Pool Boiling Heat Transfer Enhancement Using Femtosecond Laser Surface Processed Aluminum in Saturated PF-5060

Abstract

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. Two 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. In addition, each surface was tested under two conditions: as processed and post processed. Post processing consisted of a 60-minute ultrasonic bath to remove loosely adhered nanoparticles. Each surface was tested up to critical heat flux (CHF) and compared to a polished baseline sample. Results reveal drastically enhanced performance compared to the polished surface. The greatest increase in the maximum heat transfer coefficient was 459% for an FLSP surface without post processing. As processed only samples were shown to have a minor impact on the CHF, however, the inclusion of a post processing ultrasonic bath had significantly larger adverse effects on the CHF compared to their as processed counterparts. This adverse impact on the CHF arose from altering the nano-porous layer covering each surface feature, thereby reducing the surfaces’ ability to draw in cooler replenishing liquid to delay CHF. 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.