Augmented Pool Boiling Heat Transfer of PF-5060 Using Femtosecond Laser Surface Processed Aluminum: Effect of Laser Fluence

In this work, pool boiling results using functionalized 6061 aluminum surfaces with PF-5060 as the working fluid are presented. Femtosecond laser surface processing (FLSP) is used as a surface modification technique to create self-organized, multiscale surface features which lead to additional nucleation sites and augmented surface area available for heat transfer. Four functionalized surfaces were fabricated by varying the laser fluence at a fixed pulse count to examine the impact of surface morphology on the heat transfer performance. Each surface was tested twice for repeatability up to critical heat flux (CHF) and compared to a polished baseline sample. Results reveal drastically enhanced performance compared to the polished surface. The enhancement in the maximum heat transfer coefficient over the reference surface ranged from 390% to 680% for the FLSP surfaces tested, which is attributed to the abundance of potential nucleation sites formed during laser processing. Each functionalized surface kept the surface temperature below the recommended limit of 85°C despite the temperature overshoots observed and yielded nearly isothermal behavior within the nucleate boiling regime, with most superheats remaining between 5 and 6°C. Superheat at the onset of nucleate boiling was reduced for all functionalized surfaces with reductions ranging from 35% to 53% compared to the baseline surface. Additionally, all FLSP surfaces exhibited an increase in the CHF, ranging from 9% to 49%. This work demonstrates the potential of FLSP-functionalized aluminum surfaces as a viable means of achieving significant two-phase heat transfer enhancement with dielectric fluids.