Boiling Heat Transfer at the Coexistence of Nucleate and Film Regions

E. Zielinski discovered experimentally a comparatively easy method to reproduce film boiling. According to his method, if a wire which is making nucleate boiling with heating current adjusted to a rather low heat flux is pulled out of water for a short time, the surface of the wire dries up and its temperature rises because of the contact of the wire and air, even when heat flux is kept constant. If the wire is dipped in water later on, for the second time, it heats red-hot in a few seconds, followed by the appearance of film boiling. Film boiling is to be reproduced with comparative easiness by breaking temporarily the contact of heating surface with water. The authors who paid attention to Zielinski's method followed it with the result in which nucleate boiling and film boiling are made to coexist stably on the same heating surface by heating them with a given heat flux. This is considered to be a kind of transition boiling, and the present paper deals with the boiling phenomena at the coexistence of nucleate and film regions in saturated water, subcooled water and sodium oleate solution as well as their relation with boiling characteristic curve. In this region the coefficient of heat transfer decreases with the increase of temperature difference, while heat flux increases with the increase of temperature difference.