Investigation on Critical Heat Flux Enhancement with Nanocoated Surface under Different Orientation

Description

Boiling, a common phenomenon in our daily life, is extensively employed in industry due to its excellent heat transfer performance. The classic pool boiling curves mainly consist of three distinct regimes: nucleate, transition, and film boiling. Among them, nucleate boiling is the most effective heat transfer method and has been widely applied in high-techs such as computer chips, electronic devices, and energy systems. As the technology advances, more efficient heat transfer over smaller surface areas, i.e. higher surface heat flux, is often required. However, the surface heat flux should be carefully controlled below the critical heat flux (CHF). Beyond that, boiling crisis will be triggered which sharply increase the wall temperature and would cause damages to the devices or systems. Therefore, it is essential to enhance the CHF in order to augment the limit of boiling heat transfer.It has been verified that the surface intrinsic wettability and surface structures have significant impact on the CHF and boiling heat transfer. Extensive researches have been conducted by different research groups around the world to improve the CHF through surface modifications. However, for those modified surfaces with hydrophilic nano/micro structures, the impact of surface wettability and structures on CHF are usually coupled together. To distinguish their individual impacts in order to better understand the underlying mechanism, it is worth conducting researches in decoupling them. In this research, surfaces coated with nanograss under different cover density will be used to compare with various hydrophilic surfaces through extensive experiments in order to identify the underlying mechanism of CHF enhancement for individual factor. In addition, some researches show that the surface orientation has very significant impact on the CHF. However, the research is still very limited on this topic and most of the research so far used smooth surface and the range of orientation angles is narrow. In this research, both bare substrates and the nanograss coated surface will be experimentally investigated and the orientation will change from 0° to 180° with an interval of 30°. A widely applicable correlation for CHF prediction of nanostructured surface under different orientation will be derived. Finally, to comprehensively understand the underlying mechanism of CHF, molecular dynamics (MD) simulations that study the boiling process from the nanoscale point of view will be carried out. It is strongly believed that with this technique, some atomic level information about CHF enhancement mechanism, which are unavailable using conventional method, could be obtained.