Enhanced Pool Boiling Using Carbon Nanotube Arrays on a Silicon Surface

Abstract

Progress in integrated circuit technology has caused device density and power dissipation to increase, resulting in significant cooling challenges. Pool boiling is an attractive cooling option because of its unique combination of passive fluid circulation and high heat flux capability. Having no mechanical pumps, pool boiling hardware is less complex, easier to seal, and free of pump-induced fluid pulsations that are present with many alternative approaches. One of the main obstacles for improvements in pool boiling technology is the limiting factor of critical heat flux (CHF), which limits cooling capacity. The present experimental work considers the introduction of carbon nanotube (CNT) arrays on the chip surface to delay CHF and to enhance boiling heat transfer. Pool boiling curves for a smooth silicon surface and a silicon surface coated with CNTs were obtained. Tests were conducted in which power was input in 1 W increments to the respective silicon surfaces immersed in FC-72 fluid. These experiments reveal significant boiling enhancement. Testing reveals a measured CHF of approximately 15 W/cm2 for a CNT-coated silicon wafer and a CHF of approximately 10 W/cm2 for bare silicon wafers. Further, superheat at fully developed boiling is reduced on CNT-coated surfaces by up to 60%, and effective heat transfer coefficients are enhanced by approximately 400% by the presence of CNTs.