04. Boiling and Multi-Phase Flow

In highly subcooled boiling, the heat flux increases higher than critical heat flux (CHF) with emitting microbubbles from a large bubble formed on the heating surface at the end of nucleate boiling. The boiling regime has been called Microbubble Emission Boiling (MEB). It was found in subcooled boiling of water by Inada S. [1] and Kumagai S. [2]. Ueno I. showed an important phenomenon for MEB in the experiment on a vapor bubble issued into the stagnant water that the instability of vapor bubble was accelerated with increasing of liquid subcooling and the bubble collapsed instantaneously into may fine bubbles at about 40 K of liquid subcooling under the atmospheric condition [3]. A large bubble formed on the heating surface near CHF collapses into many fine bubbles at higher than 20 K of liquid subcooling in the authors many experiments and the liquid is supplied into the heating surface at the same time of the bubble collapse. The solid-liquid contact and the boiling are performed in a very short period in MEB. Tsuruta T. approached the mechanism of MEB by applying the microlayer boiling model into the experiment on subcooled boiling of water [4]. In the present paper, the authors approach closely the mechanism of MEB and the higher heat flux than CHF by reviewing the authors’ experiments on MEB. Then, we discuss some problems that occur with MEB for an application to cooling technology in power electronics. [1] Inada S., et al, Trans.JSME 47(417), (852-861),1981. [2] Kumagai S., et al., Trans. JSME 58(546), (498-502), 1992. [3] Ueno I., et al., Microgravity Sci. Technol.23,(73-77) 2011.[4] Tsuruta T., et al., Trans. JSME 84(859), 2018.

Prof.

Chungpyo Hong