Surface Erosion Caused by Microbubble Emission Boiling

Abstract

Microbubble emission boiling (MEB) is the phenomenon that shows emission of micro bubbles from a heat transfer surface in a wall temperature region corresponding to transition boiling. Since MEB performs higher heat flux than critical heat flux of nucleate boiling, application to engineering field is expected. However, MEB has unknown characters such that it sometimes results in serious erosion on the surface. Scanning electron microscope observation on the heat transfer surface after MEB occurred, shows that the surface erosion is consisted of numerous craters. This result leads to a hypothesis that the mechanism of MEB includes bubble collapse process caused by liquid micro jets. Surface roughness was measured in various heat flux conditions and the relation of it with heat transfer was considered. The results made it clear that there is a critical heat flux to cause surface erosion. This heat flux is also the transition point of bubble collapse regimes in MEB, from heat transfer dominant to inertia controlling.