Capillary-Assisted Evaporation/Boiling in PDMS Microchannel Integrated with Wicking Microstructures

To enable rapid development of flexible microelectronic systems, effective thermal management is needed. Flexible polydimethylsiloxane (PDMS)-based microchannel flow boiling may provide a desirable solution. However, the heat transfer performance of PDMS-based microchannels is diminished by its poor thermophysical properties. The development of PDMS wick is proposed to address this dilemma. Herein, a new PDMS wick structure is designed and integrated in the microfluidic device to significantly enhance its thermal performance by promoting capillary-driven flow. Furthermore, to achieve highly efficient vapor removal, a dedicated vapor pathway is designed in the microfluidic device. Experiments have been conducted to investigate the capillary-assisted evaporation/boiling for mass flux ranging from 70 to 245 kg/m² s on dielectric fluid HFE-7100. The capillary-assisted sustainable and stable thin film evaporation and efficient vapor removal have been demonstrated through the visualization studies. With this new wick design, the liquid rewetting at global and local levels is facilitated through the capillary-driven flow and the efficient vapor removal. This hybrid liquid rewetting mechanism is experimentally demonstrated to significantly enhance the capillary-assisted evaporation/boiling in PDMS-based microchannel. A critical heat flux (CHF) of 14.7 W/cm² is achieved at a mass flux of 245 kg/m² s. The heat transfer coefficients (HTC) range from 2000 to 9800 W/m² K. These values are comparable to that in copper/silicon microchannels, with the aforementioned benefits of flexibility. Equally importantly, stable two-phase transport is achieved as well.