Because of increasing power densities, refrigeration systems are being explored for two-phase cooling of ultra high power electronic components. Flow instabilities are potential problems in any two-phase refrigeration cooling system especially in transient applications. Oscillatory two-phase flow in a boiling channel can trigger transition to the critical heat flux (CHF). Active control methods can help better dynamic thermal management of electronic systems, even though transient two-phase boiling flow mechanisms are complicated. This paper presents a framework for the transient analysis and active control of pressure-drop flow instabilities under varying imposed heat loads. The first part of the paper is to study the external effects on boiling flow characteristics and the boiling oscillatory flow responses to transient heat load changes. Then based on the theoretical analysis of boiling flow oscillations, a set of active control schemes are developed and studied to suppress flow oscillations and, therefore, to increase the CHF. With the available control devices (i.e., inlet valve and supply pump), different active control schemes are studied to improve the transient two-phase cooling performance. Finally, a discussion is included to address potential future research.

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