Influence of the Excitation Frequency and Orifice Geometry on the Fluid Flow and Heat Transfer Characteristics of Synthetic Jet Actuators

Abstract

Synthetic jet is a novel fluctuating time dependent flow technique that transfers linear momentum to the surroundings by ingesting and expelling fluid from a cavity containing an oscillating diaphragm and is conceivably useful for electronic cooling. In this paper numerical analysis is performed to address the effects of the variation in geometric parameters of orifice and excitation frequency on the synthetic jet fluidic. The moving piezoelectric diaphragm is modeled with constant voltage amplitude boundary condition. Computations are carried out by using COMSOL 5.3a Multiphysics software. The present study focuses on the synthetic jets which are formed from a single cylindrical cavity but with different orifices, such as single-hole, three-holes, single-rectangular slots and three-rectangular slots. The exit areas for single-hole and single rectangular-slot has been chosen as 7.0 mm2, while exit areas for multiple holes and slots has been chosen as 21.0 mm2. The velocity of the synthetic jet reaches a maximum value when the diaphragm is excited at an optimum frequency. In case of single-hole synthetic jet, the optimum frequency is nearly the same as that of single rectangular- slot type orifice; however the optimum frequency for the multi-orifices is lower than that of singleorifice synthetic jet. The quality of the simulation results is verified by grid, time and domain independence studies, and validated with the existing experimental data. The simulation results obtained in this study are remarkable as they provide primary design guidepost for the excitation frequency and orifice shape. The present investigation also indicates the maximum value of average heat transfer coefficient is 86.5 W/m2 K with single rectangular-slot orifice, which is 21% higher as compared with a single-hole orifice. For single rectangular-slot orifice when distance ratio of orifice-to-heater is (Z/b) = 80 the value of heat transfer coefficient is 112.5 W/m2 K which is about 20.3% higher as compared to that of single-hole at (Z/d) = 14 thereby leading to better performance.