Ph.D. Dissertation Defense by Shuo Li
Wedneday, April 6, 2005

(Dr. Marc Smith, Chair)

"Numerical Investigation of Micro Synthetic Jet and Its Applications in Thermal Management"

Abstract

Thermal management becomes more and more challenging in modern micro electronic systems. Micro synthetic jet as a novel fluidic actuator has been used in active flow control. Its unique no-flux characteristic makes it attractive in thermal management applications too. Numerical studies of synthetic jet flow, cavity modeling, synthetic jet impingement and its applications in thermal management were conducted in this research.

Free synthetic jet flow was studied using SST k-ω turbulence model. Typical vortex dynamics and flow structures of free synthetic jet flow were identified. Time mean jet flow characteristics were analyzed. Working frequency, cavity geometry and nozzle geometry were varied to investigate the synthetic jet flow formation and evolution. The synthetic jet flow could be divided three regions analogy to conventional jets based on the time mean velocity field analysis. A synthetic jet model was derived based on it. Two first order ODEs were obtained if consider the synthetic jet as two subsystems. The inputs of this model are the volume change, working frequency and geometries of cavity and nozzle. The ODE system could be solved numerically to determine the cavity pressure and average velocity through the nozzle/orifice, which are the two outputs. Once the design and operating parameters are known, the synthetic jet flow is fully characterized by this model. The output of this model could be used to replace the actual cavity in CFD simulations and the saving of computational costs is significant.

A numerical study on synthetic jet impingement heat transfer was performed. The general characteristics of flow structure of different configurations were identified. It was found that synthetic jet technique significantly enhances the impingement heat transfer compared to conventional jet technique. Parametric study including nozzle to impingement plate distance ratio, nozzle/orifice diameter, working frequency and diaphragm displacement was performed.

A parametric study of active heat sink was conducted. Cells of the active heat sink were studied numerically using Large Eddy Simulation (LES). Parameters studied include the nozzle/slit geometry, channel geometry, inlet velocity boundary condition and wall temperature boundary condition were investigated numerically. Optimized parameters were recommended.