ABSTRACT
The postdry-out heat transfer in steam generators may be considerably improved by another geometrical arrangement with respect to straight channels: the choice of coiled channels of appropriate geometries. In flow boiling, velocity multiplies the number of possible heat transfer situations. An inverted annular flow occurs with cold water in the bulk of the channel and with a narrow vapor film between the superheated wall and the bulk liquid. With particular reference to nuclear reactor cores, if thermal critical power is exceeded, the emergency core cooling system is required to inject water into the primary cooling loops. The rewetting of hot surfaces by a liquid film of gravity-driven water is of primary importance for nuclear safety analyses. The quenching of these surfaces is another conduction-controlled phenomenon, like core bottom reflooding. The swirl flow in once-through steam generators is a very promising means of increasing heat transfer and power densities, thus reducing the heat transfer surface and the equipment cost.
