Femtosecond laser-treated copper sintering surface to enhance pool boiling heat transfer

Abstract

Surface properties have a crucial effect on advancing boiling heat transfer (BHT). This study proposes a porous microgroove-structured surface fabricated via copper powder sintering and femtosecond laser processing to enhance pool boiling heat transfer. Copper powder sintering creates a porous layer, and the application of a femtosecond laser subsequently induces the formation of a microgroove structure atop the porous layer. Eight porous microgroove-structured surfaces were fabricated under different laser surface energy densities. Laser surface energy density was controlled by laser power and scanning speed. Pool boiling experiments were conducted for each sample, including smooth, porous, microgroove, and porous microgroove structures. Interestingly, a distinctive displacement was identified within the heat flux curve of porous microgroove-structured surfaces. The wall superheat decreased with increasing heat flux, causing the graph to shift to the left. To elucidate this phenomenon bubble visualization on the boiling surfaces was performed for each sample. It was observed that a porous microgroove-structured surface could effectively activate several bubble nucleation sites. Additionally, secondary pool boiling on the porous microgroove-structured surface was observed leading to the unique "hook back" shift in the boiling curve and the nonlinear increase of HTC. A pool boiling enhancement mechanism was proposed based on experimental data and bubble visualization. This study offers a pathway for advancing heat dissipation efficiency and understanding of surface engineering strategies.