electronics cooling system. Unique to this study are the geometry of the cooled surface and the variations in geometry of the jet nozzle or nozzles. Also unique are measurements in actual-scale systems and in a scaled-up system, and computation. In the computation, the diaphragm movement of the synthetic jet is a moving wall and the flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. The effects of different parameters, such as amplitude and frequency of diaphragm movement and jet-to-stagnation-line spacing, are recorded. The computational results show a good match with the experimental results. In the experiments, an actual-scale system is tested and, for finer spatial resolution and improved control over geometric and operational conditions, a large-scale mock-up is tested. The three approaches are used to determine heat transfer coefficients on the fin on and near the stagnation line. Focus is on the large scale test results and the computation. Application to the actual-size cases is discussed. The dynamically-similar mock-up matches the dimensionless Reynolds number, Stokes number, and Prandtl number of the actual setting with a scale factor of 44. A linear relationship for heat transfer coefficient versus frequency of diaphragm movement is shown. Heat transfer coefficient values as high as 650 W/m²K are obtained with high-frequency diaphragm movement. Cases with different orifice shapes show how cooling performance changes with orifice design.