ABSTRACT
Flow nucleate boiling has an extremely high heat transfer coefficient. It is used in various kinds of compact heat exchangers, most notably in nuclear water reactors. The transition of boiling mechanism, characterized by a sudden rise of surface temperature due to the drop of heat transfer coefficient, is called the boiling crisis. The maximum heat flux just before boiling crisis is called critical heat flux and can occur in various flow patterns. Boiling crisis occurring in a bubbly flow is sometimes called departure from nucleate boiling (DNB); and boiling crisis occurring in an annular flow is sometimes called dryout. Boiling crisis is caused essentially by the lack of cooling liquid near a heated surface. The physical interpretation of flow boiling crisis can be considered primarily a hydrodynamic phenomenon of radial bubble injection to the axial flow with a momentum exchange near the wall.
