Enhancement of flow boiling heat transfer by laser-induced periodic surface structures using femtosecond laser

Abstract

This study proposes a new surface processing method using a femtosecond laser to enhance the flow boiling heat transfer in a single mini/micro-channel duct. The suggested method is suitable for mini/micro-channel surface processing because the femtosecond laser with a short pulse duration (∼220 femtoseconds) simplifies the fabrication procedure and minimizes the thermal damage of surfaces during laser processing. Three types of laser-induced surfaces different in the nano-surface structure were fabricated. Three surfaces include laser-induced periodic surface structure (LIPSS), micro-groove covered clustered cavity by low fluence (MGCC-LF), and micro-groove covered clustered cavity by high fluence (MGCC-HF). Flow boiling heat transfer of each surface was experimentally investigated through a comparison with that of the plain copper surface in single-channel experiments. Experimental results demonstrated that LIPSS enhanced the boiling heat transfer by increasing the bubble nucleation sites with a self-organized nanosized ripple structure. Consequently, the MGCC-HF surface with nanosized clustered cavities and hydrophilic characteristics has the most prominent flow boiling heat transfer and critical heat flux enhancement. This enhancement is due to a synergy between increased nucleation sites and the wicking effects, promoting liquid rewetting and hindering local dry out. The present study confirmed that the flow boiling performance of the metal surface could be significantly improved through a relatively easy and fast process using a femtosecond laser.