Silicon-based microscale-oscillating heat pipes for high power and high heat flux operation

Microscale-oscillating heat pipes (micro-OHPs) have recently drawn interest for electronic cooling applications due to their compact size and passive operating mechanism. The occurrence of dryout in OHPs, however, at which the working liquid no longer wets the evaporator, limits the maximum operating cooling power, preventing their integration for direct cooling of high heat flux semiconductor chips. Here, we report on high power and high flux operation of silicon-based OHPs by using microchannels with hydraulic diameters of ∼200 μm. Particularly, a micro-OHP with 100 μm channel height is shown to effectively operate at 210 W using a dielectric working fluid, corresponding to an unprecedented cooling power density of 145 W/cm2, without dryout. A distinctive oscillating mode with highly periodic bulk circulations occurs at high heating power and can provide efficient heat dissipation. The flow speed of the liquid under this bulk circulation mode can be as high as 10 m/s. The empirical relationships between the heat transfer rate, oscillating frequency, and device temperatures are studied.