Micro/nanoscale surface on enhancing the microchannel flow boiling performance : A Lattice Boltzmann simulation

Microchannel Heat Sink (MCHS) has been widely adopted in thermal engineering fields, such as refrigerators, chip cooling, battery packs, etc. To meet the ever-increasing demand for heat dissipation, surface modification methods adopting micro/nanoscale-modified surfaces have received considerable attention. In this paper, an advanced micro/nanoscale surface modification design is proposed based on a Lattice Boltzmann method (LBM) simulation study. Coupled boundary treatments at the inlet/outlet are developed with better numerical stability. The effects of surface wettability and micropillar on MCHS heat transfer performance are analyzed through bubbles' dynamic behaviors, Nusselt number, heat flux, and pressure drop. Design-based suggestions are proposed, and the enhancement mechanisms are explained. Results show that hydrophobic surface is more preferred for temperature-sensitive devices with low superheat requirement (Ja < 0.1115), while the hydrophilic surface is more preferred for devices with a large heat dissipation requirement (Ja ≥ 0.1286). Furthermore, the micropillar surfaces with pillar geometric factor S_p of 7 can yield the optimum heat transfer performance under a wide range of superheat conditions. Finally, an advanced design of a biphilic micropillar surface is proposed with superhydrophobic regions located at the top of the pillars, and other regions remain hydrophilic surfaces. An excellent heat transfer enhancement of 105.8% is achieved even compared with a pure hydrophilic micropillar surface. The enhancement is attributed to the superhydrophobic top regions efficiently blocking the bubbles merging process, which leads to more intense bubbles departure. These results provide a valuable guide for MCHS design and unravel the enhancement mechanism of the flow boiling process.