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Scaling of Downward Facing Boiling and Steam Venting in a Heated Hemispherical Annular Channel
F.B. Cheung, J. Yang, M.B. Dizon, J.L. Rempe, K.Y. Suh and S.B. Kim

A scaling analysis has been performed to study the phenomena of downward facing boiling and steam venting in a heated hemispherical annular channel. Five key transfer processes have been considered and the characteristic time for each of these processes has been determined and compared with the residence time for the two-phase mixture in the flow channel. To complement the scaling analysis, an upward co-current two-phase flow model has been developed to predict the total mass flow rate and the steam venting velocity induced in the annular channel by the process of downward facing boiling. The model takes into account the wall heat flux level, the geometry of the flow channel, the local variation of the cross-sectional flow area, and the pressure drops through various segments of the channel. Based on the results of the flow calculations and the scaling analysis, criteria for experimental simulation have been established to assure that the phenomena simulated in laboratory-scale experiments would have the same effects as those anticipated for the fullscale system.

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