Abstract
Pool boiling CHFs for a highly wetting liquid due to steady state and transient heat input were studied. Boiling heat transfer processes on a platinum cylinder in a pool of ethanol due to exponentially increasing heat inputs, Q=Q0exp(t/τ), ranging from quasi-steadily increasing one to rapidly increasing one with periods, τ were measured for a 1.0-mm diameter horizontal cylinder with different surface roughness of commercially-available or roughly-finished surface cylinders for saturated and subcooled liquid at various pressures. Steady-state CHFs at various pressures gradually increased with an increase in subcooling. It was confirmed that the CHFs for lower subcoolings at every pressure almost show little dependence on surface roughness. However the CHF data for the roughly-finished one in many cases were increased for higher subcoolings over pressures. Typical trends of the CHFs were clarified to three groups corresponding to periods: the 1st, 2nd and 3rd groups of CHF were for longer periods, for shorter and for intermediate ones, respectively. It was clarified that the transient CHFs belonging to the 2nd and 3rd group were significantly affected by the surface roughness of cylinders. It appears that more study on the multi-parametric surface roughness and a wider range of experimental conditions need to be included in the study.
