Suppressing high-frequency temperature oscillations in microchannels with surface structures

Abstract

Two-phase microchannel heat sinks are attractive for thermal management of high heat flux electronic devices, yet flow instability which can lead to thermal and mechanical fatigue remains a significant challenge. Much work has focused on long-timescale (∼seconds) flow oscillations which are usually related to the compressible volume in the loop. The rapid growth of vapor bubbles which can also cause flow reversal, however, occurs on a much shorter timescale (∼tens of milliseconds). While this high-frequency oscillation has often been visualized with high-speed imaging, its effect on the instantaneous temperature has not been fully investigated due to the typical low sampling rates of the sensors. Here, we investigate the temperature response as a result of the high-frequency flow oscillation in microchannels and the effect of surface microstructures on this temperature oscillation with a measurement data acquisition rate of 1000 Hz. For smooth surface microchannels, fluid flow oscillated between complete dry-out and rewetting annular flow due to the short-timescale flow instability, which caused high-frequency and large amplitude temperature oscillations (10 °C in 25 ms). In comparison, hydrophilic surface structures on the microchannel promoted capillary flow which delayed and suppressed dry-out in each oscillation cycle, and thus significantly reduced the temperature oscillation at high heat fluxes. This work suggests that promoting capillary wicking via surface structures is a promising technique to reduce thermal fatigue in high heat flux two-phase microchannel thermal management devices.