Date of Award

Summer 2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Oktay Baysal

Committee Member

Osama A. Kandil

Committee Member

Gene Hou

Abstract

Effectiveness of an actuator is investigated for thermal-flow control in microchannels. First, simulations of a single actuator in a quiescent external medium are performed in order to study the parameters characterizing the synthetic jet flow from the actuator. For this purpose, a simplified, two-dimensional configuration is considered. The membrane motion is modeled in a realistic manner as a moving boundary in order to accurately compute the flow inside the actuator cavity. The geometric and actuation parameters of the actuator are investigated to define the effectiveness of the jet flow. The study is done initially at macro scales. Then, the flow in the Knudsen number range of less than 0.1 is modeled starting with a conventional compressible Navier-Stokes solver valid for continuum approach. Its boundary conditions, however, are modified to account for the slip velocity and the temperature jump boundary conditions encountered in micron-level devices. Compressibility effects are also taken into account and modeled through the compressible flow solver. The utility of synthetic jet actuators for manipulating fluid flows has been shown for mostly macro- and mini-scale applications. To the best of the author's knowledge, there have been only a few studies on micro-sized synthetic jets; also they have only been modeled assuming continuum flow regime with no-slip at the walls. Therefore, several issues must still be addressed for micron-scale synthetic jets and also their applications to micron-level problems. Thus, as the second part of the study, a micron-level synthetic jet is proposed as a flow control device to manipulate the separated flow past a backward facing step in a microchannel. First, an uncontrolled flow past a backward facing step in a channel is computed. Then, a synthetic jet actuator is placed downstream of the step where the separation occurs. A large number of test cases have been analyzed. It is observed that the size of the separation bubble and its enstrophy are functions of the geometry of the actuator cavity and the membrane oscillation parameters. Considerable reduction in separation bubble size as well as in enstrophy is achieved using the actuator. Finally, a design for thermal management of a semiconductor device using the present actuator is introduced. For this purpose, a single microchip dissipating heat is placed in a two dimensional rectangular channel. Then, the different cavity and actuation parameters are considered in order to infer some characteristics of the effect of controlled synthetic jet thermal management. Using the actuator, a circulation region is generated on the top surface of the microelectronic chip. It is found that the fluctuating jet interacts with the channel flow and increases the convection rate by transferring linear momentum to the channel flow.

It is seen from the results of the computations that the synthetic jets can be utilized effectively to control separation in internal flow applications and that they guarantee an efficient thermal management of microelectronic devices. Therefore, the synthetic jet actuator proves itself to be an effective device for thermal-fluid control applications where low-speed flows are encountered.

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DOI

10.25777/zbhg-6z71

ISBN

9780542855351

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