Abstract
Steady-state and transient boiling heat transfer characteristics for highly wetting liquid due to an exponentially increasing heat input with time have been investigated. It is important to make the best of existing energy conversion technology for the utilization of boiling heat transfer. Steady-state and transient critical heat fluxes (CHFs) were measured by using a 1.0 mm-diameter horizontal cylinder in a pool of water and highly wetting liquid such as ethanol with a period ranging from about 10 ms to 20s for wide ranges of subcooling and pressure. The transient CHFs depending on the periods were divided into two principal groups: the first one was in long period and the CHF occurred with fully developed nucleate boiling heat transfer processes, and the second one was in short period with explosive boiling heat transfer processes from non-boiling and the direct transition to film boiling occurred. The CHFs increase with an increase in subcooling at pressures and they are independent of pressures at high subcoolings. A large part of the transition processes to film boiling at CHFs for highly subcooled liquid measured can not be explained by the mechanism based on the conventional hydrodynamic instability (HI) model. However, the transition processes to film boiling at high subcooling can be explained by the heterogeneous spontaneous nucleation (HSN) model suggested by Sakurai et al.. In the HSN model, it is assumed that the transition occurs due to the explosive boiling in originally flooded cavities on the solid surface in liquid. The measured transition processes to film boiling at CHFs for wide ranges of subcooling and pressure in the test liquids with steady and transient conditions were reasonably explained by the HI and HSN models.
