Enhanced pool-boiling heat transfer and critical heat flux using femtosecond laser surface processing

In this paper, we present the experimental investigation of pool boiling heat transfer on multiscale (micro/nano) functionalized metallic surfaces. The multiscale structures were fabricated via a femtosecond laser surface process (FLSP) technique which forms mound-like microstructures covered by layers of nanoparticles. Using a pool boiling experimental setup with deionized water as the working fluid, both the heat transfer coefficient and critical heat flux were investigated. The polished reference sample was found to have a critical heat flux of 91 W/cm² at 40 °C of superheat and a maximum heat transfer coefficient of 23,000 W/m²-K. The processed sample was found to have a critical heat flux of 122 W/cm² at 18 °C superheat and a maximum heat transfer coefficient of 67,400 W/m²-K. Flow visualization revealed nucleate boiling to be the main two-phase heat transfer mechanism. The overall heat transfer performance of the metallic multiscale structured surface has been attributed to both augmented heat transfer surface area and enhanced nucleate boiling regime. On the other hand, increase in the critical heat flux can be attributed to the superhydrophilic nature of the laser processed surface and the presence of nanoparticle layers.