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

Abstract

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.

Superbiphilic Laser‐Microengineered Surfaces with A Self‐Assembled Monolayer Coating for Exceptional Boiling Performance

“…Although boiling heat transfer is one of the most intense heat transfer mechanisms, researchers in this field have extensively investigated numerous types of methods in the last few decades [8,9] to further improve the boiling performance. Studies range from enhancements based on boiling fluid modification, [9,10] such as with the addition of nanoparticles (i.e., nanofluids) [11,12] or with mixtures of different surface tensions, [13,14] to studies focusing on surface modification, [15,16] with an emphasis on changing the surface topography [17,18] and morphology [19,20] alongside with its wetting behavior. [21,22] In recent years, various technologies have been explored to tailor the surface topography and morphology to improve boiling performance.…”

Advances in micro and nanoengineered surfaces for enhancing boiling and condensation heat transfer: a review

“…To overcome this limitation, PDMS wick structures with separate vapor removal pathways have been designed. 178 Such micropillars enable high capillary pressure and high permeability enabling stable liquid film evaporation characterized by stable wall temperatures at high heat flux operating conditions. Phase separation and improved global liquid supply allow CHFs to approach those observed on silicon and copper microchannel heat sinks.…”

Experimental and numerical investigations of heat transfer and flow characteristics during flow boiling in straight and diverging PDMS microchannel

“…They have studied the temperature distribution along the length of the channel using high spatial resolution infrared thermography coupled with flow pattern using a high-speed camera. Li and Joshi [32] developed a new PDMS wick structure to improve thermal performance by promoting capillary-driven flow. They achieved a stable flow using a dedicated vapour path and obtained heat transfer coefficients comparable to traditional microchannels.…”