Digitized Heat Transfer: Thermal Management of Compact Micro Systems using Electrostatic Droplet Actuation

Abstract

This paper presents theoretical and numerical results describing digitized heat transfer (DHT), a newly developing active management technique for high-power-density electronics and integrated micro systems. In DHT, thermal energy is transported by a discretized array of electrostatically activated microdroplets of liquid alloy or aqueous solution; internal circulation within each fluid slug results in significantly increased overall heat transfer coecients when compared to continuous Graetz-type flows. This paper identifies and describes a periodic fluctuation in Nusselt number resulting from this circulation eect. Proposed DHT coolants, especially liquid metals and alloys, support significantly higher heat transfer rates than classical air-cooled heat sinks, and can be digitally actuated and controlled with a high degree of both precision and programmability. As a consequence, DHT can be used both for steady state cooling of an entire integrated device and for precise, ecient, on-demand suppression of transient hot spots. A theoretical characterization of the governing parameters for DHT is presented, with a basic comparison of the heat transfer rates achieveable by liquid alloys and aqueous solutions. The eectiveness of DHT for managing both localized temperature spikes and steady state cooling is demonstrated. This analysis defines the key parameters for optimization of the DHT method and forms the basis of ongoing experimental work.