Enhanced pool boiling heat transfer by coupling multiscale structures and mixed wettability

Abstract

With the extensive application of boiling heat transfer in engineering, enhanced boiling heat transfer has become a prominent research focus. Micro/nanostructures and surface wettability are pivotal factors affecting the pool boiling heat transfer performance. In this paper, the effects of the mini-pillar, micro-nano composite structure, and mixed wettability on boiling heat transfer performance were investigated. The experimental outcomes indicate that the critical heat flux (CHF) and the heat transfer coefficient (HTC) on the mini-pillar structured surface (S2) are improved significantly. Compared to S2, the boiling heat transfer performance near the CHF is further enhanced on the surface with micro/nanostructures atop mini-pillars (S3). Furthermore, the size of the hydrophobic spots atop the mini-pillars also profoundly influences the boiling performance, by decreasing the wall superheat significantly. A synergistic pool boiling heat transfer enhancement is achieved by constructing micro/nanostructures on the top of the mini-pillar and controlling the diameter of hydrophobic spots at 0.5 mm atop the mini-pillar (S5 surface), with the maximum HTC and CHF of 230.00 kW/(m2·K) and 2360.20 kW/m2, respectively. These values are 3.82 times and 1.88 times higher than those of the smooth copper surface, respectively.