Experimental investigation on thermal and flow characteristics of synthetic jet with multiple-orifice of different shapes

The impingement heat transfer characteristics of a multiple-orifice synthetic jet of circular, oval and diamond orifice shapes are investigated experimentally at different Stokes number, normalized axial distance and pitch ratio. In this study, particle image velocimetry (PIV) based measurements are also undertaken to better understand the underlying flow characteristics of multiple-orifice synthetic jet and to support the associated heat transfer data. The average Nusselt number (Nu(avg)) obtained with multiple-orifice synthetic jet is up to 75% higher than a single orifice synthetic jet using the same input power to synthetic jet actuator. For larger pitch ratio (R > 1.25), the maximum value of Nu(avg) is observed to be reduced and obtained closer to heated surface. Multiple-orifice configurations with diamond shape exhibited better thermal performance as compared to other shapes examined in the study. The multiple-orifice configurations with one and two satellite orifices demonstrated two local peaks in Nu(avg) and are observed only with smaller values of pitch ratio. The location of these local peaks illustrated very little or no dependence on Stokes number (S). Configurations with no center orifice exhibited significantly lower heat transfer as compared to the configurations with center orifice as well as the case with single center orifice. The secondary maxima in Nu(avg) are entirely missing in the configurations with no center orifice. The PIV data reveals interactions between the adjacent synthetic jets in multiple-orifice case to form a combined synthetic jet with better mixing characteristics as compared to a single orifice synthetic jet and therefore the former exhibits higher heat transfer rate. The PIV data further illustrated the individual behavior of synthetic jets resulting from satellite orifices in multiple-orifice configurations with no center orifice. In addition to heat and flow characteristics of multiple-orifice synthetic jet, the heat transfer correlations are also developed from the experimental data for different orifice shapes. The study of multiple-orifice synthetic jet presented here is expected to be useful in designing the cooling modules for electronic devices