Novec 7000 flow boiling heat transfer enhancement via femtosecond laser texturing: impact of fluid degradation

Efficient cooling using boiling heat transfer is crucial in space applications for thermal management systems. This paper aims to report a study performed on flow boiling enhancement using femtosecond laser-textured surfaces and flat plain copper surfaces using 3M^™ Novec 7000 as the working fluid. In particular, we investigate the impact of hierarchical textures consisting of a microscale pillar pattern overlapped with submicron-scale Laser-Induced Periodic Surface Structures (LIPSS) on the heat transfer coefficients (HTC) and the dynamics of bubble formation and detachment. We demonstrate that in our specific conditions, an enhancement of about 25% in the HTC can be reached with smaller bubbles detaching from the surface. However, this augmentation in the HTC rapidly decreased with time due to what we observed as fluid degradation and deposition on the surfaces. Similar fluid degradation was also found in pool boiling tests with Novec 7100 and Novec 7200. No degradation was noted when using perfluorohexane (FC-72 and its equivalent, Flutec PP1).