In this study, a novel valveless impedance pump is applied, for the first time, in the thermal management of high performance electronic systems. This small pump comprises an amber latex rubber tube, connected at both ends to rigid copper tubes of different acoustic impedance, and a simple, economic, quiet and energy-efficient actuation mechanism, which combines a small DC motor and a cam. The motor activated cam periodically compresses the elastic tube at a position asymmetric from the tube ends.Traveling waves, emitted from the compression, combine with reflected waves, at the impedance-mismatched positions (rubber tube/copper tube interfaces). The resulting wave interference creates a pressure gradient, with the potential to generate a net flow. Several experimental set-ups for performance tests, using a single impedance pump, open system, with isothermal flow, and a closed liquid cooling system were designed and implemented.The performance of the impedance pump was affected significantly by the actuation This is the Pre-Published Version.
It is often desirable to predict acoustic propagation in a circular duct carrying a locally heated flow. Common examples include jet engines and certain industrial and commercial burners whose combustion-related noise can be an environmental problem if allowed to penetrate into the surroundings. In these cases axial gradients in the steady flow variables, established as a result of local combustion heating of the flowing gas, lead to important modifications of the usual linearized equations expressing conservation of mass, momentum, and energy in the acoustic variables. Thus the classical three-dimensional wave equation no longer applies and a new wave equation must be formulated. In the present work the appropriate modified wave equation is derived for and applied to a duct whose cross section is a sector of a circle of sufficiently small included angle to preclude the existence of circumferential modes in the frequency range of interest. This two-dimensional geometry, though somewhat artificial, has been chosen to allow the first radial mode to be isolated and studied separately. The analysis reveals that the first radial mode, when damped near the inlet to the duct, may under certain circumstances recover and even grow in amplitude as it passes through the heating region. [Work partially supported by NASA under Grant NAG3-124.]
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