SINOPSIS

If a flow obstacle such as a spacer is placed in a boiling two-phase flow within a channel, the temperature on the surface of the heating tube is severely affected by the existence of the spacer. Under certain conditions, a spacer has a cooling effect, and under other conditions, the spacer causes dryout of the cooling water film on the heating surface. The burnout mechanism, which always occurs upstream of a spacer, however, remains unclear.
In a previous paper (Fukano et al. (2002)), we reported that the disturbance wave has a significant effect on dryout and burnout occurrence and that a spacer greatly affects the behavior of the liquid film downstream of the spacer. In the present paper, we will discuss in detail the influence of a spacer on the heat transfer and film thickness characteristics downstream of a spacer. Moreover, at the end of this paper, we will propose a new burnout occurrence model in consideration of the unsteady nature of two-phase flow.