Numerical Simulations and Optimization Analysis of the Heat Transfer in Piezoelectric Fans
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A combined theoretical/computational study is performed to investigate an innovative cooling technology using piezoelectric actuators. The piezoelectric fan is an ultra-low energy air mover which induces unsteady periodic flow. This study focuses on the characteristics of the fluid flow and heat transfer as well as system optimisation in terms of the operational parameters of the piezoelectric fan blade. Regarding the dynamics of piezoelectric fan movements, the fan blades vibrate as a wave-like motion. The fan blade can be simplified as a homogeneous viscoelastic beam with uniform cross-section. In the theoretical analysis, the method of complex orthogonal decomposition is adopted to analyse the blade motions, and the travelling index is proposed to evaluate the curvature of piezoelectric fan blade. The unsteady fluid flow and heat transfer have been studied by computational fluid dynamics based on three-dimensional large-eddy simulation. A parametric study has been performed to investigate the effects of three dynamic parameters of the blade oscillation: oscillating frequency, oscillating amplitude and wave number. In the heat transfer study, a heat source represented by a high temperature wall is added to the computational model. The temperature and the surface Nusselt number of the hot wall serve the purpose of evaluating the characteristics of heat transfer. It is found that the oscillation frequency and amplitude have significant impacts on the fluid flow and heat transfer. In addition, the response surface method facilitates the process of finding the optimal operational parameters of piezoelectric fans. Considering practical limitations imposed by fan geometries and materials, factors determining the optimal operational parameters are outlined as the theoretical optimal operational parameters may not be achievable in practical applications. The results and analyses provide fundamental knowledge to guide the design of a piezoelectric fan system for cooling applications.
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