Introduction

Active Thermal Management Requirements Increasing for the Full Range of Heat Sinks Cooling, Including Industrial Spot Cooling in Microelectronics

In the microelectronics industry, advances in technology have brought about an increase in transistor density and faster electronic chips. As electronic packages increase in speed and capability, the heat sinks cooling required to maintain reasonable chip temperatures has also risen. Cooling fluxes are projected to reach the 1000 W/cm2 level for some high power electronic applications. Two-phase heat transfer, involving the evaporation of a liquid in a hot region and the condensation of the resulting vapor in a cooler region, can provide the hot spot thermal management needed for microelectronic packages to operate at acceptable temperature levels.

By changing the phase of the working fluid, a two-phase heat transfer cooling scheme supports high heat transfer rates across moderately small temperature differences. Heat pipes and thermosyphons are examples of efficient heat transfer devices that exploit the benefits of two-phase heat transfer [2-4]. Immersion cooling, which involves the pool boiling of a working fluid on a heated surface, is another example of a two-phase cooling technology used in a wide range of microelectronic applications requiring localized spot cooling.

Abstract

Active Thermal Management for Industrial Spot Cooling

This paper describes a new two-phase cooling heat transfer cell based on a submerged vibration-induced bubble ejection process in which small vapor bubbles attached to a solid surface are dislodged and propelled into the cooler bulk liquid. This ejection technique involves forcibly removing the attached vapor bubbles with a submerged pressure difference generated by a vibrating piezoelectric diaphragm operating at ultrasonic frequencies.

The piezoelectric driver induces pressure oscillations in the liquid near the heated surface, resulting in vapor bubble and liquid instabilities. These pressure differences generated by the piezoelectric driver operating at resonance enhance boiling heat transfer by removing attached vapor bubbles that insulate the surface. A small-scale vibration-induced bubble ejection module that produced a pressure difference at a heated surface using an ultrasonic piezoelectric actuator was used in this initial study. The initial experimental data that was obtained include the cooling capabilities of the cell. The efficacy of this heat sinks cooling approach was tested on a calibrated heater that dissipated 107 W/cm2 at 120°C in the absence of the jet using natural convection. When the jet was on, the heat flux increased to 191 W/cm2 at the same surface temperature, resulting in a 78% improvement in hot spot thermal management.

Applications

Active thermal management for heat sinks cooling, especially related to industrial spot cooling

Enhanced boiling heat transfer by submerged ultrasonic vibrations creates hot spot thermal management for heat sinks cooling applicable to a full range of applications.

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