Enhancement of pool boiling heat transfer using 3D-printed polymer fixtures

Abstract

Surface modification is a key technique which significantly enhances pool boiling heat transfer rates. There are several methods and manufacturing technologies that are used to alter surface morphologies, such as machining, surface coating, metal powder sintering, photolithography, and chemical processing, which create varied topologies at various length scales. However, some of these techniques are expensive, difficult to manufacture, limited to simple structures, or degrade over time.In the present study, additive manufacturing (AM) is utilized to produce low-cost, porous polymer fixtures that are designed to alter bubble dynamics and improve the pool boiling heat transfer characteristics from flat copper surfaces. The fixtures examined here consist of a uniform pattern of square cells. An open-source fused filament fabrication 3D printer was used to manufacture the fixtures from PLA, and they were attached mechanically to the boiling surface. The wickability of the printed porous samples was investigated using the rate-of-rise method, which showed that printing build orientation can affect their capillary pressure. The boiling experiments were performed under saturated conditions using deionized water as the working fluid at a pressure of 1 atm.Using fixtures with a small unit cell size, we were able to control the nucleation locations and increase the boiling heat transfer coefficient at low heat fluxes by approximately 80%. However, this did not have a significant effect on critical heat flux (CHF). This was attributed to the presence of a low-conductivity structure covering part of the boiling surface which caused the heat to preferentially flow to the bare regions of the surface and initiated nucleation earlier, even at low heat fluxes. It was also found that increasing the unit cell size was not beneficial at the low heat fluxes; however, it did enhance the CHF by approximately 28% compared with the bare surface.