Study of Oscillating Liquid Flow as a Thermal Management Solution

For many electronic devices where air cooling is the norm, heat loads continue to increase and are projected to soon require a transition to liquid cooling, where more efficient thermal energy transport is achievable due to better fluid properties. In most scenarios, a liquid cooled solution entails a bulk fluid motion traveling past a heated surface, but flows that oscillate back and forth also show promise. However, before this is realized, some fundamental performance models must be extended. This paper focuses on characterizing the dynamics of the flow inside a U-tube manometer under continuous oscillation. For oscillating flow, the dimensionless parameter of interest is the Womersley number (W_0) or the Valensi number (V_a) (one can simply be expressed in terms of the other), and can be used to predict velocity profiles of oscillating flow. In this study, an air blower is utilized to force the fluid to move inside a U-tube manometer by providing an oscillating pressure signal. The dynamic response is the key metric of interest in this work, and is characterized by experimentally measuring the resonance frequency (ω_n) and the damping ratio (ζ), the latter of which is dependent on frictional losses. When the working fluid is under continuous oscillation, additional sources of frictional losses exist, and a non-standard analysis is needed to adequately predict the damping. The dynamic response is measured for different amounts of fluid in a range of tube sizes and empirical correlations are developed to better predict the observed data. Results suggest that the velocity profiles under continuous oscillation are not parabolic and hence quantifying the damping based on the theoretical damped oscillation analysis is not applicable. The results of this study are conceptually applied to a microchannel heat sink, where oscillating flows show promise in handling large heat fluxes